Elucidating Tuta absoluta (Meyrick) invasion and enhancing its management in Eastern Africa : spread, socio-ecological impacts, and potential of a newly imported larval parasitoid for classical biological control Eastern in Africa
- Aigbedion-Atalor, Pascal Osabhahiemen
- Authors: Aigbedion-Atalor, Pascal Osabhahiemen
- Date: 2021
- Subjects: Tuta absoluta -- Biological control , Tomatoes -- Diseases and pests -- Africa, East , Braconidae , Gelechiidae -- Biological control -- Africa, East , Insects as biological pest control agents -- Africa, East
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/170421 , vital:41920 , 10.21504/10962/170421
- Description: Agriculture is a fundamental source of sustainable livelihoods in sub-Saharan Africa and millions of people in the region rely solely on small-scale farming for their food security. However, the impacts of invasive alien species (IAS) on crop production are serious, and there is no sign of this abating. Among the recent IAS that have invaded Africa in the last decade, the South American tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has been one of the most damaging. Following its first record in the Maghreb region of Africa in 2008, T. absoluta rapidly spread throughout Africa with substantial impacts on tomato production, often causing 100% yield loss. Management options adopted against T. absoluta by tomato growers in Africa have been based on the use of synthetic insecticides. While chemical insecticide applications are an important component of an integrated pest management programme, misuse and over-reliance often exacerbates the impacts of T. absolutadue to the development of resistance to commonly used active substances, increasing the fitness of the pest. This thesis sought to understand the socio-economic impacts of the spread of T. absoluta in Eastern Africa and provide effective sustainable pest management strategies to reduce its impacts below economic thresholds. Mapping surveys of Tabsoluta were conducted in 226 tomato agro-ecosystems across four eastern countries (Kenya, Sudan, Tanzania, and Uganda) Eastern Africa from 2016 to 2018 to determine the spatiotemporal distribution of the pest. The impacts of T. absoluta on the livelihoods of tomato growers were also assessed. Here, 200 tomato growers in Kenya were interviewed using a semi-structured questionnaire. Although T. absoluta, a recent invader, was distributed at high infestation levels throughout the subregion (all four countries) and was considered as the most damaging invasive alien species of agriculturally sustainable livelihoods. The arrival of T. absoluta in the subregion has resulted in livelihood losses and increased the cost of tomato production and price of the fruit, and the frequency of pesticide applications. The impact of this pest and the and the absence of effective indigenous natural enemies of the pest in Eastern Africa, was the rationale for the importation of a larval parasitoid, Dolichogenidea gelechiidivoris Marsh Syn.: Apanteles gelechiidivoris Marsh) (Hymenoptera: Braconidae), of T. absoluta from Peru into the quarantine facility of the International Centre of Insect Physiology and ecologyz(icipe), in Kenya. Pre-release assessments on the parasitzation potential of D. gelechiidivoris, encompassing host larval preference and the host suitability, and its reproductive strategy, for classical biological control of T. absoluta in Africa were conducted. Dolichogenidea gelechiidivoris females preferentially oviposited in early (1st and 2nd) larval instars of T. absoluta but parasitized and completed development in all four instars of the host. Host instar did not affect D. gelechiidivoris sex-ratio but females reared on the first instar had significantly fewer eggs than when reared in late larval instars (3rd and 4th). Females of the parasitoid emerged with a high mature egg load which peaked 2 d post-eclosion. The females of D. gelechiidivoris survived 8.51±0.65 d and produced 103±8 offspring per female at 26±4°C (range: 24 to 29°C) and 50–70% relative humidity (RH) in the presence of males and fed honey-water (80% honey). Increasing maternal age decreased the proportion of female offspring. Under the aforementioned laboratory conditions, the Gross and Net reproductive rates were 72 and 39.5 respectively, while the mean generation time was 20 d. The estimated intrinsic rate of natural increase was 0.18. These findings indicate that D. gelechiidivorisis a potential biological control agent of T. absoluta and should be considered for augmentative/inundative release in Kenya and across Africa following host specificity testing and risk assessments. The nature of the interaction between D. gelechidivoris and the predatory mirid bug Nesidiocoris tenuis(Reuter) (Hemiptera: Miridae), an important and widespread natural enemy of T. absoluta in Africa was evaluated because N. tenuis, although being a voracious predator of T. absoluta eggs, it can also prey on the early host larval instars (1st and 2nd) which are the preferred oviposition host stages of D. gelechiidivoris. Here, the impact of N. tenuis feeding on T. absoluta and the effects on D. gelechiidivoris performance was tested. Regardless of the order of introductions (i.e. the sequence of combination with D. gelechiidivoris) and densities (i.e. number of N. tenuis combined with D. gelechiidivoris), there was no intraguild predation by N. tenuis on D. gelechiidivorisas there was little host larval feeding behaviour. Also, the presence of N. tenuis did not affect the oviposition performance of D. gelechiidivoris. Further investigations revealed that the combined efficacy of N. tenuis and D. gelechiidivorison T. absoluta population was significantly higher than either natural enemy alone, thus contributes to the data supporting the release of D. gelechiidivoris in Africa. In concluding, integrating D. gelechiidivoris and N. tenuis in the management of T. absolut could potentially reduce yield losses in tomato in Eastern Africa where the socio-economic impacts of the pest are very serious.
- Full Text:
- Date Issued: 2021
- Authors: Aigbedion-Atalor, Pascal Osabhahiemen
- Date: 2021
- Subjects: Tuta absoluta -- Biological control , Tomatoes -- Diseases and pests -- Africa, East , Braconidae , Gelechiidae -- Biological control -- Africa, East , Insects as biological pest control agents -- Africa, East
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/170421 , vital:41920 , 10.21504/10962/170421
- Description: Agriculture is a fundamental source of sustainable livelihoods in sub-Saharan Africa and millions of people in the region rely solely on small-scale farming for their food security. However, the impacts of invasive alien species (IAS) on crop production are serious, and there is no sign of this abating. Among the recent IAS that have invaded Africa in the last decade, the South American tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has been one of the most damaging. Following its first record in the Maghreb region of Africa in 2008, T. absoluta rapidly spread throughout Africa with substantial impacts on tomato production, often causing 100% yield loss. Management options adopted against T. absoluta by tomato growers in Africa have been based on the use of synthetic insecticides. While chemical insecticide applications are an important component of an integrated pest management programme, misuse and over-reliance often exacerbates the impacts of T. absolutadue to the development of resistance to commonly used active substances, increasing the fitness of the pest. This thesis sought to understand the socio-economic impacts of the spread of T. absoluta in Eastern Africa and provide effective sustainable pest management strategies to reduce its impacts below economic thresholds. Mapping surveys of Tabsoluta were conducted in 226 tomato agro-ecosystems across four eastern countries (Kenya, Sudan, Tanzania, and Uganda) Eastern Africa from 2016 to 2018 to determine the spatiotemporal distribution of the pest. The impacts of T. absoluta on the livelihoods of tomato growers were also assessed. Here, 200 tomato growers in Kenya were interviewed using a semi-structured questionnaire. Although T. absoluta, a recent invader, was distributed at high infestation levels throughout the subregion (all four countries) and was considered as the most damaging invasive alien species of agriculturally sustainable livelihoods. The arrival of T. absoluta in the subregion has resulted in livelihood losses and increased the cost of tomato production and price of the fruit, and the frequency of pesticide applications. The impact of this pest and the and the absence of effective indigenous natural enemies of the pest in Eastern Africa, was the rationale for the importation of a larval parasitoid, Dolichogenidea gelechiidivoris Marsh Syn.: Apanteles gelechiidivoris Marsh) (Hymenoptera: Braconidae), of T. absoluta from Peru into the quarantine facility of the International Centre of Insect Physiology and ecologyz(icipe), in Kenya. Pre-release assessments on the parasitzation potential of D. gelechiidivoris, encompassing host larval preference and the host suitability, and its reproductive strategy, for classical biological control of T. absoluta in Africa were conducted. Dolichogenidea gelechiidivoris females preferentially oviposited in early (1st and 2nd) larval instars of T. absoluta but parasitized and completed development in all four instars of the host. Host instar did not affect D. gelechiidivoris sex-ratio but females reared on the first instar had significantly fewer eggs than when reared in late larval instars (3rd and 4th). Females of the parasitoid emerged with a high mature egg load which peaked 2 d post-eclosion. The females of D. gelechiidivoris survived 8.51±0.65 d and produced 103±8 offspring per female at 26±4°C (range: 24 to 29°C) and 50–70% relative humidity (RH) in the presence of males and fed honey-water (80% honey). Increasing maternal age decreased the proportion of female offspring. Under the aforementioned laboratory conditions, the Gross and Net reproductive rates were 72 and 39.5 respectively, while the mean generation time was 20 d. The estimated intrinsic rate of natural increase was 0.18. These findings indicate that D. gelechiidivorisis a potential biological control agent of T. absoluta and should be considered for augmentative/inundative release in Kenya and across Africa following host specificity testing and risk assessments. The nature of the interaction between D. gelechidivoris and the predatory mirid bug Nesidiocoris tenuis(Reuter) (Hemiptera: Miridae), an important and widespread natural enemy of T. absoluta in Africa was evaluated because N. tenuis, although being a voracious predator of T. absoluta eggs, it can also prey on the early host larval instars (1st and 2nd) which are the preferred oviposition host stages of D. gelechiidivoris. Here, the impact of N. tenuis feeding on T. absoluta and the effects on D. gelechiidivoris performance was tested. Regardless of the order of introductions (i.e. the sequence of combination with D. gelechiidivoris) and densities (i.e. number of N. tenuis combined with D. gelechiidivoris), there was no intraguild predation by N. tenuis on D. gelechiidivorisas there was little host larval feeding behaviour. Also, the presence of N. tenuis did not affect the oviposition performance of D. gelechiidivoris. Further investigations revealed that the combined efficacy of N. tenuis and D. gelechiidivorison T. absoluta population was significantly higher than either natural enemy alone, thus contributes to the data supporting the release of D. gelechiidivoris in Africa. In concluding, integrating D. gelechiidivoris and N. tenuis in the management of T. absolut could potentially reduce yield losses in tomato in Eastern Africa where the socio-economic impacts of the pest are very serious.
- Full Text:
- Date Issued: 2021
Prioritising biological control agents for release against Sporobolus pyramidalis and Sporobolus natalensis (Poaceae) in Australia
- Authors: Sutton, Guy Frederick
- Date: 2021
- Subjects: Grasses -- Diseases and pests , Bruchophagus , Wasps , Alien plants -- Biological control -- Australia , Sporobolus -- Biological control -- Africa , Sporobolus -- Biological control -- Australia , Insects as biological pest control agents -- Australia , Insects as biological pest control agents -- Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/172445 , vital:42201 , 10.21504/10962/172445
- Description: Sporobolus pyramidalis Beauv. and S. natalensis (Steud.) Th. Dur. and Schinz. (giant rat’s tail grass) (Poaceae), invade rangelands and pastures in eastern Australia, costing the livestock industry approximately AUS$ 60 million per annum in grazing losses. Mechanical and chemical control options are costly and largely ineffective. Biological control is viewed as the most promising control option, however this management strategy has largely been avoided for grasses, due to their perceived lack of suitably host-specific and damaging natural enemies. In this thesis, the prospects for using biological control against S. pyramidalis and S. natalensis in Australia was assessed, in light of these potential challenges. Climate matching models were used to identify high-priority geographic regions within the plants’ native distributions to survey for potential biological control agents. High-priority regions to perform surveys were identified by modelling the climatic suitability for S. pyramidalis and S. natalensis in sub-Saharan Africa (i.e. their potential native ranges’), and climatic compatibility with regions where biological control is intended in Australia. High-priority regions for S. pyramidalis included: (1) coastal East Africa, ranging from north-eastern South Africa to Uganda, including south-eastern DRC, (2) some parts of West Africa, including inland regions of the Ivory Coast and western Nigeria, (3) northern Angola and (4) eastern Madagascar, and for S. natalensis included: (1) eastern South Africa, (2) eastern Zimbabwe, (3) Burundi, (4) central Ethiopia and (5) central Madagascar. Prospective control agents collected from these regions have the highest probability of establishing and proliferating in Australia, if released. In surveys of the insect assemblages on S. pyramidalis and S. natalensis in the climatically-matched region of eastern South Africa fifteen insect herbivores associated with the grasses were identified. Insect feeding guild, geographic distributions, and seasonal abundances suggest that three stem-boring phytophagous wasps, Tetramesa sp. 1, Tetramesa sp. 2 and Bruchophagus sp. 1 (Hymenoptera: Eurytomidae), have potential as control agents. Species accumulation curves indicated that additional surveys in South Africa are unlikely to yield additional potential control agents. Field host-range surveys of 47 non-target grass species in South Africa showed that Tetramesa sp. 1, Tetramesa sp. 2, and Bruchophagus sp. 1, were only recorded from S. pyramidalis and S. natalensis. Integrating field host-range with phylogenetic relationships between plant species indicated that no native Australian Sporobolus species or economic crops and pastures are expected to be attacked by these wasps. All three wasp species are predicted to be suitably host-specific for release in Australia. Three other endophagous herbivores attacked non-target native African Sporobolus species that share a close phylogenetic relationship to native Australian Sporobolus species, and therefore, demonstrate considerable risk of non-target damage. These species should not be considered as potential control agents. Under native-range, open-field conditions, Tetramesa sp. 1 caused an approximately 5-fold greater reduction in plant survival and reproductive output than Tetramesa sp. 2 and Bruchophagus sp. 1. Tetramesa sp. 1 in combination with Tetramesa sp. 2 did not significantly increase the level of damage, while Bruchophagus sp. 1 may decrease the efficiency of Tetramesa sp. 1, if released in combination. Tetramesa 1 is therefore the most promising candidate agent. Prioritising potential agents using predicted efficacy allowed otherwise equally suitable prospective agents to be prioritised in a strategic manner. Prioritising which natural enemies to target as biological control agents is a complex task. Field host range and damage assessments in the native range may provide more realistic data than typical studies performed under artificial conditions in a laboratory or quarantine. Moreover, it could assist practitioners in prioritising the most suitable agent(s) at the earliest stage in the programme as possible. This study demonstrated that grasses are suitable targets for biological control as they can harbour host-specific and damaging natural enemies.
- Full Text:
- Date Issued: 2021
- Authors: Sutton, Guy Frederick
- Date: 2021
- Subjects: Grasses -- Diseases and pests , Bruchophagus , Wasps , Alien plants -- Biological control -- Australia , Sporobolus -- Biological control -- Africa , Sporobolus -- Biological control -- Australia , Insects as biological pest control agents -- Australia , Insects as biological pest control agents -- Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/172445 , vital:42201 , 10.21504/10962/172445
- Description: Sporobolus pyramidalis Beauv. and S. natalensis (Steud.) Th. Dur. and Schinz. (giant rat’s tail grass) (Poaceae), invade rangelands and pastures in eastern Australia, costing the livestock industry approximately AUS$ 60 million per annum in grazing losses. Mechanical and chemical control options are costly and largely ineffective. Biological control is viewed as the most promising control option, however this management strategy has largely been avoided for grasses, due to their perceived lack of suitably host-specific and damaging natural enemies. In this thesis, the prospects for using biological control against S. pyramidalis and S. natalensis in Australia was assessed, in light of these potential challenges. Climate matching models were used to identify high-priority geographic regions within the plants’ native distributions to survey for potential biological control agents. High-priority regions to perform surveys were identified by modelling the climatic suitability for S. pyramidalis and S. natalensis in sub-Saharan Africa (i.e. their potential native ranges’), and climatic compatibility with regions where biological control is intended in Australia. High-priority regions for S. pyramidalis included: (1) coastal East Africa, ranging from north-eastern South Africa to Uganda, including south-eastern DRC, (2) some parts of West Africa, including inland regions of the Ivory Coast and western Nigeria, (3) northern Angola and (4) eastern Madagascar, and for S. natalensis included: (1) eastern South Africa, (2) eastern Zimbabwe, (3) Burundi, (4) central Ethiopia and (5) central Madagascar. Prospective control agents collected from these regions have the highest probability of establishing and proliferating in Australia, if released. In surveys of the insect assemblages on S. pyramidalis and S. natalensis in the climatically-matched region of eastern South Africa fifteen insect herbivores associated with the grasses were identified. Insect feeding guild, geographic distributions, and seasonal abundances suggest that three stem-boring phytophagous wasps, Tetramesa sp. 1, Tetramesa sp. 2 and Bruchophagus sp. 1 (Hymenoptera: Eurytomidae), have potential as control agents. Species accumulation curves indicated that additional surveys in South Africa are unlikely to yield additional potential control agents. Field host-range surveys of 47 non-target grass species in South Africa showed that Tetramesa sp. 1, Tetramesa sp. 2, and Bruchophagus sp. 1, were only recorded from S. pyramidalis and S. natalensis. Integrating field host-range with phylogenetic relationships between plant species indicated that no native Australian Sporobolus species or economic crops and pastures are expected to be attacked by these wasps. All three wasp species are predicted to be suitably host-specific for release in Australia. Three other endophagous herbivores attacked non-target native African Sporobolus species that share a close phylogenetic relationship to native Australian Sporobolus species, and therefore, demonstrate considerable risk of non-target damage. These species should not be considered as potential control agents. Under native-range, open-field conditions, Tetramesa sp. 1 caused an approximately 5-fold greater reduction in plant survival and reproductive output than Tetramesa sp. 2 and Bruchophagus sp. 1. Tetramesa sp. 1 in combination with Tetramesa sp. 2 did not significantly increase the level of damage, while Bruchophagus sp. 1 may decrease the efficiency of Tetramesa sp. 1, if released in combination. Tetramesa 1 is therefore the most promising candidate agent. Prioritising potential agents using predicted efficacy allowed otherwise equally suitable prospective agents to be prioritised in a strategic manner. Prioritising which natural enemies to target as biological control agents is a complex task. Field host range and damage assessments in the native range may provide more realistic data than typical studies performed under artificial conditions in a laboratory or quarantine. Moreover, it could assist practitioners in prioritising the most suitable agent(s) at the earliest stage in the programme as possible. This study demonstrated that grasses are suitable targets for biological control as they can harbour host-specific and damaging natural enemies.
- Full Text:
- Date Issued: 2021
An integrative approach to understanding vulnerability of an alpine range-restricted bird to climate warming
- Authors: Oswald, Krista Natasha
- Date: 2020
- Subjects: Passeriformes -- South Africa -- Western Cape , Passeriformes -- Physiology -- South Africa -- Western Cape , Passeriformes -- Behavior -- Climatic factors -- South Africa -- Western Cape , Passeriformes -- Reproduction -- Climatic factors -- South Africa -- Western Cape , Passeriformes -- Dispersal -- South Africa -- Western Cape , Passeriformes -- Food -- South Africa -- Western Cape , Passeriformes -- Nests-- South Africa -- Western Cape , Blue Hill Nature Reserve , Cape Rockjumper -- Climatic factors , Chaetops frenatus
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/148517 , vital:38746
- Description: Understanding species' vulnerability to climate change requires an integrative ecological approach involving, at minimum, physiology, behaviour, reproductive success, and limitations on dispersal. In this thesis I determined potential negative effects of increasing temperatures on behaviour, reproduction, and ability to disperse in an alpine-restricted bird, the Cape Rockjumper Chaetops frenatus ("Rockjumper"). Here I provide a comprehensive ecological set of data for understanding the link between Rockjumper population declines and warming habitats. I tested whether Rockjumper microsite-use at high temperatures resulted in decreased time spent on important behaviours, such as foraging. I found Rockjumpers made increased use of rock-shade as air temperature increased and so spent less time panting, but birds in rock-shade foraged less. Birds may be constrained to foraging in sun at high temperatures to sustain energy or water requirements, despite risks of high thermal load, or else face lost foraging opportunities by remaining in rock-shade. I determined if adult nest attendance and causes of nest failure were related to high temperatures. I filmed nests over two breeding seasons to examine temperature-effects on adult time in nests, provisioning rate, and resultant nestling daily mass gain. The only temperature effect I found was decreased percent daily change in body mass for older nestlings at hotter temperatures. I also examined causes of nest failure over three breeding seasons in relation to nest concealment and habitat openness by observing failure/success. Nests in more open territories (i.e. early post-fire habitat) had greater success, and the main cause of predation came from Boomslang Dispholydus typus. Importantly, the probability of Boomslang predation increased significantly at hotter temperatures. These findings show there may be direct negative effects of increasing temperatures on reproductive success and population recruitment, and so hotter temperature during the breeding season may be at least partly responsible for observed population declines. Lastly, I examined genetic structure of populations across mountain ranges separated from one another by lowland habitat unsuitable for Rockjumpers. I predicted I would find little evidence for dispersal between mountain ranges separated by unsuitable lowland habitat, but instead found Rockjumpers show little evidence for inbreeding. I also found evidence for a past bottleneck event or founder effect, and little overall genetic diversity (possibly as their specialized niche exerts selective pressure). Low diversity may limit Rockjumpers' ability to adapt to a changing environment. Adult physiological and behavioural thresholds to increasing temperatures are often used to create predictions of climate change effects. My past physiological research and current behavioural research suggest no particularly strong evidence that temperature-related population declines are driven by poor physiological capacity to tolerate heat or negative behaviour trade-offs. Instead, my current research shows that understanding negative effects of increasing temperatures may require a more in-depth approach involving investigation of fine-scale ecological interactions. No single one of my chapters provides the insight necessary for understanding Rockjumper population declines at warming temperatures. Instead, I show how an integrative approach may be necessary for assessing species' vulnerability to climate change by examining multiple ecological aspects of a single sentinel species, using an alpine species with a narrow thermal range and highly specialized habitat niche.
- Full Text:
- Date Issued: 2020
- Authors: Oswald, Krista Natasha
- Date: 2020
- Subjects: Passeriformes -- South Africa -- Western Cape , Passeriformes -- Physiology -- South Africa -- Western Cape , Passeriformes -- Behavior -- Climatic factors -- South Africa -- Western Cape , Passeriformes -- Reproduction -- Climatic factors -- South Africa -- Western Cape , Passeriformes -- Dispersal -- South Africa -- Western Cape , Passeriformes -- Food -- South Africa -- Western Cape , Passeriformes -- Nests-- South Africa -- Western Cape , Blue Hill Nature Reserve , Cape Rockjumper -- Climatic factors , Chaetops frenatus
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/148517 , vital:38746
- Description: Understanding species' vulnerability to climate change requires an integrative ecological approach involving, at minimum, physiology, behaviour, reproductive success, and limitations on dispersal. In this thesis I determined potential negative effects of increasing temperatures on behaviour, reproduction, and ability to disperse in an alpine-restricted bird, the Cape Rockjumper Chaetops frenatus ("Rockjumper"). Here I provide a comprehensive ecological set of data for understanding the link between Rockjumper population declines and warming habitats. I tested whether Rockjumper microsite-use at high temperatures resulted in decreased time spent on important behaviours, such as foraging. I found Rockjumpers made increased use of rock-shade as air temperature increased and so spent less time panting, but birds in rock-shade foraged less. Birds may be constrained to foraging in sun at high temperatures to sustain energy or water requirements, despite risks of high thermal load, or else face lost foraging opportunities by remaining in rock-shade. I determined if adult nest attendance and causes of nest failure were related to high temperatures. I filmed nests over two breeding seasons to examine temperature-effects on adult time in nests, provisioning rate, and resultant nestling daily mass gain. The only temperature effect I found was decreased percent daily change in body mass for older nestlings at hotter temperatures. I also examined causes of nest failure over three breeding seasons in relation to nest concealment and habitat openness by observing failure/success. Nests in more open territories (i.e. early post-fire habitat) had greater success, and the main cause of predation came from Boomslang Dispholydus typus. Importantly, the probability of Boomslang predation increased significantly at hotter temperatures. These findings show there may be direct negative effects of increasing temperatures on reproductive success and population recruitment, and so hotter temperature during the breeding season may be at least partly responsible for observed population declines. Lastly, I examined genetic structure of populations across mountain ranges separated from one another by lowland habitat unsuitable for Rockjumpers. I predicted I would find little evidence for dispersal between mountain ranges separated by unsuitable lowland habitat, but instead found Rockjumpers show little evidence for inbreeding. I also found evidence for a past bottleneck event or founder effect, and little overall genetic diversity (possibly as their specialized niche exerts selective pressure). Low diversity may limit Rockjumpers' ability to adapt to a changing environment. Adult physiological and behavioural thresholds to increasing temperatures are often used to create predictions of climate change effects. My past physiological research and current behavioural research suggest no particularly strong evidence that temperature-related population declines are driven by poor physiological capacity to tolerate heat or negative behaviour trade-offs. Instead, my current research shows that understanding negative effects of increasing temperatures may require a more in-depth approach involving investigation of fine-scale ecological interactions. No single one of my chapters provides the insight necessary for understanding Rockjumper population declines at warming temperatures. Instead, I show how an integrative approach may be necessary for assessing species' vulnerability to climate change by examining multiple ecological aspects of a single sentinel species, using an alpine species with a narrow thermal range and highly specialized habitat niche.
- Full Text:
- Date Issued: 2020
Biogeographic patterns of endolithic cyanobacteria and their negative impacts on mussels along the South African coast
- Authors: Ndhlovu, Aldwin
- Date: 2020
- Subjects: Cyanobacteria -- South Africa , Cyanobacteria -- Geographical distribution , Prokaryotes -- South Africa , Mexilhao mussel -- South Africa , Mytilus galloprovincialis -- South Africa , Coastal biology -- South Africa , Coastal ecology -- South Africa , Mussels -- Geographical distribution , Mussels -- Predators of , Mussels -- Mortality -- South Africa , Mussels -- Ecology -- South Africa , Mussels -- Growth -- South Africa , Mussels -- Fertility -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/144656 , vital:38367
- Description: Endolithic cyanobacterial species occur in a wide range of environments including cold and hot deserts as well as marine systems where they attack biological material such as corals and the shells of molluscs including limpets, mussels and abalone. Endoliths live as parasites in mussel shells, where they erode and extract calcium carbonate leading to shell weakening, creating fracture holes that lead to shell collapse and death, but they also have positive effects when they lead to discolouration of mussel shells hence giving them the ability to reduce stressful heat gain during periods of extreme heat stress. Mussels are ecological engineers on which the abundance and diversity of associated species assemblages depend. Understanding how endolithic cyanobacteria affect mussels will not only help in predicting future patterns of mussel abundances, but also future patterns of the infauna that depend on them. Firstly, I identified endolithic species infesting mussels and assessed the prevalence of endolithic parasitism in two intertidal mussel species in South Africa, the native Perna perna and the invasive Mytilus galloprovincialis. Large-scale surveys of endolithic infestation of mussels were conducted along 2500 km of the South African coast, covering three biogeographic regions: the subtropical east coast, dominated by P. perna, the warm temperate south coast where the indigenous species coexists with M. galloprovincialis, and the cool temperate west coast which is dominated by M. galloprovincialis. The prevalence of endolithic infestation was higher in the cool temperate bioregion than in the warm temperate and subtropical bioregions which did not differ and for P. perna endolithic species assemblages revealed clear groupings by bioregion. Results for endolithic induced mortality followed the same trend, with no significant difference between the two mussel species where they coexist and these results attribute biogeography of endoliths to environmental factors rather than host identity. Secondly, I assessed energy budgets of infested and clean mussels, to evaluate the energetic cost of infestation. This involved measuring energy acquisition, expenditure, calculating scope for growth and lethal temperatures (LT50s). The results revealed that endolithic cyanobacteria have a negative effect on scope for growth due to increased metabolic rates for infested mussels, with no effect of endoliths on the rates or efficiency of energy acquisition through filtration and no effect on lethal temperatures. The effects of infestation were then examined in more detail through a qualitative and quantitative analysis of mussel gonads and byssal attachment strength to the substratum. Endolithic infestation was found to affect reproduction by affecting the size (mass) of gonads, but not the density of eggs within them. Attachment strength was affected by endolithic infestation with very infested mussels requiring much less force to detach them from the substratum compared to mussels with low or no infestation. These results show that endolithic infestation affects mussel fitness by directly affecting attachment strength and by reducing their reproductive output. Thirdly, endolithic succession within mussel shells was examined by assessing endolithic species composition in different regions of the shell and as a function of time. The results on the spatial distribution of endolith species within a shell supported those for temporal succession in shells deployed in the field. Endolithic species that were early colonists of clean shells were similar to those that were found in the distal edge, the new and growing region of the shell and species that arrived late in succession were similar to endolithic species found near the umbo, the oldest region of the shell. Overall, the study shows that endolithic cyanobacteria show the effects of biogeography on species distribution and clear patterns of succession within mussel shells. Cyanobacteria affect mussels negatively; they lead to low scope for growth and hence low growth rates, low reproductive output and reduced attachment strength for infested mussels. This, in turn is expected to have indirect consequences for other species that rely on mussels as ecological engineers for their survival.
- Full Text:
- Date Issued: 2020
- Authors: Ndhlovu, Aldwin
- Date: 2020
- Subjects: Cyanobacteria -- South Africa , Cyanobacteria -- Geographical distribution , Prokaryotes -- South Africa , Mexilhao mussel -- South Africa , Mytilus galloprovincialis -- South Africa , Coastal biology -- South Africa , Coastal ecology -- South Africa , Mussels -- Geographical distribution , Mussels -- Predators of , Mussels -- Mortality -- South Africa , Mussels -- Ecology -- South Africa , Mussels -- Growth -- South Africa , Mussels -- Fertility -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/144656 , vital:38367
- Description: Endolithic cyanobacterial species occur in a wide range of environments including cold and hot deserts as well as marine systems where they attack biological material such as corals and the shells of molluscs including limpets, mussels and abalone. Endoliths live as parasites in mussel shells, where they erode and extract calcium carbonate leading to shell weakening, creating fracture holes that lead to shell collapse and death, but they also have positive effects when they lead to discolouration of mussel shells hence giving them the ability to reduce stressful heat gain during periods of extreme heat stress. Mussels are ecological engineers on which the abundance and diversity of associated species assemblages depend. Understanding how endolithic cyanobacteria affect mussels will not only help in predicting future patterns of mussel abundances, but also future patterns of the infauna that depend on them. Firstly, I identified endolithic species infesting mussels and assessed the prevalence of endolithic parasitism in two intertidal mussel species in South Africa, the native Perna perna and the invasive Mytilus galloprovincialis. Large-scale surveys of endolithic infestation of mussels were conducted along 2500 km of the South African coast, covering three biogeographic regions: the subtropical east coast, dominated by P. perna, the warm temperate south coast where the indigenous species coexists with M. galloprovincialis, and the cool temperate west coast which is dominated by M. galloprovincialis. The prevalence of endolithic infestation was higher in the cool temperate bioregion than in the warm temperate and subtropical bioregions which did not differ and for P. perna endolithic species assemblages revealed clear groupings by bioregion. Results for endolithic induced mortality followed the same trend, with no significant difference between the two mussel species where they coexist and these results attribute biogeography of endoliths to environmental factors rather than host identity. Secondly, I assessed energy budgets of infested and clean mussels, to evaluate the energetic cost of infestation. This involved measuring energy acquisition, expenditure, calculating scope for growth and lethal temperatures (LT50s). The results revealed that endolithic cyanobacteria have a negative effect on scope for growth due to increased metabolic rates for infested mussels, with no effect of endoliths on the rates or efficiency of energy acquisition through filtration and no effect on lethal temperatures. The effects of infestation were then examined in more detail through a qualitative and quantitative analysis of mussel gonads and byssal attachment strength to the substratum. Endolithic infestation was found to affect reproduction by affecting the size (mass) of gonads, but not the density of eggs within them. Attachment strength was affected by endolithic infestation with very infested mussels requiring much less force to detach them from the substratum compared to mussels with low or no infestation. These results show that endolithic infestation affects mussel fitness by directly affecting attachment strength and by reducing their reproductive output. Thirdly, endolithic succession within mussel shells was examined by assessing endolithic species composition in different regions of the shell and as a function of time. The results on the spatial distribution of endolith species within a shell supported those for temporal succession in shells deployed in the field. Endolithic species that were early colonists of clean shells were similar to those that were found in the distal edge, the new and growing region of the shell and species that arrived late in succession were similar to endolithic species found near the umbo, the oldest region of the shell. Overall, the study shows that endolithic cyanobacteria show the effects of biogeography on species distribution and clear patterns of succession within mussel shells. Cyanobacteria affect mussels negatively; they lead to low scope for growth and hence low growth rates, low reproductive output and reduced attachment strength for infested mussels. This, in turn is expected to have indirect consequences for other species that rely on mussels as ecological engineers for their survival.
- Full Text:
- Date Issued: 2020
Carnivore intra-guild competition in Selati Game Reserve, Limpopo Province, South Africa
- Authors: Comley, Jessica
- Date: 2020
- Subjects: Hyenas -- Behavior -- South Africa , Hyenas -- South Africa , Hyenas -- Ecology -- South Africa , Top predators -- South Africa , Top predators -- Ecology -- South Africa , Animal communities -- South Africa , Animal behavior -- South Africa , Mutualism (Biology) -- South Africa , Coexistence of species -- South Africa , Game farms -- South Africa , Selati Game Reserve (South Africa)
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/115558 , vital:34163
- Description: Carnivore intra-guild interactions can be important drivers of carnivore community composition and ecosystem functioning. Large carnivores are particularly important since they occupy the highest trophic levels and can exert extensive influences on subordinate carnivores and prey species. Given Africa’s rapidly expanding human population, enclosed reserves such as those found in South Africa, may become increasingly important for carnivore conservation. A major concern, however, is that the interactions and co-existence of multiple carnivores in these systems is poorly understood. Additionally, the majority of reserves in South Africa are small ( 400km²), potentially increasing the likelihood of competition. My research aimed to provide insight into the interactions and co-existence of a multi-carnivore community within a small, enclosed reserve in South Africa (Selati Game Reserve). I tackled this task by using a combination of field techniques including camera trap surveys, ungulate transect surveys, aerial count surveys, location data collected from collared large carnivores and scat and kill site analyses. I found that carnivore-carnivore interactions, and their associated impacts, varied within the carnivore guild and that co-existence may be due to trade-offs between various risks (i.e. interference and exploitative competition) and benefits (i.e. resources such as food and space). My findings also revealed that large carnivores, such as lions (Panthera leo), spotted hyaenas (Crocuta crocuta) and leopards (Panthera pardus) do not have homogenous effects and that site-specific research on multiple-carnivores is integral for conserving biodiversity and ecosystem dynamics. Lions were the dominant large carnivore (in terms of intra-guild predation, space use and resource use) despite being outnumbered seven to one by spotted hyaenas. Leopard occupancy was negatively influenced by lions and leopard diet overlapped almost completely (91%) with spotted hyaenas, suggesting increased kleptoparasitism of leopard kills by spotted hyaenas. While my study provides valuable insight into the complexity of carnivore intra-guild competition in a small, enclosed reserve it also highlights major research gaps and emphasises the need for ecosystem-based research throughout southern Africa to fully understand how multiple sympatric carnivores co-exist in these systems.
- Full Text:
- Date Issued: 2020
- Authors: Comley, Jessica
- Date: 2020
- Subjects: Hyenas -- Behavior -- South Africa , Hyenas -- South Africa , Hyenas -- Ecology -- South Africa , Top predators -- South Africa , Top predators -- Ecology -- South Africa , Animal communities -- South Africa , Animal behavior -- South Africa , Mutualism (Biology) -- South Africa , Coexistence of species -- South Africa , Game farms -- South Africa , Selati Game Reserve (South Africa)
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/115558 , vital:34163
- Description: Carnivore intra-guild interactions can be important drivers of carnivore community composition and ecosystem functioning. Large carnivores are particularly important since they occupy the highest trophic levels and can exert extensive influences on subordinate carnivores and prey species. Given Africa’s rapidly expanding human population, enclosed reserves such as those found in South Africa, may become increasingly important for carnivore conservation. A major concern, however, is that the interactions and co-existence of multiple carnivores in these systems is poorly understood. Additionally, the majority of reserves in South Africa are small ( 400km²), potentially increasing the likelihood of competition. My research aimed to provide insight into the interactions and co-existence of a multi-carnivore community within a small, enclosed reserve in South Africa (Selati Game Reserve). I tackled this task by using a combination of field techniques including camera trap surveys, ungulate transect surveys, aerial count surveys, location data collected from collared large carnivores and scat and kill site analyses. I found that carnivore-carnivore interactions, and their associated impacts, varied within the carnivore guild and that co-existence may be due to trade-offs between various risks (i.e. interference and exploitative competition) and benefits (i.e. resources such as food and space). My findings also revealed that large carnivores, such as lions (Panthera leo), spotted hyaenas (Crocuta crocuta) and leopards (Panthera pardus) do not have homogenous effects and that site-specific research on multiple-carnivores is integral for conserving biodiversity and ecosystem dynamics. Lions were the dominant large carnivore (in terms of intra-guild predation, space use and resource use) despite being outnumbered seven to one by spotted hyaenas. Leopard occupancy was negatively influenced by lions and leopard diet overlapped almost completely (91%) with spotted hyaenas, suggesting increased kleptoparasitism of leopard kills by spotted hyaenas. While my study provides valuable insight into the complexity of carnivore intra-guild competition in a small, enclosed reserve it also highlights major research gaps and emphasises the need for ecosystem-based research throughout southern Africa to fully understand how multiple sympatric carnivores co-exist in these systems.
- Full Text:
- Date Issued: 2020
Ecological assessment of a temperate river system using biomonitoring techniques: a case study of the Bloukrans River system, South Africa
- Authors: Magadze, Tinotenda
- Date: 2020
- Subjects: Bloukrans River , Ecological assessment (Biology) -- South Africa , Stream ecology -- South Africa , Rivers -- Environmental aspects -- South Africa , Benthic animals -- Effect of human beings on -- South Africa , Water quality biological assessment -- South Africa , Diatoms -- South Africa -- Data processing
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142933 , vital:38177
- Description: Escalating pressures from growing human populations and environmental impacts increasingly imperil freshwater ecosystems. The Bloukrans River, which drains an urbanised and agricultural catchment in the Eastern Cape province of South Africa, is no exception. Detailed knowledge of the structure and function of the aquatic ecosystems is required in order to create models and matrices that predict, guide assessment and direct intervention on ecological integrity and water quality management in these systems. The main objectives of this research were to: examine the effects of urbanization on the benthic macroinvertebrate functional feeding guild structure among different stream orders; determine if benthic diatoms can be used as effective and reliable indicators of ionic composition and conductivity in different stream order categories and finally; to evaluate the applicability of the South African Diatom Index (SADI) and other indices in the Eastern Cape region of South Africa. Field studies were carried out to explore temporal patterns in community structure (macroinvertebrates and diatoms) and ecosystem function related to land-use patterns, instream habitat availability, and water quality parameters in the Bloukrans River system across four study periods: February (summer) and July (winter) 2016 and February (summer) and May/July (winter) 2018. The study was conducted along a gradient of impacts from less impacted agricultural headwaters to highly impacted urban sites located immediately downstream of the city of Makhanda. Macroinvertebrates were separated into functional feeding groups (FFGs) (i.e. collector-gatherer, collector-filterer, scraper, shredder, and predator) which were then used to assess the effects of selected physico-chemical variables and riparian zone condition on FFG organization. Collector-gatherers were the most abundant in the Bloukrans River and represented 71.3 % of the macroinvertebrate assemblages. Stream order 1species such as Nitzschia palea, Gomphonema parvulum, Tryblionella apiculata, Diploneis vulgaris and Staurosira elliptica. Multivariate analysis (Canonical correspondence analysis (CCA)) indicated that differences in diatom community assemblages were best explained by calcium, magnesium, pH, phosphate, nitrate, dissolved oxygen, sediment nitrate, conductivity and salinity. These results indicate that diatoms can be used as bioindicators for monitoring highly impacted river systems and to also further examine pollution gradients and impacts of specific/point pollution sources. In order to further test the application of diatom indices, nine sites with contrasting water quality were sampled along the length river system in February, May and July 2018. Diatom-based indices incorporated in OMNIDIA software were applied to assess the integrity of the water quality as indicated by diatom communities. For comparative purposes, several foreign indices (e.g. the trophic diatom index (TDI), the percentage pollution-tolerant valves (%PTV), biological diatom index (BDI)) and the South African Diatom Index (SADI) were used in the study. From the results, the Percentage Pollution-Tolerant Valves (%PTV) of most urban sites in the Bloukrans River was above the 20% limit indicating the presence of organic pollutants. Although the foreign diatom indices were applicable in the study, the SADI had significant correlations with most water quality variables (p < 0.05) compared to other indices such as Watanabe Index (WAT), Biological Index of Water Quality Trophic Index (BIWQ) and Trophic Index (TI)). These results support wider use of the SADI as an indicator of water quality conditions in South African river systems. Finally, the observed variations in diatom community structure and composition as a result of changes in water quality were broadly in agreement with the results of macroinvertebrate FFG structure indicating that the two biological indicators can, and should, be used as complementary techniques in the biomonitoring of rivers and streams in South Africa.
- Full Text:
- Date Issued: 2020
- Authors: Magadze, Tinotenda
- Date: 2020
- Subjects: Bloukrans River , Ecological assessment (Biology) -- South Africa , Stream ecology -- South Africa , Rivers -- Environmental aspects -- South Africa , Benthic animals -- Effect of human beings on -- South Africa , Water quality biological assessment -- South Africa , Diatoms -- South Africa -- Data processing
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/142933 , vital:38177
- Description: Escalating pressures from growing human populations and environmental impacts increasingly imperil freshwater ecosystems. The Bloukrans River, which drains an urbanised and agricultural catchment in the Eastern Cape province of South Africa, is no exception. Detailed knowledge of the structure and function of the aquatic ecosystems is required in order to create models and matrices that predict, guide assessment and direct intervention on ecological integrity and water quality management in these systems. The main objectives of this research were to: examine the effects of urbanization on the benthic macroinvertebrate functional feeding guild structure among different stream orders; determine if benthic diatoms can be used as effective and reliable indicators of ionic composition and conductivity in different stream order categories and finally; to evaluate the applicability of the South African Diatom Index (SADI) and other indices in the Eastern Cape region of South Africa. Field studies were carried out to explore temporal patterns in community structure (macroinvertebrates and diatoms) and ecosystem function related to land-use patterns, instream habitat availability, and water quality parameters in the Bloukrans River system across four study periods: February (summer) and July (winter) 2016 and February (summer) and May/July (winter) 2018. The study was conducted along a gradient of impacts from less impacted agricultural headwaters to highly impacted urban sites located immediately downstream of the city of Makhanda. Macroinvertebrates were separated into functional feeding groups (FFGs) (i.e. collector-gatherer, collector-filterer, scraper, shredder, and predator) which were then used to assess the effects of selected physico-chemical variables and riparian zone condition on FFG organization. Collector-gatherers were the most abundant in the Bloukrans River and represented 71.3 % of the macroinvertebrate assemblages. Stream order 1species such as Nitzschia palea, Gomphonema parvulum, Tryblionella apiculata, Diploneis vulgaris and Staurosira elliptica. Multivariate analysis (Canonical correspondence analysis (CCA)) indicated that differences in diatom community assemblages were best explained by calcium, magnesium, pH, phosphate, nitrate, dissolved oxygen, sediment nitrate, conductivity and salinity. These results indicate that diatoms can be used as bioindicators for monitoring highly impacted river systems and to also further examine pollution gradients and impacts of specific/point pollution sources. In order to further test the application of diatom indices, nine sites with contrasting water quality were sampled along the length river system in February, May and July 2018. Diatom-based indices incorporated in OMNIDIA software were applied to assess the integrity of the water quality as indicated by diatom communities. For comparative purposes, several foreign indices (e.g. the trophic diatom index (TDI), the percentage pollution-tolerant valves (%PTV), biological diatom index (BDI)) and the South African Diatom Index (SADI) were used in the study. From the results, the Percentage Pollution-Tolerant Valves (%PTV) of most urban sites in the Bloukrans River was above the 20% limit indicating the presence of organic pollutants. Although the foreign diatom indices were applicable in the study, the SADI had significant correlations with most water quality variables (p < 0.05) compared to other indices such as Watanabe Index (WAT), Biological Index of Water Quality Trophic Index (BIWQ) and Trophic Index (TI)). These results support wider use of the SADI as an indicator of water quality conditions in South African river systems. Finally, the observed variations in diatom community structure and composition as a result of changes in water quality were broadly in agreement with the results of macroinvertebrate FFG structure indicating that the two biological indicators can, and should, be used as complementary techniques in the biomonitoring of rivers and streams in South Africa.
- Full Text:
- Date Issued: 2020
Investigations into biological control options for Lycium ferocissimum Miers, African Boxthorn (Solanaceae) for Australia
- Authors: Mauda, Evans Vusani
- Date: 2020
- Subjects: Lycium ferocissimum , Solanaceae -- Biological control -- Australia , Weeds -- Control -- Australia , Invasive plants -- Biological control -- Australia , Insects as biological pest control agents -- Australia , Insect-plant relationships
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167142 , vital:41441
- Description: Lycium ferocissimum Miers (Solanaceae) (African boxthorn or boxthorn) is a shrub native to South Africa,and has become naturalised and invasive in Australia and New Zealand. The plant is listed on the Noxious Weed List for Australian States and territories. Although other control methods are available, biological control presents a potentially sustainable intervention for reducing populations of this weed in Australia. In South Africa, the plant has been recorded from two allopatric populations, one in the Eastern Cape Province, the other in the Western Cape Provinces, however, there taxonomic and morphological uncertainties are reported in the literature. Therefore, before native range surveys for potential biological control agents could be considered, the taxonomic uncertainty needed to be resolved. The two geographically distinct areas, as well as the Australia population were sampled to assess morphological and genetic variation. All samples collected in Australia were confirmed as L.ferocissimum, with no evidence of hybridisation with any other Lycium species. Nuclear and chloroplast genetic diversity within L.ferocissimum across South Africa was high, and Australia was low, with no evidence of genetic seperation. One ehaplotypes found across Australia was found at only two sites in South Africa, both in the Western Cape, suggesting that the Australian lineage may have originated from this region. Ten samples from South Africa, putatively identified in the field as L.ferocissimum, were genetically characterised as different (unidentified) Lycium species. The majority of plants sampled were confirmed as L.ferocissimum, sharing a common haplotype (haplotype 5) with sampled specimens from Australia. Morphological analyses across different Lycium species in South Africa did not identify any leaf or floral characteristics unique to L.ferocissimum, and thus morphological identification in the native range remains problematic. Surveys for phytophagous in sects on L.ferocissimum were carried out regularly over a two-year period in the two regions. The number of insect species found in the Eastern Cape Province (55) was higher than in the Western Cape Province (41), but insect diversity based on Shannon indices was highest in the Western Cape Province. Indicator species analysis revealed eight insect herbivore species driving the differences in the herbivore communities between the two provinces. Based on insect distribution, abundance, feeding preference and available literature, three species were prioritised as potential biological control agents. These include the leaf-chewing beetles, Cassida distinguenda Spaeth (Chrysomelidae) and Cleta eckloni Mulsant (Coccinellidae), and the leaf-mining weevil, Neoplatygaster serietuberculata Gyllenhal (Curculionidae). Native range studies such as this are perhaps the most technically difficult and logistically time-consuming part of the biological control programme. Yet, the entire outcome of a programme depends on the suite of potential agents feeding on the weed. The information gained during this stage significantly contributed to the prioritization of agents for further host-range testing and possible release. Here we showed how molecular and genetic characterisations of the target weed can be us ed to accurately define the identity and phylogeny of the target species. In addition, the study also highlighted the importance of considering plant morphology and how phenotypic plasticity may influence infield plant identifications while conducting native range surveys. By gaining further information during long-term and wide spread native range surveys we were not just able to provide a list of herbivorous insect fauna and fungi associated with the plant, but were able to prioritise the phytophagous species that held the most potential as biological control agents.
- Full Text:
- Date Issued: 2020
- Authors: Mauda, Evans Vusani
- Date: 2020
- Subjects: Lycium ferocissimum , Solanaceae -- Biological control -- Australia , Weeds -- Control -- Australia , Invasive plants -- Biological control -- Australia , Insects as biological pest control agents -- Australia , Insect-plant relationships
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167142 , vital:41441
- Description: Lycium ferocissimum Miers (Solanaceae) (African boxthorn or boxthorn) is a shrub native to South Africa,and has become naturalised and invasive in Australia and New Zealand. The plant is listed on the Noxious Weed List for Australian States and territories. Although other control methods are available, biological control presents a potentially sustainable intervention for reducing populations of this weed in Australia. In South Africa, the plant has been recorded from two allopatric populations, one in the Eastern Cape Province, the other in the Western Cape Provinces, however, there taxonomic and morphological uncertainties are reported in the literature. Therefore, before native range surveys for potential biological control agents could be considered, the taxonomic uncertainty needed to be resolved. The two geographically distinct areas, as well as the Australia population were sampled to assess morphological and genetic variation. All samples collected in Australia were confirmed as L.ferocissimum, with no evidence of hybridisation with any other Lycium species. Nuclear and chloroplast genetic diversity within L.ferocissimum across South Africa was high, and Australia was low, with no evidence of genetic seperation. One ehaplotypes found across Australia was found at only two sites in South Africa, both in the Western Cape, suggesting that the Australian lineage may have originated from this region. Ten samples from South Africa, putatively identified in the field as L.ferocissimum, were genetically characterised as different (unidentified) Lycium species. The majority of plants sampled were confirmed as L.ferocissimum, sharing a common haplotype (haplotype 5) with sampled specimens from Australia. Morphological analyses across different Lycium species in South Africa did not identify any leaf or floral characteristics unique to L.ferocissimum, and thus morphological identification in the native range remains problematic. Surveys for phytophagous in sects on L.ferocissimum were carried out regularly over a two-year period in the two regions. The number of insect species found in the Eastern Cape Province (55) was higher than in the Western Cape Province (41), but insect diversity based on Shannon indices was highest in the Western Cape Province. Indicator species analysis revealed eight insect herbivore species driving the differences in the herbivore communities between the two provinces. Based on insect distribution, abundance, feeding preference and available literature, three species were prioritised as potential biological control agents. These include the leaf-chewing beetles, Cassida distinguenda Spaeth (Chrysomelidae) and Cleta eckloni Mulsant (Coccinellidae), and the leaf-mining weevil, Neoplatygaster serietuberculata Gyllenhal (Curculionidae). Native range studies such as this are perhaps the most technically difficult and logistically time-consuming part of the biological control programme. Yet, the entire outcome of a programme depends on the suite of potential agents feeding on the weed. The information gained during this stage significantly contributed to the prioritization of agents for further host-range testing and possible release. Here we showed how molecular and genetic characterisations of the target weed can be us ed to accurately define the identity and phylogeny of the target species. In addition, the study also highlighted the importance of considering plant morphology and how phenotypic plasticity may influence infield plant identifications while conducting native range surveys. By gaining further information during long-term and wide spread native range surveys we were not just able to provide a list of herbivorous insect fauna and fungi associated with the plant, but were able to prioritise the phytophagous species that held the most potential as biological control agents.
- Full Text:
- Date Issued: 2020
Post release evaluation of the distribution and efficacy of Eccritotarsus catarinensis and Eccritotarsus eichhorniae on Pontederia crassipes in South Africa
- Authors: Maseko, Zolile
- Date: 2020
- Subjects: Water hyacinth -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Miridae -- South Africa , Insects as biological pest control agents -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/143046 , vital:38196
- Description: Biological control involves the release of new species into the environment and therefore, needs to be carefully monitored through post-release assessments which have been largely neglected in the science. Post-release evaluations of biological control programmes reveal whether the control agent has established and if it impacts weed demography, while cost-benefit analyses require a different set of data that show the magnitude on return on investment. The biological control effort on Pontederia crassipes in South Africa uses, amongst others, two species of mirid, Eccritotarsus catarinensis and E. eichhorniae. Initially, they were released as a single species, but were recently divided using molecular techniques. Eccritotarsus catarinensis was released in 1999, and E. eichhorniae in 2007. After many releases over two decades, there was need to assess where each species was established in the country. Molecular techniques proved to be valuable in identifying the two species as they are morphologically indistinguishable in the field. Therefore, molecular techniques should be routinely used for screening biocontrol agents, whether new or as re-introductions. Annual surveys of the mirid release sites around South Africa were undertaken between 2016 and 2019. At each site both insect and plant parameters were measured. Only E. catarinensis is established in the field in South Africa despite the multiple releases of E. eichhorniae at over 70 sites across the country, and E. catarinensis has established at only 22 of the 45 release sites accessed during this study. This thesis tested climate, interaction with other agents already on P. crassipes, and direct competition between the two mirid species as reasons for the lack of establishment of E. eichhorniae. The results of the country-wide surveys showed that climate and water trophic status were the major determinants in the establishment of E. catarinensis. Most of the establishment was recorded in the warmer regions of the country, however, a few populations of the mirid also established in cooler areas, thus demonstrating a degree of thermal plasticity, and possible microclimates as the mirids persisted at sites shaded by riparian vegetation. Stochastic events such as active herbicide campaigns, winter frosts, droughts and floods were responsible for the absence of the mirid at some sites. At some of the eutrophic sites, despite the abundance of E. catarinensis, plants still proliferated as the water trophic status facilitated plant growth, thus, plants were able to compensate for the damage inflicted by the mirid. A more intensive, monthly, post-release evaluation was conducted on the Kubusi River, Eastern Cape Province between 2016 and 2019. This is regarded as one of the cooler water hyacinth sites. Populations of biological control agents at this site fluctuated seasonally. At this site, cold winters caused frosting of the leaves of P. crassipes with the exception of plants growing under overhanging vegetation that provided a refuge for the mirid. But, cool temperatures in the winter months (May to August) severely reduced the populations of E. catarinensis that required a long recovery phase in spring. The consequence of this was that the plants grew unchecked from the onset of the growing season forming dense mats. Of the four agents at the Kubusi River site, Eccritotarsus catarinensis recovered slowest after winter, with lag phases ranging from two months to several months of the three-year period. The release of a suite of agents has implications on the agents themselves, where interactions between the agents can be important. Interactions between pairs and even multiple agents can have implications for biocontrol, where agents are either complimentary or interfere with each other. In this case, because E. catarinensis recovered the slowest of the four agents at the site, plants were of a poor quality by mid-summer resulting in low mirid populations. Competition in weed biological control could be expected to be strongest between pairs of agents that share the same niche, and this could be the reason why E. eichhorniae failed to establish at sites where E. catarinensis had already been established for several years. When the two mirids were combined in manipulated trials in a polytunnel, populations were lower compared to when the two mirids occurred separately. Under warm conditions, it is likely that E. eichhorniae would be the superior agent compared to E. catarinensis. The evaluations discussed in this thesis highlighted gaps in agent release methodology in multispecies settings, as well as the need for strategic augmentation pre- and post-winter. It is important to release agents that will complement each other rather than compete, therefore, when releasing agents in a multispecies setting, niche differentiation needs to be considered. Here it is concluded that the best practice for dealing with the mirids is that they should be released individually, and at sites that have no other biological control agents in order to ultimately assess their efficacy. Landscape level, long-term monitoring of biological control programmes shows the impact of the control programme at a broader scale and, are far more informative than short-term studies and at fewer sites. Long-term post-release evaluations should be mandatory in biological control programmes. Furthermore, these assessments will help develop new strategies or improve on existing ones, thus achieve greater success in control.
- Full Text:
- Date Issued: 2020
- Authors: Maseko, Zolile
- Date: 2020
- Subjects: Water hyacinth -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Miridae -- South Africa , Insects as biological pest control agents -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/143046 , vital:38196
- Description: Biological control involves the release of new species into the environment and therefore, needs to be carefully monitored through post-release assessments which have been largely neglected in the science. Post-release evaluations of biological control programmes reveal whether the control agent has established and if it impacts weed demography, while cost-benefit analyses require a different set of data that show the magnitude on return on investment. The biological control effort on Pontederia crassipes in South Africa uses, amongst others, two species of mirid, Eccritotarsus catarinensis and E. eichhorniae. Initially, they were released as a single species, but were recently divided using molecular techniques. Eccritotarsus catarinensis was released in 1999, and E. eichhorniae in 2007. After many releases over two decades, there was need to assess where each species was established in the country. Molecular techniques proved to be valuable in identifying the two species as they are morphologically indistinguishable in the field. Therefore, molecular techniques should be routinely used for screening biocontrol agents, whether new or as re-introductions. Annual surveys of the mirid release sites around South Africa were undertaken between 2016 and 2019. At each site both insect and plant parameters were measured. Only E. catarinensis is established in the field in South Africa despite the multiple releases of E. eichhorniae at over 70 sites across the country, and E. catarinensis has established at only 22 of the 45 release sites accessed during this study. This thesis tested climate, interaction with other agents already on P. crassipes, and direct competition between the two mirid species as reasons for the lack of establishment of E. eichhorniae. The results of the country-wide surveys showed that climate and water trophic status were the major determinants in the establishment of E. catarinensis. Most of the establishment was recorded in the warmer regions of the country, however, a few populations of the mirid also established in cooler areas, thus demonstrating a degree of thermal plasticity, and possible microclimates as the mirids persisted at sites shaded by riparian vegetation. Stochastic events such as active herbicide campaigns, winter frosts, droughts and floods were responsible for the absence of the mirid at some sites. At some of the eutrophic sites, despite the abundance of E. catarinensis, plants still proliferated as the water trophic status facilitated plant growth, thus, plants were able to compensate for the damage inflicted by the mirid. A more intensive, monthly, post-release evaluation was conducted on the Kubusi River, Eastern Cape Province between 2016 and 2019. This is regarded as one of the cooler water hyacinth sites. Populations of biological control agents at this site fluctuated seasonally. At this site, cold winters caused frosting of the leaves of P. crassipes with the exception of plants growing under overhanging vegetation that provided a refuge for the mirid. But, cool temperatures in the winter months (May to August) severely reduced the populations of E. catarinensis that required a long recovery phase in spring. The consequence of this was that the plants grew unchecked from the onset of the growing season forming dense mats. Of the four agents at the Kubusi River site, Eccritotarsus catarinensis recovered slowest after winter, with lag phases ranging from two months to several months of the three-year period. The release of a suite of agents has implications on the agents themselves, where interactions between the agents can be important. Interactions between pairs and even multiple agents can have implications for biocontrol, where agents are either complimentary or interfere with each other. In this case, because E. catarinensis recovered the slowest of the four agents at the site, plants were of a poor quality by mid-summer resulting in low mirid populations. Competition in weed biological control could be expected to be strongest between pairs of agents that share the same niche, and this could be the reason why E. eichhorniae failed to establish at sites where E. catarinensis had already been established for several years. When the two mirids were combined in manipulated trials in a polytunnel, populations were lower compared to when the two mirids occurred separately. Under warm conditions, it is likely that E. eichhorniae would be the superior agent compared to E. catarinensis. The evaluations discussed in this thesis highlighted gaps in agent release methodology in multispecies settings, as well as the need for strategic augmentation pre- and post-winter. It is important to release agents that will complement each other rather than compete, therefore, when releasing agents in a multispecies setting, niche differentiation needs to be considered. Here it is concluded that the best practice for dealing with the mirids is that they should be released individually, and at sites that have no other biological control agents in order to ultimately assess their efficacy. Landscape level, long-term monitoring of biological control programmes shows the impact of the control programme at a broader scale and, are far more informative than short-term studies and at fewer sites. Long-term post-release evaluations should be mandatory in biological control programmes. Furthermore, these assessments will help develop new strategies or improve on existing ones, thus achieve greater success in control.
- Full Text:
- Date Issued: 2020
Quantifying ecosystem restoration recovery and restoration practice following the biological control of invasive alien macrophytes in Southern Africa
- Authors: Motitsoe, Samuel Nkopane
- Date: 2020
- Subjects: Salvinia molesta , Ceratophyllum demersum , Nymphaea mexicana , Invasive plants -- Biological control -- South Africa , Aquatic weeds -- Biological control -- South Africa , Restoration monitoring (Ecology) -- South Africa , Biolotical invasions -- Environmental aspects
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167519 , vital:41488
- Description: Invasive alien aquatic plants (IAAP) species are known to have deleterious effects on the freshwater ecosystems they invade. This includes both socio-economic and ecologically important ecosystem goods and services. Thus, IAAP species are declared a serious threat, second only to habitat modification for causing a loss of aquatic biodiversity. Three control methods have been widely applied to control IAAP species invasion globally; mechanical, chemical and biological control. Both mechanical and chemical control methods are considered short-term and expensive, whereas biological control methods are regarded an effective and long-term solution for IAAP species control at the landscape level. But, little is known of the ecological recovery following the biological control of IAAP species, with mechanical control known to have had mixed success and chemical control to have non-targeted effects on aquatic ecosystems, causing harm to wildlife and human well-being. Biological control practitioners measure the success of biological control based on: (1) the biological control agents’ establishment and the negative impacts they impose on the targeted weed; and (2) the weeds biomass reduction and an increase in native macrophytes species. Arguably, measures of biological control success have been subjective and variable across the globe. Although some field studies have demonstrated biological control success to have positive socio-economic returns, there is little literature on ecological benefits. Furthermore, there is limited understanding on ecosystem recovery and possible restoration efforts following the biological control IAAP species, as compared to alien weeds in terrestrial and riparian ecosystems. Thus, this thesis aimed to quantify the ecological recovery i.e. aquatic biodiversity, ecosystem processes and trophic interactions following the management of Salvinia molesta in freshwater ecosystems. The research employed a suite of Before-After Control-Impact mesocosm and field studies to investigate the response of aquatic microalgae, macroinvertebrates and their interactions (food web structure and function) during S. molesta infestation and after mechanical and biological control. The mesocosm experiment (Before invasion, During invasion & After control) showed that both aquatic microalgae and macroinvertebrate diversity indices were reliable biological indicators of S. molesta ecological impacts and recovery following control. The restored treatment (100% S. molesta cover + biological control agents), demonstrated complete aquatic microalgae and macroinvertebrate recovery following biological control, similar to the control treatment (open water), where the degraded/impacted treatment (100% S. molesta cover with no biological control agents) showed a drastic decline in aquatic biodiversity and a complete shift in aquatic biota assemblage structure. Thus, the biological control effort by Cyrtobagous salviniae, the biological control agent for S. molesta, assisted in the recovery of aquatic biota following successful biological control. The field study (four field sites, two sites controlled mechanically and two biologically) investigated water quality, aquatic biodiversity and community trophic interactions (aquatic food web) “before and after” S. molesta control. The study showed a drastic decline in aquatic biodiversity (with three sites showing no record of aquatic macroinvertebrates, thus no biotic interactions during infestation) and poor water quality due to the shade-effect (light barrier due to floating S. molesta mats on the water surface) during the “before” S. molesta control phase. However, following both mechanical and biological control (“after” S. molesta control phase), there was a significant shift in abiotic and biotic ecosystem characteristics as compared to the “before” S. molesta control phase. Thus, rapid ecosystem recovery was apparent as a result of aquatic microalgae and macroinvertebrates recolonisation. Sites showed a normal functioning ecosystem where improved water quality, increased biodiversity, productivity and trophic interactions, was indicative of the return of biologically and functionally important species which were lost during the “before” S. molesta phase. Although the clear water state showed positive outcomes at Westlake River, these were short lived when the system was dominated by a cosmopolitan submerged Ceratophyllum demersum, and later replaced by a floating-leaved emergent IAAP Nymphaea mexicana. Each state was responsible for a significant shift in both biotic and abiotic characteristics, affirming macrophyte abilities to influence aquatic environments structure and functions. Furthermore, this event showed a clear example of a secondary invasion. Thus, a holistic IAAP species management strategy is necessary to restore previously invaded ecosystems and prevent subsequent secondary invasion and ecosystem degradation. In conclusion, the S. molesta shade-effect like any other free-floating IAAP species, was identified as the main degrading factor and responsible for water quality reduction, loss of aquatic diversity and shift in aquatic biota assemblage structure. Following S. molesta removal (or shade-effect elimination), there was a positive response to aquatic ecosystem species abundance, richness, diversity and community structure. Therefore, in combination, aquatic biota recolonisation rate and increases in biological and functional diversity were instrumental in the recovery of ecosystem structure and functions, following the control of S. molesta. Echoing existing literature, this thesis recommends: (1) IAAP species management programmes (mechanical and/or biological control) should not only aim to control the weed but also focus on ecosystems recovery and possible restoration goals; (2) biological control should be used where appropriate to combat free-floating IAAP species in freshwater ecosystems, followed by active introduction of native macrophyte propagules since they are limited by anthropogenic activities; and (3) more freshwater case studies are needed to add to our understanding of IAAP species management and restoration effort incorporating long-term monitoring.
- Full Text:
- Date Issued: 2020
- Authors: Motitsoe, Samuel Nkopane
- Date: 2020
- Subjects: Salvinia molesta , Ceratophyllum demersum , Nymphaea mexicana , Invasive plants -- Biological control -- South Africa , Aquatic weeds -- Biological control -- South Africa , Restoration monitoring (Ecology) -- South Africa , Biolotical invasions -- Environmental aspects
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/167519 , vital:41488
- Description: Invasive alien aquatic plants (IAAP) species are known to have deleterious effects on the freshwater ecosystems they invade. This includes both socio-economic and ecologically important ecosystem goods and services. Thus, IAAP species are declared a serious threat, second only to habitat modification for causing a loss of aquatic biodiversity. Three control methods have been widely applied to control IAAP species invasion globally; mechanical, chemical and biological control. Both mechanical and chemical control methods are considered short-term and expensive, whereas biological control methods are regarded an effective and long-term solution for IAAP species control at the landscape level. But, little is known of the ecological recovery following the biological control of IAAP species, with mechanical control known to have had mixed success and chemical control to have non-targeted effects on aquatic ecosystems, causing harm to wildlife and human well-being. Biological control practitioners measure the success of biological control based on: (1) the biological control agents’ establishment and the negative impacts they impose on the targeted weed; and (2) the weeds biomass reduction and an increase in native macrophytes species. Arguably, measures of biological control success have been subjective and variable across the globe. Although some field studies have demonstrated biological control success to have positive socio-economic returns, there is little literature on ecological benefits. Furthermore, there is limited understanding on ecosystem recovery and possible restoration efforts following the biological control IAAP species, as compared to alien weeds in terrestrial and riparian ecosystems. Thus, this thesis aimed to quantify the ecological recovery i.e. aquatic biodiversity, ecosystem processes and trophic interactions following the management of Salvinia molesta in freshwater ecosystems. The research employed a suite of Before-After Control-Impact mesocosm and field studies to investigate the response of aquatic microalgae, macroinvertebrates and their interactions (food web structure and function) during S. molesta infestation and after mechanical and biological control. The mesocosm experiment (Before invasion, During invasion & After control) showed that both aquatic microalgae and macroinvertebrate diversity indices were reliable biological indicators of S. molesta ecological impacts and recovery following control. The restored treatment (100% S. molesta cover + biological control agents), demonstrated complete aquatic microalgae and macroinvertebrate recovery following biological control, similar to the control treatment (open water), where the degraded/impacted treatment (100% S. molesta cover with no biological control agents) showed a drastic decline in aquatic biodiversity and a complete shift in aquatic biota assemblage structure. Thus, the biological control effort by Cyrtobagous salviniae, the biological control agent for S. molesta, assisted in the recovery of aquatic biota following successful biological control. The field study (four field sites, two sites controlled mechanically and two biologically) investigated water quality, aquatic biodiversity and community trophic interactions (aquatic food web) “before and after” S. molesta control. The study showed a drastic decline in aquatic biodiversity (with three sites showing no record of aquatic macroinvertebrates, thus no biotic interactions during infestation) and poor water quality due to the shade-effect (light barrier due to floating S. molesta mats on the water surface) during the “before” S. molesta control phase. However, following both mechanical and biological control (“after” S. molesta control phase), there was a significant shift in abiotic and biotic ecosystem characteristics as compared to the “before” S. molesta control phase. Thus, rapid ecosystem recovery was apparent as a result of aquatic microalgae and macroinvertebrates recolonisation. Sites showed a normal functioning ecosystem where improved water quality, increased biodiversity, productivity and trophic interactions, was indicative of the return of biologically and functionally important species which were lost during the “before” S. molesta phase. Although the clear water state showed positive outcomes at Westlake River, these were short lived when the system was dominated by a cosmopolitan submerged Ceratophyllum demersum, and later replaced by a floating-leaved emergent IAAP Nymphaea mexicana. Each state was responsible for a significant shift in both biotic and abiotic characteristics, affirming macrophyte abilities to influence aquatic environments structure and functions. Furthermore, this event showed a clear example of a secondary invasion. Thus, a holistic IAAP species management strategy is necessary to restore previously invaded ecosystems and prevent subsequent secondary invasion and ecosystem degradation. In conclusion, the S. molesta shade-effect like any other free-floating IAAP species, was identified as the main degrading factor and responsible for water quality reduction, loss of aquatic diversity and shift in aquatic biota assemblage structure. Following S. molesta removal (or shade-effect elimination), there was a positive response to aquatic ecosystem species abundance, richness, diversity and community structure. Therefore, in combination, aquatic biota recolonisation rate and increases in biological and functional diversity were instrumental in the recovery of ecosystem structure and functions, following the control of S. molesta. Echoing existing literature, this thesis recommends: (1) IAAP species management programmes (mechanical and/or biological control) should not only aim to control the weed but also focus on ecosystems recovery and possible restoration goals; (2) biological control should be used where appropriate to combat free-floating IAAP species in freshwater ecosystems, followed by active introduction of native macrophyte propagules since they are limited by anthropogenic activities; and (3) more freshwater case studies are needed to add to our understanding of IAAP species management and restoration effort incorporating long-term monitoring.
- Full Text:
- Date Issued: 2020
Temporal patterns and seasonal variation in microplastic loads in the water column and in the tissues of consumers along the southern and south-eastern coasts of South Africa
- Authors: Redelinghuys, Suzanne
- Date: 2020
- Subjects: Microplastics -- South Africa -- Eastern Cape , Plastic marine debris -- South Africa -- Eastern Cape , Marine pollution -- South Africa -- Eastern Cape , Ocean circulation -- South Africa -- Eastern Cape , Marine invertebrates -- Effect of pollution on -- South Africa -- Eastern Cape , Marine animals -- Effect of pollution on -- South Africa -- Eastern Cape , Mexilhao mussel -- Effect of pollution on -- South Africa -- Eastern Cape , Mytilus galloprovincialis -- Effect of pollution on -- South Africa -- Eastern Cape , Barnacles -- Effect of pollution on -- South Africa -- Eastern Cape , Tetraclita -- Effect of pollution on -- South Africa -- Eastern Cape , Octomeris angulosa -- Effect of pollution on -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/115623 , vital:34201
- Description: Plastic pollution in the marine environment has become an environmental concern and a subject of ecological research. The field of microplastic pollution in particular has expanded dramatically in the last few years. Though much data exists on the spatial variability of microplastics in the marine environment globally, little is known about temporal variability, especially on short-term time scales in the southern hemisphere. Similarly, virtually nothing is known about the temporal patterns in microplastic ingestion by marine invertebrates, despite the fact that numerous studies have demonstrated that vertebrates and invertebrates routinely ingest microplastics with varied physiological effects. This study aimed to, 1) provide base-line data for microplastic loads in the nearshore environment along the Eastern Cape Province of South Africa over four short-term time scales: daily, weekly, monthly, and yearly; and, 2) assess whether there are any seasonal patterns in microplastics ingested by selected filter-feeding consumers at two sites along the southern and south-eastern Cape coastlines of South Africa. Results for part one of this study demonstrate no temporal patterns over the different time scales considered (ANOVA, p > 0.05 in all cases). Microplastic counts ranged on average from 55 ± 289 to 930 ± 462 microplastic particles.m-3. With the exception of two instances, microfibres constituted > 50 % (range: 47 to 97 %) of the total microplastic counts. Part two of this study assessed the size range of, and seasonal and spatial patterns in ingested microplastic. No significant differences were found in the number of microplastics ingested within seasons between the mussels Perna perna (Linnaeus, 1758) and Mytilus galloprovincialis (Lamarck, 1819), and the barnacles, Octomeris angulosa (Sowerby, 1825) and Tetraclita serrata (Darwin 1954) (Student’s t-test; d.f = 18; p > 0.05 in all cases), or between the two sites sampled, Kenton-on-Sea, Eastern Cape, and Wilderness, Western Cape (ANOVA; d.f. = 18; p > 0.05 in all cases). The nitric acid digestion technique was used to determine the presence of ingested microplastics. Microplastic loads ranged from 2 ± 1 to 33 ± 19 microplastics.g-1 wwt across all consumers, and the size of ingested microplastics ranged from 1 to 16 μm. Though highly variable, the absence of statistically significant differences in ingestion rates points to a ubiquity in the availability of microplastics within the water column over time and space.
- Full Text:
- Date Issued: 2020
- Authors: Redelinghuys, Suzanne
- Date: 2020
- Subjects: Microplastics -- South Africa -- Eastern Cape , Plastic marine debris -- South Africa -- Eastern Cape , Marine pollution -- South Africa -- Eastern Cape , Ocean circulation -- South Africa -- Eastern Cape , Marine invertebrates -- Effect of pollution on -- South Africa -- Eastern Cape , Marine animals -- Effect of pollution on -- South Africa -- Eastern Cape , Mexilhao mussel -- Effect of pollution on -- South Africa -- Eastern Cape , Mytilus galloprovincialis -- Effect of pollution on -- South Africa -- Eastern Cape , Barnacles -- Effect of pollution on -- South Africa -- Eastern Cape , Tetraclita -- Effect of pollution on -- South Africa -- Eastern Cape , Octomeris angulosa -- Effect of pollution on -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/115623 , vital:34201
- Description: Plastic pollution in the marine environment has become an environmental concern and a subject of ecological research. The field of microplastic pollution in particular has expanded dramatically in the last few years. Though much data exists on the spatial variability of microplastics in the marine environment globally, little is known about temporal variability, especially on short-term time scales in the southern hemisphere. Similarly, virtually nothing is known about the temporal patterns in microplastic ingestion by marine invertebrates, despite the fact that numerous studies have demonstrated that vertebrates and invertebrates routinely ingest microplastics with varied physiological effects. This study aimed to, 1) provide base-line data for microplastic loads in the nearshore environment along the Eastern Cape Province of South Africa over four short-term time scales: daily, weekly, monthly, and yearly; and, 2) assess whether there are any seasonal patterns in microplastics ingested by selected filter-feeding consumers at two sites along the southern and south-eastern Cape coastlines of South Africa. Results for part one of this study demonstrate no temporal patterns over the different time scales considered (ANOVA, p > 0.05 in all cases). Microplastic counts ranged on average from 55 ± 289 to 930 ± 462 microplastic particles.m-3. With the exception of two instances, microfibres constituted > 50 % (range: 47 to 97 %) of the total microplastic counts. Part two of this study assessed the size range of, and seasonal and spatial patterns in ingested microplastic. No significant differences were found in the number of microplastics ingested within seasons between the mussels Perna perna (Linnaeus, 1758) and Mytilus galloprovincialis (Lamarck, 1819), and the barnacles, Octomeris angulosa (Sowerby, 1825) and Tetraclita serrata (Darwin 1954) (Student’s t-test; d.f = 18; p > 0.05 in all cases), or between the two sites sampled, Kenton-on-Sea, Eastern Cape, and Wilderness, Western Cape (ANOVA; d.f. = 18; p > 0.05 in all cases). The nitric acid digestion technique was used to determine the presence of ingested microplastics. Microplastic loads ranged from 2 ± 1 to 33 ± 19 microplastics.g-1 wwt across all consumers, and the size of ingested microplastics ranged from 1 to 16 μm. Though highly variable, the absence of statistically significant differences in ingestion rates points to a ubiquity in the availability of microplastics within the water column over time and space.
- Full Text:
- Date Issued: 2020
The management of lions (Panthera Leo) in small, fenced wildlife reserves
- Authors: McEvoy, Orla
- Date: 2020
- Subjects: Lion -- Behavior -- South Africa , Spatial behavior in animals -- South Africa , Animal populations -- South Africa , Game reserves -- South Africa -- Management
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/143471 , vital:38249
- Description: Reintroduced lion (Panthera leo) populations pose several ecological and management challenges in small (< 1,000 km2), fenced wildlife reserves. Changes in the natural socialecological conditions of reintroduced lion populations may lead to rapid population growth and a breakdown of natural predator-prey relationships. Reduced competition with other lions also likely reduces the potential for reintroduced lions to naturally form groups. My study used a combination of questionnaire surveys with tourists, existing lion demographic data from 16 wildlife reserves across South Africa and a controlled lion social experiment to address these ecological and management issues. Tourism was the primary reason for lion reintroductions. Tourists scored lions highly in terms of preference for viewing on safari, in particular, lions in larger, natural groups and adult males. Viewing lions also enhanced a tourists’ overall safari experience. The breakdown of natural social behaviour may likely therefore reduce tourist satisfaction related to lions. The number of resident prides and male coalitions in a reserve affected lion vital rates. Lion population growth rate was highest in reserves that contained a single resident pride, and the presence of unknown adult males significantly reduced cub survival and lioness birth intervals. The ratio of male cubs born also increased in reserves with a higher density of unknown adult males. Fertility control measures (deslorelin implants and unilateral hysterectomy) were effective at limiting lion population growth. Deslorelin treatment increased the age of first reproduction or the birth interval and decreased the subsequent litter size of treated lionesses to closer reflect natural vital rates in larger (> 10, 000 km2) systems. However, there was variability in infertility response between lionesses including adverse reactions in a small proportion of treated individuals. The number of resident prides and male coalitions in a reserve affected lion social behaviour. Lionesses formed larger groups in reserves with a higher density of unknown adult female neighbours, likely driven by territory defence. Lion prides with resident cubs were generally more fragmented, likely in response to reduced competition from unknown adult males. However, in areas with a high density of unknown adult female neighbours, prides with cubs formed larger groups likely in response to heightened territory defence. Therefore, with smaller foraging group sizes, predation rate was increased in reserves with reduced competition from unknown lions. My study supports a metapopulation approach for the management of lions in small, fenced reserves, and the standardisation of lion management procedures and database management. Endorsed by the Biodiversity Management Plan for lions in South Africa, this will enhance the long-term conservation potential of isolated populations.
- Full Text:
- Date Issued: 2020
- Authors: McEvoy, Orla
- Date: 2020
- Subjects: Lion -- Behavior -- South Africa , Spatial behavior in animals -- South Africa , Animal populations -- South Africa , Game reserves -- South Africa -- Management
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/143471 , vital:38249
- Description: Reintroduced lion (Panthera leo) populations pose several ecological and management challenges in small (< 1,000 km2), fenced wildlife reserves. Changes in the natural socialecological conditions of reintroduced lion populations may lead to rapid population growth and a breakdown of natural predator-prey relationships. Reduced competition with other lions also likely reduces the potential for reintroduced lions to naturally form groups. My study used a combination of questionnaire surveys with tourists, existing lion demographic data from 16 wildlife reserves across South Africa and a controlled lion social experiment to address these ecological and management issues. Tourism was the primary reason for lion reintroductions. Tourists scored lions highly in terms of preference for viewing on safari, in particular, lions in larger, natural groups and adult males. Viewing lions also enhanced a tourists’ overall safari experience. The breakdown of natural social behaviour may likely therefore reduce tourist satisfaction related to lions. The number of resident prides and male coalitions in a reserve affected lion vital rates. Lion population growth rate was highest in reserves that contained a single resident pride, and the presence of unknown adult males significantly reduced cub survival and lioness birth intervals. The ratio of male cubs born also increased in reserves with a higher density of unknown adult males. Fertility control measures (deslorelin implants and unilateral hysterectomy) were effective at limiting lion population growth. Deslorelin treatment increased the age of first reproduction or the birth interval and decreased the subsequent litter size of treated lionesses to closer reflect natural vital rates in larger (> 10, 000 km2) systems. However, there was variability in infertility response between lionesses including adverse reactions in a small proportion of treated individuals. The number of resident prides and male coalitions in a reserve affected lion social behaviour. Lionesses formed larger groups in reserves with a higher density of unknown adult female neighbours, likely driven by territory defence. Lion prides with resident cubs were generally more fragmented, likely in response to reduced competition from unknown adult males. However, in areas with a high density of unknown adult female neighbours, prides with cubs formed larger groups likely in response to heightened territory defence. Therefore, with smaller foraging group sizes, predation rate was increased in reserves with reduced competition from unknown lions. My study supports a metapopulation approach for the management of lions in small, fenced reserves, and the standardisation of lion management procedures and database management. Endorsed by the Biodiversity Management Plan for lions in South Africa, this will enhance the long-term conservation potential of isolated populations.
- Full Text:
- Date Issued: 2020
Large scale spatio-temporal forcing of pelagic-coastal coupling: disentangling the effects of environmental change on intertidal invertebrate recruitment
- Authors: Muñiz, Carlota Fernández
- Date: 2019
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/75317 , vital:30400
- Description: Marine systems are driven by the relationships among organisms and environmental conditions. Anthropogenic-induced changes during the past decades have started to alter climatic drivers which have the potential to alter the physical, chemical and biological environment. In coastal systems, biogeography is influenced by the temporal variability in the conditions of the water mass. In addition, many marine benthic organisms develop in the water mass and rely on the conditions that link the pelagic and benthic systems for population maintenance. Such pelagic-coastal coupling indicates that changes in the trophic system during development can be transferred to the adult populations through changes in propagule supply. Thus, changes in environmental conditions can influence benthic populations directly (e.g. through larval advection) or indirectly, through their influence on the phytoplankton community (e.g. through the development of HABs). The South African coastline shows clear alongshore patterns of faunal biomass and species richness. On the south coast, strong longitudinal patterns of recruitment of intertidal organisms exist, with areas of particularly high recruitment. HABs of unprecedented spatio-temporal magnitude have recently developed along the south coast, including the areas where benthic recruitment is most intense. The present thesis used these blooms to study changes in intertidal recruitment directly or indirectly associated with their occurrence. Using a combination of remote sensing data to study the environmental conditions of the water mass in the innermost part of the Agulhas Bank, and estimates of mussel and barnacle recruitment rates to integrate the effects of conditions in the water mass during larval development, this thesis aimed to: (1) understand the conditions that triggered the development of an HAB of the dinoflagellate Lingulodinium polyedrum during summer of 2014, (2) determine the direct or indirect effects of that bloom on recruitment of intertidal organisms, and understand the factors that affect recruitment along the coast, (3) determine if the environmental factors during bloom development produced any carryover effects on recruit growth and mortality, and (4) determine the factors that drive changes in community biomass and composition along the south coast, the long-term trends in those factors, and possible changes experienced in recent years. Water column stability during spring, before the development of the red tide, followed by alternating periods of upwelling and relaxation during summer and autumn, seemed to promote the development and persistence of L. polyedrum. Recruitment of mussels and barnacles was estimated during the reproductive season of mussels in 2014, coinciding with the red tide, and during the following year. Alongshore patterns in recruitment were found, with higher mussel recruitment in the absence of the red tide and the opposite pattern in barnacles. Alongshore patterns in SST and chlorophyll matching those of recruitment were also found, with higher SSTs and lower chlorophyll during the red tide than the following year. Growth and mortality rates in barnacles did not differ between years during the first five months after settlement. This suggests that the factors which produced differences in recruitment between years did not produce carryover effects detectable at the temporal scales studied. Further analysis of 15 years of satellite-derived environmental data showed significant cooling trends potentially driven by a long-term seasonal acceleration of the Agulhas Current in autumn around two upwelling centres on the south coast, coinciding temporally with the reproductive period of mussels and barnacles, and spatially with the areas of highest recruitment. In addition, the comparison of SST and chl-a conditions during the first and the second half of the period of study showed that seasonality of both variables has changed in large areas over the shelf, with increasing importance of shorter-term variability, which would in turn decrease environmental predictability. Thus, the conditions observed during the present study, particularly during 2015, when upwelling seemed to be more intense, may presage the potential effects of identified long-term cooling trends at the upwelling centres. Although the general trend shows cooling around those areas, conditions can vary greatly among years, favouring different taxa. Changes in the Agulhas Current System are affected by changes in distant areas in the Indian Ocean basin. Such tele-connection is unlikely to be unique to this system and indicates the importance of understanding trends in major large scale climatic drivers and their regional effects in order to make predictions about coastal systems.
- Full Text:
- Date Issued: 2019
- Authors: Muñiz, Carlota Fernández
- Date: 2019
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/75317 , vital:30400
- Description: Marine systems are driven by the relationships among organisms and environmental conditions. Anthropogenic-induced changes during the past decades have started to alter climatic drivers which have the potential to alter the physical, chemical and biological environment. In coastal systems, biogeography is influenced by the temporal variability in the conditions of the water mass. In addition, many marine benthic organisms develop in the water mass and rely on the conditions that link the pelagic and benthic systems for population maintenance. Such pelagic-coastal coupling indicates that changes in the trophic system during development can be transferred to the adult populations through changes in propagule supply. Thus, changes in environmental conditions can influence benthic populations directly (e.g. through larval advection) or indirectly, through their influence on the phytoplankton community (e.g. through the development of HABs). The South African coastline shows clear alongshore patterns of faunal biomass and species richness. On the south coast, strong longitudinal patterns of recruitment of intertidal organisms exist, with areas of particularly high recruitment. HABs of unprecedented spatio-temporal magnitude have recently developed along the south coast, including the areas where benthic recruitment is most intense. The present thesis used these blooms to study changes in intertidal recruitment directly or indirectly associated with their occurrence. Using a combination of remote sensing data to study the environmental conditions of the water mass in the innermost part of the Agulhas Bank, and estimates of mussel and barnacle recruitment rates to integrate the effects of conditions in the water mass during larval development, this thesis aimed to: (1) understand the conditions that triggered the development of an HAB of the dinoflagellate Lingulodinium polyedrum during summer of 2014, (2) determine the direct or indirect effects of that bloom on recruitment of intertidal organisms, and understand the factors that affect recruitment along the coast, (3) determine if the environmental factors during bloom development produced any carryover effects on recruit growth and mortality, and (4) determine the factors that drive changes in community biomass and composition along the south coast, the long-term trends in those factors, and possible changes experienced in recent years. Water column stability during spring, before the development of the red tide, followed by alternating periods of upwelling and relaxation during summer and autumn, seemed to promote the development and persistence of L. polyedrum. Recruitment of mussels and barnacles was estimated during the reproductive season of mussels in 2014, coinciding with the red tide, and during the following year. Alongshore patterns in recruitment were found, with higher mussel recruitment in the absence of the red tide and the opposite pattern in barnacles. Alongshore patterns in SST and chlorophyll matching those of recruitment were also found, with higher SSTs and lower chlorophyll during the red tide than the following year. Growth and mortality rates in barnacles did not differ between years during the first five months after settlement. This suggests that the factors which produced differences in recruitment between years did not produce carryover effects detectable at the temporal scales studied. Further analysis of 15 years of satellite-derived environmental data showed significant cooling trends potentially driven by a long-term seasonal acceleration of the Agulhas Current in autumn around two upwelling centres on the south coast, coinciding temporally with the reproductive period of mussels and barnacles, and spatially with the areas of highest recruitment. In addition, the comparison of SST and chl-a conditions during the first and the second half of the period of study showed that seasonality of both variables has changed in large areas over the shelf, with increasing importance of shorter-term variability, which would in turn decrease environmental predictability. Thus, the conditions observed during the present study, particularly during 2015, when upwelling seemed to be more intense, may presage the potential effects of identified long-term cooling trends at the upwelling centres. Although the general trend shows cooling around those areas, conditions can vary greatly among years, favouring different taxa. Changes in the Agulhas Current System are affected by changes in distant areas in the Indian Ocean basin. Such tele-connection is unlikely to be unique to this system and indicates the importance of understanding trends in major large scale climatic drivers and their regional effects in order to make predictions about coastal systems.
- Full Text:
- Date Issued: 2019
Large scale spatio-temporal forcing of pelagic-coastal coupling: disentangling the effects of environmental change on intertidal invertebrate recruitment
- Authors: Muñiz, Carlota Fernández
- Date: 2019
- Subjects: Dinoflagellates -- South Africa , Coastal ecology -- South Africa , Climatic changes -- South Africa , Benthic ecology -- South Africa , Agulhas Current , Ocean temperature -- Agulhas Current , Ocean temperature -- Physiological effect
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/151541 , vital:39140
- Description: Marine systems are driven by the relationships among organisms and environmental conditions. Anthropogenic-induced changes during the past decades have started to alter climatic drivers which have the potential to alter the physical, chemical and biological environment. In coastal systems, biogeography is influenced by the temporal variability in the conditions of the water mass. In addition, many marine benthic organisms develop in the water mass and rely on the conditions that link the pelagic and benthic systems for population maintenance. Such pelagic-coastal coupling indicates that changes in the trophic system during development can be transferred to the adult populations through changes in propagule supply. Thus, changes in environmental conditions can influence benthic populations directly (e.g. through larval advection) or indirectly, through their influence on the phytoplankton community (e.g. through the development of HABs). The South African coastline shows clear alongshore patterns of faunal biomass and species richness. On the south coast, strong longitudinal patterns of recruitment of intertidal organisms exist, with areas of particularly high recruitment. HABs of unprecedented spatio-temporal magnitude have recently developed along the south coast, including the areas where benthic recruitment is most intense. The present thesis used these blooms to study changes in intertidal recruitment directly or indirectly associated with their occurrence. Using a combination of remote sensing data to study the environmental conditions of the water mass in the innermost part of the Agulhas Bank, and estimates of mussel and barnacle recruitment rates to integrate the effects of conditions in the water mass during larval development, this thesis aimed to: (1) understand the conditions that triggered the development of an HAB of the dinoflagellate Lingulodinium polyedrum during summer of 2014, (2) determine the direct or indirect effects of that bloom on recruitment of intertidal organisms, and understand the factors that affect recruitment along the coast, (3) determine if the environmental factors during bloom development produced any carryover effects on recruit growth and mortality, and (4) determine the factors that drive changes in community biomass and composition along the south coast, the long-term trends in those factors, and possible changes experienced in recent years. Water column stability during spring, before the development of the red tide, followed by alternating periods of upwelling and relaxation during summer and autumn, seemed to promote the development and persistence of L. polyedrum. Recruitment of mussels and barnacles was estimated during the reproductive season of mussels in 2014, coinciding with the red tide, and during the following year. Alongshore patterns in recruitment were found, with higher mussel recruitment in the absence of the red tide and the opposite pattern in barnacles. Alongshore patterns in SST and chlorophyll matching those of recruitment were also found, with higher SSTs and lower chlorophyll during the red tide than the following year. Growth and mortality rates in barnacles did not differ between years during the first five months after settlement. This suggests that the factors which produced differences in recruitment between years did not produce carryover effects detectable at the temporal scales studied. Further analysis of 15 years of satellite-derived environmental data showed significant cooling trends potentially driven by a long-term seasonal acceleration of the Agulhas Current in autumn around two upwelling centres on the south coast, coinciding temporally with the reproductive period of mussels and barnacles, and spatially with the areas of highest recruitment. In addition, the comparison of SST and chl-a conditions during the first and the second half of the period of study showed that seasonality of both variables has changed in large areas over the shelf, with increasing importance of shorter-term variability, which would in turn decrease environmental predictability. Thus, the conditions observed during the present study, particularly during 2015, when upwelling seemed to be more intense, may presage the potential effects of identified long-term cooling trends at the upwelling centres. Although the general trend shows cooling around those areas, conditions can vary greatly among years, favouring different taxa. Changes in the Agulhas Current System are affected by changes in distant areas in the Indian Ocean basin. Such tele-connection is unlikely to be unique to this system and indicates the importance of understanding trends in major large scale climatic drivers and their regional effects in order to make predictions about coastal systems.
- Full Text:
- Date Issued: 2019
- Authors: Muñiz, Carlota Fernández
- Date: 2019
- Subjects: Dinoflagellates -- South Africa , Coastal ecology -- South Africa , Climatic changes -- South Africa , Benthic ecology -- South Africa , Agulhas Current , Ocean temperature -- Agulhas Current , Ocean temperature -- Physiological effect
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/151541 , vital:39140
- Description: Marine systems are driven by the relationships among organisms and environmental conditions. Anthropogenic-induced changes during the past decades have started to alter climatic drivers which have the potential to alter the physical, chemical and biological environment. In coastal systems, biogeography is influenced by the temporal variability in the conditions of the water mass. In addition, many marine benthic organisms develop in the water mass and rely on the conditions that link the pelagic and benthic systems for population maintenance. Such pelagic-coastal coupling indicates that changes in the trophic system during development can be transferred to the adult populations through changes in propagule supply. Thus, changes in environmental conditions can influence benthic populations directly (e.g. through larval advection) or indirectly, through their influence on the phytoplankton community (e.g. through the development of HABs). The South African coastline shows clear alongshore patterns of faunal biomass and species richness. On the south coast, strong longitudinal patterns of recruitment of intertidal organisms exist, with areas of particularly high recruitment. HABs of unprecedented spatio-temporal magnitude have recently developed along the south coast, including the areas where benthic recruitment is most intense. The present thesis used these blooms to study changes in intertidal recruitment directly or indirectly associated with their occurrence. Using a combination of remote sensing data to study the environmental conditions of the water mass in the innermost part of the Agulhas Bank, and estimates of mussel and barnacle recruitment rates to integrate the effects of conditions in the water mass during larval development, this thesis aimed to: (1) understand the conditions that triggered the development of an HAB of the dinoflagellate Lingulodinium polyedrum during summer of 2014, (2) determine the direct or indirect effects of that bloom on recruitment of intertidal organisms, and understand the factors that affect recruitment along the coast, (3) determine if the environmental factors during bloom development produced any carryover effects on recruit growth and mortality, and (4) determine the factors that drive changes in community biomass and composition along the south coast, the long-term trends in those factors, and possible changes experienced in recent years. Water column stability during spring, before the development of the red tide, followed by alternating periods of upwelling and relaxation during summer and autumn, seemed to promote the development and persistence of L. polyedrum. Recruitment of mussels and barnacles was estimated during the reproductive season of mussels in 2014, coinciding with the red tide, and during the following year. Alongshore patterns in recruitment were found, with higher mussel recruitment in the absence of the red tide and the opposite pattern in barnacles. Alongshore patterns in SST and chlorophyll matching those of recruitment were also found, with higher SSTs and lower chlorophyll during the red tide than the following year. Growth and mortality rates in barnacles did not differ between years during the first five months after settlement. This suggests that the factors which produced differences in recruitment between years did not produce carryover effects detectable at the temporal scales studied. Further analysis of 15 years of satellite-derived environmental data showed significant cooling trends potentially driven by a long-term seasonal acceleration of the Agulhas Current in autumn around two upwelling centres on the south coast, coinciding temporally with the reproductive period of mussels and barnacles, and spatially with the areas of highest recruitment. In addition, the comparison of SST and chl-a conditions during the first and the second half of the period of study showed that seasonality of both variables has changed in large areas over the shelf, with increasing importance of shorter-term variability, which would in turn decrease environmental predictability. Thus, the conditions observed during the present study, particularly during 2015, when upwelling seemed to be more intense, may presage the potential effects of identified long-term cooling trends at the upwelling centres. Although the general trend shows cooling around those areas, conditions can vary greatly among years, favouring different taxa. Changes in the Agulhas Current System are affected by changes in distant areas in the Indian Ocean basin. Such tele-connection is unlikely to be unique to this system and indicates the importance of understanding trends in major large scale climatic drivers and their regional effects in order to make predictions about coastal systems.
- Full Text:
- Date Issued: 2019
Occurrence, feeding ecology, and population structure of two dolphin species, Tursiops aduncus and Delphinus delphis, off the Wild Coast of South Africa
- Authors: Caputo, Michelle Anne
- Date: 2019
- Subjects: Delphinus -- South Africa-- Kwazulu-Natal -- Ecology , Tursoops -- South Africa-- Kwazulu-Natal -- Ecology , Delphinus -- South Africa-- Kwazulu-Natal -- Feeding and feeds , Tursoops -- South Africa-- Kwazulu-Natal -- Feeding and feeds , Dolphins -- South Africa-- Kwazulu-Natal , Delphinus -- South Africa-- Kwazulu-Natal -- Behavior , Tursoops -- South Africa-- Kwazulu-Natal -- Behavior , Marine ecology -- South Africa -- Kwazulu-Natal
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/115612 , vital:34197
- Description: Dolphins are apex predators and their movements, foraging activities and population dynamics play an important role in shaping their environment. Understanding their occurrence, movement patterns, and trophic ecology is essential to their conservation, especially as they are considered sentinel species. The Wild Coast of South Africa’s Eastern Cape, is characterized by the annual sardine (Sardinops sagax) run, which serves as an important foraging event for apex predators, including Indo-Pacific bottlenose (Tursiops aduncus) and long-beaked common dolphins (Delphinus delphis). Despite the ecological significance of this event, no dedicated surveys for these species have previously been conducted in this area. The main objectives of this research were to: investigate long-term occurrence of dolphins during the sardine run to determine if there have been any changes over the past 19 years, as has been predicted from common dolphin dietary investigations and anecdotal evidence; to determine short-term occurrence and movement patterns of selected inshore delphinids within the area, which is characterized by three marine protected areas (MPAs); and to use stable isotope analyses to determine trophic relationships and population structure of bottlenose and common dolphins within the region. Long-term data consisted of 131 opportunistic aerial surveys conducted between May and July over the period 1996 to 2014. Results from these surveys indicate that common dolphins, typically associated with sardines, decreased significantly in average group size over the study period (p=0.0343). Bottlenose dolphins, demonstrated no such trend (p=0.916). For both species, greater majority (> 70% of total counts) of sightings were made inside the MPAs. Short-term boat-based surveys were conducted three times a year between June 2014 and December 2016, contributing to a total of 47 days of surveys divided into three locations: Amathole, Hluleka, and Pondoland, each containing a MPA. Density and group size data were analyzed for both species and photographic identification analysis was performed for photographs of bottlenose dolphin dorsal fins. Results indicate that animal and sighting density did not differ temporally (bottlenose dolphin: sighting density – p=0.398, individual density –p=0.781; common dolphin: sighting density –p=0.472, individual density – p=0.204). Environmental factors (sea surface temperature, depth, substrate, and distance from shore) appeared to have limited effect on individual and sighting density and group size for both species (p>0.05). Photographic identification of bottlenose dolphins resulted in 2149 individuals, with a 11.8% resighting rate, with the highest resighting rate within the Pondoland MPA (16.1%). The resighting count did not differ temporally between monthly survey based on generalized linear models (p=0.866), but did differ between study areas (p<0.0001). These results provide the first evidence of the occurrence of both species of dolphin off the Wild Coast, as they were sighted in this region in all survey months. There was no trend in density based on temporal or environmental factors, which suggests other factors are influencing their occurrence. Resightings of bottlenose dolphins within the area suggest that there is some degree of residency, though the majority of animals were only sighted on a single occasion and there was no plateau in the discovery curve. A total of 256 biopsy samples (bottlenose dolphins =128; common dolphins=128) were collected during boat-based surveys. Bottlenose dolphin samples were also collected from adjacent areas to the southwest (Algoa Bay, n=22) and northeast (KwaZulu-Natal (KZN), n=20) of the Wild Coast to investigate similarities and differences between these areas. Despite a high degree of niche overlap between the two species (41%), common dolphins fed with a broader niche (standard ellipse area probability 0.89) than bottlenose dolphins in the summer and a narrower niche in the winter (probability 0.94). There was a clear spatial variation in the diet of bottlenose dolphins along the coast, with individuals from Algoa Bay and Amathole demonstrating 0% niche overlap with individuals from KZN, but the mechanism for these differences remains unclear as other species from South African waters demonstrate a strong southwest to northeast gradient in nitrogen for the Eastern Cape coastline. This research provides valuable baseline information regarding dolphins off the Wild Coast of South Africa, which remained largely unknown. My results indicate that bottlenose dolphins may be more resident in the Wild Coast than previous predicted, and confirm that common dolphins are highly mobile in this area.
- Full Text:
- Date Issued: 2019
- Authors: Caputo, Michelle Anne
- Date: 2019
- Subjects: Delphinus -- South Africa-- Kwazulu-Natal -- Ecology , Tursoops -- South Africa-- Kwazulu-Natal -- Ecology , Delphinus -- South Africa-- Kwazulu-Natal -- Feeding and feeds , Tursoops -- South Africa-- Kwazulu-Natal -- Feeding and feeds , Dolphins -- South Africa-- Kwazulu-Natal , Delphinus -- South Africa-- Kwazulu-Natal -- Behavior , Tursoops -- South Africa-- Kwazulu-Natal -- Behavior , Marine ecology -- South Africa -- Kwazulu-Natal
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/115612 , vital:34197
- Description: Dolphins are apex predators and their movements, foraging activities and population dynamics play an important role in shaping their environment. Understanding their occurrence, movement patterns, and trophic ecology is essential to their conservation, especially as they are considered sentinel species. The Wild Coast of South Africa’s Eastern Cape, is characterized by the annual sardine (Sardinops sagax) run, which serves as an important foraging event for apex predators, including Indo-Pacific bottlenose (Tursiops aduncus) and long-beaked common dolphins (Delphinus delphis). Despite the ecological significance of this event, no dedicated surveys for these species have previously been conducted in this area. The main objectives of this research were to: investigate long-term occurrence of dolphins during the sardine run to determine if there have been any changes over the past 19 years, as has been predicted from common dolphin dietary investigations and anecdotal evidence; to determine short-term occurrence and movement patterns of selected inshore delphinids within the area, which is characterized by three marine protected areas (MPAs); and to use stable isotope analyses to determine trophic relationships and population structure of bottlenose and common dolphins within the region. Long-term data consisted of 131 opportunistic aerial surveys conducted between May and July over the period 1996 to 2014. Results from these surveys indicate that common dolphins, typically associated with sardines, decreased significantly in average group size over the study period (p=0.0343). Bottlenose dolphins, demonstrated no such trend (p=0.916). For both species, greater majority (> 70% of total counts) of sightings were made inside the MPAs. Short-term boat-based surveys were conducted three times a year between June 2014 and December 2016, contributing to a total of 47 days of surveys divided into three locations: Amathole, Hluleka, and Pondoland, each containing a MPA. Density and group size data were analyzed for both species and photographic identification analysis was performed for photographs of bottlenose dolphin dorsal fins. Results indicate that animal and sighting density did not differ temporally (bottlenose dolphin: sighting density – p=0.398, individual density –p=0.781; common dolphin: sighting density –p=0.472, individual density – p=0.204). Environmental factors (sea surface temperature, depth, substrate, and distance from shore) appeared to have limited effect on individual and sighting density and group size for both species (p>0.05). Photographic identification of bottlenose dolphins resulted in 2149 individuals, with a 11.8% resighting rate, with the highest resighting rate within the Pondoland MPA (16.1%). The resighting count did not differ temporally between monthly survey based on generalized linear models (p=0.866), but did differ between study areas (p<0.0001). These results provide the first evidence of the occurrence of both species of dolphin off the Wild Coast, as they were sighted in this region in all survey months. There was no trend in density based on temporal or environmental factors, which suggests other factors are influencing their occurrence. Resightings of bottlenose dolphins within the area suggest that there is some degree of residency, though the majority of animals were only sighted on a single occasion and there was no plateau in the discovery curve. A total of 256 biopsy samples (bottlenose dolphins =128; common dolphins=128) were collected during boat-based surveys. Bottlenose dolphin samples were also collected from adjacent areas to the southwest (Algoa Bay, n=22) and northeast (KwaZulu-Natal (KZN), n=20) of the Wild Coast to investigate similarities and differences between these areas. Despite a high degree of niche overlap between the two species (41%), common dolphins fed with a broader niche (standard ellipse area probability 0.89) than bottlenose dolphins in the summer and a narrower niche in the winter (probability 0.94). There was a clear spatial variation in the diet of bottlenose dolphins along the coast, with individuals from Algoa Bay and Amathole demonstrating 0% niche overlap with individuals from KZN, but the mechanism for these differences remains unclear as other species from South African waters demonstrate a strong southwest to northeast gradient in nitrogen for the Eastern Cape coastline. This research provides valuable baseline information regarding dolphins off the Wild Coast of South Africa, which remained largely unknown. My results indicate that bottlenose dolphins may be more resident in the Wild Coast than previous predicted, and confirm that common dolphins are highly mobile in this area.
- Full Text:
- Date Issued: 2019
The performance and preference of a specialist herbivore, Catorhintha schaffneri (Coreidae), on its polytypic host plant, Pereskia aculeata (Cactaceae)
- Authors: Egbon, Ikponmwosa Nathaniel
- Date: 2019
- Subjects: Insects and biological pest control agents -- South Africa , Pereskia -- Biological control -- South Africa , Cactus -- Biological control -- South Africa , Coreida-- South Africa , Invasive plants -- Biological control -- South Africa , Catorhintha schaffneri
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/68250 , vital:29223
- Description: Plant species moved beyond their natural ranges may be liberated into enemy-free spaces, where they increase resource allocation to fitness, rather than defence against natural enemies, and become invasive as suggested by the Evolution of Increased Competitive Ability (EICA) Hypothesis. Several cacti are notable invaders and are targeted for biological control. The leafy cactus, Pereskia aculeata Miller, introduced into South Africa from South America, has become a target for biological control after becoming invasive. The absence of natural enemies of P. aculeata in the introduced range may be the reason for its invasiveness. This thesis seeks to investigate the role of the evolution of increased competitive ability (enemy release) as the probable driver of P. aculeata’s success, and ascertain how the plant’s intraspecific variation influences the impact, fitness of, and preference by its biological control agent, Catorhintha schaffneri Brailovsky and Garcia (Coreidae), in South Africa. Enemy release and evolution of traits in P. aculeata were examined by quantifying plant growth parameters of fifteen genotypes of P. aculeata from both the native and invaded distribution of the plant. Ten genotypes of P. aculeata were used in testing the effect of agent herbivory (impact and damage) under similar conditions. These studies indicated that most invaded-range genotypes were more vigorous than the native genotypes. Rapid growth may account for the quick access of invasive genotypes of P. aculeata to tree canopies. Catorhintha schaffneri damage varied between genotypes but differences in the damage and impact from the agent could not be explained by whether the plant originated in the introduced or native distribution. In sum, while the growth of the invasive genotypes largely conforms to the EICA hypothesis, the impact of C. schaffneri did not support the hypothesis. The influence of host variation in P. aculeata on the fitness of C. schaffneri within the context of local adaptation to plant genotypes from different localities was tested using agent survival, stage-specific and total developmental time, and the extent of damage to ten host genotypes. Maw’s Host Suitability Index (HIS) and Dobie’s Susceptibility Index (DSI) showed the preference by and performance of C. schaffneri on the different genotypes of the plant. Catorhintha schaffneri survived to the adult stage on 70% of genotypes tested. Evidence consistent with the assumption that C. schaffneri would be fitter on the native genotypes than the invasive genotypes due to local adaptation was not found. In addition, there was no evidence in support of fitter agents on the invasive genotypes than on the native genotypes as proposed by EICA hypothesis. Catorhintha schaffneri developed equally well on the invasive genotypes of P. aculeata as on the native genotypes. To establish whether host variation would affect diet selection by C. schaffneri, both nymphs and adults were examined in paired-choice and multiple-choice trials. The nymphs and adults chose their hosts regardless of host genotype differences. The agent may be good at selecting good succulent shoots from bad shoots, but is incapable of distinguishing a good host genotype from a poorer one. This thesis shows, therefore, that P. aculeata and its array of genotypes in South Africa could be effectively controlled by C. schaffneri, as it has the potential to suitably utilise and impact the different genotypes of the weed in South Africa with neither any demonstrable preference nor local adaptation for the native genotypes. Consequently, the use of C. schaffneri, as a biological control agent in the weed biological control programme of P. aculeata remains promising, as the agent is insensitive to the intraspecific variation of the invasive host plants.
- Full Text:
- Date Issued: 2019
- Authors: Egbon, Ikponmwosa Nathaniel
- Date: 2019
- Subjects: Insects and biological pest control agents -- South Africa , Pereskia -- Biological control -- South Africa , Cactus -- Biological control -- South Africa , Coreida-- South Africa , Invasive plants -- Biological control -- South Africa , Catorhintha schaffneri
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/68250 , vital:29223
- Description: Plant species moved beyond their natural ranges may be liberated into enemy-free spaces, where they increase resource allocation to fitness, rather than defence against natural enemies, and become invasive as suggested by the Evolution of Increased Competitive Ability (EICA) Hypothesis. Several cacti are notable invaders and are targeted for biological control. The leafy cactus, Pereskia aculeata Miller, introduced into South Africa from South America, has become a target for biological control after becoming invasive. The absence of natural enemies of P. aculeata in the introduced range may be the reason for its invasiveness. This thesis seeks to investigate the role of the evolution of increased competitive ability (enemy release) as the probable driver of P. aculeata’s success, and ascertain how the plant’s intraspecific variation influences the impact, fitness of, and preference by its biological control agent, Catorhintha schaffneri Brailovsky and Garcia (Coreidae), in South Africa. Enemy release and evolution of traits in P. aculeata were examined by quantifying plant growth parameters of fifteen genotypes of P. aculeata from both the native and invaded distribution of the plant. Ten genotypes of P. aculeata were used in testing the effect of agent herbivory (impact and damage) under similar conditions. These studies indicated that most invaded-range genotypes were more vigorous than the native genotypes. Rapid growth may account for the quick access of invasive genotypes of P. aculeata to tree canopies. Catorhintha schaffneri damage varied between genotypes but differences in the damage and impact from the agent could not be explained by whether the plant originated in the introduced or native distribution. In sum, while the growth of the invasive genotypes largely conforms to the EICA hypothesis, the impact of C. schaffneri did not support the hypothesis. The influence of host variation in P. aculeata on the fitness of C. schaffneri within the context of local adaptation to plant genotypes from different localities was tested using agent survival, stage-specific and total developmental time, and the extent of damage to ten host genotypes. Maw’s Host Suitability Index (HIS) and Dobie’s Susceptibility Index (DSI) showed the preference by and performance of C. schaffneri on the different genotypes of the plant. Catorhintha schaffneri survived to the adult stage on 70% of genotypes tested. Evidence consistent with the assumption that C. schaffneri would be fitter on the native genotypes than the invasive genotypes due to local adaptation was not found. In addition, there was no evidence in support of fitter agents on the invasive genotypes than on the native genotypes as proposed by EICA hypothesis. Catorhintha schaffneri developed equally well on the invasive genotypes of P. aculeata as on the native genotypes. To establish whether host variation would affect diet selection by C. schaffneri, both nymphs and adults were examined in paired-choice and multiple-choice trials. The nymphs and adults chose their hosts regardless of host genotype differences. The agent may be good at selecting good succulent shoots from bad shoots, but is incapable of distinguishing a good host genotype from a poorer one. This thesis shows, therefore, that P. aculeata and its array of genotypes in South Africa could be effectively controlled by C. schaffneri, as it has the potential to suitably utilise and impact the different genotypes of the weed in South Africa with neither any demonstrable preference nor local adaptation for the native genotypes. Consequently, the use of C. schaffneri, as a biological control agent in the weed biological control programme of P. aculeata remains promising, as the agent is insensitive to the intraspecific variation of the invasive host plants.
- Full Text:
- Date Issued: 2019
Aspects of the population ecology, habitat use and behaviour of the endangered Knysna seahorse (Hippocampus capensis Boulenger, 1900) in a residential marina estate, Knysna, South Africa: implications for conservation
- Authors: Claassens, Louw
- Date: 2018
- Subjects: Endangered species -- South Africa -- Knysna , Sea horses -- Behavior -- South Africa -- Knysna , Sea horses -- Habitat -- South Africa -- Knysna , Sea horses -- Ecology -- South Africa -- Knysna
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/54789 , vital:26616
- Description: The Knysna seahorse Hippocampus capensis is South Africa’s only endemic seahorse species, and is found in only three adjacent estuaries along the southern coast. The conservation of this endangered species is important on a national and international level. This study presents the first research on this species within the Knysna estuary since 2001 and specifically focuses on aspects of its ecology within a residential marina estate (Thesen Islands Marina). The physico-chemical and habitat features of the marina were described and the population ecology, habitat use, and behaviour of the Knysna seahorse were investigated. Physico-chemical conditions within the western section of the marina, characterised by high water current velocities, were similar to that of the adjacent estuary. The eastern section of the marina was characterised by lower water current velocities and higher turbidity. Four major habitat types were identified within the marina canals: (I) artificial Reno mattress (wire baskets filled with rocks); (II) Codium tenue beds; (III) mixed vegetation on sediment; and (IV) barren canal floor. Seahorse densities within the marina were significantly higher compared to densities found historically within the estuary. Highest seahorse densities were specifically found within the artificial Reno mattress structures and within the western section of the marina. Seahorse density varied spatially and temporally and the type of habitat was an important predictor for seahorse occurrence. An experimental investigation found that H. capensis chooses artificial Reno mattress habitat over Zostera capensis when given a choice. GoPro cameras were used successfully to investigate daytime seahorse behaviour within the Reno mattress habitat. Seahorses were more active during the morning, spent most of their time (> 80 %) feeding, and morning courting behaviour for this species were confirmed. However, during the summer holiday period (mid-December to mid-January) few seahorses were observed on camera, which suggests that the increase in motor boat activity and the related increase in noise had a negative effect on H. capensis feeding and courting behaviour. The marina development, and in particular the Reno mattresses, created a new habitat for this endangered species within the Knysna estuary. In addition to the protection and restoration of natural habitats in which H. capensis is found, the conservation potential of artificial structures such as Reno mattresses should be realised.
- Full Text:
- Date Issued: 2018
- Authors: Claassens, Louw
- Date: 2018
- Subjects: Endangered species -- South Africa -- Knysna , Sea horses -- Behavior -- South Africa -- Knysna , Sea horses -- Habitat -- South Africa -- Knysna , Sea horses -- Ecology -- South Africa -- Knysna
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/54789 , vital:26616
- Description: The Knysna seahorse Hippocampus capensis is South Africa’s only endemic seahorse species, and is found in only three adjacent estuaries along the southern coast. The conservation of this endangered species is important on a national and international level. This study presents the first research on this species within the Knysna estuary since 2001 and specifically focuses on aspects of its ecology within a residential marina estate (Thesen Islands Marina). The physico-chemical and habitat features of the marina were described and the population ecology, habitat use, and behaviour of the Knysna seahorse were investigated. Physico-chemical conditions within the western section of the marina, characterised by high water current velocities, were similar to that of the adjacent estuary. The eastern section of the marina was characterised by lower water current velocities and higher turbidity. Four major habitat types were identified within the marina canals: (I) artificial Reno mattress (wire baskets filled with rocks); (II) Codium tenue beds; (III) mixed vegetation on sediment; and (IV) barren canal floor. Seahorse densities within the marina were significantly higher compared to densities found historically within the estuary. Highest seahorse densities were specifically found within the artificial Reno mattress structures and within the western section of the marina. Seahorse density varied spatially and temporally and the type of habitat was an important predictor for seahorse occurrence. An experimental investigation found that H. capensis chooses artificial Reno mattress habitat over Zostera capensis when given a choice. GoPro cameras were used successfully to investigate daytime seahorse behaviour within the Reno mattress habitat. Seahorses were more active during the morning, spent most of their time (> 80 %) feeding, and morning courting behaviour for this species were confirmed. However, during the summer holiday period (mid-December to mid-January) few seahorses were observed on camera, which suggests that the increase in motor boat activity and the related increase in noise had a negative effect on H. capensis feeding and courting behaviour. The marina development, and in particular the Reno mattresses, created a new habitat for this endangered species within the Knysna estuary. In addition to the protection and restoration of natural habitats in which H. capensis is found, the conservation potential of artificial structures such as Reno mattresses should be realised.
- Full Text:
- Date Issued: 2018
Biotic and abiotic drivers of macroinvertebrate assemblages in a South African river
- Authors: Bellingan, Terence Andrew
- Date: 2018
- Subjects: Aquatic insects -- South Africa -- Eastern Cape , Stream ecology -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape , Riparian areas -- Management , Ecosystem management -- South Africa -- Eastern Cape , Mayflies -- South Africa -- Eastern Cape , Stoneflies -- South Africa -- Eastern Cape , Keiskamma River
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/61839 , vital:28067
- Description: Aquatic insects are the most numerically abundant and diverse group of organisms found in lotic ecosystems in South Africa and the world over. They play vital roles in freshwater ecosystem functioning, processing nutrients and in turn forming integral links in stream food-webs. This thesis focussed on examining the macroinvertebrate fauna within three reaches of headwater streams of the Keiskamma River system: reaches that were considered to be fishless; reaches that were invaded by non-native salmonid species; and reaches that were dominated by native fish. I described the effects of predatory fish presence through detailed examination of macroinvertebrate assemblage composition; macroinvertebrate drift timing and density; and through niche utilisation determined from stable isotope data. Patterns in the macroinvertebrate assemblages of the headwaters of the Keiskamma River appear to be driven more strongly by flow rate and seasonal influences, but fish presence and biotope availability were also significant drivers. Niche shifts due to predator presence were not easy to detect and, while patterns of influence may have been evident, they were not found to be significant. However, I demonstrated that salmonids selectively feed on native fish species when the opportunity is presented, occupying significantly higher trophic levels when co-occurring with native fish than in invaded reaches where native fish are absent. Drift timing and density were demonstrated to be significantly different between reach for specific macroinvertebrate species from the Ephemeroptera and Plecoptera, under differing fish predation regimes, in agreement with what has been observed from studies in rivers elsewhere. In freshwater ecosystems of South Africa and worldwide, mitigation of negative effects of alien fishes through their removal using piscicides may also affect non-target organisms. To better understand the effects of just such a removal operation, employed for the first time in the history of freshwater conservation in South Africa, macroinvertebrate communities were assessed for non-target effects of rotenone. The fish eradication operations were demonstrated to have a short-term negative effect on the macroinvertebrate assemblage, through water quality index measurements and alteration of densities of macroinvertebrate taxa collected from stone surfaces. However, no long-term detrimental impact was observed as macroinvertebrate faunas returned to a comparable pre-treatment state within a year of each rotenone application.
- Full Text:
- Date Issued: 2018
- Authors: Bellingan, Terence Andrew
- Date: 2018
- Subjects: Aquatic insects -- South Africa -- Eastern Cape , Stream ecology -- South Africa -- Eastern Cape , Freshwater ecology -- South Africa -- Eastern Cape , Riparian areas -- Management , Ecosystem management -- South Africa -- Eastern Cape , Mayflies -- South Africa -- Eastern Cape , Stoneflies -- South Africa -- Eastern Cape , Keiskamma River
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/61839 , vital:28067
- Description: Aquatic insects are the most numerically abundant and diverse group of organisms found in lotic ecosystems in South Africa and the world over. They play vital roles in freshwater ecosystem functioning, processing nutrients and in turn forming integral links in stream food-webs. This thesis focussed on examining the macroinvertebrate fauna within three reaches of headwater streams of the Keiskamma River system: reaches that were considered to be fishless; reaches that were invaded by non-native salmonid species; and reaches that were dominated by native fish. I described the effects of predatory fish presence through detailed examination of macroinvertebrate assemblage composition; macroinvertebrate drift timing and density; and through niche utilisation determined from stable isotope data. Patterns in the macroinvertebrate assemblages of the headwaters of the Keiskamma River appear to be driven more strongly by flow rate and seasonal influences, but fish presence and biotope availability were also significant drivers. Niche shifts due to predator presence were not easy to detect and, while patterns of influence may have been evident, they were not found to be significant. However, I demonstrated that salmonids selectively feed on native fish species when the opportunity is presented, occupying significantly higher trophic levels when co-occurring with native fish than in invaded reaches where native fish are absent. Drift timing and density were demonstrated to be significantly different between reach for specific macroinvertebrate species from the Ephemeroptera and Plecoptera, under differing fish predation regimes, in agreement with what has been observed from studies in rivers elsewhere. In freshwater ecosystems of South Africa and worldwide, mitigation of negative effects of alien fishes through their removal using piscicides may also affect non-target organisms. To better understand the effects of just such a removal operation, employed for the first time in the history of freshwater conservation in South Africa, macroinvertebrate communities were assessed for non-target effects of rotenone. The fish eradication operations were demonstrated to have a short-term negative effect on the macroinvertebrate assemblage, through water quality index measurements and alteration of densities of macroinvertebrate taxa collected from stone surfaces. However, no long-term detrimental impact was observed as macroinvertebrate faunas returned to a comparable pre-treatment state within a year of each rotenone application.
- Full Text:
- Date Issued: 2018
Scale-specific processes underlying the genetic population structure of seabirds in the tropical western Indian Ocean
- Authors: Danckwerts, Daniel Keith
- Date: 2018
- Subjects: Sea birds -- Indian Ocean , Sea birds -- Behavior -- Indian Ocean , Sea birds -- Mortality -- Indian Ocean , Sea birds -- Mortality -- Prevention , Sea birds -- Reproduction , Bird declines -- Indian Ocean , Sea birds -- Indian Ocean -- Effect of human beings on , Sooty tern , Red-footed booby , Pterodroma
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/63944 , vital:28513
- Description: Global seabird populations have declined by 70%, since 1950, largely in response to human mediated threats. Identifying the pressures that the remaining populations face has therefore become a top priority. Many breeding colonies are now monitored annually, though others have been almost completely neglected. Considerable bias also exists towards higher latitude species, while fewer studies have been conducted on tropical groups. Beyond tracking population sizes, numerous knowledge gaps also exist that severely restrict conservation efforts. This includes the understanding of seabird meta-population structure and the processes underlying population divergence. The importance of these studies lies in the fact that the preservation of biodiversity requires the conservation of diversification processes. Generating this knowledge is therefore an important first step towards recognising responses to episodic disturbance and long-term environmental change, as well as recovery potential. In this context, the present study employed microsatellite analysis and ringing information to investigate the processes underlying the metapopulation structure of seabirds in the tropical western Indian Ocean. Three species were selected as proxies to cover a range of population sizes, distributional ranges, and intrinsic behavioural (e.g. migratory behaviour) and morphological (e.g. polymorphism) characteristics. These were the Sooty Tern (Onychoprion fuscatus), Red-footed Booby (Sula sula), and Barau’s Petrel (Pterodorma baraui). The overall objective was to provide insight into the mechanisms underlying divergence across a range of scales. Microsatellite information highlighted that genetic populations of the Red-footed Booby and Barau’s Petrel were weakly, though significantly, structured. For the Barau’s Petrel, this was supported by ringing information that indicated extreme colony fidelity. Some gene flow appears to occur among the breeding colonies of the Red-footed Booby, though the scale and frequency of this remains uncertain as banding information is insufficient at this stage. Nevertheless, though populations of both species were genetically structured, the processes underlying divergence were different. Extreme natal philopatry appears to have driven divergence between the two colonies of the Barau’s Petrel, while local selective forces (e.g. kleptoparasitism risk and/or selection against immigrants) appear to have isolated the three studied breeding colonies of the Red-footed Booby. Conversely, microsatellite information identified a total lack of genetic structure among breeding colonies of the Sooty Tern in the western Indian Ocean, and between colonies in the western Indian and Eastern Pacific Oceans. This accords with banding recoveries, which illustrate considerable inter-colony exchange of individuals among most islands of the Seychelles and between breeding colonies in the western Indian and West Pacific Oceans. The processes underlying the genetic population structure (or, in this case, lack thereof) in the Sooty Tern therefore appear to operate at extremely large scales. The species’ low natal philopatry and high dispersal capabilities, combined with an importance of social stimulation and a reliance on seasonally favourable marine conditions, appears to influence the decisions of where and when individual Sooty Terns choose to breed. Anthropogenic disturbance at breeding sites, particularly that related to egg harvesting activities, also appears to drive dispersal in the Sooty Tern. These results improve our understanding of the mechanisms underlying the genetic population structure in seabirds at low latitudes. However, numerous questions remain unanswered and warrant further study. Clear conservation implications were also identified for the three studied species. Nevertheless, caution should still be applied when extrapolating this information across other species.
- Full Text:
- Date Issued: 2018
- Authors: Danckwerts, Daniel Keith
- Date: 2018
- Subjects: Sea birds -- Indian Ocean , Sea birds -- Behavior -- Indian Ocean , Sea birds -- Mortality -- Indian Ocean , Sea birds -- Mortality -- Prevention , Sea birds -- Reproduction , Bird declines -- Indian Ocean , Sea birds -- Indian Ocean -- Effect of human beings on , Sooty tern , Red-footed booby , Pterodroma
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/63944 , vital:28513
- Description: Global seabird populations have declined by 70%, since 1950, largely in response to human mediated threats. Identifying the pressures that the remaining populations face has therefore become a top priority. Many breeding colonies are now monitored annually, though others have been almost completely neglected. Considerable bias also exists towards higher latitude species, while fewer studies have been conducted on tropical groups. Beyond tracking population sizes, numerous knowledge gaps also exist that severely restrict conservation efforts. This includes the understanding of seabird meta-population structure and the processes underlying population divergence. The importance of these studies lies in the fact that the preservation of biodiversity requires the conservation of diversification processes. Generating this knowledge is therefore an important first step towards recognising responses to episodic disturbance and long-term environmental change, as well as recovery potential. In this context, the present study employed microsatellite analysis and ringing information to investigate the processes underlying the metapopulation structure of seabirds in the tropical western Indian Ocean. Three species were selected as proxies to cover a range of population sizes, distributional ranges, and intrinsic behavioural (e.g. migratory behaviour) and morphological (e.g. polymorphism) characteristics. These were the Sooty Tern (Onychoprion fuscatus), Red-footed Booby (Sula sula), and Barau’s Petrel (Pterodorma baraui). The overall objective was to provide insight into the mechanisms underlying divergence across a range of scales. Microsatellite information highlighted that genetic populations of the Red-footed Booby and Barau’s Petrel were weakly, though significantly, structured. For the Barau’s Petrel, this was supported by ringing information that indicated extreme colony fidelity. Some gene flow appears to occur among the breeding colonies of the Red-footed Booby, though the scale and frequency of this remains uncertain as banding information is insufficient at this stage. Nevertheless, though populations of both species were genetically structured, the processes underlying divergence were different. Extreme natal philopatry appears to have driven divergence between the two colonies of the Barau’s Petrel, while local selective forces (e.g. kleptoparasitism risk and/or selection against immigrants) appear to have isolated the three studied breeding colonies of the Red-footed Booby. Conversely, microsatellite information identified a total lack of genetic structure among breeding colonies of the Sooty Tern in the western Indian Ocean, and between colonies in the western Indian and Eastern Pacific Oceans. This accords with banding recoveries, which illustrate considerable inter-colony exchange of individuals among most islands of the Seychelles and between breeding colonies in the western Indian and West Pacific Oceans. The processes underlying the genetic population structure (or, in this case, lack thereof) in the Sooty Tern therefore appear to operate at extremely large scales. The species’ low natal philopatry and high dispersal capabilities, combined with an importance of social stimulation and a reliance on seasonally favourable marine conditions, appears to influence the decisions of where and when individual Sooty Terns choose to breed. Anthropogenic disturbance at breeding sites, particularly that related to egg harvesting activities, also appears to drive dispersal in the Sooty Tern. These results improve our understanding of the mechanisms underlying the genetic population structure in seabirds at low latitudes. However, numerous questions remain unanswered and warrant further study. Clear conservation implications were also identified for the three studied species. Nevertheless, caution should still be applied when extrapolating this information across other species.
- Full Text:
- Date Issued: 2018
Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) population ecology in citrus orchards: the influence of orchard age
- Authors: Albertyn, Sonnica
- Date: 2018
- Subjects: Cryptophlebia leucotreta , Population biology , Insect populations , Orchards , Insect nematodes , Entomopathogenic fungi
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62615 , vital:28213
- Description: Anecdotal reports in the South African citrus industry claim higher populations of false codling moth (FCM), Thaumatotibia (Cryptophlebia) leucotreta (Meyr) (Lepidoptera: Tortricidae), in orchards during the first three to five harvesting years of citrus planted in virgin soil, after which, FCM numbers seem to decrease and remain consistent. Various laboratory studies and field surveys were conducted to determine if, and why juvenile orchards (four to eight years old) experience higher FCM infestation than mature orchards (nine years and older). In laboratory trials, Washington Navel oranges and Nova Mandarins from juvenile trees were shown to be significantly more susceptible to FCM damage and significantly more attractive for oviposition in both choice and no-choice trials, than fruit from mature trees. Although fruit from juvenile Cambria Navel trees were significantly more attractive than mature orchards for oviposition, they were not more susceptible to FCM damage. In contrast, fruit from juvenile and mature Midnight Valencia orchards were equally attractive for oviposition, but fruit from juvenile trees were significantly more susceptible to FCM damage than fruit from mature trees. Artificial diets were augmented with powder from fruit from juvenile or mature Washington Navel orchards at 5%, 10%, 15% or 30%. Higher larval survival of 76%, 63%, 50% and 34%, respectively, was recorded on diets containing fruit powder from the juvenile trees than on diets containing fruit powder from the mature trees, at 69%, 57%, 44% and 27% larval survival, respectively. Bioassays were conducted to determine if differences in plant chemistry between fruit from juvenile and mature trees will have an impact on the susceptibility FCM to entomopathogenic nematodes (EPN), entomopathogenic fungi (EPF) and Cryptophlebia leucotreta granulovirus (CrleGV). No significant differences in the susceptibility of larvae reared on diets containing 15% fruit powder from juvenile and mature trees to EPN and EPF were recorded. Mortality of neonate larvae was significantly lower when placed on diets containing 15% fruit powder from mature trees (45% mortality) than diets containing 15% fruit powder from juvenile trees (61% mortality), after larvae ingested the lowest virus concentration tested, being 2 x104 OBs/ml. Data collected from field surveys showed significantly lower egg parasitism, virus infection of larvae and EPF occurrence in juvenile orchards than mature orchards. Egg parasitism was between 11% and 54% higher in mature orchards than juvenile orchards, with the exception of Mandarins during 2015, where egg parasitism was slightly higher in juvenile orchards, but not significantly so. A significantly higher proportion of larvae retrieved from mature orchards (7% of larvae) were infected with CrleGV than larvae retrieved from juvenile orchards (4% of larvae). A significantly higher occurrence of EPF was recorded in non-bearing and mature orchards, with 40% and 37% occurrence respectively, than in juvenile orchards, with 25% occurrence recorded. EPF occurrence in juvenile orchards increased significantly by 16% to 32% from the first to the third year of sampling. In contrast to results recorded in laboratory trials, similar or higher pest pressure in juvenile orchards than mature orchards did not always result in significantly higher levels of FCM damage under field conditions. FCM damage in juvenile orchards may have been lower than expected, as greater extremes of temperature and lower humidity were recorded in juvenile orchards, which would increase larval mortality. Results of this study showed that juvenile and mature orchards are significantly different and should be managed differently.
- Full Text:
- Date Issued: 2018
- Authors: Albertyn, Sonnica
- Date: 2018
- Subjects: Cryptophlebia leucotreta , Population biology , Insect populations , Orchards , Insect nematodes , Entomopathogenic fungi
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/62615 , vital:28213
- Description: Anecdotal reports in the South African citrus industry claim higher populations of false codling moth (FCM), Thaumatotibia (Cryptophlebia) leucotreta (Meyr) (Lepidoptera: Tortricidae), in orchards during the first three to five harvesting years of citrus planted in virgin soil, after which, FCM numbers seem to decrease and remain consistent. Various laboratory studies and field surveys were conducted to determine if, and why juvenile orchards (four to eight years old) experience higher FCM infestation than mature orchards (nine years and older). In laboratory trials, Washington Navel oranges and Nova Mandarins from juvenile trees were shown to be significantly more susceptible to FCM damage and significantly more attractive for oviposition in both choice and no-choice trials, than fruit from mature trees. Although fruit from juvenile Cambria Navel trees were significantly more attractive than mature orchards for oviposition, they were not more susceptible to FCM damage. In contrast, fruit from juvenile and mature Midnight Valencia orchards were equally attractive for oviposition, but fruit from juvenile trees were significantly more susceptible to FCM damage than fruit from mature trees. Artificial diets were augmented with powder from fruit from juvenile or mature Washington Navel orchards at 5%, 10%, 15% or 30%. Higher larval survival of 76%, 63%, 50% and 34%, respectively, was recorded on diets containing fruit powder from the juvenile trees than on diets containing fruit powder from the mature trees, at 69%, 57%, 44% and 27% larval survival, respectively. Bioassays were conducted to determine if differences in plant chemistry between fruit from juvenile and mature trees will have an impact on the susceptibility FCM to entomopathogenic nematodes (EPN), entomopathogenic fungi (EPF) and Cryptophlebia leucotreta granulovirus (CrleGV). No significant differences in the susceptibility of larvae reared on diets containing 15% fruit powder from juvenile and mature trees to EPN and EPF were recorded. Mortality of neonate larvae was significantly lower when placed on diets containing 15% fruit powder from mature trees (45% mortality) than diets containing 15% fruit powder from juvenile trees (61% mortality), after larvae ingested the lowest virus concentration tested, being 2 x104 OBs/ml. Data collected from field surveys showed significantly lower egg parasitism, virus infection of larvae and EPF occurrence in juvenile orchards than mature orchards. Egg parasitism was between 11% and 54% higher in mature orchards than juvenile orchards, with the exception of Mandarins during 2015, where egg parasitism was slightly higher in juvenile orchards, but not significantly so. A significantly higher proportion of larvae retrieved from mature orchards (7% of larvae) were infected with CrleGV than larvae retrieved from juvenile orchards (4% of larvae). A significantly higher occurrence of EPF was recorded in non-bearing and mature orchards, with 40% and 37% occurrence respectively, than in juvenile orchards, with 25% occurrence recorded. EPF occurrence in juvenile orchards increased significantly by 16% to 32% from the first to the third year of sampling. In contrast to results recorded in laboratory trials, similar or higher pest pressure in juvenile orchards than mature orchards did not always result in significantly higher levels of FCM damage under field conditions. FCM damage in juvenile orchards may have been lower than expected, as greater extremes of temperature and lower humidity were recorded in juvenile orchards, which would increase larval mortality. Results of this study showed that juvenile and mature orchards are significantly different and should be managed differently.
- Full Text:
- Date Issued: 2018
The role of upwelling in determining the composition, species distribution and genetic structure of intertidal communities in a time of climate change
- Lourenço, Carla Sofia Emídio Rodrigues
- Authors: Lourenço, Carla Sofia Emídio Rodrigues
- Date: 2018
- Subjects: Upwelling (Oceanography) , Intertidal organisms -- Morocco -- Atlantic Coast , Intertidal organisms -- Canary Current -- Effect of water currents on , Intertidal animals -- Canary Current -- Effect of water currents on , Intertidal animals -- Morocco -- Atlantic Coas , Mytilus galloprovincialis -- Morocco -- Atlantic Coast , Mytilus galloprovincialis -- Canary Current -- Effect of water currents on , Intertidal ecology -- Canary Current , Sea surface microlayer -- Morocco -- Atlantic Coast
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/61614 , vital:28042
- Description: Upwelling is an oceanographic process that strongly influences coastal species and the communities they belong to. In upwelling areas, colder, denser, nutrient-rich subsurface waters are transported to the nearshore surface, replacing warmer superficial waters that are advected offshore. Such effects influence the composition and dynamics of coastal communities, for example by affecting species abundance, recruitment, dispersal and distribution. Upwelling areas are key model regions to study the responses of coastal species to climate change because they are characterized by cooler conditions and experience lower warming rates than adjacent regions. In particular, intertidal rocky shore species are ideal coastal sentinel organisms to study distributional changes driven by climate warming because they inhabit the interface between marine and terrestrial habitats and are exposed to extremely severe environmental conditions. In fact, sharp distributional shifts have been reported for multiple intertidal species as a response to ocean warming. Although some studies have investigated the role of upwelling in influencing abundance and distribution of intertidal species, little is known about its potential as refugia against climate warming and the degree to which upwelling shapes species genetic structure is yet not fully understood. The aim of this thesis is to understand the influence of the Canary Current upwelling system on intertidal community composition, including species distribution and the genetic structure of intertidal species under current climate change. To do this, I investigated community structure of intertidal assemblages along the Atlantic shores of Morocco and Western Sahara, performed large scale surveys on species distribution, evaluated species abundance and frequency of parasitism and examined species genetic patterns. I further coupled biological data with upwelling indices, sea surface temperatures (SST) and the rate of SST warming. I demonstrate that strong upwelling influences abundance and distribution of intertidal rocky shore species and that upwelling cells can act as refugia from climate change by ameliorating thermal conditions. Upwelling cells also conserve the genetic diversity of the marine macroalga Fucus guiryi, promoting intraspecific genetic diversity by preserving unique genetic lineages. However, no evidence was found that upwelling affects the genetic structure for either F. guiryi or the brown mussel Perna perna. Instead, the genetic patterns presented in this thesis seem to result from a combination of species’ life history traits, population size and habitat suitability. My results also suggest that upwelling intensity affects the frequency of endolithic parasitism on the Mediterranean mussel Mytilus galloprovincialis. In times of climate change, upwelling events provide suitable environmental conditions for species to counter act climatic change. As upwelling is project to intensify in the future, its influence on benthic intertidal species might be greater than previously anticipated.
- Full Text:
- Date Issued: 2018
- Authors: Lourenço, Carla Sofia Emídio Rodrigues
- Date: 2018
- Subjects: Upwelling (Oceanography) , Intertidal organisms -- Morocco -- Atlantic Coast , Intertidal organisms -- Canary Current -- Effect of water currents on , Intertidal animals -- Canary Current -- Effect of water currents on , Intertidal animals -- Morocco -- Atlantic Coas , Mytilus galloprovincialis -- Morocco -- Atlantic Coast , Mytilus galloprovincialis -- Canary Current -- Effect of water currents on , Intertidal ecology -- Canary Current , Sea surface microlayer -- Morocco -- Atlantic Coast
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/61614 , vital:28042
- Description: Upwelling is an oceanographic process that strongly influences coastal species and the communities they belong to. In upwelling areas, colder, denser, nutrient-rich subsurface waters are transported to the nearshore surface, replacing warmer superficial waters that are advected offshore. Such effects influence the composition and dynamics of coastal communities, for example by affecting species abundance, recruitment, dispersal and distribution. Upwelling areas are key model regions to study the responses of coastal species to climate change because they are characterized by cooler conditions and experience lower warming rates than adjacent regions. In particular, intertidal rocky shore species are ideal coastal sentinel organisms to study distributional changes driven by climate warming because they inhabit the interface between marine and terrestrial habitats and are exposed to extremely severe environmental conditions. In fact, sharp distributional shifts have been reported for multiple intertidal species as a response to ocean warming. Although some studies have investigated the role of upwelling in influencing abundance and distribution of intertidal species, little is known about its potential as refugia against climate warming and the degree to which upwelling shapes species genetic structure is yet not fully understood. The aim of this thesis is to understand the influence of the Canary Current upwelling system on intertidal community composition, including species distribution and the genetic structure of intertidal species under current climate change. To do this, I investigated community structure of intertidal assemblages along the Atlantic shores of Morocco and Western Sahara, performed large scale surveys on species distribution, evaluated species abundance and frequency of parasitism and examined species genetic patterns. I further coupled biological data with upwelling indices, sea surface temperatures (SST) and the rate of SST warming. I demonstrate that strong upwelling influences abundance and distribution of intertidal rocky shore species and that upwelling cells can act as refugia from climate change by ameliorating thermal conditions. Upwelling cells also conserve the genetic diversity of the marine macroalga Fucus guiryi, promoting intraspecific genetic diversity by preserving unique genetic lineages. However, no evidence was found that upwelling affects the genetic structure for either F. guiryi or the brown mussel Perna perna. Instead, the genetic patterns presented in this thesis seem to result from a combination of species’ life history traits, population size and habitat suitability. My results also suggest that upwelling intensity affects the frequency of endolithic parasitism on the Mediterranean mussel Mytilus galloprovincialis. In times of climate change, upwelling events provide suitable environmental conditions for species to counter act climatic change. As upwelling is project to intensify in the future, its influence on benthic intertidal species might be greater than previously anticipated.
- Full Text:
- Date Issued: 2018