The phenologies of macadamia (Proteaceae) and thrips (Insecta: Thysanoptera) communities in Mpumalanga Province, South Africa
- Authors: Hepburn, Colleen
- Date: 2017
- Subjects: Macadamia nut -- South Africa , Macadamia nut -- Ecology -- South Africa , Macadamia nut -- Diseases and pests -- South Africa , Thrips -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:21183 , http://hdl.handle.net/10962/6817
- Description: Macadamia (Proteaceae) is indigenous to Australia; four of the nine species have been used in plant breeding for cultivation and the production of a rapidly growing product. First introduced to Hawaii in the 1880s, macadamias’ potential as a crop was only really considered in 1910. It is due to the early Hawaiian pioneers’ research and the development of Hawaiian cultivars upon which most of the current world’s production is based today. Prior to the 1980s, cultivation in Australia was based mainly on Hawaiian cultivars. Extensive research has been conducted on cultivar development, performance, best practice, production, crop protection and processing. South Africa has become one of the world’s leading producers and exporters of macadamias. The cultivation of macadamia in South Africa began 80 years ago, but the phenology of macadamia has not been rigorously studied under local conditions, and neither has the thrips communities in macadamia. Data collected during this study on the macadamia phenological stages can be used as a foundation on which seasonal data of all insect pests can be plotted, as a basis on which an extensive Integrated Pest Management (IPM) programme can be developed for the macadamia industry in South Africa. Extensive sampling of thrips communities present in macadamias was undertaken over two years, with more than 142,000 individuals collected. The most basic, common trait into which specimens could be sorted were colour groups. Specimens from each colour group were identified through slide-mounting individuals. Fifteen species of thrips were identified to species-level, excluding specimens from the Panchaetothripinae, Haplothrips and Scolothrips which occurred only periodically. The presence of larvae indicated that macadamia is a host plant for some species. Due to their size and morphology, identification i of the total collection could not be processed to species level using a dissection microscope, although Scirtothrips aurantii Faure were distinguishable from other species and their distribution over the seasons observed. Due to logistical constraints and events beyond the author’s control, the results are mainly qualitative. There seems to be phenological variation within and between cultivars. The date of anthesis and duration of immature nut-drop was estimated; some cultivars set out- of-season flowers and nuts; this “secondary crop” could have far-reaching effects on the implementation of an IPM programme. Comparisons of the phenological data of macadamia and thrips showed the highest abundances and diversity of thrips species occurred when flowers were present. An extensive study of abscised nuts showed no significant difference between most cultivars or at the sites where management practices were implemented and those sites where these practices were not. There was however a consistent difference between the two seasons. There was no difference in maturity of abscised nuts, regardless of whether thrips damage to the husk was present or not. Excessive Bathycoelia distincta (Hemiptera: Pentatomidae) damage was found on the kernels of the abscised nuts processed for maturity testing, which is more likely to have been the primary cause of abscission. The Author’s opinion is that thrips damage to the outer husk does not lead to abscission of maturing nuts. Ascertaining the cause of abscission at nut-set and immature nut-drop is more problematic as there are numerous other potential causes. Damage to new flush, especially the late summer flush essential for the build-up of carbohydrates and resources for the following yield, should be carefully monitored and controlled when necessary.
- Full Text:
- Date Issued: 2017
The phytophagous insect community on the Veld Fig, Ficus Burtt-Davyi Hutch
- Authors: Ross, Sally Jane
- Date: 1994
- Subjects: Phytophagous insects -- South Africa , Phytophagous insects , Insect-plant relationships
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5739 , http://hdl.handle.net/10962/d1005425 , Phytophagous insects -- South Africa , Phytophagous insects , Insect-plant relationships
- Description: The quest for patterns in community organisation is a daunting task which may be made easier by concentrating on communities associated with a restricted range of resources and therefore of relative simplicity. Here, the phytophagous insect community on the African fig tree Ficus burtt-davyi Hutch. was studied in an attempt to gain some insight into the factors which influence the composition of insect herbivore communities at a very local level, on individual plants of one host species at a single location. The tree's phenological patterns were detennined, due to their relevance to herbivores, particularly those which are host-specific feeders. The trees exhibited inter-tree asynchrony and intra-tree synchrony in fruit crop initiation, whereas leaf production was synchronous both within and between trees. Sixteen frequently occurring phytophagous insect species fed on the 123 F. burtt-davyi trees in the study area over a period of one year. Factors with the potential to influence the composition of this community were investigated at levels of the whole community (species richness), the guild, and the individual species. At each 'level' the effects of the measured factors on fluctuations in community composition were investigated, both over time (i.e. temporally) and spatially from tree to tree. During the year the phytophage community was influenced largely by temperature, although rainfall and tree phenological changes did exert varying influences on the abundances of guilds and individual species. Tree to tree variation in species richness (and thus commensurately, in the frequencies of occurrence of guilds and individual species) was influenced primarily by tree architectural complexity. Architecturally more complex trees hosted a greater number of species, a relationship largely attributable to effects of passive sampling and within-tree microhabitat heterogeneity and/or the availability of living space. The distributions of the leaf and stem piercing species were strongly associated with the presence of ants and this relationship manifested itself within the community as a whole. The degree of isolation of trees had consequences for individual species and for overall species richness, with the numbers of species present decreasing as trees became more isolated. A detailed analysis of guild distributional patterns revealed that the most important influential factors were those also evident at the level of the whole community and that species within guilds were, on the whole, no more similar to one another with respect to their habitat preferences than species from different guilds. The grouping of species into functional units therefore threw no additional light on the way in which this community is organised. An analysis of possible interspecific interactions between all of the phytophagous species in the community revealed only positive associations, both between species within guilds and between those in different guilds. These were doubtless attributable to autocorrelation as a result of similar habitat preferences. Competition was therefore rejected as an organising force within the community.
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- Date Issued: 1994
The population dynamics of an indigenous Psyllid Acizzia Russellae (Homoptera: Psyllidae )with special reference to the influence of the host plant Acacia Karroo
- Authors: Webb, John Warren
- Date: 1975
- Subjects: Homoptera , Jumping plant-lice , Insect populations , Insects -- Ecology , Acacia -- Karroo
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5894 , http://hdl.handle.net/10962/d1013415
- Description: The biology and ecology of an indigenous, non-pest insect on an indigenous host plant were investigated. The study includes a taxonomic description of this new species, an account of its general biology, monitoring of the seasonal fluctuations in numbers of the psyllid and its hymenopterous parasitoids, and a study of various aspects of the host plant, including nitrogen levels, water stress, leaf hardness, and the effect of cutting, in relation to spatial and temporal differences in insect population numbers. Natural enemies, inter- and intra-specific competition had very little determining influence on the population numbers of the psyllid. Temperature and humidity had little direct effect, but may have influenced the population dynamics via its effects on the host plant. Seasonal patterns in psyllid numbers followed fluctuations in nitrogen levels; statistically valid correlations were obtained between leaf nitrogen and psyllid numbers on individual trees at various times. These findings were supported by the results of preliminary laboratory experiments employing different fertilizer treatments. No effect of water stress or leaf hardness was clearly discerned. Cutting of trees altered the characteristics of the subsequent regenerative growth so as to allow massive psyllid infestations to develop, thus showing the tremendous importance of the host plant in determining population levels in this insect. Preliminary investigations of the nature and mechanism of this effect were conducted, and its significance is discussed. The relevance of these findings to modern concepts of regulation in insect populations and to principles of pest management is discussed.
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- Date Issued: 1975
The population dynamics of the rock hyrax procavia capensis (Pallas, 1766) in the Mountain Zebra National Park
- Authors: Fourie, Leon Johan
- Date: 1984
- Subjects: Rock hyrax Mountain Zebra National Park (South Africa)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5743 , http://hdl.handle.net/10962/d1005429
- Description: The chief objective of the study was to investigate the population dynamics of the hyrax in the Mountain Zebra National Park (MZNP). To realise this objective information on growth, age determination, reproduction, habitat utilization, behaviour, parasites and mortality had to be gathered. The growth of hyrax in relation to age is described by means of Stevens asymptotic regression equations. Near asymptotic measurements are attained first in hind foot length (at 30-33 months of age), head/body length (at 37-39 months of age), girth (at 41-48 months of age) and body mass (at 68-70 months of age). Allometric growth of the various body measurements was investigated and useful predictive relationships for mass are presented. Age determination of hyrax was studied in detail. Cementum annuli counts provided reliable estimates of age. One primary cementum line is formed annually. The dried eye lens mass was an accurate means of age determination up to c. 72 months of age. A summary of findings which will facilitate age determination of dead animals or skulls, and live animals, is provided. Reproduction in the hyrax was studied with emphasis on breeding season, age-specific litter sizes, prenatal mortality and lactation. Male hyrax attained puberty at 15-17 months of age or one year later. Females generally attained puberty at 15-17 months of age. One female (1,4% of total shot sample for the specific age group) attained puberty at 4-5 months of age. Middle-aged hyrax had significantly larger litter sizes than younger animals. Hyrax in the MZNP feed on at least 80 different plant species belonging to 33 plant families. Crude protein of stomach contents and faecal samples showed little seasonal fluctuation implying that hyrax in the MZNP were on a stable quality diet. Female hyrax enjoyed a significantly better quality diet than males for the four month period prior to parturition and during the first two months of lactation. The crude protein values of faecal and stomach samples had a significant correlation. Body fat of male and female hyrax showed seasonal variation related to physiologically stressful periods. Seasonal differences in activity patterns were demonstrated. The basic structure of hyrax social organization is the multi-female kinship group that is matrilocal. Territorial dominant males maintain harems and exclude all other adult males. Peripheral males occupy areas on the periphery of the activity areas of other members of the hyrax colony. Peripheral males do not form bachelor groups and are normally younger than territorial males. It is suggested that territorial males are able to monopolize between 3-17 females in a successful and energetic manner. Both natal and breeding dispersal occurred, the former being considerably more extensive than the latter. The ecto- and endoparasites of hyrax were identified and their burdens quantified over a 13 month period. Juveniles had significantly larger burdens of ectoparasites than did adults. Information on age-specific mortality was obtained from skulls collected in the field and at black eagles' nests. Losses that occurred in the study population due to caracal and black eagle predation were quantified. Evidence is supplied which indicates that juvenile mortality may fluctuate markedly. The population dynamics of the hyrax population in the MZNP was studied by the use of time specific life-tables, models on population growth rates, population simulation models and sensitivity analysis. Sensitivity coefficients were used as a predictor of population regulation. Female juvenile mortality was considered to be the main regulating factor. Changes in fecundity schedule are important compensatory mechanisms and also play an important role in the regulation of a hyrax population. Predation, particularly by caracal, is thought to dampen population fluctuations.
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- Date Issued: 1984
The population structure of two estuarine fish species, atherina breviceps (Pisces: Atherinidae) and gilchristella aestuaria (Pisces: Clupeidae), along the Southern African coastline
- Authors: Norton, Olivia Bridget
- Date: 2006
- Subjects: Estuarine fishes -- South Africa , Estuarine ecology -- South Africa , Clupeidae -- South Africa , Silversides -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5745 , http://hdl.handle.net/10962/d1005431 , Estuarine fishes -- South Africa , Estuarine ecology -- South Africa , Clupeidae -- South Africa , Silversides -- South Africa
- Description: Phylogeographic patterns of coastal organisms with different life histories and breeding strategies may reveal patterns not consistent with the current delineation of the biogeographic provinces around South Africa. The subdivision of the South African coastline into these three main climatological or biogeographic regions: namely the cool temperate west coast, the warm temperate south coast and the subtropical east coast, is based on average seawater temperatures and hydrological conditions. Genealogies of two estuarine fish species Atherina breviceps, a marine breeder, and Gilchristella aestuaria, an estuarine spawner, were reconstructed using mitochondrial DNA (mtDNA) control region sequences. The study comprised two components, an assessment of a small dataset of both fish species to compare their population structure along the South African coastline and a more comprehensive investigation of the phylogeography of G. aestuaria collected from 21 estuaries around the coast. The comparative study of A. breviceps and G. aestuaria indicate different population distribution patterns along the South African coastline. Results of the A. breviceps analysis demonstrate substantial gene flow due to the random mixing of alleles, while the comparative G. aestuaria dataset indicates a more structured population and considerably less gene flow. The G. aestuaria population demonstrates geographic separation into four groups, namely the west coast (Great Berg), Bot (south coast), Seekoei (south coast) and east coast (Bushmans, Kasouga and Cefane). Results from the larger G. aestuaria dataset indicate that the phylogeographic patterns observed during this study do not conform to existing biogeographic boundaries along the southern African coastline. The delineation identified during this study between the warm temperate and subtropical regions is further south than originally perceived and this southward extension can be ascribed to the prevailing hydrology. The life history patterns and ecology of these two estuarine fish species appears key to understanding their population structure. These factors interact with environmental characteristics such as physical oceanography and the distribution of estuaries (along the coastline) to explain the observed distribution patterns and population structure of A. breviceps and G. aestuaria.
- Full Text:
- Date Issued: 2006
The possible effect of insecticide drift from citrus orchards, and acute toxicity of insecticides on the biocontrol agents of Pontederia crassipes (Mart.) Solms-Laub (Pontederiaceae) established along citrus orchards in the Lowveld region of Mpumalanga Province, South Africa
- Authors: Mabuza, Mefika Michael
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424468 , vital:72156
- Description: This study investigated the possible effect of insecticide drift on naturalized biological control agents of Pontederia crassipes (Mart.) Solms-Laub (Pontederiaceae), in the Lowveld region of Mpumalanga Province of South Africa. Occurrence and abundance of biocontrol agents were recorded at three sites on the Crocodile River and at three dams adjacent to citrus orchards. Leaves of P. crassipes and water samples were collected for insecticide residues and also nutrient status of the water and plants. Eccritotarsus catarinensis Carvalho (Hemiptera: Miridae), Neochetina spp. (combined) (Coleoptera: Curculionidae), and Orthogalumna terebrantis Wallwork (Sarcoptiformes: Galumnidae) were recorded with notable variation in abundance between the river and dams across regions. Insecticide residues were not detected on all leaves sampled across study regions, however, nutrients were detected with nitrate ranging between oligotrophic and mesotrophic. Phosphorus was also detected, but, neither of the nutrients correlated with the occurrence and abundance of naturalized biological control agents of P. crassipes. Bioassays were conducted to measure the effect of commonly used insecticides (viz. Methomyl and Chlorpyrifos) on the survival and feeding damage of biological control agents of P. crassipes. Survival of individual insects was recorded between 0.5 and 120 hours for Megamelus scutellaris and Neochetina eichhorniae Warner (Coleoptera: Curculionidae) adults for treatments where insecticides were topically applied onto the insects or leaves were dipped into the pesticides. Concentrations below field rates, recommended and above field rates of Methomyl and Chlorpyrifos on either exposure techniques significantly reduced survival and feeding of biocontrol agents. Methomyl was more toxic compared to Chlorpyrifos and it significantly reduced the survival of M. scutellaris and N. eichhorniae. In conclusion, in this study, population abundance of biocontrol agents of P. crassipes at the Lowveld region of Mpumalanga was not influenced by pesticide drift, but, insecticides commonly used in the citrus orchards has the potential to negatively impact naturalized biological control of P. crassipes as demonstrated by the bioassays. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
The potential of hydrellia egeriae rodrigues (diptera: ephydridae) as a biocontrol agent for egeria densa planch. (hydrocharitaceae) in South Africa
- Authors: Smith, Rosali
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/53733 , vital:26314
- Description: The integrity of South Africa’s valuable freshwater ecosystems has been threatened by aquatic invasive plants since the 1900s. Floating aquatic weeds, such as Eichhornia crassipes (C. Mart) Solms (Pondederiaceae), Pistia stratiotes L. (Araceae), Salvinia molesta D.S. Mitchell (Salviniaceae), Azolla filiculoides Lam. (Azollaceae), and the emergent weed, Myriophyllum aquaticum Verdc. (Haloragaceae) benefited from open, nutrient-rich water bodies. Due to the limitations of mechanical and chemical control in aquatic environments, classical biological control has been a huge asset in managing these weeds; consequently bringing them under complete or substantial control. However, submerged aquatic weeds are widely distributed through the aquarium trade in South Africa; facilitating their invasion into new habitats. The removal of surface mats following the successful management of floating weeds has enhanced the growth and competitive ability of submerged aquatic weeds, such as Hydrilla verticillata (L.f.) Royle (Hydrocharitaceae), Myriophyllum spicatum L. (Haloragaceae) and Egeria densa Planch. (Hydrocharitaceae) in South Africa. Of these species, E. densa has become the most widely distributed, invading numerous systems across South Africa. Compared to other exotic submerged aquatic plants, E. densa is the only species capable of inhabiting freshwater systems in every province and therefore, it is vital to manage existing populations and prevent its further distribution and invasion. Hydrellia spp. (Diptera: Ephydridae) biological control agents have been used extensively in the management of submerged aquatic weeds elsewhere, particularly those in the Hydrocharitaceae (Balciunas and Burrows 1996; Wheeler and Center 2001. Hydrellia egeriae Rodrigues (Diptera: Ephydridae) has been identified as a promising candidate for E. densa and was imported into quarantine at Rhodes University, Grahamstown in 2014. The aims of this study were to conduct a pre-release assessment of the potential of H. egeriae as a biological control agent for E. densa in South Africa. The first objective of this study was to establish the life history of the agent under controlled conditions on E. densa found in South Africa, as well as its population growth parameters to predict its invasion success in the field. Secondly, laboratory host-specificity testing was conducted to validate the host range of the agent, in view of published native range host-specificity testing, and to establish potential risks to non-target species, should it be released. Finally, a biological control agent should also effectively reduce the fitness of its host plant, and therefore, impact studies were conducted. Laboratory impact studies have been limited in the past, in that they only investigate agent damage for short ecological periods, thus underestimating the damage capacity of the agent under investigation. Therefore, the damage capacity of H. egeriae was investigated over three consecutive generations in multi-generational impact trials. In a controlled environment of 22 ± 2°C, H. egeriae exhibited the ability to rapidly increase in population size within a short period of time, which will enhance agent establishment and build-up in the field. Host-specificity trials indicated that H. egeriae has a host range restricted to the Hydrocharitaceae, with exploratory feeding and development on Lagarosiphon major Ridley, L. muscoides Harvey and Vallisneria spiralis L. However, only L. major supported agent development during paired larval choice tests, and continuation trials showed that the test species was not physiologically capable of supporting viable agent populations. Risk analysis illustrated that the feeding and reproductive risks that H. egeriae pose to non-target species are very low and therefore, H. egeriae should be safe for release in South Africa. Additionally, significant damage to vital plant structures (shoot growth and side shoot length) was only recorded under high (five larvae) agent abundances. Encouragingly, the number of leaves mined at the end of the experiment was similar for both intermediate (three) and high (five) larval abundances, suggesting that cumulative leaf-mining under intermediate larval abundances has the potential to reduce the fitness of E. densa, given sufficient time. Results from pre-release assessments provide a robust understanding of the specialization of the potential biological control agent to its host plant. Nevertheless, the absolute success of a biological control programme depends on the many factors after prerelease assessments that determine agent establishment, persistence and target weed suppression, e.g. mass-rearing, release protocols and a/biotic factors within the recipient community. Considering these factors, the best mass-rearing and release protocols are proposed here and future research priorities are identified. Finally, the long term success for managing E. densa in South Africa will require a holistic approach to address the underlying factors, such as eutrophication and human-mediated distribution that drive submerged aquatic plant invasions.
- Full Text:
- Date Issued: 2017
The refinement of protective salinity guidelines for South African freshwater resources
- Authors: Slaughter, Andrew Robert
- Date: 2005
- Subjects: Water salinization -- South Africa Salinization -- Control -- South Africa Salinity -- South Africa Freshwater ecology -- South Africa Water resources development -- South Africa Caridina Caridina -- Effect of pollution
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:6031 , http://hdl.handle.net/10962/d1006170
- Description: South Africa is an arid country and its growing population is putting freshwater resources under increasing pressure. Natural salinization of freshwater systems is being exacerbated by anthropogenic influences. The National Water Act (No. 36 of 1998) stipulates the need for an ecological Reserve, that quantity and quality of freshwater needed to protect freshwater ecosystems while allowing sustainable use of freshwater resources. Water guidelines do exist in the form of the South African Water Quality Guidelines (DWAF, 1996) and more recently, Jooste and Rossouw (2002) compiled benchmark values for water quality variables marking the boundaries between ecological health classes in the 4-category classification system. Predominantly international toxicity data were used to compile the guidelines and the benchmark values. In addition, there is a paucity of chronic toxicity data nationally and internationally. This thesis showed that it is statistically possible to derive protective chronic endpoints for salinity from acute toxicity data through extrapolation. The Acute to Chronic Ratio (ACR), Two-Step Linear Regression (LRA) and Multi-Factor Probit Analysis (MPA) extrapolation methods were investigated to derive chronic toxicity data from acute toxicity data. The authors of LRA and MPA recommend associating a time independent LCx value in the range of LC₀¸₀₁ to LC₁₀ with a Predicted No Effect Concentration (PNOEC). In addition to published methods, this thesis studied the possibility of equating a time independent LC₅₀ value and subjected to a safety factor of 5 (LRA LC₅₀/5), to the PNOEC. Extrapolated chronic toxicity data where the toxicants are NaCl and Na₂SO₄ were derived for indigenous South African macroinvertebrates. NaCl and Na₂SO₄ are salts associated with salinisation in South Africa. In addition, a chronic salinity toxicity test protocol for an indigenous South African aquatic macroinvertebrate was designed and chronic toxicity test were performed using NaCl and Na₂SO₄ as toxicants. The experimental chronic toxicity data produced were used to validate results from the acute to chronic extrapolation methods. Extrapolated chronic toxicity data were inputted into Species Sensitivity Distribution curves, and concentrations that were predicted to protect 95 % of species (PC95) were compared to the sub-lethality benchmarks proposed by Jooste and Rossouw (2002) for NaCl and Na₂SO₄. This study concluded that the LRA LC₅₀/5 extrapolation method is the most protective and accurate and proposed that LRA replace the ACR method in future guideline development for inorganic salts.
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- Date Issued: 2005
The relationship between acquired resistance and transmission of Schistosoma Weinland, 1858, in man and its influences on the prevalence of S Capense (Harley, 1864) and S Mansoni Sambon, 1907, in Southern Rhodesia
- Authors: Clarke, H V de V
- Date: 1965
- Subjects: Platyhelminthes , Schistosoma , Schistosomiasis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5842 , http://hdl.handle.net/10962/d1010500 , Platyhelminthes , Schistosoma , Schistosomiasis
- Description: Bilharziasis ranks with Tuberculosis and Malaria as the three most important endemic diseases of man in Rhodesia. The prominence given to bilharziasis in the endemic diseases pattern arises from its high prevalence, particularly in the African population. It is probable that bilharziasis was endemic in the country even prior to the arrival in the conntry of the European settlers in 1890, but it was not until Orpen (1915) described the results of a small survey that local infections were proven. He reported 182 (31 percent) urinary infections in 592 African prisoners examined in the Salisbury gaol. In the ensuing 15 years there was only scanty evidence of the prevalence of the disease. However, in the decade 1931 to 1940 the Annual Public Health Reports of Southern Rhodesia indicated increasing prevalence, and this stimulated interest in the problem and led to the establishment in 1939 of a specialised laboratory to study the parasites causing the disease. The unpublished records of this laboratory indicate that in more recent years the disease has increased not only in prevalence but also in its intensity in infected individuals. Surveys show that the urinary form of the disease is more widespread than the intestinal form. Both forms are becoming more prevalent but the rapid increase of the latter, considered by most authorities to be the more severe, indicates that a greater importance must be accorded to it in the future. Introduction, p. 1.
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- Date Issued: 1965
The reported prevalence of aircrew fatigue and the contributing factors within the South African aviation industry
- Authors: Blair, Dylan Ross
- Date: 2022-10-14
- Subjects: Fatigue , Flight crews , Fatigue in the workplace , Sleep deprivation , Sleep-wake cycle , Air travel Safety measures , Airlines South Africa
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362762 , vital:65360
- Description: Fatigue in aviation results from the complex interaction of various factors (both work and non-work-related) that are important to understand when attempting to manage it. Managing fatigue effectively is important given that it has and continues to influence crew wellness and aviation safety. One of the ways of managing fatigue is through appropriately designed Flight Time Limitations (FTLs) however; in South Africa there have been calls from the unions and the crew to update these in line with the latest science and operational demands and insights. Doing this requires the generation of context specific data, which this thesis aimed to provide as an initial step. Firstly, this study aimed to explore the reported prevalence of fatigue across the South African aviation industry. Secondly, it elucidated what factors (both work and non-work related) crew perceived contributed to fatigue and lastly, the crew‟s perceptions regarding the current FTLs were explored. Methods: To realize the aims of the study, an online survey was developed using existing literature initially, and through consulting with and getting information from aviation industry stakeholders and other experts in the field of aviation and fatigue. This consultation (which occurred over a number of iterations of the survey) ensured that there was a balance between the scientific and the actual operational perspectives on how best to explore crew perceptions around fatigue. The finalized survey was divided into five parts: part one was consent to participate; part two included questions pertaining to the participants‟ demographic information; part three included questions pertaining to the crews‟ perceptions around fatigue (its prevalence, its impact on safety and how it affected crew); part four explored crew‟s perceptions on fatigue contributory factors, both work and non-work related; finally part five included questions pertaining to crew perceptions about the current South African FTLs, specifically their concerns, suggestions for improvement and any aspects they considered as fatigue mitigating. The survey was made available via the South African Civil Aviation Authority‟s (SACAA) website as well as via the industry stakeholder‟s networks that encouraged all crew across the different sectors of the industry to participate. All numerical data collected were analysed descriptively through inferential statistics, while the qualitative data were analysed using thematic analysis. Results: 194 participants completed the survey, 167 were from cockpit and 27 were from the cabin crew. The results of the study highlight that there is a high perceived prevalence of fatigue. The crew also recognized that fatigue is a significant safety risk, but less indicated that fatigue interfered with their ability to do their duties. Crew reported that the length of duties, number of sectors flown, insufficient sleep at night, early sign-on‟s, late sign-offs, working too many consecutive days in a row, inadequate or irregular sleep before and during periods of duty, night flying, bad weather, severe turbulence, having young children or dependents to look after, financial stress, extended commuting to get to and from work, and poor diet were some of the work and non-work-related contributory factors to fatigue. In line with these findings, questions around the perceived concerns about the current FTLs revealed that crew were concerned about unclear definitions of the civil aviation regulations (CARs), the lack of control of disruptive rostering schedules, periods of high workload due to the number of sectors flown per duty, the length of duty periods and effects of being on standby duty, inadequate rest between duties and strings of duty. The crew also had concerns regarding the Flight Duty Periods (FDPs) where the crew were concerned with the flying limits being used as targets by the operators, a lack of science applied to the FDPs, and that the current FDPs are outdated. The recommendations included limiting disruptive rostering schedules by altering standby provisions for the crew, instilling a block roster schedule, disallowing double signing on and off on the same day, and reducing split shifts. The crew also recommended adjusting duty durations by adjusting daily and monthly limits, tapering duty lengths, but also limiting discretionary extensions. Increasing rest provision was another recommendation suggested by the crew and included increasing the number of rest days off as well as the minimum hours of rest between duties needs to be increased. The fatigue mitigating aspects were minimal if any. Conclusion: Overall the study revealed that there is a high perceived prevalence of fatigue within this sample of the South African aviation industry and that the concerns outlined by crew around the contributory factors to fatigue are consistent with previous research, but also reflect the unique operating context of South Africa. This study serves as a base from which to explore more specific areas of the crew working time that are disruptive to sleep. This may help operator‟s roster duties in a more predictable way to limit the incidence of fatigue, while also offering the opportunity for the regulator and other stakeholders to focus their efforts on how to better design the current FTLs to limit the prevalence and risks associated with crew fatigue. , Thesis (MSc) -- Human Kinetics and Ergonomics, 2022
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- Date Issued: 2022-10-14
The reproduction biology of four species of South African dolphins
- Authors: Reddy, Kasturi
- Date: 1996
- Subjects: Dolphins -- South Africa -- Reproduction , Bottlenose dolphin -- Reproduction , Striped dolphin -- Reproduction , Chinese white dolphin -- Reproduction
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5753 , http://hdl.handle.net/10962/d1005441 , Dolphins -- South Africa -- Reproduction , Bottlenose dolphin -- Reproduction , Striped dolphin -- Reproduction , Chinese white dolphin -- Reproduction
- Description: Seasonality of reproduction in common dolphins (Delphinus delphis), bottlenosed dolphins (Tursiops aduncus), striped dolphins (Stenella coeruleoalba) and humpbacked dolphins (Sousa chinensis) was examined using standard light microscope techniques. In the males four stages of testicular development could be identified. Individuals less than 2.26m in length and 105kg in mass had testes that contained small seminiferous tubules (0.048mm ± O.Olmm in diameter) and were classified either as juveniles (gonocytes present) or inactive (no gonocytes). Adults whose testes contained spermatozoa were said to be in late spermatogenesis while those whose testes contained no spermatids or spermatozoa were referred to as being in early spermatogenesis. In the males of D. delphis, T. aduncus and S. chinensis, late spermatogenesis occurred throughout the year and there was no significant difference in the monthly mean seminiferous tubule diameters (p > 0.05) within species. I conclude therefore that in these three species spermatogenesis is aseasonal. No conclusions about seasonality of spermatogenesis could be made for S. coeruleoalba owing to the small sample size. Large Graafian follicles occurred in the ovaries of all four species in most months of the year. However, the presence of Graafian follicles can not be taken as an indication of timing of reproduction since they may be remnants of follicles that have not yet degenerated. In D. delphis, T. aduncus and S. coeruleoalba luteal bodies (corpora albicans or corpora lutea) occurred in most months of the year. Active corpora lutea will be present in all months, in some members of the population, since gestation is approximately 12 months. The sperm structure of D. delphis was examined by scanning electron microscopy. The sperm of D. delphis is essentially similar to that described for two other species of Cetacea (Physeter catodon and Tursiops aduncus), having an ellipsoidally shaped head and a short mid-piece with nine mitochondria. The sperm dimensions for D. delphis were head length, 4.4pm; head width, 2.0pm and mid-piece length, 2.4pm. An analysis of foetal age in D. delphis showed that the majority of the foetuses were conceived in January with birth occurring the following summer (December), suggesting that reproduction is seasonal. Neonates of T. aduncus were found throughout the year suggesting aseasonal reproduction. Foetal material was not available for S. coeruleoalba and S. chinensis. Seasonality of reproduction in the four species of dolphins studied has been discussed in relation to feeding, migration and worldwide distribution of the species.
- Full Text:
- Date Issued: 1996
The reproductive performance, demography and spatial ecology of an extralimital white rhinoceros population
- Authors: Truter, Anja
- Date: 2021-04
- Subjects: White rhinoceros -- South Africa -- Eastern Cape , White rhinoceros -- Effect of poaching on -- South Africa -- Eastern Cape , White rhinoceros -- South Africa -- Eastern Cape -- Reproduction , White rhinoceros -- Dispersal -- South Africa -- Eastern Cape , White rhinoceros -- Food -- South Africa -- Eastern Cape , White rhinoceros -- Behavior -- South Africa -- Eastern Cape , Spatial ecology -- South Africa -- Eastern Cape , Animal populations -- South Africa -- Eastern Cape , Endangered species -- South Africa -- Eastern Cape , Spatial behavior in animals -- South Africa -- Eastern Cape , Shamwari Game Reserve (South Africa)
- Language: English
- Type: thesis , text , Master , MSc
- Identifier: http://hdl.handle.net/10962/177975 , vital:42895
- Description: The white rhinoceros (Ceratotherium simum) (hereafter rhino) is under threat of becoming extinct due to continued poaching for its horns. In South Africa and elsewhere in Africa private landowners have, over the last few decades, contributed to the conservation of various species, including rhinos, even in areas where they have not occurred historically (i.e., where they are extralimital). Unfortunately, very few studies have investigated the conservation contribution of extralimital white rhinos on private reserves to the overall meta-population and/or their reproductive performance. The first aim of my study was therefore to determine whether or not the white rhinos introduced to a private game reserve in the Eastern Cape Province in 1992 have been successful from a reproductive perspective. I calculated inter-calving intervals, age at first calving, conception period, sex ratio, fecundity and fertility rates for white rhinos over this 28-year period. The average annual population growth rate for the rhinos was 10%, which is higher than the recommended 5% by the Rhino Management Group. Trends in density-dependent parameters such as age at first calving and inter-calving intervals also indicated that my study population is still well below carrying capacity for white rhinos and is contributing positively to white rhino conservation in South Africa. The second aim of my study was to investigate home range size and vegetation preferences of white rhinos. Home ranges were mostly larger for all age groups compared to rhinos in their native range. Previously cultivated lands (dominated by several grass species) were preferred by all rhino age groups. The rehabilitation of these previous agricultural-based pastures has likely contributed to the successful introduction of the white rhino as an extralimital megaherbivore in the Eastern Cape. I conclude that although extralimital white rhino populations in the Eastern Cape can be successful from a reproductive perspective, their potential impact on the indigenous biodiversity of the region should be a key future research priority. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-04
The role of a symbiotic bryozoan in the chemical ecology of a marine benthic predator-prey interaction
- Authors: Gray, Christopher Anthony
- Date: 2001
- Subjects: Marine animals , Marine ecology , Benthic animals
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5756 , http://hdl.handle.net/10962/d1005444 , Marine animals , Marine ecology , Benthic animals
- Description: The subtidal whelk Burnupena papyracea (Brugière) co-occurs with a voracious predator, the rock lobster Jasus lalandii (Milne Edwards), in situations where other potential prey are largely eliminated. This has been ascribed to a symbiotic bryozoan, Alcyonidium nodosum (O’Donoghue and de Watteville), which characteristically encrusts the shells of B. papyracea and deters feeding by Jasus. In this study it is shown that this is not due to physical effects of either induced physical defences in the bryozoan or increased shell strength due to the presence of the bryozoan. Neither spectroscopic screening of chemical extracts of the bryozoan nor analysis for volatile constituents revealed any apparent chemical components that are likely to deter feeding. Chemical extracts also failed to show larvicidal effects in a standard toxicity assay using the brine shrimp Artemia salina (Leach). Despite this, bioassays using individual Jasus indicated a chemical basis for feeding deterrence. The assays were run separately on three sets of Jasus and some repeats of assays gave contradictory results. However, assays showing no significant effect of treatment occurred with moulting Jasus, involved very low overall feeding rates and so gave a less convincing result. In other assays Jasus always avoided Burnupena papyracea with live Alcyonidium encrusting the shell, and food pellets containing Alcyonidium or an Alcyonidium extract. Significant preferences were shown for an unencrusted whelk, B. cincta (Röding), over B. papyracea; for B. papyracea with the bryozoan scraped off over natural B. papyracea; for B. papyracea on which the bryozoans had been killed with liquid nitrogen over untreated B. papyracea; and for food pellets prepared from ground, dried mussel over pellets prepared with dried mussel mixed with A. nodosum or its crude organic extract. It is concluded that the protection which Alcyonidium confers on Burnupena papyracea does have a chemical basis, but that the chemical responsible is either present in only trace quantities, or that it is a structurally unremarkable compound which is distasteful to Jasus. This work highlights both the advantages of using ecologically relevant bioassays (positive results when standard techniques give a negative result) and also the disadvantages (logistic constraints on sample sizes when using large test animals and individual variability in a relatively sophisticated test animal).
- Full Text:
- Date Issued: 2001
The role of aardvarks (Orycteropus afer) as ecosystem engineers in arid and semi-arid landscapes of South Africa
- Authors: Whittington-Jones, Gareth Morgan
- Date: 2007
- Subjects: Aardvark , Aardvark -- South Africa , Aardvark -- South Africa -- Habitations , Animal burrowing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5757 , http://hdl.handle.net/10962/d1005445 , Aardvark , Aardvark -- South Africa , Aardvark -- South Africa -- Habitations , Animal burrowing
- Description: Arid and semi arid environments are characterised by extreme fluctuations in temperature and low rainfall which present significant challenges to the animals inhabiting these areas. Mammals, such as aardvarks (Orycteropus afer, Pallas 1766), excavate burrows in order to avoid predators and climatic extremes and are termed “ecosystem engineers” as they physically modify their environment and in doing so create new habitats and alter the availability of resources to other species. In this study I assessed the microhabitat conditions (maximum and minimum temperature, relative humidity and seed abundance) of aardvark burrows in relation to paired control sites. In addition, I evaluated the use of aardvark burrows by other vertebrate and invertebrate species and investigated the impact of aardvark burrow mounds on landscape scale floristic diversity. Maximum temperatures were significantly lower (p < 0.05) and minimum temperatures and midday humidity were significantly higher (p < 0.05) inside the burrows at the three study sites, Kwandwe Private Game Reserve (Kwandwe), Mountain Zebra National Park (MZNP) and Tswalu Kalahari Reserve (Tswalu). There were no significant differences between the concentration of seeds, the average numbers of unique individual small mammals, trap success or small mammal species richness recorded inside the burrows compared to outside (p > 0.05). At all three sites, small mammal species diversity was higher in the burrows but this result was also not significant (p > 0.05 for all). Trap success and the number of individuals captured was higher at Tswalu than the other two sites (p < 0.05 for both). The different methods used in this study revealed a total of 25 mammal, seven bird, one amphibian and six reptile species utilising aardvark burrows. There were significant differences in insect community assemblages between the burrows and open control areas at Kwandwe and Tswalu (p < 0.05 for both) but not at MZNP (p > 0.05). The parasitic guild was more prominent inside the burrows than outside but their abundance was not as high as anticipated, possibly due to the placement of traps closer to the burrow entrances than the sleeping chambers. The complex structure of the burrows prevented the placement of traps in close proximity to the sleeping chambers. As expected, the amount of bare earth was significantly higher on active and recently abandoned burrow mounds compared to the old burrow mounds and reference plots at all three sites (p < 0.05 for all), with the exception of the active burrows at Tswalu. Overall, the different plot types were characterised by significantly different plant communities during all the seasons at MZNP, during three of the seasons at Kwandwe and only during winter at Tswalu. The total species richness recorded on the reference plots was higher than on the burrow mounds at all three sites. However, species diversity on the reference plots was not significantly higher than the burrows at any of the sites (p > 0.05 for all sites). Although the results were not significant, the overall species diversity at a site level was greater than the reference patches at Kwandwe and Tswalu (p > 0.05 for both). Aardvarks fulfil the criteria of a significant ecosystem engineer and their presence in arid and semi-arid environments is likely to be critical to the survival of other individual organisms and species, particularly when alternative burrowing animals are either absent or restricted in their activities. Thus, aardvark populations should be considered a conservation priority in arid and semi-arid ecosystems.
- Full Text:
- Date Issued: 2007
The role of ants in structuring insect communities on the canopies of senegalia drepanolobium near Laikipia, Kenya
- Authors: Kuria, Simon Kamande
- Date: 2007
- Subjects: Ants -- Kenya Ants -- Behavior Insect societies -- Kenya Forest canopy ecology -- Kenya
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5758 , http://hdl.handle.net/10962/d1005446
- Description: In the black cotton ecosystem of Laikipia, Kenya, four symbiotic ants coexist at a fine spatial scale on canopies of Senegalia drepanolobium. They exhibit different aggressive behaviours and modify their tree canopies differently. These diverse behaviours were expected to affect the associated canopy arthropod communities. At the Kenya long-term exclosure experiment (KLEE) and its immediate environs at Mpala Research Centre, Laikipia, the insect communities coexisting with each of the four ant species were characterized, and their response to different vertebrate herbivory. Other ant species inhabiting the tree canopies or the ground were surveyed too. Pitfall trapping was used in sampling terrestrial ants, while beating and mist-blowing were used in collecting arboreal insects. Different sampling methods had varying efficacies, revealing the importance of using several methods. There are at least sixteen ant species in this ecosystem, all occurring on the ground, but only ten species on the trees. Terrestrial ant communities in this ecosystem cannot be used as indicators of grazing pressure for range management. A total of 10,145 individual insects were collected from the tree canopies, comprising of 117 species from seven orders and 25 families, forming a complex community of species interacting at different levels. Symbiotic ant species had a significant effect on insect community structure and composition. Crematogaster sjostedti was associated with a community that was significantly different from the other ant species. There was no significant effect of vertebrate feeding pressure on the canopy insect community, but there was an interaction effect between ant species and treatments. Significant differences between ant species mostly occurred on treatment plots where only cows were allowed to graze. One or more of the ant species may be a keystone species in this ecosystem even though experimental manipulations failed to confirm earlier findings. It was concluded that the one-year period during which experimental manipulations were carried out was not long enough to reflect takeover effects on the insect community. The four symbiotic ant species colonizing S. drepanolobium comprises of two guilds, the hemipteran-tending ants (C. sjostedti and Crematogaster mimosae) and non-tending ants (Crematogaster nigriceps and Tetraponera penzigi). Communities associated with these guilds were found to be significantly different in all four diversity indices. The black cotton ecosystem is species-poor compared to other ecosystem such as forests. The number of insect species that colonizes S. drepanolobium and coexists with acacia-ants forms a large proportion of the invertebrate community. Therefore, this ecosystem should be conserved to safeguard this invertebrate community. This will also give scientists a chance to establish how the various insect species coexist with symbiotic ants on tree canopies.
- Full Text:
- Date Issued: 2007
The role of ecological processes in structuring reef fish communities in the Agulhas Ecoregion, South Africa
- Authors: Dyer, Alexander
- Date: 2018
- Subjects: Reef fishes -- South Africa -- Agulhas, Cape (Cape) , Reef fishes -- Ecology -- South Africa -- Agulhas, Cape (Cape) , Marine biodiversity -- South Africa -- Agulhas, Cape (Cape) , Biotic communities -- South Africa -- Agulhas, Cape (Cape) , Sparidae -- South Africa -- Agulhas, Cape (Cape) , Reef fishes -- Size -- South Africa -- Agulhas, Cape (Cape) , Baited remote underwater stereo-video systems (stereo-BRUVs)
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/63899 , vital:28504
- Description: Local, niche-based processes, which arise from the interplay between biotic interactions and abiotic constraints are considered to be important regulators of community structure. However, it is increasingly recognised that patterns of diversity can also be strongly influenced by dispersal-driven processes. While empirical research on the diversity of coral reef fishes on shallow tropical reefs has contributed greatly to the development of general concepts in ecology, there have been considerably fewer studies on the processes which shape the diversity of fish communities on shallow (10 - 30 m) and deep (30 - 75 m) rocky reefs. Consequently, it is less clear at which spatial scales niche partitioning and dispersal limitation contribute most strongly to the structure of reef-associated fish communities within rocky reef ecosystems. To address this caveat, research was conducted at four rocky reef complexes within the warm-temperate Agulhas Ecoregion, South Africa. The diversity of reef-associated fishes was sampled by baited remote underwater stereo-video systems (stereo-BRUVs) to incorporate the range of heterogeneous reef habitat in Tsitsikamma National Park Marine Protected Area (TNP MPA) and Algoa Bay (AB). To examine how niche-based and dispersal-driven processes influence patterns of diversity among species within the dominant family of resident fishes, the sparids (Sparidae), components of diversity were quantified at several spatial scales. Turnover in the number of species which locally co-occurred was found to be largely driven by the limited dispersal of species over hundreds of kilometres. When relative species abundances were taken into account, sparid communities were characterised by higher than expected rates of compositional turnover among local habitat patches separated by hundreds to thousands of metres of contiguous reef. Patterns of compositional turnover were associated with the spatial aggregation of conspecifics, particularly at scales which facilitate the post-settlement dispersal of fishes. Niche-based segregation of species along the depth gradient was found to be the primary driver of compositional turnover among both protected and exploited communities. However, spatial structuring within reefs, which was independent of variation in the environment, suggests that compositional differences among communities are also influenced by the limited post-settlement dispersal of resident fishes to adjacent areas during their ontogeny. Together, the results suggest that the diversity of reef-associated sparids is likely to depend both on an adequate diversity of suitable reef habitat and a sufficient degree of spatial connectivity to facilitate ontogenetic habitat shifts. Taxon-based descriptors of diversity do not adequately account for ecological difference among conspecifics within size-structured populations. To test whether differences in body size facilitated coexistence among sparid fishes, the number of species which coexisted at the local scale was related to variation in the size structure of communities. In communities which have been historically protected from fishing, local coexistence between a greater number of species was promoted by reduced levels of intraspecific variation in size of fishes. This suggests that, among species with similar trophic requirements, further niche segregation along a prey-size and body-size gradient is likely to mitigate the direct impacts of competition for shared food resources. Among exploited communities, size structure did not influence the number of species which coexisted at the local scale. This finding suggests that fishing-induced mortality of larger-bodied fishes is likely to remove some of the constraints to colonisation which arise from asymmetries in competitive fitness between small and large-bodied fishes. Together, these results highlight the importance of post-settlement processes and population size structure to the maintenance of reef-associated fish diversity within contiguous rocky reef habitats.
- Full Text:
- Date Issued: 2018
The role of male competition and female choice in the mating success of a Lek-breeding Southern African Cichlid fish Pseudocrenilabrus Philander (Pisces: Cichlidae)
- Authors: Chan, Tin-Yam
- Date: 1988
- Subjects: Cichlids -- Africa, Southern -- Physiology Courtship in animals Fishes -- Reproduction Cichlids Pseudocrenilabrus philander Lek-breeding Courtship Reproduction Spawning Competition Rivalry
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5599 , http://hdl.handle.net/10962/d1002049
- Description: A lek-breeding cichlid fish Pseudocrenilabrus philander was studied experimentally. Females in choice-chamber experiments showed no active choice for male size and colour, or for other male attributes, but preferred males which courted most actively. In a laboratory lek, the significant determinants of the strongly skewed mating success in males were territory size, side-shake and female chasing frequency. Together these three variables explained 79% of the variation in male mating success, with territory size alone accounting for 75% of the variation and the other two variables each accounting for 2% of the remaining variation. As there was no difference in territory quality in the laboratory lek, territory size became the principal measure of the effect of male-male competition since it was directly related to dominance. Both side-shake and female chasing could be identified as the basic factors influencing female choice, as they had an immediate effect on the display-response mating system of females. Thus, the relative importance of these three variables indicated that sexual selection in this particular lek mating species operated chiefly through the agency of intrasexual competition for dominance. However, both female behaviour and their requirement for a prolonged pre-spawning courtship had the effect of promoting male rivalry and favouring mating with dominant males. Although the intense male competition excluded subordinate males from practising normal courtship behaviour, competitively inferior males might "make the best of a bad situation" by facultatively adopting an alternative sneaking tactic to gain access to females. Spawning intrusions by females to steal freshly-laid eggs also occurred frequently. However, territorial males appeared to be relatively more tolerant of female intruders than male sneakers. Interference during spawning could lead to a longer pre-spawning courtship and even multiple-mating by females. The results of the present study and the behavioural evidence shown by males and females did not support the ʺrunaway selection modelʺ of the mating pattern in terms of sexual selection in leks, but conformed to the rival ʺwar propaganda modelʺ
- Full Text:
- Date Issued: 1988
The role of microzooplankton in carbon cycling in the Southern Ocean
- Authors: Froneman, Pierre William
- Date: 1996
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:21066 , http://hdl.handle.net/10962/6234
- Description: A 3-year study was carried out on the role of microzooplankton in carbon cycling in the south Atlantic and the Atlantic sector of the Southern Ocean. Microzooplankton grazing impact on phytoplankton was estimated during austral summer and winter employing the dilution technique. Carnivory by larger zooplankton on microzooplankton during summer was estimated using in vitro incubations. Microzooplankton assemblages were always dominated by protozoans comprising ciliates and dinoflagellates. In the ( 20 um chlorophyll fraction, microzooplankton grazing was sufficient to control the growth of the nano- and picophytoplankton suggesting that, where larger microphytoplankton cells dominate, micro zooplankton maintain the background concentrations of the nano- and picophytoplankton. During winter, when small nano- and picophytoplankton cells dominate total chlorophyll concentrations, the microzooplankton grazing impact on phytoplankton is dramatically increased. Microzooplankton removed on average 37% of the initial phytoplankton stock or 70% of the daily phytoplankton production. These results suggest that in winter, micro zooplankton are the main sink for phytoplankton production. Carnivory experiments conducted with selected meso- (copepods) and macro zooplankton (euphausiids and tunicates) showed that all species examined consumed micro zooplankton in the presence of substantial chlorophyll concentrations. Microzooplankton can, therefore, be regarded as trophic intermediates between bacterioplankton, small phytoplankton cells and larger zooplankton species in the Southern Ocean. The results of this investigation suggest a spatiotemporal shift in efficiency of the biological pump mediated by changes in the size composition of the phytoplankton assemblages. South of the Antarctic Polar Front (APF) large IV microphytoplankton cells dominate the summer chlorophyll biomass, suggesting that larger zooplankton grazers represent the main sink for phytoplankton production. Under these conditions, carbon flux to the interior of the ocean will be high due to diel vertical migrations by grazers and the production of large, fast sinking faecal pellets. The sedimentation of large phytoplankton cells also contributes to flux. In the permanently open waters south of the APF and throughout the Southern Ocean during winter, small phytoplankton cells dominate total chlorophyll, resulting in the microbial loop being the main sink for phytoplankton production. The close coupling between the micro zooplankton and the microbial loop dramatically reduces the transfer of organic carbon from the surface layers to depth. Carnivory by metazoans on microzooplankton may reduce the high grazing impact of micro zooplankton and, may also represent an important source of carbon flux originating from the microbial loop.
- Full Text:
- Date Issued: 1996
The role of nutrients in the biological control of water lettuce, Pistia stratiotes lamarck (Araceae) by the leaf-feeding weevil, Neohydronomus affinis Hustache (Coleoptera: Curculionidae) with particular reference to eutrophic conditions
- Authors: Moore, Gareth Ryan
- Date: 2006
- Subjects: Water lettuce -- Biological control , Araceae , Beetles , Curculionidae , Weeds -- Biological control , Pests -- Biological control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5759 , http://hdl.handle.net/10962/d1005447 , Water lettuce -- Biological control , Araceae , Beetles , Curculionidae , Weeds -- Biological control , Pests -- Biological control
- Description: Water lettuce, Pistia stratiotes Lamarck (Araceae) is a South American plant that has the potential to be a very damaging and important aquatic weed in many tropical countries, including South Africa. It has the potential to rapidly multiply vegetatively and completely cover watercourses in a very short space of time outside of its natural range under ideal conditions and without its natural enemies. In such instances, the weed may cause hindrances to water transport and fishing, increasing chances of malaria, as well as affecting the natural ecology of the system. Water lettuce can also set seed, which may lay dormant for long periods, germinating when conditions are favourable. It is therefore very necessary to adopt control methods against the weed where it is a problem. However, water lettuce has also been effectively and completely controlled in many countries by the leaf-feeding weevil, Neohydronomus affinis Hustache. High nutrient levels in the form of nitrates and phosphates have been shown to have largely negative effects on biological control in several studies, with control being incomplete or taking longer than in similar areas with lower nutrient levels. The effectiveness of N. affinis on the biological control of water lettuce was investigated in a laboratory study, growing P. stratiotes plants with and without insects at different nutrient concentrations. In these studies biological control of water lettuce with N. affinis was found to be complete under eutrophic nutrient conditions, although control took longer when higher nutrient levels were tested. A field site study was conducted at a sewage settlement pond in Cape Recife Nature Reserve near Port Elizabeth, South Africa. This highly eutrophic system was used as a field example for the effectiveness of biocontrol of P. stratiotes by N. affinis under eutrophic conditions. The weevils at Cape Recife caused a massive and rapid crash in the percentage coverage of the weed, from 100% in May 2003, to approximately 0.5 % in September 2003. Plant growth parameters were also found to decrease considerably in size correspondingly with this crash from May 2003 until spring 2003. Plant size only again started to increase gradually but steadily through spring 2003 and into summer. In the laboratory studies, the fecundity of weevils was shown to be much higher on plants grown under higher nutrient concentrations than on plants grown in lower nutrient concentrations. The results from the wing-muscle analysis under different nutrient concentrations were not easy to interpret, and there were few differences in wing muscle state between most of the concentrations. From these findings it is suggested that nutrient concentration, particularly high levels of nitrates and phosphates is not a limiting factor in terms of effective biological control of P. stratiotes with N. affinis, but that under high nutrient conditions biological control might take longer.
- Full Text:
- Date Issued: 2006
The role of small antelope in ecosystem functioning in the Matobo Hills, Zimbabwe
- Authors: Lunt, Nicola
- Date: 2011
- Subjects: Antelopes -- Zimbabwe -- Rhodes Matopos National Park Ecosystem health -- Zimbabwe -- Rhodes Matopos National Park Forest ecology -- Zimbabwe -- Rhodes Matopos National Park Savanna ecology -- Zimbabwe -- Rhodes Matopos National Park Woody plants -- Effect of fires on -- Zimbabwe -- Rhodes Matopos National Park Duikers -- Zimbabwe -- Rhodes Matopos National Park Bushbuck -- Zimbabwe -- Rhodes Matopos National Park Greater kudu -- Zimbabwe -- Rhodes Matopos National Park
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5760 , http://hdl.handle.net/10962/d1005448
- Description: The 28-month study assessed the impacts of five syntopic medium-sized mammalian browsers and one fire event in a woodland savanna in the Matobo Hills, Zimbabwe. Aspects of herbivory, mechanical pressures, seed dispersal and nutrient cycling were investigated for three species of small antelope (common duiker [Sylvicapra grimmia]1, klipspringer [Oreotragus oreotragus] and steenbok [Raphicerus campestris]) and two medium-sized species (bushbuck [Tragelaphus scriptus] and greater kudu [T. strepsiceros]). Focusing on Burkea africana2 woodland, in a system that does not include elephant (Loxodonta africana), effects of browsing antelope on woody and herbaceous vegetation development were investigated using exclusion plots. Browsers regulated woody plant cover (measured as basal stem area), with smaller antelope having a greater impact than larger species. This was linked to feeding height, feeding selectivity and mechanical pressures (e.g. twig breakage and trampling). Fire caused an initial reduction in above-ground standing biomass, but in the presence of fauna, pre-fire equilibria were attained within 15 months. In antelope exclosures, herbaceous biomass increased and woody biomass decreased following fire. Responses by woody vegetation to browsing varied among species, with highly palatable species typically exhibiting compensatory regrowth. Woody species richness and abundance (especially of palatable species) increased in the absence of browsers, but species richness of the herbaceous layer was promoted by moderate disturbance (trampling or fire). Faecal deposition behaviour, primarily the use of latrines by small antelope, resulted in localised soil enrichment within defended territories. Decomposition rates (and therefore return of nutrients to the soil) varied among species and seasons, due to defecation site selection, accessibility to decomposers and desiccation rates of faecal pellets. Controlled seed germination experiments indicated that ingestion by small antelope enhances germination rates of large, hard-seeded fruits such as Sclerocarya birrea. However, germination of savanna seeds may require multiple cues. This study demonstrated the critical roles of small antelope in ecosystem functioning, and highlights the importance of the less visible impacts of frequently overlooked smaller mammalian herbivores. Perturbations to the faunal community, especially small antelope, are predicted to have substantial impacts on woody plant cover.
- Full Text:
- Date Issued: 2011