The feeding and spatial ecology of cheetahs (Acinonyx jubatus) and lions (Panthera leo) in the Little Karoo, South Africa
- Authors: Vorster, Paul Hendrik
- Date: 2012
- Subjects: Sanbona Wildlife Reserve , Cheetah -- South Africa -- Little Karoo , Lion -- South Africa -- Little Karoo , Cheetah -- Behavior -- South Africa -- Little Karoo , Lion -- Behavior -- South Africa -- Little Karoo , Cheetah -- Food -- South Africa -- Little Karoo , Lion -- Food -- South Africa -- Little Karoo , Spatial behavior in animals , Predation (Biology) , Game reserves -- Management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5693 , http://hdl.handle.net/10962/d1005379 , Sanbona Wildlife Reserve , Cheetah -- South Africa -- Little Karoo , Lion -- South Africa -- Little Karoo , Cheetah -- Behavior -- South Africa -- Little Karoo , Lion -- Behavior -- South Africa -- Little Karoo , Cheetah -- Food -- South Africa -- Little Karoo , Lion -- Food -- South Africa -- Little Karoo , Spatial behavior in animals , Predation (Biology) , Game reserves -- Management
- Description: The re-introduction of large carnivores into relatively small conservation areas that fall within the historic distribution range of the species is becoming an increasingly common occurrence. The success of such re-introductions depends very much on the quality of the information that is available to guide management decisions, but in many cases, little information is available. The re-introduction of lions and cheetahs to Sanbona created the opportunity to monitor the behaviour of re-introduced predators to a relatively large system that was characterised by a low ungulate stocking density and little standing water. The broad aims were to study the feeding and spatial ecologies of the lions and cheetahs, to collect standard base-line data, and to examine the effects of the low prey density and limited standing water on habitat selection, range size and diet. The diet (data collected from direct observation and faecal analysis) was similar to that reported in previous studies, and lions and cheetahs preferred greater kudu, black wildebeest and springbok. Lions preferred medium to large prey items, and cheetahs preferred medium to small prey items. The hilly and mountainous terrain of much of the reserve meant that only 50% of the total space was available to the predators. Home ranges of most of the predators were focused around the single large body of standing water. This is likely to have been a response to the water, the vegetation, and the prey that was attracted to these. Habitat selection was also influenced by inter and intra-specific interactions at least for a solitary male lion and female cheetahs. Range sizes were larger than on some other reserves and it is suggested that this was a result of the low prey density. These results form the basis for management recommendations including the importance of continuing to monitor the system and opening up additional parts of the reserve to the predators.
- Full Text:
- Date Issued: 2012
- Authors: Vorster, Paul Hendrik
- Date: 2012
- Subjects: Sanbona Wildlife Reserve , Cheetah -- South Africa -- Little Karoo , Lion -- South Africa -- Little Karoo , Cheetah -- Behavior -- South Africa -- Little Karoo , Lion -- Behavior -- South Africa -- Little Karoo , Cheetah -- Food -- South Africa -- Little Karoo , Lion -- Food -- South Africa -- Little Karoo , Spatial behavior in animals , Predation (Biology) , Game reserves -- Management
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5693 , http://hdl.handle.net/10962/d1005379 , Sanbona Wildlife Reserve , Cheetah -- South Africa -- Little Karoo , Lion -- South Africa -- Little Karoo , Cheetah -- Behavior -- South Africa -- Little Karoo , Lion -- Behavior -- South Africa -- Little Karoo , Cheetah -- Food -- South Africa -- Little Karoo , Lion -- Food -- South Africa -- Little Karoo , Spatial behavior in animals , Predation (Biology) , Game reserves -- Management
- Description: The re-introduction of large carnivores into relatively small conservation areas that fall within the historic distribution range of the species is becoming an increasingly common occurrence. The success of such re-introductions depends very much on the quality of the information that is available to guide management decisions, but in many cases, little information is available. The re-introduction of lions and cheetahs to Sanbona created the opportunity to monitor the behaviour of re-introduced predators to a relatively large system that was characterised by a low ungulate stocking density and little standing water. The broad aims were to study the feeding and spatial ecologies of the lions and cheetahs, to collect standard base-line data, and to examine the effects of the low prey density and limited standing water on habitat selection, range size and diet. The diet (data collected from direct observation and faecal analysis) was similar to that reported in previous studies, and lions and cheetahs preferred greater kudu, black wildebeest and springbok. Lions preferred medium to large prey items, and cheetahs preferred medium to small prey items. The hilly and mountainous terrain of much of the reserve meant that only 50% of the total space was available to the predators. Home ranges of most of the predators were focused around the single large body of standing water. This is likely to have been a response to the water, the vegetation, and the prey that was attracted to these. Habitat selection was also influenced by inter and intra-specific interactions at least for a solitary male lion and female cheetahs. Range sizes were larger than on some other reserves and it is suggested that this was a result of the low prey density. These results form the basis for management recommendations including the importance of continuing to monitor the system and opening up additional parts of the reserve to the predators.
- Full Text:
- Date Issued: 2012
The trophic ecology of parrotfish of Zanzibar application of stable isotope analysis
- Plass-Johnson, Jeremiah Grahm
- Authors: Plass-Johnson, Jeremiah Grahm
- Date: 2012
- Subjects: Parrotfishes -- Tanzania -- Zanzibar , Parrotfishes , Parrotfishes -- Ecology -- Tanzania -- Zanzibar , Parrotfishes -- Behavior -- Tanzania -- Zanzibar , Parrotfishes -- Food -- Tanzania -- Zanzibar , Scleractinia -- Tanzania -- Zanzibar , Algae -- Tanzania -- Zanzibar , Coral reefs and islands -- Tanzania -- Zanzibar , Coral reef fishes -- Tanzania -- Zanzibar , Stable isotopes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5789 , http://hdl.handle.net/10962/d1005477 , Parrotfishes -- Tanzania -- Zanzibar , Parrotfishes , Parrotfishes -- Ecology -- Tanzania -- Zanzibar , Parrotfishes -- Behavior -- Tanzania -- Zanzibar , Parrotfishes -- Food -- Tanzania -- Zanzibar , Scleractinia -- Tanzania -- Zanzibar , Algae -- Tanzania -- Zanzibar , Coral reefs and islands -- Tanzania -- Zanzibar , Coral reef fishes -- Tanzania -- Zanzibar , Stable isotopes
- Description: Parrotfish are a critical component of the herbivore functional group on tropical coral reefs around the world because they mediate competition that occurs between algae and scleractinian corals. Also, because of their feeding technique, which consists of rasping at the substratum with their beak-like teeth, they play an important role in carbonate turnover and the clearing of reef surface area for the settlement of new sessile organisms. Because of these roles, parrotfishes are an important structuring component of coral reef communities. However, individual species can play different roles depending on their physiology, behaviour and ecology. Despite the possible ecological differences that may exist amongst species, specific roles of the fishes remain unclear as the group is most often studied at higher community levels. This thesis applied stable isotope analysis to differing levels of organisation within a parrotfish community to help elucidate their trophic ecology on coral reefs in Zanzibar. Firstly, blood and muscle tissues were compared to identify differences in their isotope signatures. In other organisms, blood turns over faster than muscle tissue so that muscle tissue represents the diet as integrated over a longer period of time. In most species of parrotfish the blood and muscle δ¹³C signatures were not found to be significantly different, but the δ¹⁵N signatures were significantly different between tissues. This indicated that the δ¹³C signature of both tissues would reveal similar dietary information. Conversely, differences in the δ¹⁵N signature indicated that the nitrogen relationship between tissues was more complicated. Secondly, spatial variability in parrotfish, coral, detritus and macroalgae isotope signatures was assessed at different scales. In macroalgae and coral tissues (zooxanthellae and polyp treated separately), the δ¹³C signatures were shown to differ with depth, presumably because of changes in photosynthetic processes related to depth-associated changes in light. While δ¹⁵N signatures were not affected by depth, all organisms showed enrichment at the Nyange reef, the closest reef to the capital of Zanzibar, Stone Town, presumably reflecting the effects of sewage outfall. These results show that processes that impact the δ¹⁵N signatures of primary producers (macroalgae and zooxanthellae) can be traced to higher trophic levels (coral polyps and fish). Lastly, δ¹³C and δ¹⁵N signatures were used to identify ontogenetic dietary changes in multiple species of parrotfish. Four of the species showed stages that varied from the diets that are normally assumed on the basis of their dentition and feeding technique. This indicates that functional roles based on taxonomy or morphology may fail to include possible ontogenetic dietary changes, and may also fail to elucidate the full impact a species could have on coral reef communities. The conclusions from these studies indicate that the species-specific ecological role of parrotfish in coral reef communities can be complex within and between species, and may differ amongst reefs. In light of the natural and anthropogenic pressures that affect coral reef systems, management decisions based on a more complete understanding of the role of these fish in coral reef communities will help decisions that maintain resilience in these fragile systems.
- Full Text:
- Date Issued: 2012
- Authors: Plass-Johnson, Jeremiah Grahm
- Date: 2012
- Subjects: Parrotfishes -- Tanzania -- Zanzibar , Parrotfishes , Parrotfishes -- Ecology -- Tanzania -- Zanzibar , Parrotfishes -- Behavior -- Tanzania -- Zanzibar , Parrotfishes -- Food -- Tanzania -- Zanzibar , Scleractinia -- Tanzania -- Zanzibar , Algae -- Tanzania -- Zanzibar , Coral reefs and islands -- Tanzania -- Zanzibar , Coral reef fishes -- Tanzania -- Zanzibar , Stable isotopes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5789 , http://hdl.handle.net/10962/d1005477 , Parrotfishes -- Tanzania -- Zanzibar , Parrotfishes , Parrotfishes -- Ecology -- Tanzania -- Zanzibar , Parrotfishes -- Behavior -- Tanzania -- Zanzibar , Parrotfishes -- Food -- Tanzania -- Zanzibar , Scleractinia -- Tanzania -- Zanzibar , Algae -- Tanzania -- Zanzibar , Coral reefs and islands -- Tanzania -- Zanzibar , Coral reef fishes -- Tanzania -- Zanzibar , Stable isotopes
- Description: Parrotfish are a critical component of the herbivore functional group on tropical coral reefs around the world because they mediate competition that occurs between algae and scleractinian corals. Also, because of their feeding technique, which consists of rasping at the substratum with their beak-like teeth, they play an important role in carbonate turnover and the clearing of reef surface area for the settlement of new sessile organisms. Because of these roles, parrotfishes are an important structuring component of coral reef communities. However, individual species can play different roles depending on their physiology, behaviour and ecology. Despite the possible ecological differences that may exist amongst species, specific roles of the fishes remain unclear as the group is most often studied at higher community levels. This thesis applied stable isotope analysis to differing levels of organisation within a parrotfish community to help elucidate their trophic ecology on coral reefs in Zanzibar. Firstly, blood and muscle tissues were compared to identify differences in their isotope signatures. In other organisms, blood turns over faster than muscle tissue so that muscle tissue represents the diet as integrated over a longer period of time. In most species of parrotfish the blood and muscle δ¹³C signatures were not found to be significantly different, but the δ¹⁵N signatures were significantly different between tissues. This indicated that the δ¹³C signature of both tissues would reveal similar dietary information. Conversely, differences in the δ¹⁵N signature indicated that the nitrogen relationship between tissues was more complicated. Secondly, spatial variability in parrotfish, coral, detritus and macroalgae isotope signatures was assessed at different scales. In macroalgae and coral tissues (zooxanthellae and polyp treated separately), the δ¹³C signatures were shown to differ with depth, presumably because of changes in photosynthetic processes related to depth-associated changes in light. While δ¹⁵N signatures were not affected by depth, all organisms showed enrichment at the Nyange reef, the closest reef to the capital of Zanzibar, Stone Town, presumably reflecting the effects of sewage outfall. These results show that processes that impact the δ¹⁵N signatures of primary producers (macroalgae and zooxanthellae) can be traced to higher trophic levels (coral polyps and fish). Lastly, δ¹³C and δ¹⁵N signatures were used to identify ontogenetic dietary changes in multiple species of parrotfish. Four of the species showed stages that varied from the diets that are normally assumed on the basis of their dentition and feeding technique. This indicates that functional roles based on taxonomy or morphology may fail to include possible ontogenetic dietary changes, and may also fail to elucidate the full impact a species could have on coral reef communities. The conclusions from these studies indicate that the species-specific ecological role of parrotfish in coral reef communities can be complex within and between species, and may differ amongst reefs. In light of the natural and anthropogenic pressures that affect coral reef systems, management decisions based on a more complete understanding of the role of these fish in coral reef communities will help decisions that maintain resilience in these fragile systems.
- Full Text:
- Date Issued: 2012
Trophic ecology of breeding northern rockhopper penguins, Eudyptes Moseleyi, at Tristan da Cunha, South Atlantic Ocean
- Authors: Booth, Jenny Marie
- Date: 2012
- Subjects: Penguins -- Breeding -- Tristan da Cunha , Penguins -- Ecology -- Tristan da Cunha , Penguins -- Food
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5788 , http://hdl.handle.net/10962/d1005476 , Penguins -- Breeding -- Tristan da Cunha , Penguins -- Ecology -- Tristan da Cunha , Penguins -- Food
- Description: Northern Rockhopper penguin populations, Eudyptes moseleyi, are declining globally, and at Tristan da Cunha have undergone severe declines (> 90% in the last 130 years), the cause(s)of which are unknown. There is a paucity of data on this species in the South Atlantic Ocean, therefore their trophic ecology at Tristan da Cunha was studied, specifically focusing on diet, using stomach content analysis and stable isotope analysis (SIA), in conjunction with an analysis of diving behaviour, assessed using temperature-depth recorders. In order to evaluate the influence of gender on foraging, a morphometric investigation of sexual dimorphism was confirmed using molecular analysis. Additionally, plasma corticosterone levels were measured to examine breeding stage and presence of blood parasites as potential sources of stress during the breeding season. Northern Rockhopper penguins at Tristan da Cunha displayed a high degree of foraging plasticity, and fed opportunistically on a wide variety of prey, probably reflecting local small-scale changes in prey distribution. Zooplankton dominated (by mass) the diet of guard stage females, whereas small meso-pelagic fish (predominantly Photichthyidae)dominated diet of adults of both sexes in the crèche stage, with cephalopods contributing equally in both stages. Adults consistently fed chicks on lower-trophic level prey (assessed using SIA), probably zooplankton, than they consumed themselves indicating that the increasing demands of growing chicks were not met by adults through provisioning of higher- quality prey. SIA also indicated that adults foraged in different oceanic water masses when feeding for self-maintenance and for chick provisioning, thus temporally segregating the prey consumed for different purposes. It is possible that adults ‘selected’ these higher quality prey for themselves, or this may be a reflection of opportunistic behaviour. At Tristan da Cunha sexual dimorphism was observed in culmen dimensions (length, depth, width), with males having larger beaks and feeding on larger individuals of squid and fish than females. No sexual segregation in terms of foraging habitat (i.e. different water masses, based on ð¹³N or trophic level ð¹⁵N) during the breeding season or pre-moult period was revealed through SIA, and stomach content analysis revealed no sexual differences in prey species targeted. The results of SIA of feathers indicate that during the pre-moult period birds foraged in different water masses than during the breeding period. The fact that throughout the breeding season birds foraged in similar habitats suggests no intra-specific competition, despite both sexes feeding on the same prey.Birds were generally diurnal, daily foragers (12 – 16 hr trips), with extended trips (maximum duration 35.5 hours) and nocturnal diving recorded in a few individuals. Birds dived well within their physiological limits, predominantly utilising the upper 20m of the water column, employing two different strategies to target different prey items. Long, deep (30 – 40 m), energetically costly dives were performed when targeting energy-rich prey (fish), and a greater number of shorter, shallower (5 – 20 m), energy-efficient dives were performed when targeting prey with a lower energy content (zooplankton). More than half of the sampled study population were infected with the intra-cellular blood parasite Babesia, but infection showed no relationship to body mass, corticosterone levels or breeding success. Fasting birds showed no signs of elevated corticosterone levels, suggesting they had acquired sufficient fat reserves prior to breeding. Failed breeders did not exhibit elevated corticosterone levels. Tristan skuas, Catharacta antarctica hamiltoni, were observed to be a significant cause of egg and chick mortality. The absence of sex-based differences in foraging, and the absence of any signs of stress in relation to body mass, presence of Babesia or breeding stage, suggest that there are no obvious signs of high levels of stress or food limitations during breeding at Tristan da Cunha.
- Full Text:
- Date Issued: 2012
- Authors: Booth, Jenny Marie
- Date: 2012
- Subjects: Penguins -- Breeding -- Tristan da Cunha , Penguins -- Ecology -- Tristan da Cunha , Penguins -- Food
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5788 , http://hdl.handle.net/10962/d1005476 , Penguins -- Breeding -- Tristan da Cunha , Penguins -- Ecology -- Tristan da Cunha , Penguins -- Food
- Description: Northern Rockhopper penguin populations, Eudyptes moseleyi, are declining globally, and at Tristan da Cunha have undergone severe declines (> 90% in the last 130 years), the cause(s)of which are unknown. There is a paucity of data on this species in the South Atlantic Ocean, therefore their trophic ecology at Tristan da Cunha was studied, specifically focusing on diet, using stomach content analysis and stable isotope analysis (SIA), in conjunction with an analysis of diving behaviour, assessed using temperature-depth recorders. In order to evaluate the influence of gender on foraging, a morphometric investigation of sexual dimorphism was confirmed using molecular analysis. Additionally, plasma corticosterone levels were measured to examine breeding stage and presence of blood parasites as potential sources of stress during the breeding season. Northern Rockhopper penguins at Tristan da Cunha displayed a high degree of foraging plasticity, and fed opportunistically on a wide variety of prey, probably reflecting local small-scale changes in prey distribution. Zooplankton dominated (by mass) the diet of guard stage females, whereas small meso-pelagic fish (predominantly Photichthyidae)dominated diet of adults of both sexes in the crèche stage, with cephalopods contributing equally in both stages. Adults consistently fed chicks on lower-trophic level prey (assessed using SIA), probably zooplankton, than they consumed themselves indicating that the increasing demands of growing chicks were not met by adults through provisioning of higher- quality prey. SIA also indicated that adults foraged in different oceanic water masses when feeding for self-maintenance and for chick provisioning, thus temporally segregating the prey consumed for different purposes. It is possible that adults ‘selected’ these higher quality prey for themselves, or this may be a reflection of opportunistic behaviour. At Tristan da Cunha sexual dimorphism was observed in culmen dimensions (length, depth, width), with males having larger beaks and feeding on larger individuals of squid and fish than females. No sexual segregation in terms of foraging habitat (i.e. different water masses, based on ð¹³N or trophic level ð¹⁵N) during the breeding season or pre-moult period was revealed through SIA, and stomach content analysis revealed no sexual differences in prey species targeted. The results of SIA of feathers indicate that during the pre-moult period birds foraged in different water masses than during the breeding period. The fact that throughout the breeding season birds foraged in similar habitats suggests no intra-specific competition, despite both sexes feeding on the same prey.Birds were generally diurnal, daily foragers (12 – 16 hr trips), with extended trips (maximum duration 35.5 hours) and nocturnal diving recorded in a few individuals. Birds dived well within their physiological limits, predominantly utilising the upper 20m of the water column, employing two different strategies to target different prey items. Long, deep (30 – 40 m), energetically costly dives were performed when targeting energy-rich prey (fish), and a greater number of shorter, shallower (5 – 20 m), energy-efficient dives were performed when targeting prey with a lower energy content (zooplankton). More than half of the sampled study population were infected with the intra-cellular blood parasite Babesia, but infection showed no relationship to body mass, corticosterone levels or breeding success. Fasting birds showed no signs of elevated corticosterone levels, suggesting they had acquired sufficient fat reserves prior to breeding. Failed breeders did not exhibit elevated corticosterone levels. Tristan skuas, Catharacta antarctica hamiltoni, were observed to be a significant cause of egg and chick mortality. The absence of sex-based differences in foraging, and the absence of any signs of stress in relation to body mass, presence of Babesia or breeding stage, suggest that there are no obvious signs of high levels of stress or food limitations during breeding at Tristan da Cunha.
- Full Text:
- Date Issued: 2012
Development of techniques for the isolation of a granulovirus from potato tuber moth, phthorimaea operculella (Zeller)
- Authors: King, Shirley Anne
- Date: 2011
- Subjects: Potato tuberworm -- Larvae , Agricultural pests -- Biological control , Potato tuberworm , Baculoviruses
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5910 , http://hdl.handle.net/10962/d1015202
- Description: Phthorimaea operculella, commonly known as the Potato Tuber Moth, is an economically important agricultural pest worldwide. The baculovirus, Phthorimaea operculella granulovirus (PhoGV) has been considered as a means of control alternative to chemical control because of its host specificity and harmless impact on other organisms and ecosystems. An isolate of PhoGV obtained from a South African PTM population would be beneficial in the production of a biopesticide, which is not yet available. An efficient and cost-effective rearing method would be advantageous for potential commercial production. Commercial table and seed potato plantations and storage facilities located in Patensie, Bathurst, Howick and Ivanhoe were surveyed for PTM infestations. Patensie was the only site where milky discoloured larvae were found, a potential symptom of PhoGV infection. TEM analysis revealed no virus in these samples. Since no virus was found in the field-collected samples, PTM insects were collected to initiate rearing in the laboratory. PTM was raised by three different methods in the laboratory. A cost/benefit analysis, survival rate, fertility and sex ratio were recorded for each rearing method. Rearing method one was deemed unsuccessful for efficient commercial rearing, as survival percentage and fertility were low. Rearing methods two and three had high survival rates and high fertility, and were efficient and less labour intensive than rearing method one. Rearing method three was the most productive technique, but for commercial production rearing method two was considered the most manageable and efficient. The sex ratio was 1:1 for all three cultures. The cost analysis revealed that rearing methods two and three were less expensive than rearing method one because less labour was required to monitor insects. The success of rearing PTM for 19 months will enable these cultures to be up-scaled to a large production facility for mass rearing. Virus was not found in the field surveys or in laboratory cultures, therefore chemical, temperature, humidity and carbon dioxide stressors were used in an attempt to initiate a baculoviral infection. Symptoms were exhibited in larvae subjected to chemical, temperature and humidity treatments, but these were confirmed by TEM analysis not to be a result of PhoGV infection. The success of rearing PTM in the laboratory suggests that the method could be used in the commercial rearing of the insects in a large mass-rearing facility. The data obtained from induction protocols have allowed for better understanding for future induction for PhoGV and other baculoviruses in other insect species. The failure to isolate a South African PhoGV strain for developing a biopesticide against PTM has motivated further studies in obtaining a baculovirus in order for South Africa to develop a commercial product against this pest.
- Full Text:
- Date Issued: 2011
- Authors: King, Shirley Anne
- Date: 2011
- Subjects: Potato tuberworm -- Larvae , Agricultural pests -- Biological control , Potato tuberworm , Baculoviruses
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5910 , http://hdl.handle.net/10962/d1015202
- Description: Phthorimaea operculella, commonly known as the Potato Tuber Moth, is an economically important agricultural pest worldwide. The baculovirus, Phthorimaea operculella granulovirus (PhoGV) has been considered as a means of control alternative to chemical control because of its host specificity and harmless impact on other organisms and ecosystems. An isolate of PhoGV obtained from a South African PTM population would be beneficial in the production of a biopesticide, which is not yet available. An efficient and cost-effective rearing method would be advantageous for potential commercial production. Commercial table and seed potato plantations and storage facilities located in Patensie, Bathurst, Howick and Ivanhoe were surveyed for PTM infestations. Patensie was the only site where milky discoloured larvae were found, a potential symptom of PhoGV infection. TEM analysis revealed no virus in these samples. Since no virus was found in the field-collected samples, PTM insects were collected to initiate rearing in the laboratory. PTM was raised by three different methods in the laboratory. A cost/benefit analysis, survival rate, fertility and sex ratio were recorded for each rearing method. Rearing method one was deemed unsuccessful for efficient commercial rearing, as survival percentage and fertility were low. Rearing methods two and three had high survival rates and high fertility, and were efficient and less labour intensive than rearing method one. Rearing method three was the most productive technique, but for commercial production rearing method two was considered the most manageable and efficient. The sex ratio was 1:1 for all three cultures. The cost analysis revealed that rearing methods two and three were less expensive than rearing method one because less labour was required to monitor insects. The success of rearing PTM for 19 months will enable these cultures to be up-scaled to a large production facility for mass rearing. Virus was not found in the field surveys or in laboratory cultures, therefore chemical, temperature, humidity and carbon dioxide stressors were used in an attempt to initiate a baculoviral infection. Symptoms were exhibited in larvae subjected to chemical, temperature and humidity treatments, but these were confirmed by TEM analysis not to be a result of PhoGV infection. The success of rearing PTM in the laboratory suggests that the method could be used in the commercial rearing of the insects in a large mass-rearing facility. The data obtained from induction protocols have allowed for better understanding for future induction for PhoGV and other baculoviruses in other insect species. The failure to isolate a South African PhoGV strain for developing a biopesticide against PTM has motivated further studies in obtaining a baculovirus in order for South Africa to develop a commercial product against this pest.
- Full Text:
- Date Issued: 2011
Effects of habitat patch size and isolation on the population structure of two siphonarian limpets
- Authors: Johnson, Linda Gail
- Date: 2011
- Subjects: Siphonaria , Limpets , Population biology , Marine ecology , Habitat selection , Animals -- Dispersal , Ecological heterogeneity , Animal populations , Biodiversity
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5679 , http://hdl.handle.net/10962/d1005364 , Siphonaria , Limpets , Population biology , Marine ecology , Habitat selection , Animals -- Dispersal , Ecological heterogeneity , Animal populations , Biodiversity
- Description: Habitat fragmentation is a fundamental process that determines trends and patterns of distribution and density of organisms. These patterns and trends have been the focus of numerous terrestrial and marine studies and have led to the development of several explanatory hypotheses. Systems and organisms are dynamic and no single hypothesis has adequately accounted for these observed trends. It is therefore important to understand the interaction of these processes and patterns to explain the mechanisms controlling population dynamics. The main aim of this thesis was to test the effect of patch size and isolation on organisms with different modes of dispersal. Mode of dispersal has previously been examined as a factor influencing the effects that habitat fragmentation has on organisms. Very few studies have, however, examined the mode of dispersal of marine organisms because it has long been assumed that marine animals are not directly influenced by habitat fragmentation because of large-scale dispersal. I used two co-occurring species of siphonariid limpets with different modes of dispersal to highlight that not only are marine organisms affected by habitat fragmentation but that they are affected in different ways. The two species of limpet, Siphonaria serrata and Siphonaria concinna, are found within the same habitat and have the same geographic range along the South African coastline, however, they have different modes of dispersal and development. The effect of patch size on organism density has been examined to a great extent with varied results. This study investigated whether habitat patch size played a key role in determining population density and limpet body sizes. The two species are found on the eastern and southern coasts of South Africa were examined across this entire biogeographic range. Patch size was found to have a significant effect on population density of the pelagic developer, S. concinna, but not the direct developing S. serrata. Patch size did play a role in determining limpet body size for both species. S. concinna body size was proposed to be effected directly by patch size whilst S. serrata body size was proposed to be affected indirectly by the effects of the S. concinna densities. The same patterns and trends were observed at five of the seven examined regions across the biogeographic range. The trends observed for S. concinna with respect to patch size conform to the source-sink hypothesis with large habitat patches acting as the source populations whilst the small habitat patches acted as the sink populations. Many previous studies have focused on the effects of habitat patch size at one point in time or over one season. I tested the influence of habitat patch size on the two species of limpets over a period of twelve months to determine whether the trends observed were consistent over time or whether populations varied with time. S. concinna showed a consistently significant difference between small and large patches; whilst S. serrata did not follow a consistent pattern. The mode of dispersal for the two limpets was used to explain the different trends shown by the two species. This examination allowed for the determining of source and sink populations for S. concinna through the examination of fluctuations in limpet body sizes and population densities at small and large habitat patches over twelve months. The direct developing S. serrata trends could not be explained using source-sink theory, as populations were independent from one another. S. serrata demonstrated body size differences at small and large patches which, may be explained by interspecific and intraspecific competition. Habitat isolation is known to play an important role in determining the structure of assemblages and the densities of populations. In this study the population density of the pelagic developing S. concinna showed a weak influence of degree of isolation whilst that of the direct developing S. serrata did not, which may be because of habitat patches along the South African coastline not having great enough degrees of isolation. The population size-structure was influenced directly influenced by isolation for S. concinna, whilst the different population size structure for S. serrata may be explained by assemblage co-dependence. The mode of dispersal showed effects on the relationship of population density and population size-structure with habitat size and isolation. This study indicates the importance of investigating patterns and processes across a range of spatial and temporal scales to gain a comprehensive understanding of factors effecting intertidal organisms.
- Full Text:
- Date Issued: 2011
- Authors: Johnson, Linda Gail
- Date: 2011
- Subjects: Siphonaria , Limpets , Population biology , Marine ecology , Habitat selection , Animals -- Dispersal , Ecological heterogeneity , Animal populations , Biodiversity
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5679 , http://hdl.handle.net/10962/d1005364 , Siphonaria , Limpets , Population biology , Marine ecology , Habitat selection , Animals -- Dispersal , Ecological heterogeneity , Animal populations , Biodiversity
- Description: Habitat fragmentation is a fundamental process that determines trends and patterns of distribution and density of organisms. These patterns and trends have been the focus of numerous terrestrial and marine studies and have led to the development of several explanatory hypotheses. Systems and organisms are dynamic and no single hypothesis has adequately accounted for these observed trends. It is therefore important to understand the interaction of these processes and patterns to explain the mechanisms controlling population dynamics. The main aim of this thesis was to test the effect of patch size and isolation on organisms with different modes of dispersal. Mode of dispersal has previously been examined as a factor influencing the effects that habitat fragmentation has on organisms. Very few studies have, however, examined the mode of dispersal of marine organisms because it has long been assumed that marine animals are not directly influenced by habitat fragmentation because of large-scale dispersal. I used two co-occurring species of siphonariid limpets with different modes of dispersal to highlight that not only are marine organisms affected by habitat fragmentation but that they are affected in different ways. The two species of limpet, Siphonaria serrata and Siphonaria concinna, are found within the same habitat and have the same geographic range along the South African coastline, however, they have different modes of dispersal and development. The effect of patch size on organism density has been examined to a great extent with varied results. This study investigated whether habitat patch size played a key role in determining population density and limpet body sizes. The two species are found on the eastern and southern coasts of South Africa were examined across this entire biogeographic range. Patch size was found to have a significant effect on population density of the pelagic developer, S. concinna, but not the direct developing S. serrata. Patch size did play a role in determining limpet body size for both species. S. concinna body size was proposed to be effected directly by patch size whilst S. serrata body size was proposed to be affected indirectly by the effects of the S. concinna densities. The same patterns and trends were observed at five of the seven examined regions across the biogeographic range. The trends observed for S. concinna with respect to patch size conform to the source-sink hypothesis with large habitat patches acting as the source populations whilst the small habitat patches acted as the sink populations. Many previous studies have focused on the effects of habitat patch size at one point in time or over one season. I tested the influence of habitat patch size on the two species of limpets over a period of twelve months to determine whether the trends observed were consistent over time or whether populations varied with time. S. concinna showed a consistently significant difference between small and large patches; whilst S. serrata did not follow a consistent pattern. The mode of dispersal for the two limpets was used to explain the different trends shown by the two species. This examination allowed for the determining of source and sink populations for S. concinna through the examination of fluctuations in limpet body sizes and population densities at small and large habitat patches over twelve months. The direct developing S. serrata trends could not be explained using source-sink theory, as populations were independent from one another. S. serrata demonstrated body size differences at small and large patches which, may be explained by interspecific and intraspecific competition. Habitat isolation is known to play an important role in determining the structure of assemblages and the densities of populations. In this study the population density of the pelagic developing S. concinna showed a weak influence of degree of isolation whilst that of the direct developing S. serrata did not, which may be because of habitat patches along the South African coastline not having great enough degrees of isolation. The population size-structure was influenced directly influenced by isolation for S. concinna, whilst the different population size structure for S. serrata may be explained by assemblage co-dependence. The mode of dispersal showed effects on the relationship of population density and population size-structure with habitat size and isolation. This study indicates the importance of investigating patterns and processes across a range of spatial and temporal scales to gain a comprehensive understanding of factors effecting intertidal organisms.
- Full Text:
- Date Issued: 2011
Feeding ecology and diet shift of long-beaked common dolphins Delphinus Capensis (Gray 1828) incidentally caught in anti-shark nets off Kwazulu-Natal, South Africa
- Authors: Ambrose, Shan Taryn
- Date: 2011
- Subjects: Common dolphin -- South Africa -- Kwazulu-Natal , Common dolphin -- Food -- South Africa -- Kwazulu-Natal , Common dolphin -- Ecology -- South Africa -- Kwazulu-Natal , Sardinops sagax -- South Africa -- Kwazulu-Natal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5697 , http://hdl.handle.net/10962/d1005383 , Common dolphin -- South Africa -- Kwazulu-Natal , Common dolphin -- Food -- South Africa -- Kwazulu-Natal , Common dolphin -- Ecology -- South Africa -- Kwazulu-Natal , Sardinops sagax -- South Africa -- Kwazulu-Natal
- Description: The long-beaked common dolphin, Delphinus capensis (Gray 1828), is one of the most enigmatic predators feeding in the annual sardine run (Sardinops sagax) off the coast of KwaZulu-Natal (KZN), South Africa. In recent years, unpredictable inter-annual variations in the timing, spatial extent and intensity of the sardine run have been documented, possibly resulting in changes in the suite of prey available to the common dolphin during winter. Although the diets of a number of predators during the sardine run have been studied in detail (e.g. sharks and flying seabirds), little is known about the diet of long-beaked common dolphins during this period. Each year, a low number of common dolphins are incidentally caught in the anti-shark nets in the waters of KwaZulu-Natal. These captures provide a valuable source of data on selected aspects of the ecology of the long-beaked common dolphins along the KwaZulu-Natal coastline. The objective of this study was to provide new dietary data for the common dolphins feeding in the waters of KwaZulu-Natal during winter over the period 2000 to 2009, as well as to determine if any dietary changes had taken place since the common dolphin diet was last assessed, over 15 years ago. Stomach contents from 95 common dolphins (55 females, 40 males) caught between 2000 and 2009 were analysed and compared to historical data from dolphins caught between 1974 and 1992. Mesopelagic fish and squid dominated the diet, with 23 fish and 5 squid species represented in adult dolphins. Multidimensional Scaling (MDS) indicated that there was no resource partitioning between adult male and female dolphins. Numerical analyses indicated that there was a shift in the principal prey species consumed by the dolphins over the past decade, particularly during the winter. Prior to 1992, sardine comprised up to 49% of the total stomach contents, while chub mackerel (Scomber japonicus) was the dominant prey item (66% by mass) recorded in the stomach contents over the period 2000 to 2009. The shift in the relative contributions of sardine and mackerel in the diets of the dolphin appeared to correspond to fluctuations in the availability of the two principal prey species. Between 2000 and 2009, the diversity of the dolphins' diets was highest during the sardine run, reflecting the presence of a wide suite of predatory teleosts in the waters of KwaZulu-Natal during the annual sardine run. Conversely, prior to 2000, the diet was dominated by sardine during the peak of the sardine run, whilst diet diversity increased after this period. Apart from sardine and chub mackerel, elf (Pomatomus saltatrix), maasbanker (Trachurus delagoa), strepie (Sarpa salpa) and flying fish (Exocoetid sp.) also formed important components of the diet both prior to 1992, and over the last decade. Blubber thickness was assessed as an indicator of animal condition. No significant change in blubber total weight (R² = 0.0016, N = 185), nor dorsal, lateral or ventral blubber thickness (R² = 0.3146, R² = 0.0003, and R² = 0.0003 respectively, N = 78) was seen over the last 30 years (1970 to 2009). Results of stable isotope analyses conducted on tissue derived from the teeth of D. capensis indicated that there has been no significant shift in the trophic position (δ¹⁵N) and potential prey consumed (δ¹³C) over the corresponding period. These data would suggest that the long-beaked common dolphins along the KwaZulu-Natal coastline can be considered as opportunistic predators generally consuming the most abundant prey species available locally. As common dolphins feed opportunistically, this dietary shift appears to indicate changes in the shoaling characteristics of the most abundant fish prey in KwaZulu-Natal during winter. Given the “Data Deficient” status of the long-beaked common dolphin on the IUCN Red Data List, and the strong climatic forcing of the sardine run, such dietary data have important implications for their conservation in the light of expanding fisheries and climate change.
- Full Text:
- Date Issued: 2011
- Authors: Ambrose, Shan Taryn
- Date: 2011
- Subjects: Common dolphin -- South Africa -- Kwazulu-Natal , Common dolphin -- Food -- South Africa -- Kwazulu-Natal , Common dolphin -- Ecology -- South Africa -- Kwazulu-Natal , Sardinops sagax -- South Africa -- Kwazulu-Natal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5697 , http://hdl.handle.net/10962/d1005383 , Common dolphin -- South Africa -- Kwazulu-Natal , Common dolphin -- Food -- South Africa -- Kwazulu-Natal , Common dolphin -- Ecology -- South Africa -- Kwazulu-Natal , Sardinops sagax -- South Africa -- Kwazulu-Natal
- Description: The long-beaked common dolphin, Delphinus capensis (Gray 1828), is one of the most enigmatic predators feeding in the annual sardine run (Sardinops sagax) off the coast of KwaZulu-Natal (KZN), South Africa. In recent years, unpredictable inter-annual variations in the timing, spatial extent and intensity of the sardine run have been documented, possibly resulting in changes in the suite of prey available to the common dolphin during winter. Although the diets of a number of predators during the sardine run have been studied in detail (e.g. sharks and flying seabirds), little is known about the diet of long-beaked common dolphins during this period. Each year, a low number of common dolphins are incidentally caught in the anti-shark nets in the waters of KwaZulu-Natal. These captures provide a valuable source of data on selected aspects of the ecology of the long-beaked common dolphins along the KwaZulu-Natal coastline. The objective of this study was to provide new dietary data for the common dolphins feeding in the waters of KwaZulu-Natal during winter over the period 2000 to 2009, as well as to determine if any dietary changes had taken place since the common dolphin diet was last assessed, over 15 years ago. Stomach contents from 95 common dolphins (55 females, 40 males) caught between 2000 and 2009 were analysed and compared to historical data from dolphins caught between 1974 and 1992. Mesopelagic fish and squid dominated the diet, with 23 fish and 5 squid species represented in adult dolphins. Multidimensional Scaling (MDS) indicated that there was no resource partitioning between adult male and female dolphins. Numerical analyses indicated that there was a shift in the principal prey species consumed by the dolphins over the past decade, particularly during the winter. Prior to 1992, sardine comprised up to 49% of the total stomach contents, while chub mackerel (Scomber japonicus) was the dominant prey item (66% by mass) recorded in the stomach contents over the period 2000 to 2009. The shift in the relative contributions of sardine and mackerel in the diets of the dolphin appeared to correspond to fluctuations in the availability of the two principal prey species. Between 2000 and 2009, the diversity of the dolphins' diets was highest during the sardine run, reflecting the presence of a wide suite of predatory teleosts in the waters of KwaZulu-Natal during the annual sardine run. Conversely, prior to 2000, the diet was dominated by sardine during the peak of the sardine run, whilst diet diversity increased after this period. Apart from sardine and chub mackerel, elf (Pomatomus saltatrix), maasbanker (Trachurus delagoa), strepie (Sarpa salpa) and flying fish (Exocoetid sp.) also formed important components of the diet both prior to 1992, and over the last decade. Blubber thickness was assessed as an indicator of animal condition. No significant change in blubber total weight (R² = 0.0016, N = 185), nor dorsal, lateral or ventral blubber thickness (R² = 0.3146, R² = 0.0003, and R² = 0.0003 respectively, N = 78) was seen over the last 30 years (1970 to 2009). Results of stable isotope analyses conducted on tissue derived from the teeth of D. capensis indicated that there has been no significant shift in the trophic position (δ¹⁵N) and potential prey consumed (δ¹³C) over the corresponding period. These data would suggest that the long-beaked common dolphins along the KwaZulu-Natal coastline can be considered as opportunistic predators generally consuming the most abundant prey species available locally. As common dolphins feed opportunistically, this dietary shift appears to indicate changes in the shoaling characteristics of the most abundant fish prey in KwaZulu-Natal during winter. Given the “Data Deficient” status of the long-beaked common dolphin on the IUCN Red Data List, and the strong climatic forcing of the sardine run, such dietary data have important implications for their conservation in the light of expanding fisheries and climate change.
- Full Text:
- Date Issued: 2011
Initial investigations into dynamics of mesozooplankton community structure in Algoa Bay, South Africa
- Authors: Dali, Luzuko O'Brian
- Date: 2011
- Subjects: Zooplankton -- Research -- Indian Ocean -- South Africa , Phytoplankton -- Research -- Indian Ocean -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5715 , http://hdl.handle.net/10962/d1005401 , Zooplankton -- Research -- Indian Ocean -- South Africa , Phytoplankton -- Research -- Indian Ocean -- South Africa
- Description: As part of a long-term monitoring programme initiated by the South African Environmental Observation Network (SAEON) Elwandle Node, the spatio-temporal dynamics of mesozooplankton (200–2000 μm) community structure in Algoa Bay, on the Eastern Cape coastline of southern Africa, was investigated in summer and winter of 2008. Physical-chemical and biological variables were measured at selected sites in the eastern and western sectors of the Bay. During summer, nutrient rich waters upwelling into the eastern sector of the Bay contributed to significant spatial variation in selected physical-chemical variables. During winter, virtually no significant spatial patterns in the physical-chemical variables were observed (P>0.05 in all cases). For the majority of physical-chemical variables, no significant seasonal patterns in values were detected (P>0.05 in all cases). Notable exceptions were water column stability and water temperatures which were highest during summer, and seston, turbidity and ammonium concentrations which attained the highest values in winter. The striking seasonal pattern observed in the water column stability, coupled with the upwelling event, coincided with a strong seasonal pattern in the total surface and integrated chlorophyll-a concentrations within the Bay. During summer, the total surface phytoplankton biomass ranged from 1.87–3.11 μg.L⁻¹ and the integrated biomass values between 44.6 and 89.1 mg chl-a m⁻². In winter, surface chl-a concentrations ranged from 0.49 to 0.55 μg.L⁻¹ and integrated biomass from 13.5 to 13.8 mg chl-a m⁻². During both seasons, the large microphytoplankton (>20 μm) fraction contributed the most (>80%) to the total phytoplankton biomass suggesting that phytoplankton growth is not nutrient limited within the Bay. The total mesozooplankton abundance and biomass values during summer varied between 10088.92 and 28283.21 ind.m⁻³ and between 76.59 and 161.94 mg.m⁻³, respectively. During winter, total abundance and biomass of mesozooplankton within the Bay were significantly lower, ranging from 2392.49 to 11145.29 ind.m⁻³, and from 34.49 to 42.49 mg.m⁻³, respectively (P<0.05). During both seasons, cosmopolitan copepod species 200–500μm in size dominated the total mesozooplankton counts, numerically and in biomass. Hierarchical cluster analyses identified distinct zooplankton groupings within the Bay during both the summer (three groupings) and winter (four groupings) surveys. The different groupings identified during the two seasons were not associated with any specific geographic region or hydrological feature. Nonetheless, a distinct seasonal pattern in the mesozooplankton community was evident, largely reflecting the increased abundance of mesozooplankton during the summer survey. Canonical Correspondence Analyses (CCA) indicated that the zooplankton community structure within Algoa Bay reflected a complex interaction between physical-chemical (e.g. temperature, water column stability, turbidity, and nitrate, dissolved oxygen and nitrite concentrations) and biological factors (e.g. microphytoplankton and picophytoplankton concentrations). These data provide baseline information towards long-term monitoring programs that will be conducted in Algoa Bay, as part of the South African Environmental Observation Network (SAEON), in the near future.
- Full Text:
- Date Issued: 2011
- Authors: Dali, Luzuko O'Brian
- Date: 2011
- Subjects: Zooplankton -- Research -- Indian Ocean -- South Africa , Phytoplankton -- Research -- Indian Ocean -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5715 , http://hdl.handle.net/10962/d1005401 , Zooplankton -- Research -- Indian Ocean -- South Africa , Phytoplankton -- Research -- Indian Ocean -- South Africa
- Description: As part of a long-term monitoring programme initiated by the South African Environmental Observation Network (SAEON) Elwandle Node, the spatio-temporal dynamics of mesozooplankton (200–2000 μm) community structure in Algoa Bay, on the Eastern Cape coastline of southern Africa, was investigated in summer and winter of 2008. Physical-chemical and biological variables were measured at selected sites in the eastern and western sectors of the Bay. During summer, nutrient rich waters upwelling into the eastern sector of the Bay contributed to significant spatial variation in selected physical-chemical variables. During winter, virtually no significant spatial patterns in the physical-chemical variables were observed (P>0.05 in all cases). For the majority of physical-chemical variables, no significant seasonal patterns in values were detected (P>0.05 in all cases). Notable exceptions were water column stability and water temperatures which were highest during summer, and seston, turbidity and ammonium concentrations which attained the highest values in winter. The striking seasonal pattern observed in the water column stability, coupled with the upwelling event, coincided with a strong seasonal pattern in the total surface and integrated chlorophyll-a concentrations within the Bay. During summer, the total surface phytoplankton biomass ranged from 1.87–3.11 μg.L⁻¹ and the integrated biomass values between 44.6 and 89.1 mg chl-a m⁻². In winter, surface chl-a concentrations ranged from 0.49 to 0.55 μg.L⁻¹ and integrated biomass from 13.5 to 13.8 mg chl-a m⁻². During both seasons, the large microphytoplankton (>20 μm) fraction contributed the most (>80%) to the total phytoplankton biomass suggesting that phytoplankton growth is not nutrient limited within the Bay. The total mesozooplankton abundance and biomass values during summer varied between 10088.92 and 28283.21 ind.m⁻³ and between 76.59 and 161.94 mg.m⁻³, respectively. During winter, total abundance and biomass of mesozooplankton within the Bay were significantly lower, ranging from 2392.49 to 11145.29 ind.m⁻³, and from 34.49 to 42.49 mg.m⁻³, respectively (P<0.05). During both seasons, cosmopolitan copepod species 200–500μm in size dominated the total mesozooplankton counts, numerically and in biomass. Hierarchical cluster analyses identified distinct zooplankton groupings within the Bay during both the summer (three groupings) and winter (four groupings) surveys. The different groupings identified during the two seasons were not associated with any specific geographic region or hydrological feature. Nonetheless, a distinct seasonal pattern in the mesozooplankton community was evident, largely reflecting the increased abundance of mesozooplankton during the summer survey. Canonical Correspondence Analyses (CCA) indicated that the zooplankton community structure within Algoa Bay reflected a complex interaction between physical-chemical (e.g. temperature, water column stability, turbidity, and nitrate, dissolved oxygen and nitrite concentrations) and biological factors (e.g. microphytoplankton and picophytoplankton concentrations). These data provide baseline information towards long-term monitoring programs that will be conducted in Algoa Bay, as part of the South African Environmental Observation Network (SAEON), in the near future.
- Full Text:
- Date Issued: 2011
Quantifying crop damage by Grey crowned crane balearica regulorum regulorum and evaluating changes in crane distribution in the North Eastern Cape, South Africa
- Authors: Van Niekerk, Mark Harry
- Date: 2011
- Subjects: Cranes (Birds) -- South Africa -- Eastern Cape , Cranes (Birds) -- Geographical distribution -- South Africa -- Eastern Cape , Cranes (Birds) -- Behavior -- South Africa -- Eastern Cape , Cranes (Birds) -- Food -- South Africa -- Eastern Cape , Corn -- Effect of grazing on -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5749 , http://hdl.handle.net/10962/d1005436 , Cranes (Birds) -- South Africa -- Eastern Cape , Cranes (Birds) -- Geographical distribution -- South Africa -- Eastern Cape , Cranes (Birds) -- Behavior -- South Africa -- Eastern Cape , Cranes (Birds) -- Food -- South Africa -- Eastern Cape , Corn -- Effect of grazing on -- South Africa -- Eastern Cape
- Description: Complaints of crop damage by cranes on planted maize in the North Eastern Cape, South Africa, have been increasing since the mid-1990‘s, and in some instances severe losses have been reported. Crop damage by the Grey Crowned Crane Balearica regulorum regulorum near the town of Maclear (31º04´S 28º22´E), has been quantified over two growing seasons, and assessed relative to losses caused by foraging Cape Crows Corvus capensis and other feeding damage assumed to be caused by insects. Twelve fields were selected based on previous patterns of crop depredation. Maize seed in seven of the fields was treated with the chemical ‗Gaucho‘ and five fields were planted with untreated maize. In order to determine the source of losses, twenty quadrats (4 m x 4 m) randomly distributed within each field were visited on average every second day, for a period of up to twenty eight days. Results indicate that seed treatments do act as a deterrent to feeding by both cranes and crows, however crane damage is generally insignificant compared to other sources of damage. My study also reviewed past sightings data of the Grey Crowned Crane in an effort to determine if the conversion of former grassland to plantations in this region may have increased foraging activity in maize fields. The data did not allow for clear-cut conclusions regarding changes in distribution or population trends. Conclusions provide direct input into the management of agricultural areas by enabling landowners to take steps to mitigate crop damage. These mitigation measures may either involve the application of seed treatments, or the planting of low risk crops in high risk areas. Future studies should consider the ppossible detrimental effects of chemical seed treatments on crane biology.
- Full Text:
- Date Issued: 2011
- Authors: Van Niekerk, Mark Harry
- Date: 2011
- Subjects: Cranes (Birds) -- South Africa -- Eastern Cape , Cranes (Birds) -- Geographical distribution -- South Africa -- Eastern Cape , Cranes (Birds) -- Behavior -- South Africa -- Eastern Cape , Cranes (Birds) -- Food -- South Africa -- Eastern Cape , Corn -- Effect of grazing on -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5749 , http://hdl.handle.net/10962/d1005436 , Cranes (Birds) -- South Africa -- Eastern Cape , Cranes (Birds) -- Geographical distribution -- South Africa -- Eastern Cape , Cranes (Birds) -- Behavior -- South Africa -- Eastern Cape , Cranes (Birds) -- Food -- South Africa -- Eastern Cape , Corn -- Effect of grazing on -- South Africa -- Eastern Cape
- Description: Complaints of crop damage by cranes on planted maize in the North Eastern Cape, South Africa, have been increasing since the mid-1990‘s, and in some instances severe losses have been reported. Crop damage by the Grey Crowned Crane Balearica regulorum regulorum near the town of Maclear (31º04´S 28º22´E), has been quantified over two growing seasons, and assessed relative to losses caused by foraging Cape Crows Corvus capensis and other feeding damage assumed to be caused by insects. Twelve fields were selected based on previous patterns of crop depredation. Maize seed in seven of the fields was treated with the chemical ‗Gaucho‘ and five fields were planted with untreated maize. In order to determine the source of losses, twenty quadrats (4 m x 4 m) randomly distributed within each field were visited on average every second day, for a period of up to twenty eight days. Results indicate that seed treatments do act as a deterrent to feeding by both cranes and crows, however crane damage is generally insignificant compared to other sources of damage. My study also reviewed past sightings data of the Grey Crowned Crane in an effort to determine if the conversion of former grassland to plantations in this region may have increased foraging activity in maize fields. The data did not allow for clear-cut conclusions regarding changes in distribution or population trends. Conclusions provide direct input into the management of agricultural areas by enabling landowners to take steps to mitigate crop damage. These mitigation measures may either involve the application of seed treatments, or the planting of low risk crops in high risk areas. Future studies should consider the ppossible detrimental effects of chemical seed treatments on crane biology.
- Full Text:
- Date Issued: 2011
Responses of intertidal macroalgae and associated fauna to interactive processes acting over multiple spatial scales
- Authors: Mostert, Bruce Petrus
- Date: 2011 , 2010-12-01
- Subjects: Biodiversity -- South Africa , Spatial ecology , Marine algae -- South Africa , Marine organisms -- Effect of water pollution on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5890 , http://hdl.handle.net/10962/d1013370
- Description: The decrease of biological diversity from low latitudes near the equator towards high latitudes is one of the most fundamental patterns noted in ecology. These trends have been the subject of numerous terrestrial and marine studies and have caused the proposal of several explanatory hypotheses. No single hypothesis has adequately accounted for these observed trends. Furthermore, large-scale patterns are frequently modified by processes acting at meso- to small-scales. It is imperative to understand the interaction of these processes to elucidate the mechanisms controlling the structure of intertidal assemblages. The main aim of this thesis was to test the influence of multiple processes at a range of spatial scales on biogenic engineers. Biogenic engineers, such as macroalgae, have been reported to be strongly influenced by processes such as grazing, biogeography and upwelling and subsequent effects are expected to be linked to their associated assemblages. I used infaunal assemblages associated with macroalgae as a model system to understand the interactive effects of meso-scale upwelling in conjunction with large-scale factors (regional and biogeographic). Three species of macroalgae, Hypnea spicifera, Champia lumbricalis and Bifurcaria brassicaeformis, inhabiting different but overlapping home ranges were used in this study. Smaller scale, physical attributes and the associated fauna of these algal species were compared. The effects of meso- to large-scale physical gradients on marine organisms have been investigated in many instances and resultant gradients in physical variables observed. This study was undertaken to investigate morphological trends exhibited by Hypnea spicifera and Champia lumbricalis to compare possible similarities between coastlines and to determine if inferred meso- to large-scale processes influence physical trends in a similar manner despite the coastlines being affected by different hydrodynamic processes. The macroalgae were located in two distinctly different upwelling regimes, Hypnea spicifera on the east and south coasts and Champia lumbricalis on the west coast. Upwelling (delivery of nutrients and primary production) was not found to be an important factor in determining the physical characteristics of macroalgae but there were clear patterns linked to latitude. Mean percentage cover of Hypnea spicifera was positively correlated with distance along the east and south coasts. Mean mass and mean surface area of H. spicifera were, however, negatively correlated with distance from Port St Johns. Mean frond length showed a negative trend but this relationship was not statistically significant. On the west coast, there was a significant increase in mean frond length from north to south for Champia lumbricalis. Mean surface area and mean mass of C. lumbricalis exhibited non-significant negative trends from north to south while there was a non-significant positive trend for mean percentage cover. Following the “Productivity Hypothesis”, these patterns from north to south along the coastlines of South Africa could have important implications for biodiversity associated with these algae. Many previous studies have focussed on the effects of upwelling on species (i.e. effects of nutrients and temperature) but have failed to separate this effect from large scale effects such as biogeography and latitudinal gradients. I tested the influence meso-scale upwelling, large-scale biogeographic processes and latitudinal gradients with two different species of macroalgae one on the east and south coasts of South Africa and the other on the west coast. Hypnea spicifera inhabits the east and south coasts of South Africa spanning two biogeographic provinces and is generally affected by relatively weak upwelling, whereas Champia lumbricalis inhabits the west coast spanning one biogeographic province which is subjected to intense persistent upwelling year round. Within the east and west coast biogeographic provinces there are, however, regions with both upwelling and non-upwelling. On the east and south coasts, entire assemblages differed significantly among the three Regions (St Lucia, Port Alfred and Knysna, while assemblages between upwelling/non-upwelling areas were not different. Assemblages on the different shores differed significantly from each other. There were no significant effects of region or upwelling for the number of individuals of Crustacea or Polychaeta, while Mollusca showed a significant effect of region. The number of individuals of other taxa showed a significant interaction of region and upwelling. Region had a significant effect on number of species of molluscs and other taxa, while there was no effect for either region or upwelling for the Crustacea or Polychaeta. In general different factors were shown to be important (region and shore) while upwelling was rarely important. On the west coast assemblages associated with C. lumbricalis were not influenced by region or upwelling but there were significant differences between shores. Region, upwelling ad shore did not affect number of individuals. There was a significant interaction of region and upwelling for the number of species of crustaceans, while numbers of species of Mollusca, Polychaeta and other taxa showed no effects. In general, regional factors strongly influenced most organisms, while upwelling played a minor role. Hypotheses about differences between upwelling and non-upwelling regions in terms of species abundances and composition due to the input of cold nutrient rich water were not supported. A link between the effects of larger-scale biogeographic factors and their influence on habitat forming taxa and the resultant effects on associated infauna would be a likely explanation for the patterns observed in this study. Diversity of assemblages is known to be influenced by the structural complexity of a habitat, increasing complexity increases the amount of available niches therefore potentially increasing the number of species found within that habitat. Three species of macroalgae, Hypnea spicifera, Champia lumbricalis and Bifurcaria brassicaeformis were selected on the basis of being structurally similar and having their distributional ranges overlap in order to elucidate the effects of structure and macroalgal species on associated assemblages. Hypnea spicifera is different in terms of surface area and biomass from Champia lumbricalis and Bifurcaria brassicaeformis. Assemblages of species found on the three rhodophytes showed both shore and the species of alga had significant effects on composition. Only numbers of individuals of molluscs were affected by the species of alga. Crustacea and Polychaeta showed an interaction of the species of alga with shore. In the case of this study, it is likely that the three species of macroalgae mitigate biological stressors such as predation and physical stressors such as wave exposure and desiccation. In general, meso-scale upwelling is suggested to be marginalised when considering the structuring of assemblages associated with macroalgae, while large scale biogeography has more of an influence. Within shores, assemblages were also strongly influenced by smaller-scale factors such as differences in the structure and species of alga. This study indicates the importance of investigating patterns across a range of spatial scales to gain a comprehensive understanding of factors influencing intertidal organisms.
- Full Text:
- Date Issued: 2011
- Authors: Mostert, Bruce Petrus
- Date: 2011 , 2010-12-01
- Subjects: Biodiversity -- South Africa , Spatial ecology , Marine algae -- South Africa , Marine organisms -- Effect of water pollution on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5890 , http://hdl.handle.net/10962/d1013370
- Description: The decrease of biological diversity from low latitudes near the equator towards high latitudes is one of the most fundamental patterns noted in ecology. These trends have been the subject of numerous terrestrial and marine studies and have caused the proposal of several explanatory hypotheses. No single hypothesis has adequately accounted for these observed trends. Furthermore, large-scale patterns are frequently modified by processes acting at meso- to small-scales. It is imperative to understand the interaction of these processes to elucidate the mechanisms controlling the structure of intertidal assemblages. The main aim of this thesis was to test the influence of multiple processes at a range of spatial scales on biogenic engineers. Biogenic engineers, such as macroalgae, have been reported to be strongly influenced by processes such as grazing, biogeography and upwelling and subsequent effects are expected to be linked to their associated assemblages. I used infaunal assemblages associated with macroalgae as a model system to understand the interactive effects of meso-scale upwelling in conjunction with large-scale factors (regional and biogeographic). Three species of macroalgae, Hypnea spicifera, Champia lumbricalis and Bifurcaria brassicaeformis, inhabiting different but overlapping home ranges were used in this study. Smaller scale, physical attributes and the associated fauna of these algal species were compared. The effects of meso- to large-scale physical gradients on marine organisms have been investigated in many instances and resultant gradients in physical variables observed. This study was undertaken to investigate morphological trends exhibited by Hypnea spicifera and Champia lumbricalis to compare possible similarities between coastlines and to determine if inferred meso- to large-scale processes influence physical trends in a similar manner despite the coastlines being affected by different hydrodynamic processes. The macroalgae were located in two distinctly different upwelling regimes, Hypnea spicifera on the east and south coasts and Champia lumbricalis on the west coast. Upwelling (delivery of nutrients and primary production) was not found to be an important factor in determining the physical characteristics of macroalgae but there were clear patterns linked to latitude. Mean percentage cover of Hypnea spicifera was positively correlated with distance along the east and south coasts. Mean mass and mean surface area of H. spicifera were, however, negatively correlated with distance from Port St Johns. Mean frond length showed a negative trend but this relationship was not statistically significant. On the west coast, there was a significant increase in mean frond length from north to south for Champia lumbricalis. Mean surface area and mean mass of C. lumbricalis exhibited non-significant negative trends from north to south while there was a non-significant positive trend for mean percentage cover. Following the “Productivity Hypothesis”, these patterns from north to south along the coastlines of South Africa could have important implications for biodiversity associated with these algae. Many previous studies have focussed on the effects of upwelling on species (i.e. effects of nutrients and temperature) but have failed to separate this effect from large scale effects such as biogeography and latitudinal gradients. I tested the influence meso-scale upwelling, large-scale biogeographic processes and latitudinal gradients with two different species of macroalgae one on the east and south coasts of South Africa and the other on the west coast. Hypnea spicifera inhabits the east and south coasts of South Africa spanning two biogeographic provinces and is generally affected by relatively weak upwelling, whereas Champia lumbricalis inhabits the west coast spanning one biogeographic province which is subjected to intense persistent upwelling year round. Within the east and west coast biogeographic provinces there are, however, regions with both upwelling and non-upwelling. On the east and south coasts, entire assemblages differed significantly among the three Regions (St Lucia, Port Alfred and Knysna, while assemblages between upwelling/non-upwelling areas were not different. Assemblages on the different shores differed significantly from each other. There were no significant effects of region or upwelling for the number of individuals of Crustacea or Polychaeta, while Mollusca showed a significant effect of region. The number of individuals of other taxa showed a significant interaction of region and upwelling. Region had a significant effect on number of species of molluscs and other taxa, while there was no effect for either region or upwelling for the Crustacea or Polychaeta. In general different factors were shown to be important (region and shore) while upwelling was rarely important. On the west coast assemblages associated with C. lumbricalis were not influenced by region or upwelling but there were significant differences between shores. Region, upwelling ad shore did not affect number of individuals. There was a significant interaction of region and upwelling for the number of species of crustaceans, while numbers of species of Mollusca, Polychaeta and other taxa showed no effects. In general, regional factors strongly influenced most organisms, while upwelling played a minor role. Hypotheses about differences between upwelling and non-upwelling regions in terms of species abundances and composition due to the input of cold nutrient rich water were not supported. A link between the effects of larger-scale biogeographic factors and their influence on habitat forming taxa and the resultant effects on associated infauna would be a likely explanation for the patterns observed in this study. Diversity of assemblages is known to be influenced by the structural complexity of a habitat, increasing complexity increases the amount of available niches therefore potentially increasing the number of species found within that habitat. Three species of macroalgae, Hypnea spicifera, Champia lumbricalis and Bifurcaria brassicaeformis were selected on the basis of being structurally similar and having their distributional ranges overlap in order to elucidate the effects of structure and macroalgal species on associated assemblages. Hypnea spicifera is different in terms of surface area and biomass from Champia lumbricalis and Bifurcaria brassicaeformis. Assemblages of species found on the three rhodophytes showed both shore and the species of alga had significant effects on composition. Only numbers of individuals of molluscs were affected by the species of alga. Crustacea and Polychaeta showed an interaction of the species of alga with shore. In the case of this study, it is likely that the three species of macroalgae mitigate biological stressors such as predation and physical stressors such as wave exposure and desiccation. In general, meso-scale upwelling is suggested to be marginalised when considering the structuring of assemblages associated with macroalgae, while large scale biogeography has more of an influence. Within shores, assemblages were also strongly influenced by smaller-scale factors such as differences in the structure and species of alga. This study indicates the importance of investigating patterns across a range of spatial scales to gain a comprehensive understanding of factors influencing intertidal organisms.
- Full Text:
- Date Issued: 2011
Testing the existence and direction of "spill-over" of mussel recruits beyond the boundaries of marine protected areas
- Authors: Ludford, Adam
- Date: 2011
- Subjects: Marine parks and reserves -- South Africa -- Transkei , Marine resources conservation -- South Africa -- Transkei , Mussels -- Ecology -- South Africa -- Transkei , Mexilhao mussel -- Reproduction -- South Africa -- Transkei , Mexilhao mussel -- Behavior -- South Africa -- Transkei
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5786 , http://hdl.handle.net/10962/d1005474 , Marine parks and reserves -- South Africa -- Transkei , Marine resources conservation -- South Africa -- Transkei , Mussels -- Ecology -- South Africa -- Transkei , Mexilhao mussel -- Reproduction -- South Africa -- Transkei , Mexilhao mussel -- Behavior -- South Africa -- Transkei
- Description: Landscape ecology helps in predicting the influence of habitat fragmentation on populations. Marine protected areas (MPAs) are expected to create areas of good quality patches and so improve connectivity among shores. MPAs are believed not only to protect adult populations, but also to enhance recruitment both within MPAs and on surrounding exploited shores, therefore improving their ability to recover from overexploitation. As such, MPAs are a preferred management tool for the conservation of natural populations. Although MPAs have been demonstrated to enhance adult abundances, little work has been done on their ability to provide so called "spill-over" of recruits nor has the generality of the influence of MPAs been investigated in a single region with multiple control sites. The Transkei region, on the east coast of South Africa, and the intertidal mussel, Perna perna, offer an ideal system to test the generality of the influence of MPAs on surrounding shores, due to the presence of multiple MPAs and exploited control sites. Patterns of adult abundance were surveyed at four MPAs and two comparably sized exploited control sites. Adult abundances were, in general, found to be higher within MPAs than at exploited control sites, with adult abundances decreasing towards the edge of MPAs and decreasing even more on the outside shores. To simplify the sorting procedure for samples of mussel recruits, a new method using fractionated elutriation was devised and tested. This new method was found to be more accurate, although not statistically significant but also substantially more time consuming. The increase in accuracy although not statistically significant could be biologically significant, especially when looking at low numbers. This new method could, therefore, be very useful especially when [...] is low. Recruitment was estimated over three months during the main reproductive season at two of the MPAs and at appropriate control sites. I predicted that recruitment patterns would mirror the patterns found in adult abundances and that there would be directionality in patterns of recruitment, with northern sites having greater recruitment due to the direction of near-shore ocean currents. Contrary to this, there were no correlations between adult abundance and recruitment for any of the months or sites, with no clear spatial pattern of recruitment in any of the three months. There was, however, a slight trend of greater recruitment at northern sites. To explain the lack of consistency in recruitment and adult abundances, wind data were used to examine the near-shore surface currents in this area, with theoretical surface currents showing similar patterns to those observed for recruitment. From a landscape perspective, the good patches created by MPAs supply recruits to the surrounding matrix but the low quality of habitat in the matrix prevents rehabilitation. The quality of the matrix must therefore be first improved by reseeding these shores. These results emphasise that while MPAs may function in protecting adult abundances, their influence on supplying recruits and hence recovery of near-by exploited shores may be overestimated. This lack of influence on near-by exploited shores highlights the need for reseeding of shores in conjunction with suitable management plans.
- Full Text:
- Date Issued: 2011
- Authors: Ludford, Adam
- Date: 2011
- Subjects: Marine parks and reserves -- South Africa -- Transkei , Marine resources conservation -- South Africa -- Transkei , Mussels -- Ecology -- South Africa -- Transkei , Mexilhao mussel -- Reproduction -- South Africa -- Transkei , Mexilhao mussel -- Behavior -- South Africa -- Transkei
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5786 , http://hdl.handle.net/10962/d1005474 , Marine parks and reserves -- South Africa -- Transkei , Marine resources conservation -- South Africa -- Transkei , Mussels -- Ecology -- South Africa -- Transkei , Mexilhao mussel -- Reproduction -- South Africa -- Transkei , Mexilhao mussel -- Behavior -- South Africa -- Transkei
- Description: Landscape ecology helps in predicting the influence of habitat fragmentation on populations. Marine protected areas (MPAs) are expected to create areas of good quality patches and so improve connectivity among shores. MPAs are believed not only to protect adult populations, but also to enhance recruitment both within MPAs and on surrounding exploited shores, therefore improving their ability to recover from overexploitation. As such, MPAs are a preferred management tool for the conservation of natural populations. Although MPAs have been demonstrated to enhance adult abundances, little work has been done on their ability to provide so called "spill-over" of recruits nor has the generality of the influence of MPAs been investigated in a single region with multiple control sites. The Transkei region, on the east coast of South Africa, and the intertidal mussel, Perna perna, offer an ideal system to test the generality of the influence of MPAs on surrounding shores, due to the presence of multiple MPAs and exploited control sites. Patterns of adult abundance were surveyed at four MPAs and two comparably sized exploited control sites. Adult abundances were, in general, found to be higher within MPAs than at exploited control sites, with adult abundances decreasing towards the edge of MPAs and decreasing even more on the outside shores. To simplify the sorting procedure for samples of mussel recruits, a new method using fractionated elutriation was devised and tested. This new method was found to be more accurate, although not statistically significant but also substantially more time consuming. The increase in accuracy although not statistically significant could be biologically significant, especially when looking at low numbers. This new method could, therefore, be very useful especially when [...] is low. Recruitment was estimated over three months during the main reproductive season at two of the MPAs and at appropriate control sites. I predicted that recruitment patterns would mirror the patterns found in adult abundances and that there would be directionality in patterns of recruitment, with northern sites having greater recruitment due to the direction of near-shore ocean currents. Contrary to this, there were no correlations between adult abundance and recruitment for any of the months or sites, with no clear spatial pattern of recruitment in any of the three months. There was, however, a slight trend of greater recruitment at northern sites. To explain the lack of consistency in recruitment and adult abundances, wind data were used to examine the near-shore surface currents in this area, with theoretical surface currents showing similar patterns to those observed for recruitment. From a landscape perspective, the good patches created by MPAs supply recruits to the surrounding matrix but the low quality of habitat in the matrix prevents rehabilitation. The quality of the matrix must therefore be first improved by reseeding these shores. These results emphasise that while MPAs may function in protecting adult abundances, their influence on supplying recruits and hence recovery of near-by exploited shores may be overestimated. This lack of influence on near-by exploited shores highlights the need for reseeding of shores in conjunction with suitable management plans.
- Full Text:
- Date Issued: 2011
The demography and population dynamics of a re-introduced black rhinoceros population on the Great Fish River Reserve, Eastern Cape Province
- Authors: Fike, Bradley Robin
- Date: 2011
- Subjects: Black rhinoceros -- South Africa -- Great Fish River Valley , Population biology -- South Africa -- Great Fish River Valley , Black rhinoceros -- Habitat -- South Africa -- Great Fish River Valley , Black rhinoceros -- Adaptation -- South Africa -- Great Fish River Valley , Black rhinoceros -- Ecology -- South Africa -- Great Fish River Valley
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5948 , http://hdl.handle.net/10962/d1020869
- Description: The re-introduction of black rhinoceros onto the Great Fish River Reserve in the Eastern Cape, following the species absence for over a century, created an opportunity to study this species in the thicket biome, and in particular the succulent thicket of the Great Fish River valley. The thicket biome is quite different from the habitats in which other extant populations of these animals are found and where studies of their demography have been undertaken. Data collection occurred from May 1986, with the arrival of the first four animals to December 2008, when the population was estimated to be 144 individuals. A variety of monitoring techniques were used including direct ground observations, aerial helicopter census, aerial monitoring by microlight aircraft, camera traps and opportunistic observations, each with its own advantages and disadvantages. The combination of methods and effort has resulted in the population being recognized as completely known with up to 97% of the animals being located at least once per year with a mean frequency of sightings of 11.5 per animal per year. In 2008, the population was about 20% juvenile, 36% sub-adult and 44% adult with a female biased sex ratio of 1.3 females per male. Mean age at first birth was about 80 months and this increased significantly with increasing density of black rhinoceroses. Mean intercalf interval was about 28 months and 41% of adult females gave birth each year. Mortality rates were low for juveniles, higher for sub-adults and higher for males than females. There was a weak but significant positive effect of density on male mortality. Population growth rate was about 10% and was not significantly affected by density. These results suggest that this population is beginning to show the first indications of density dependant constraints and that harvesting should be implemented in order to maintain the productive tempo. A secondary goal of the Management Plan will then be realized as the population functions as a donor to establish founder populations elsewhere within the Diceros bicornis minor range.
- Full Text:
- Date Issued: 2011
- Authors: Fike, Bradley Robin
- Date: 2011
- Subjects: Black rhinoceros -- South Africa -- Great Fish River Valley , Population biology -- South Africa -- Great Fish River Valley , Black rhinoceros -- Habitat -- South Africa -- Great Fish River Valley , Black rhinoceros -- Adaptation -- South Africa -- Great Fish River Valley , Black rhinoceros -- Ecology -- South Africa -- Great Fish River Valley
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5948 , http://hdl.handle.net/10962/d1020869
- Description: The re-introduction of black rhinoceros onto the Great Fish River Reserve in the Eastern Cape, following the species absence for over a century, created an opportunity to study this species in the thicket biome, and in particular the succulent thicket of the Great Fish River valley. The thicket biome is quite different from the habitats in which other extant populations of these animals are found and where studies of their demography have been undertaken. Data collection occurred from May 1986, with the arrival of the first four animals to December 2008, when the population was estimated to be 144 individuals. A variety of monitoring techniques were used including direct ground observations, aerial helicopter census, aerial monitoring by microlight aircraft, camera traps and opportunistic observations, each with its own advantages and disadvantages. The combination of methods and effort has resulted in the population being recognized as completely known with up to 97% of the animals being located at least once per year with a mean frequency of sightings of 11.5 per animal per year. In 2008, the population was about 20% juvenile, 36% sub-adult and 44% adult with a female biased sex ratio of 1.3 females per male. Mean age at first birth was about 80 months and this increased significantly with increasing density of black rhinoceroses. Mean intercalf interval was about 28 months and 41% of adult females gave birth each year. Mortality rates were low for juveniles, higher for sub-adults and higher for males than females. There was a weak but significant positive effect of density on male mortality. Population growth rate was about 10% and was not significantly affected by density. These results suggest that this population is beginning to show the first indications of density dependant constraints and that harvesting should be implemented in order to maintain the productive tempo. A secondary goal of the Management Plan will then be realized as the population functions as a donor to establish founder populations elsewhere within the Diceros bicornis minor range.
- Full Text:
- Date Issued: 2011
The diversity of aquatic insects in the Tsitsikamma region, with implications for aquatic ecosystem conservation
- Authors: Bellingan, Terence Andrew
- Date: 2011
- Subjects: Aquatic insects -- South Africa -- Tsitsikamma , Aquatic insects -- Classification -- South Africa -- Tsitsikamma , Aquatic ecology -- South Africa -- Tsitsikamma , Ecosystem management -- South Africa -- Tsitsikamma , Stream conservation -- South Africa -- Tsitsikamma
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5664 , http://hdl.handle.net/10962/d1005348 , Aquatic insects -- South Africa -- Tsitsikamma , Aquatic insects -- Classification -- South Africa -- Tsitsikamma , Aquatic ecology -- South Africa -- Tsitsikamma , Ecosystem management -- South Africa -- Tsitsikamma , Stream conservation -- South Africa -- Tsitsikamma
- Description: As a result of research carried out within the last decade to assess the diversity of macroinvertebrates of the Salt River in the Western Cape Province, South Africa, surveys of macroinvertebrates of 20 sites on 11 selected rivers from the same mountain range source were undertaken. This was done to make a preliminary assessment of the conservation status of the rivers of this region. Aquatic insects from the orders Ephemeroptera, Odonata, Plecoptera, Megaloptera, Trichoptera and the dipteran family Simuliidae were collected using techniques to maximize the number of taxa found. The insects collected were identified to species level where possible. Water physicochemical parameters were recorded at all sites for each sampling trip to characterize these rivers and to establish a set of baseline data for future comparisons. These parameters included measurements made on site and analysis of the concentrations of all the major ions in water samples in the laboratory. Multivariate analyses including Principle Components Analysis and Canonical Correspondence Analysis were used to reveal patterns within the water physicochemistry and species distributional data. Results include the identification of 123 species from 70 genera and 30 families. A total of 31 species were found to be undescribed, of which 17 were not previously collected and are thus completely new to science. In addition, four of these species could not be placed into any known genus. The analysis of water physicochemistry showed a clear distinction between rivers of Table Mountain sandstone and Bokkeveld shale origin. Downstream effects of anthropogenic influences were discernable too. Distinct macroinvertebrate assemblages were found based upon stream order and water chemistry composition. pH proved to be the most important driver of invertebrate assemblage composition. The high levels of endemism of the macroinvertebrates found within the upper reaches of these rivers and their degree of ecological specialization make these systems a priority for the conservation of aquatic biodiversity on a national and global scale.
- Full Text:
- Date Issued: 2011
- Authors: Bellingan, Terence Andrew
- Date: 2011
- Subjects: Aquatic insects -- South Africa -- Tsitsikamma , Aquatic insects -- Classification -- South Africa -- Tsitsikamma , Aquatic ecology -- South Africa -- Tsitsikamma , Ecosystem management -- South Africa -- Tsitsikamma , Stream conservation -- South Africa -- Tsitsikamma
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5664 , http://hdl.handle.net/10962/d1005348 , Aquatic insects -- South Africa -- Tsitsikamma , Aquatic insects -- Classification -- South Africa -- Tsitsikamma , Aquatic ecology -- South Africa -- Tsitsikamma , Ecosystem management -- South Africa -- Tsitsikamma , Stream conservation -- South Africa -- Tsitsikamma
- Description: As a result of research carried out within the last decade to assess the diversity of macroinvertebrates of the Salt River in the Western Cape Province, South Africa, surveys of macroinvertebrates of 20 sites on 11 selected rivers from the same mountain range source were undertaken. This was done to make a preliminary assessment of the conservation status of the rivers of this region. Aquatic insects from the orders Ephemeroptera, Odonata, Plecoptera, Megaloptera, Trichoptera and the dipteran family Simuliidae were collected using techniques to maximize the number of taxa found. The insects collected were identified to species level where possible. Water physicochemical parameters were recorded at all sites for each sampling trip to characterize these rivers and to establish a set of baseline data for future comparisons. These parameters included measurements made on site and analysis of the concentrations of all the major ions in water samples in the laboratory. Multivariate analyses including Principle Components Analysis and Canonical Correspondence Analysis were used to reveal patterns within the water physicochemistry and species distributional data. Results include the identification of 123 species from 70 genera and 30 families. A total of 31 species were found to be undescribed, of which 17 were not previously collected and are thus completely new to science. In addition, four of these species could not be placed into any known genus. The analysis of water physicochemistry showed a clear distinction between rivers of Table Mountain sandstone and Bokkeveld shale origin. Downstream effects of anthropogenic influences were discernable too. Distinct macroinvertebrate assemblages were found based upon stream order and water chemistry composition. pH proved to be the most important driver of invertebrate assemblage composition. The high levels of endemism of the macroinvertebrates found within the upper reaches of these rivers and their degree of ecological specialization make these systems a priority for the conservation of aquatic biodiversity on a national and global scale.
- Full Text:
- Date Issued: 2011
The effect of mussel bed structure on the associated infauna in South Africa and the interaction between mussel and epibiotic barnacles
- Jordaan, Tembisa Nomathamsanqa
- Authors: Jordaan, Tembisa Nomathamsanqa
- Date: 2011
- Subjects: Mytilidae -- South Africa , Mytilus galloprovincialis -- South Africa , Mussel culture -- South Africa , Shellfish culture -- South Africa , Perna -- South Africa , Barnacles -- South Africa , Mussels -- South Africa , Mussels -- Ecology , Barnacles -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5675 , http://hdl.handle.net/10962/d1005360 , Mytilidae -- South Africa , Mytilus galloprovincialis -- South Africa , Mussel culture -- South Africa , Shellfish culture -- South Africa , Perna -- South Africa , Barnacles -- South Africa , Mussels -- South Africa , Mussels -- Ecology , Barnacles -- Ecology
- Description: Mussels are important ecological engineers on intertidal rocks where they create habitat that contributes substantially to overall biodiversity. They provide secondary substratum for other free-living, infaunal or epifaunal organisms, and increase the surface area for settlement by densely packing together into complex multilayered beds. The introduction of the alien invasive mussel Mytilus galloprovincialis has extended the upper limit of mussels on the south coast of South Africa, potentially increasing habitat for associated fauna. The aim of this study was to describe the structure of mussel beds, the general biodiversity associated with multi- and monolayered mussel beds of indigenous Perna perna and alien M. galloprovincialis, and to determine the relationship between mussels and epibiotic barnacles. This was done to determine the community structure of associated macrofauna and the role of mussels as biological facilitators. Samples were collected in Plettenberg Bay, South Africa, where M. galloprovincialis dominates the high mussel zone and P. perna the low zone. Three 15 X 15 cm quadrats were scraped off the rock in the high and low zones, and in the mid zone where the two mussel species co-exist. The samples were collected on 3 occasions. In the laboratory mussel-size was measured and sediment trapped within the samples was separated through 75 μm, 1 mm and 5 mm mesh. The macrofauna was sorted from the 1 mm and 5 mm sieves and identified to species level where possible. The epibiotic relationship between mussels and barnacles was assessed by measuring the prevalence and intensity of barnacle infestation and the condition index of infested mussels. Multivariate analysis was used on the mean abundance data of the species for each treatment (Hierarchical clustering, multidimensional scaling, analysis of similarity and similarity of percentages) and ANOVA was used for most of the statistical analyses. Overall, the results showed that tidal height influences the species composition and abundance of associated fauna. While mussel bed layering influenced the accumulation of sediments; it had no significant effect on the associated fauna. Time of collection also had a strong effect. While there was an overlap of species among samples from January, May and March, the principal species contributing to similarity among the March samples were not found in the other two months. The outcomes of this study showed that low shore mussel beds not only supported a higher abundance and diversity of species, but were also the most structurally complex. Although the condition index of mussels did not correlate to the percentage cover of barnacle epibionts, it was also evident that low shore mussels had the highest prevalence. The levels of barnacle infestation (intensity) for each mussel species were highest where it was common and lowest where it was least abundant. This is viewed as a natural artefact of the distribution patterns of P. perna and M. galloprovincialis across the shore. Mussels are more efficient as facilitators on the low mussel zone than the high mussel zone possibly because they provide habitats that are more effective in protecting the associated macrofauna from the effects of competition and predation, than they are at eliminating the effects of physical stress on the high shore. Although mussels create less stressful habitats and protect organisms from the physical stress of the high shore, there are clear limitations in their ability to provide ideal habitats. The biological associations in an ecosystem can be made weak or strong depending on the external abiotic factors and the adaptability of the affected organisms.
- Full Text:
- Date Issued: 2011
- Authors: Jordaan, Tembisa Nomathamsanqa
- Date: 2011
- Subjects: Mytilidae -- South Africa , Mytilus galloprovincialis -- South Africa , Mussel culture -- South Africa , Shellfish culture -- South Africa , Perna -- South Africa , Barnacles -- South Africa , Mussels -- South Africa , Mussels -- Ecology , Barnacles -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5675 , http://hdl.handle.net/10962/d1005360 , Mytilidae -- South Africa , Mytilus galloprovincialis -- South Africa , Mussel culture -- South Africa , Shellfish culture -- South Africa , Perna -- South Africa , Barnacles -- South Africa , Mussels -- South Africa , Mussels -- Ecology , Barnacles -- Ecology
- Description: Mussels are important ecological engineers on intertidal rocks where they create habitat that contributes substantially to overall biodiversity. They provide secondary substratum for other free-living, infaunal or epifaunal organisms, and increase the surface area for settlement by densely packing together into complex multilayered beds. The introduction of the alien invasive mussel Mytilus galloprovincialis has extended the upper limit of mussels on the south coast of South Africa, potentially increasing habitat for associated fauna. The aim of this study was to describe the structure of mussel beds, the general biodiversity associated with multi- and monolayered mussel beds of indigenous Perna perna and alien M. galloprovincialis, and to determine the relationship between mussels and epibiotic barnacles. This was done to determine the community structure of associated macrofauna and the role of mussels as biological facilitators. Samples were collected in Plettenberg Bay, South Africa, where M. galloprovincialis dominates the high mussel zone and P. perna the low zone. Three 15 X 15 cm quadrats were scraped off the rock in the high and low zones, and in the mid zone where the two mussel species co-exist. The samples were collected on 3 occasions. In the laboratory mussel-size was measured and sediment trapped within the samples was separated through 75 μm, 1 mm and 5 mm mesh. The macrofauna was sorted from the 1 mm and 5 mm sieves and identified to species level where possible. The epibiotic relationship between mussels and barnacles was assessed by measuring the prevalence and intensity of barnacle infestation and the condition index of infested mussels. Multivariate analysis was used on the mean abundance data of the species for each treatment (Hierarchical clustering, multidimensional scaling, analysis of similarity and similarity of percentages) and ANOVA was used for most of the statistical analyses. Overall, the results showed that tidal height influences the species composition and abundance of associated fauna. While mussel bed layering influenced the accumulation of sediments; it had no significant effect on the associated fauna. Time of collection also had a strong effect. While there was an overlap of species among samples from January, May and March, the principal species contributing to similarity among the March samples were not found in the other two months. The outcomes of this study showed that low shore mussel beds not only supported a higher abundance and diversity of species, but were also the most structurally complex. Although the condition index of mussels did not correlate to the percentage cover of barnacle epibionts, it was also evident that low shore mussels had the highest prevalence. The levels of barnacle infestation (intensity) for each mussel species were highest where it was common and lowest where it was least abundant. This is viewed as a natural artefact of the distribution patterns of P. perna and M. galloprovincialis across the shore. Mussels are more efficient as facilitators on the low mussel zone than the high mussel zone possibly because they provide habitats that are more effective in protecting the associated macrofauna from the effects of competition and predation, than they are at eliminating the effects of physical stress on the high shore. Although mussels create less stressful habitats and protect organisms from the physical stress of the high shore, there are clear limitations in their ability to provide ideal habitats. The biological associations in an ecosystem can be made weak or strong depending on the external abiotic factors and the adaptability of the affected organisms.
- Full Text:
- Date Issued: 2011
Brood cycles in queenless colonies of Apis mellifera capensis
- Authors: Crous, Kendall Lauren
- Date: 2010
- Subjects: Cape honeybee , Bee culture -- Queen rearing , Bees -- Breeding
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5652 , http://hdl.handle.net/10962/d1005335 , Cape honeybee , Bee culture -- Queen rearing , Bees -- Breeding
- Description: In a honeybee colony, the loss of a queen is considered to be a serious occurrence and, if a new queen is not produced, ultimately doomed. However, in colonies of Apis mellifera capensis (Cape honeybees), numerous pathways are available for a colony which unexpectedly losses a queen. At the onset of this experiment, four colonies of A. m. capensis were dequeened. Following this photographs of all brood frames in each colony were taken and the contents of the cells analysed. Cells were chosen at random but once selected were repeatedly analysed for the duration of the experiment. The contents of a total of 44 888 individual cells were analysed. Any queen cells constructed during the sampling period were removed, maintaining a queenless state. In each colony, as predicted, the removal of the queen evoked a variety of responses in an attempt to rectify the sudden loss. However, ultimately three of the four colonies absconded, leaving little by way of stores. Three of the four colonies initially attempted to rear a new queen while one colony was immediately invaded by a presumed foreign queen and hence any attempt at queen cell construction ceased. An increased number of queen cells in the swarm position were recorded in all colonies. The invasion of a colony by a foreign queen was considered to be a new pathway available for queenless colonies of A.m capensis. Worker policing and suspected brood cannibalism was prevalent in all sampled colonies yet in addition, the transfer of eggs and larvae from cell to cell was also observed which may have increased the suspected cases of policing and cannibalism. It was unclear whether an egg or larva had been consumed or simply moved to another cell on the brood frame. All colonies contained eggs from laying workers to varying degrees, based on the length of each individual sampling period which varied between colonies due to differences in absconding dates. A steady breakdown in the effectiveness of the division of labour amongst the worker bees was observed in each of the colonies highlighting the vital role of a queen. This breakdown was clearly seen in the reduction in general housekeeping within a colony. An increase in stores indicated a possible increase in the number of forager bees, thereby reducing the number of worker bees available for other duties. Pathways available to broodright colonies and strategies used following sudden queen loss are discussed.
- Full Text:
- Date Issued: 2010
- Authors: Crous, Kendall Lauren
- Date: 2010
- Subjects: Cape honeybee , Bee culture -- Queen rearing , Bees -- Breeding
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5652 , http://hdl.handle.net/10962/d1005335 , Cape honeybee , Bee culture -- Queen rearing , Bees -- Breeding
- Description: In a honeybee colony, the loss of a queen is considered to be a serious occurrence and, if a new queen is not produced, ultimately doomed. However, in colonies of Apis mellifera capensis (Cape honeybees), numerous pathways are available for a colony which unexpectedly losses a queen. At the onset of this experiment, four colonies of A. m. capensis were dequeened. Following this photographs of all brood frames in each colony were taken and the contents of the cells analysed. Cells were chosen at random but once selected were repeatedly analysed for the duration of the experiment. The contents of a total of 44 888 individual cells were analysed. Any queen cells constructed during the sampling period were removed, maintaining a queenless state. In each colony, as predicted, the removal of the queen evoked a variety of responses in an attempt to rectify the sudden loss. However, ultimately three of the four colonies absconded, leaving little by way of stores. Three of the four colonies initially attempted to rear a new queen while one colony was immediately invaded by a presumed foreign queen and hence any attempt at queen cell construction ceased. An increased number of queen cells in the swarm position were recorded in all colonies. The invasion of a colony by a foreign queen was considered to be a new pathway available for queenless colonies of A.m capensis. Worker policing and suspected brood cannibalism was prevalent in all sampled colonies yet in addition, the transfer of eggs and larvae from cell to cell was also observed which may have increased the suspected cases of policing and cannibalism. It was unclear whether an egg or larva had been consumed or simply moved to another cell on the brood frame. All colonies contained eggs from laying workers to varying degrees, based on the length of each individual sampling period which varied between colonies due to differences in absconding dates. A steady breakdown in the effectiveness of the division of labour amongst the worker bees was observed in each of the colonies highlighting the vital role of a queen. This breakdown was clearly seen in the reduction in general housekeeping within a colony. An increase in stores indicated a possible increase in the number of forager bees, thereby reducing the number of worker bees available for other duties. Pathways available to broodright colonies and strategies used following sudden queen loss are discussed.
- Full Text:
- Date Issued: 2010
Effects of ant predation on the efficacy of biological control agents Hypena Laceratalis Walker (Lepidoptera : noctuirdae) ; Falconia intermedia Distant (Hemiptera : Miridae and Teleonemia scrupulosa Stål (Hemiptera: Tingidae) on Lantana Camara (Verbenaceae) in South Africa
- Authors: Tourle, Robyn
- Date: 2010
- Subjects: Lantana camara -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Hemiptera -- South Africa , Miridae -- South Africa , Insect pests -- Biological control -- South Africa , Ants -- Behavior , Lepidoptera , Lace bugs , Noctuidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5677 , http://hdl.handle.net/10962/d1005362 , Lantana camara -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Hemiptera -- South Africa , Miridae -- South Africa , Insect pests -- Biological control -- South Africa , Ants -- Behavior , Lepidoptera , Lace bugs , Noctuidae
- Description: Lantana camara L. (Verbenaceae) remains a highly invasive and ecologically damaging weed in South Africa, despite some 50 years of biological control efforts. Lack of success has been ascribed to varietal differences, climate and predation of agents but these have not been tested. In this study, the effects of ant predation were tested on populations of three biological control agents for L. camara. Colonies of two species, Crematogaster sp. 1 and 2 were investigated. Crematogaster sp. 1 colonies were offered no choice between immature stages of the agents Hypena laceratalis Walker (Lepidoptera: Noctuidae), Falconia intermedia Distant (Hemiptera: Miridae) or Teleonemia scrupulosa Stål (Hemiptera: Tingidae) on lantana shoots. Density-dependent predation on F. intermedia and T. scrupulosa nymphs on lantana shoots was tested using Crematogaster sp. 2 colonies. In choice experiments Crematogaster sp. 2 colonies were offered F. intermedia or T. scrupulosa nymphs on potted lantana plants. Preliminary food trials confirmed that colonies foraged for protein, thereby validating results of no-choice experiments. Crematogaster sp.1 foragers removed 50% of F. intermedia nymphs, followed by 45% of H. laceratalis larvae and only 9% of T. scrupulosa nymphs. Foragers recruited most actively to H. laceratalis larvae and significantly more H. laceratalis biomass was removed than either F. intermedia or T. scrupulosa. A trade-off existed in prey size selection because larger larvae provided considerably more biomass but required forager cooperation and a longer time to subdue than did smaller prey. This increases both forager energy expense and mortality risk by other predators. This study showed that all Crematogaster sp. 1 colonies removed small (≤10mm) H. laceratalis larvae more frequently than larvae larger than 10mm. Thus, of these biological control agents, predators probably prefer small H. laceratalis larvae. Significantly more F. intermedia than T. scrupulosa nymphs were removed by Crematogaster sp. 1, while Crematogaster sp. 2 colonies removed comparable numbers of both agent species. Falconia intermedia nymphs' fast movement triggered a predatory response by these ant species. In contrast, the relatively immobile behaviour of T. scrupulosa nymphs was identified as a highly effective predator avoidance strategy. Since T. scrupulosa nymphs are unable to escape predators by moving, they appear to depend on the presence of alternative prey attracting predator attention. At high agent and/or forager density, T. scrupulosa nymphs attempted escape, but foragers identified them as prey once they moved and caught them. Predation on F. intermedia was also density dependent in that at high nymph and/or forager densities, escape routes were congested and nymphs were more easily caught. Survival of F. intermedia and T. scrupulosa nymphs in particular was low on ant-accessed shrubs in choice experiments and high on ant-excluded shrubs. It is likely that ants significantly depress F. intermedia populations in the field since besides predation, ant foragers probably interrupt F. intermedia feeding and ovipositioning. The combination of parasitism and predation on early instar larvae may explain why H. laceratalis occurs across lantana's range in South Africa but populations remain low. It is unlikely that T. scrupulosa nymphs are habitually preyed on by ant species unless they attract attention by being mobile. Although biological control of L. camara is influenced by climate and physiological defence mechanisms, this study has shown that predation by two ant species severely impacts leaf-feeding agents for L. camara. Thus, it is recommended that future selection of additional agents to control lantana should exclude leaf-feeding .
- Full Text:
- Date Issued: 2010
- Authors: Tourle, Robyn
- Date: 2010
- Subjects: Lantana camara -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Hemiptera -- South Africa , Miridae -- South Africa , Insect pests -- Biological control -- South Africa , Ants -- Behavior , Lepidoptera , Lace bugs , Noctuidae
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5677 , http://hdl.handle.net/10962/d1005362 , Lantana camara -- Biological control -- South Africa , Weeds -- Biological control -- South Africa , Biological pest control agents -- South Africa , Hemiptera -- South Africa , Miridae -- South Africa , Insect pests -- Biological control -- South Africa , Ants -- Behavior , Lepidoptera , Lace bugs , Noctuidae
- Description: Lantana camara L. (Verbenaceae) remains a highly invasive and ecologically damaging weed in South Africa, despite some 50 years of biological control efforts. Lack of success has been ascribed to varietal differences, climate and predation of agents but these have not been tested. In this study, the effects of ant predation were tested on populations of three biological control agents for L. camara. Colonies of two species, Crematogaster sp. 1 and 2 were investigated. Crematogaster sp. 1 colonies were offered no choice between immature stages of the agents Hypena laceratalis Walker (Lepidoptera: Noctuidae), Falconia intermedia Distant (Hemiptera: Miridae) or Teleonemia scrupulosa Stål (Hemiptera: Tingidae) on lantana shoots. Density-dependent predation on F. intermedia and T. scrupulosa nymphs on lantana shoots was tested using Crematogaster sp. 2 colonies. In choice experiments Crematogaster sp. 2 colonies were offered F. intermedia or T. scrupulosa nymphs on potted lantana plants. Preliminary food trials confirmed that colonies foraged for protein, thereby validating results of no-choice experiments. Crematogaster sp.1 foragers removed 50% of F. intermedia nymphs, followed by 45% of H. laceratalis larvae and only 9% of T. scrupulosa nymphs. Foragers recruited most actively to H. laceratalis larvae and significantly more H. laceratalis biomass was removed than either F. intermedia or T. scrupulosa. A trade-off existed in prey size selection because larger larvae provided considerably more biomass but required forager cooperation and a longer time to subdue than did smaller prey. This increases both forager energy expense and mortality risk by other predators. This study showed that all Crematogaster sp. 1 colonies removed small (≤10mm) H. laceratalis larvae more frequently than larvae larger than 10mm. Thus, of these biological control agents, predators probably prefer small H. laceratalis larvae. Significantly more F. intermedia than T. scrupulosa nymphs were removed by Crematogaster sp. 1, while Crematogaster sp. 2 colonies removed comparable numbers of both agent species. Falconia intermedia nymphs' fast movement triggered a predatory response by these ant species. In contrast, the relatively immobile behaviour of T. scrupulosa nymphs was identified as a highly effective predator avoidance strategy. Since T. scrupulosa nymphs are unable to escape predators by moving, they appear to depend on the presence of alternative prey attracting predator attention. At high agent and/or forager density, T. scrupulosa nymphs attempted escape, but foragers identified them as prey once they moved and caught them. Predation on F. intermedia was also density dependent in that at high nymph and/or forager densities, escape routes were congested and nymphs were more easily caught. Survival of F. intermedia and T. scrupulosa nymphs in particular was low on ant-accessed shrubs in choice experiments and high on ant-excluded shrubs. It is likely that ants significantly depress F. intermedia populations in the field since besides predation, ant foragers probably interrupt F. intermedia feeding and ovipositioning. The combination of parasitism and predation on early instar larvae may explain why H. laceratalis occurs across lantana's range in South Africa but populations remain low. It is unlikely that T. scrupulosa nymphs are habitually preyed on by ant species unless they attract attention by being mobile. Although biological control of L. camara is influenced by climate and physiological defence mechanisms, this study has shown that predation by two ant species severely impacts leaf-feeding agents for L. camara. Thus, it is recommended that future selection of additional agents to control lantana should exclude leaf-feeding .
- Full Text:
- Date Issued: 2010
Investigation of entomopathogenic fungi for control of false codling moth, Thaumatotibia leucotrata, Mediterranean fruit fly, Ceratitis capitata and Natal fruit fly, C. rosa in South African citrus
- Authors: Goble, Tarryn Anne
- Date: 2010
- Subjects: Insect pests -- Biological control , Tortricidae -- Biological control -- South Africa , Tephritidae -- Biological control -- South Africa , Citrus -- Diseases and pests -- Biological control -- South Africa , Entomopathogenic fungi , Fungi as biological pest control agents , Biological pest control agents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5723 , http://hdl.handle.net/10962/d1005409 , Insect pests -- Biological control , Tortricidae -- Biological control -- South Africa , Tephritidae -- Biological control -- South Africa , Citrus -- Diseases and pests -- Biological control -- South Africa , Entomopathogenic fungi , Fungi as biological pest control agents , Biological pest control agents
- Description: The biology of key citrus pests Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae), Ceratitis capitata Wiedemann (Diptera: Tephritidae) and Ceratitis rosa Karsch (Diptera: Tephritidae) includes their dropping from host plants to pupate in the soil below citrus trees. Since most EP fungi are soil-borne microorganisms, the development and formulation of alternative control strategies using these fungi as subterranean control agents, targeted at larvae and pupae in the soil, can potentially benefit existing IPM management of citrus in South Africa. Thus, a survey of occurrence of entomopathogenic fungi was undertaken on soils from citrus orchards and natural vegetation (refugia) on conventionally and organically managed farms in the Eastern Cape Province in South Africa. A method for baiting soil samples with citrus pest T. leucotreta and C. capitata larvae, as well as with the standard bait insect, Galleria mellonella Linnaeus (Lepidoptera: Pyralidae), was implemented. Sixty-two potentially useful entomopathogenic fungal isolates belonging to four genera were collected from 288 soil samples, an occurrence frequency of 21.53%. The most frequently isolated entomopathogenic fungal species was Beauveria bassiana (Balsamo) Vuillemin (15.63%), followed by Metarhizium anisopliae var. anisopliae (Metschnikoff) Sorokin (3.82%). Galleria mellonella was the most effective insect used to isolate fungal species (χ2=40.13, df=2, P≤ 0.005), with a total of 45 isolates obtained, followed by C. capitata with 11 isolates, and T. leucotreta with six isolates recovered. There was a significantly (χ2=11.65, df=1, P≤ 0.005) higher occurrence of entomopathogenic fungi in soil samples taken from refugia compared to cultivated orchards of both organically and conventionally managed farms. No significant differences were observed in the recovery of fungal isolates when soil samples from both farming systems were compared. The physiological effects and host range of 21 indigenous fungal isolates obtained in the Eastern Cape were investigated in the laboratory to establish whether these isolates could be effectively used as biological control agents against the subterranean life stages of C. rosa, C. capitata and T. leucotreta. When these pests were treated with a fungal concentration of 1 x 10⁷ conidia ml⁻¹, the percentage of T. leucotreta adults which emerged in fungal treated sand ranged from 5 to 60% (F=33.295; df=21; P=0.0001) depending on fungal isolate and the percentage of pupae with visible signs of mycosis ranged from 21 to 93% (F= 96.436; df=21; P=0.0001). Based on fungal isolates, the percentage adult survival in C. rosa and C. capitata ranged from 30 to 90% and 55 to 86% respectively. The percentage of C. rosa and C. capitata puparia with visible signs of mycosis ranged from 1 to 14% and 1 to 11% respectively. Deferred mortality due to mycosis in C. rosa and C. capitata adult flies ranged from 1 to 58% and 1 to 33% respectively, depending on fungal isolate. Entomopathogenic fungal isolates had a significantly greater effect on the adults of C. rosa and C. capitata than they did on the puparia of these two fruit fly species. Further, C. rosa and C. capitata did not differ significantly in their response to entomopathogenic fungi when adult survival or adult and pupal mycosis were considered. The relative potency of the four most virulent Beauveria isolates as well as the commercially available Beauveria bassiana product, Bb Plus® (Biological Control Products, South Africa), were compared against one another as log-probit regressions of mortality against C. rosa, C. capitata and T. leucotreta which all exhibited a dose-dependent response. Against fruit flies the estimated LC50 values of all five Beauveria isolates ranged from 5.5 x 10¹¹ to 2.8 x 10¹² conidia/ml⁻¹. There were no significant differences between the relative potencies of these five fungal isolates. When T. leucotreta was considered, isolates: G Moss R10 and G 14 2 B5 and Bb Plus® were significantly more pathogenic than G B Ar 23 B3 and FCM 10 13 L1. The estimated LC₅₀ values of the three most pathogenic isolates ranged from 6.8 x 10⁵ to 2.1 x 10⁶ conidia/ml⁻¹, while those of the least pathogenic ranged from 1.6 x 10⁷ to 3.7 x 10⁷ conidia/ml⁻¹. Thaumatotibia leucotreta final instar larvae were exposed to two conidial concentrations, at four different exposure times (12, 48, 72 and 96 hrs) and showed an exposure time-dependant relationship (F=5.43; df=3; P=0.001). At 1 x 10⁷conidia/ml⁻¹ two Beauveria isolates: G Moss R10 and G 14 2 B5 were able to elicit a response in 50% of test insects at 72 hrs (3 days) exposure. Although a limited amount of mycosis was observed in the puparia of both fruit fly species, deferred adult mortality due to mycosis was high. The increased incidence of adult mortality suggests that post emergence mycosis in adult fruit flies may play a more significant role in field suppression than the control of fruit flies at the pupal stage. The increased incidence of pupal mortality, as well as the relatively low concentrations of conidia required to elicit meaningful responses in T. leucotreta pupae may suggest that pre-emergent control of false codling moth will play a more significant role in field suppression than the control of adult life stages using indigenous isolates of entomopathogenic fungi. Various entomopathogenic fungal application techniques targeted at key insect pests within integrated pest management (IPM) systems of citrus are discussed.
- Full Text:
- Date Issued: 2010
- Authors: Goble, Tarryn Anne
- Date: 2010
- Subjects: Insect pests -- Biological control , Tortricidae -- Biological control -- South Africa , Tephritidae -- Biological control -- South Africa , Citrus -- Diseases and pests -- Biological control -- South Africa , Entomopathogenic fungi , Fungi as biological pest control agents , Biological pest control agents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5723 , http://hdl.handle.net/10962/d1005409 , Insect pests -- Biological control , Tortricidae -- Biological control -- South Africa , Tephritidae -- Biological control -- South Africa , Citrus -- Diseases and pests -- Biological control -- South Africa , Entomopathogenic fungi , Fungi as biological pest control agents , Biological pest control agents
- Description: The biology of key citrus pests Thaumatotibia leucotreta Meyrick (Lepidoptera: Tortricidae), Ceratitis capitata Wiedemann (Diptera: Tephritidae) and Ceratitis rosa Karsch (Diptera: Tephritidae) includes their dropping from host plants to pupate in the soil below citrus trees. Since most EP fungi are soil-borne microorganisms, the development and formulation of alternative control strategies using these fungi as subterranean control agents, targeted at larvae and pupae in the soil, can potentially benefit existing IPM management of citrus in South Africa. Thus, a survey of occurrence of entomopathogenic fungi was undertaken on soils from citrus orchards and natural vegetation (refugia) on conventionally and organically managed farms in the Eastern Cape Province in South Africa. A method for baiting soil samples with citrus pest T. leucotreta and C. capitata larvae, as well as with the standard bait insect, Galleria mellonella Linnaeus (Lepidoptera: Pyralidae), was implemented. Sixty-two potentially useful entomopathogenic fungal isolates belonging to four genera were collected from 288 soil samples, an occurrence frequency of 21.53%. The most frequently isolated entomopathogenic fungal species was Beauveria bassiana (Balsamo) Vuillemin (15.63%), followed by Metarhizium anisopliae var. anisopliae (Metschnikoff) Sorokin (3.82%). Galleria mellonella was the most effective insect used to isolate fungal species (χ2=40.13, df=2, P≤ 0.005), with a total of 45 isolates obtained, followed by C. capitata with 11 isolates, and T. leucotreta with six isolates recovered. There was a significantly (χ2=11.65, df=1, P≤ 0.005) higher occurrence of entomopathogenic fungi in soil samples taken from refugia compared to cultivated orchards of both organically and conventionally managed farms. No significant differences were observed in the recovery of fungal isolates when soil samples from both farming systems were compared. The physiological effects and host range of 21 indigenous fungal isolates obtained in the Eastern Cape were investigated in the laboratory to establish whether these isolates could be effectively used as biological control agents against the subterranean life stages of C. rosa, C. capitata and T. leucotreta. When these pests were treated with a fungal concentration of 1 x 10⁷ conidia ml⁻¹, the percentage of T. leucotreta adults which emerged in fungal treated sand ranged from 5 to 60% (F=33.295; df=21; P=0.0001) depending on fungal isolate and the percentage of pupae with visible signs of mycosis ranged from 21 to 93% (F= 96.436; df=21; P=0.0001). Based on fungal isolates, the percentage adult survival in C. rosa and C. capitata ranged from 30 to 90% and 55 to 86% respectively. The percentage of C. rosa and C. capitata puparia with visible signs of mycosis ranged from 1 to 14% and 1 to 11% respectively. Deferred mortality due to mycosis in C. rosa and C. capitata adult flies ranged from 1 to 58% and 1 to 33% respectively, depending on fungal isolate. Entomopathogenic fungal isolates had a significantly greater effect on the adults of C. rosa and C. capitata than they did on the puparia of these two fruit fly species. Further, C. rosa and C. capitata did not differ significantly in their response to entomopathogenic fungi when adult survival or adult and pupal mycosis were considered. The relative potency of the four most virulent Beauveria isolates as well as the commercially available Beauveria bassiana product, Bb Plus® (Biological Control Products, South Africa), were compared against one another as log-probit regressions of mortality against C. rosa, C. capitata and T. leucotreta which all exhibited a dose-dependent response. Against fruit flies the estimated LC50 values of all five Beauveria isolates ranged from 5.5 x 10¹¹ to 2.8 x 10¹² conidia/ml⁻¹. There were no significant differences between the relative potencies of these five fungal isolates. When T. leucotreta was considered, isolates: G Moss R10 and G 14 2 B5 and Bb Plus® were significantly more pathogenic than G B Ar 23 B3 and FCM 10 13 L1. The estimated LC₅₀ values of the three most pathogenic isolates ranged from 6.8 x 10⁵ to 2.1 x 10⁶ conidia/ml⁻¹, while those of the least pathogenic ranged from 1.6 x 10⁷ to 3.7 x 10⁷ conidia/ml⁻¹. Thaumatotibia leucotreta final instar larvae were exposed to two conidial concentrations, at four different exposure times (12, 48, 72 and 96 hrs) and showed an exposure time-dependant relationship (F=5.43; df=3; P=0.001). At 1 x 10⁷conidia/ml⁻¹ two Beauveria isolates: G Moss R10 and G 14 2 B5 were able to elicit a response in 50% of test insects at 72 hrs (3 days) exposure. Although a limited amount of mycosis was observed in the puparia of both fruit fly species, deferred adult mortality due to mycosis was high. The increased incidence of adult mortality suggests that post emergence mycosis in adult fruit flies may play a more significant role in field suppression than the control of fruit flies at the pupal stage. The increased incidence of pupal mortality, as well as the relatively low concentrations of conidia required to elicit meaningful responses in T. leucotreta pupae may suggest that pre-emergent control of false codling moth will play a more significant role in field suppression than the control of adult life stages using indigenous isolates of entomopathogenic fungi. Various entomopathogenic fungal application techniques targeted at key insect pests within integrated pest management (IPM) systems of citrus are discussed.
- Full Text:
- Date Issued: 2010
Spatial and temporal patterns in the hyperbenthic community structure in a permanently open Eastern Cape estuary, South Africa
- Authors: Heyns, Elodie R
- Date: 2010
- Subjects: Sundays Estuary -- South Africa -- Eastern Cape , Groundfishes -- South Africa -- Eatern Cape , Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5768 , http://hdl.handle.net/10962/d1005456
- Description: The spatial and temporal (seasonal and diel) patterns in the hyperbenthic community structure (>500 μm) was investigated in the warm temperate, permanently open Kariega Estuary situated along the south-eastern coastline of South Africa. Spatial and seasonal patterns in the hyperbenthic community structure were assessed monthly at six stations along the length of the estuary over a period of twelve months. Data were collected using a modified hyperbenthic sledge, comprising two super-imposed nets. Physico-chemical data indicate the presence of a constant reverse salinity gradient, with highest salinities measured in the upper reaches and lowest at the mouth of the estuary. Strong seasonal patterns in temperature, dissolved oxygen and total chlorophyll-a (chl-a) concentrations were evident. Total average hyperbenthic densities ranged between 0.04 and 166 ind.m-3 in the lower net and between 0.12 and 225 ind.m-3 in the upper net. Hyperbenthic biomass values ranged between 0.02 and 11.9 mg.dry weight.m-3 in the lower net and between 0.02 and 17.4 mg.dry weight.m-3 in the upper net. A spatial and temporal pattern in total densities was detected with an increase in abundance over the period of September to October 2008 particularly in the middle reaches (Stations 3 and 4). Both the lower and upper nets were numerically dominated by decapods (mainly brachyuran crab zoeae) with the exception of June and July 2008 when mysids (mainly Mesopodopsis wooldridgei) dominated, making up 72.4 ± 58.14% of the total abundance in the lower net. A redundancy analysis (RDA) indicated that 99.2% of the variance in the hyperbenthic community structure could be explained by the first two canonical axes. Axis one, which accounted for 96.8% of the total variation detected in the ordination plot was highly correlated with sedimentary organic content and to a lesser extent the chl-a concentration within the Kariega Estuary. The correlations with the second canonical axis (2.4%) were less obvious, however, salinity and seston concentration were weakly correlated with this axis. Diel variability in the hyperbenthic community structure was assessed during March 2009. Samples were collected during the day and night (n = 6 for each period) using sampling gear described above. Total average hyperbenthic densities during the day (497.9 ± 254.1 ind.m-3) were significantly higher than night-time estimates (129.9 ± 38.5 ind.m-3; p<0.05). There were no significant differences in the average dayand night-time estimates of hyperbenthic biomass (p>0.05). A hierarchical cluster analysis identified two significantly distinct groupings, designated the day and night samples. Results from the SIMPER procedure indicated that the high densities of crab zoeae recorded during the day-time accounted for the majority of the dissimilarity between the day and night groupings (44.7%). In addition, it is apparent that several benthic species, especially from the cumacean and isopod orders, were absent from the hyperbenthos during the day-time and emerged into the water column at night.
- Full Text:
- Date Issued: 2010
- Authors: Heyns, Elodie R
- Date: 2010
- Subjects: Sundays Estuary -- South Africa -- Eastern Cape , Groundfishes -- South Africa -- Eatern Cape , Estuaries -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5768 , http://hdl.handle.net/10962/d1005456
- Description: The spatial and temporal (seasonal and diel) patterns in the hyperbenthic community structure (>500 μm) was investigated in the warm temperate, permanently open Kariega Estuary situated along the south-eastern coastline of South Africa. Spatial and seasonal patterns in the hyperbenthic community structure were assessed monthly at six stations along the length of the estuary over a period of twelve months. Data were collected using a modified hyperbenthic sledge, comprising two super-imposed nets. Physico-chemical data indicate the presence of a constant reverse salinity gradient, with highest salinities measured in the upper reaches and lowest at the mouth of the estuary. Strong seasonal patterns in temperature, dissolved oxygen and total chlorophyll-a (chl-a) concentrations were evident. Total average hyperbenthic densities ranged between 0.04 and 166 ind.m-3 in the lower net and between 0.12 and 225 ind.m-3 in the upper net. Hyperbenthic biomass values ranged between 0.02 and 11.9 mg.dry weight.m-3 in the lower net and between 0.02 and 17.4 mg.dry weight.m-3 in the upper net. A spatial and temporal pattern in total densities was detected with an increase in abundance over the period of September to October 2008 particularly in the middle reaches (Stations 3 and 4). Both the lower and upper nets were numerically dominated by decapods (mainly brachyuran crab zoeae) with the exception of June and July 2008 when mysids (mainly Mesopodopsis wooldridgei) dominated, making up 72.4 ± 58.14% of the total abundance in the lower net. A redundancy analysis (RDA) indicated that 99.2% of the variance in the hyperbenthic community structure could be explained by the first two canonical axes. Axis one, which accounted for 96.8% of the total variation detected in the ordination plot was highly correlated with sedimentary organic content and to a lesser extent the chl-a concentration within the Kariega Estuary. The correlations with the second canonical axis (2.4%) were less obvious, however, salinity and seston concentration were weakly correlated with this axis. Diel variability in the hyperbenthic community structure was assessed during March 2009. Samples were collected during the day and night (n = 6 for each period) using sampling gear described above. Total average hyperbenthic densities during the day (497.9 ± 254.1 ind.m-3) were significantly higher than night-time estimates (129.9 ± 38.5 ind.m-3; p<0.05). There were no significant differences in the average dayand night-time estimates of hyperbenthic biomass (p>0.05). A hierarchical cluster analysis identified two significantly distinct groupings, designated the day and night samples. Results from the SIMPER procedure indicated that the high densities of crab zoeae recorded during the day-time accounted for the majority of the dissimilarity between the day and night groupings (44.7%). In addition, it is apparent that several benthic species, especially from the cumacean and isopod orders, were absent from the hyperbenthos during the day-time and emerged into the water column at night.
- Full Text:
- Date Issued: 2010
The ichthyofauna and piscivorous avifauna in a small temporarily open/closed Eastern Cape estuary, South Africa
- Authors: Blake, Justin David
- Date: 2010
- Subjects: Estuarine fishes -- South Africa -- Eastern Cape , Bird populations -- South Africa -- Riet River Estuary , Estuaries -- South Africa -- Eastern Cape , Fish populations -- South Africa -- Riet River Estuary , Estuarine animals -- South Africa -- Riet River Estuary , Birds -- South Africa -- Riet River Estuary , Riet River Estuary (South Africa)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5709 , http://hdl.handle.net/10962/d1005395 , Estuarine fishes -- South Africa -- Eastern Cape , Bird populations -- South Africa -- Riet River Estuary , Estuaries -- South Africa -- Eastern Cape , Fish populations -- South Africa -- Riet River Estuary , Estuarine animals -- South Africa -- Riet River Estuary , Birds -- South Africa -- Riet River Estuary , Riet River Estuary (South Africa)
- Description: The spatial and temporal patterns in selected components of the ichthyofauna and piscivorous avifauna in the small temporarily open/closed Riet River Estuary located on the eastern seaboard of southern Africa was investigated monthly over the period August 2005 to July 2006. The ichthyofauna within the littoral zone of the estuary was sampled using a 5 m seine net (8 stations) while a 30 m seine net (4 stations) was employed to sample the fish in the channel. Bird counts were made along repeat transects along the length of the estuary. Total ichthyofaunal abundances and biomass ranged between 1.60 and 8.67 individuals m⁻² and 0.45 to 21.76 g wwt m⁻² within the littoral zone, and between 0.08 and 0.44 individuals m⁻² and 0.58 and 36.52 g wwt m⁻² in the channel of the estuary. The highest values were generally recorded during the summer months. Results of the numerical analysis indicated that the breaching events recorded over the study period did not lead to a common trend in the ichthyofaunal community. In the absence of a link to the marine environment, the ichthyofaunal community in the littoral zone was numerically dominated by the estuarine resident species, Gilchristella aestuaria and to a lesser extent by Glossogobius callidus, which collectively accounted for ca. 54% of the total ichthyofauna sampled. The establishment of a link to the marine environment coincided with increased numbers of marine breeding species including Atherina breviceps and Rhabdosargus holubi to total fish counts within the estuary. Hierarchical cluster analysis did not identify any spatial patterns in the community structure of the ichthyofauna in the littoral zone or channel zone of the estuary, which could likely be linked to the absence of any distinct horizontal patterns in salinity and temperature within the system. A total of thirteen piscivorous bird species was recorded over the study period. Of the recorded species, six species were wading piscivores, four species were aerial divers and the remaining three species were pursuit swimmers. There were no significant correlations between the estimates of the ichthyofaunal abundance and biomass and bird numbers evident during the study (P> 0.05 in both cases). The Reed Cormorant (Phalacrocorax africanus) was the dominant species throughout the study, with a mean of 8.25 (SD ± 7.90) individuals per count. Mean values of the Pied Kingfisher (Ceryle rudis) and Giant Kingfisher (Megaceryle maximus) were 3.42 (SD ± 1.20) and 1.17 (SD ± 0.60) individuals per count, respectively. The remaining species revealed mean values < 0.5 individuals per count. The highest bird numbers were recorded in winter reflecting the migration of large numbers of the Reed Cormorant into the system. Breaching events were associated with a decrease in total bird numbers, which was most likely due to loss of potential foraging habitat (littoral zone) for waders resulting from reduced water levels. Monthly food consumption by all piscivorous birds revealed large temporal variability, ranging from 26.35 to 140.58 kg per month. The observed variability could be linked to mouth phase and bird numbers.
- Full Text:
- Date Issued: 2010
- Authors: Blake, Justin David
- Date: 2010
- Subjects: Estuarine fishes -- South Africa -- Eastern Cape , Bird populations -- South Africa -- Riet River Estuary , Estuaries -- South Africa -- Eastern Cape , Fish populations -- South Africa -- Riet River Estuary , Estuarine animals -- South Africa -- Riet River Estuary , Birds -- South Africa -- Riet River Estuary , Riet River Estuary (South Africa)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5709 , http://hdl.handle.net/10962/d1005395 , Estuarine fishes -- South Africa -- Eastern Cape , Bird populations -- South Africa -- Riet River Estuary , Estuaries -- South Africa -- Eastern Cape , Fish populations -- South Africa -- Riet River Estuary , Estuarine animals -- South Africa -- Riet River Estuary , Birds -- South Africa -- Riet River Estuary , Riet River Estuary (South Africa)
- Description: The spatial and temporal patterns in selected components of the ichthyofauna and piscivorous avifauna in the small temporarily open/closed Riet River Estuary located on the eastern seaboard of southern Africa was investigated monthly over the period August 2005 to July 2006. The ichthyofauna within the littoral zone of the estuary was sampled using a 5 m seine net (8 stations) while a 30 m seine net (4 stations) was employed to sample the fish in the channel. Bird counts were made along repeat transects along the length of the estuary. Total ichthyofaunal abundances and biomass ranged between 1.60 and 8.67 individuals m⁻² and 0.45 to 21.76 g wwt m⁻² within the littoral zone, and between 0.08 and 0.44 individuals m⁻² and 0.58 and 36.52 g wwt m⁻² in the channel of the estuary. The highest values were generally recorded during the summer months. Results of the numerical analysis indicated that the breaching events recorded over the study period did not lead to a common trend in the ichthyofaunal community. In the absence of a link to the marine environment, the ichthyofaunal community in the littoral zone was numerically dominated by the estuarine resident species, Gilchristella aestuaria and to a lesser extent by Glossogobius callidus, which collectively accounted for ca. 54% of the total ichthyofauna sampled. The establishment of a link to the marine environment coincided with increased numbers of marine breeding species including Atherina breviceps and Rhabdosargus holubi to total fish counts within the estuary. Hierarchical cluster analysis did not identify any spatial patterns in the community structure of the ichthyofauna in the littoral zone or channel zone of the estuary, which could likely be linked to the absence of any distinct horizontal patterns in salinity and temperature within the system. A total of thirteen piscivorous bird species was recorded over the study period. Of the recorded species, six species were wading piscivores, four species were aerial divers and the remaining three species were pursuit swimmers. There were no significant correlations between the estimates of the ichthyofaunal abundance and biomass and bird numbers evident during the study (P> 0.05 in both cases). The Reed Cormorant (Phalacrocorax africanus) was the dominant species throughout the study, with a mean of 8.25 (SD ± 7.90) individuals per count. Mean values of the Pied Kingfisher (Ceryle rudis) and Giant Kingfisher (Megaceryle maximus) were 3.42 (SD ± 1.20) and 1.17 (SD ± 0.60) individuals per count, respectively. The remaining species revealed mean values < 0.5 individuals per count. The highest bird numbers were recorded in winter reflecting the migration of large numbers of the Reed Cormorant into the system. Breaching events were associated with a decrease in total bird numbers, which was most likely due to loss of potential foraging habitat (littoral zone) for waders resulting from reduced water levels. Monthly food consumption by all piscivorous birds revealed large temporal variability, ranging from 26.35 to 140.58 kg per month. The observed variability could be linked to mouth phase and bird numbers.
- Full Text:
- Date Issued: 2010
The ultrastructure and histology of the defensive epidermal glands of some marine pulmonates
- Authors: Pinchuck, Shirley Clare
- Date: 2010
- Subjects: Snails -- Histology , Snails -- Physiology , Snails -- Cytology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5793 , http://hdl.handle.net/10962/d1005481 , Snails -- Histology , Snails -- Physiology , Snails -- Cytology
- Description: Histology and electron microscopy were used to describe and compare the structure of the dorso-lateral pedal defensive glands of three species of marine Basommatophora, Siphonaria capensis, S. serrata and S. gigas. All three species possessed multi-cellular glands that were larger and most abundant in S. capensis. In S. capensis and S. serrata, defensive glands were composed of two types (type I and II) of large secretory cells filled with product and some irregularly shaped support cells that surrounded a central lumen. The product of both cell types was produced by organelles confined to the bases of the cells. The entire gland was surrounded by a well developed layer of smooth muscle and collagen. Type I cells stained positively for neutral and sulphated mucins, and at the transmission electron microscope level the product had a reticulated appearance. By contrast type II gland cells stained very positively for acidic mucins and the secretory product was formed as large granular vesicles. The product from both types of cell, which appeared to be secreted by holocrine secretion, mixed in the lumen of the duct. Individuals of Siphonaria gigas had two types of lateral pedal glands, a large multi-cellular type and a tubular unicellular gland. The multi-cellular glands, which were surrounded by poorly developed muscle, contained one type of gland cell that stained for neutral and sulphated mucins only, as well as some support cells. The tubular glands contained a heterogeneous product that stained very positively for neutral and sulphated mucins. In addition two species of shell-less marine Systellommatophorans, Onchidella capensis and O. hildae, were examined. Onchidellids also posses large marginal, multi-cellular, epidermal glands that produce a repugnatorial secretion. Like the multi-cellular epidermal glands of siphonariids, those of onchidellids are surrounded by layers of smooth muscle. The muscular capsule was particularly well developed in both species of onchidellid, but more so in O. hildae. In addition, this study has shown that unlike siphonariids, muscle fibres run between the gland cells of O. capensis and O. hildae. Unlike siphonariids, onchidellids have a layer of epithelial cells lining the lumen of the gland. The well developed muscle layer and the strands of muscle running between the different gland cells indicates that the glands can be constricted to forcibly propel their secretions along the length of the duct and away from the body of the animal. Based on their product, glands of O. capensis were comprised of five different types of secretory cell and O. hildae only four. Histological and histochemical staining of the glands of showed that the secretory product is largely made up of acidic mucopolysaccharides and neutral and sulphated mucins. A single species from the order Eupulmonata, Trimusculus costatus, was examined and the glands were very different to the species from the siphonariids and onchidellids. Trimusculus costatus does not have large multi-cellular glands encapsulated in a well developed muscle layer, but based on their cell contents, three different types of large unicellular gland cell can be recognised. The glands of T. costatus gave positive results for acid, neutral and sulphated mucins, but negative results for carboxylated mucin. It is possible that the mucous secreted by T. costatus is also an anti-bacterial agent and whilst not totally eliminating bacteria may prevent the accumulation of epibionts on these sedentary limpets. The acidic or sulphated nature of the secretions may help in this role. The defensive mucous secretions of Siphonaria and Onchidella contain polypropionate derivatives, whilst the active ingredients of Trimusculus mucus have been identified as labdane diterpenes, similar to those produced by opisthobranchs. The structure of the glands thought to produce these repungnatorial secretions is very different, with the glands of T. costatus resembling those of the opisthobranchs.
- Full Text:
- Date Issued: 2010
- Authors: Pinchuck, Shirley Clare
- Date: 2010
- Subjects: Snails -- Histology , Snails -- Physiology , Snails -- Cytology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5793 , http://hdl.handle.net/10962/d1005481 , Snails -- Histology , Snails -- Physiology , Snails -- Cytology
- Description: Histology and electron microscopy were used to describe and compare the structure of the dorso-lateral pedal defensive glands of three species of marine Basommatophora, Siphonaria capensis, S. serrata and S. gigas. All three species possessed multi-cellular glands that were larger and most abundant in S. capensis. In S. capensis and S. serrata, defensive glands were composed of two types (type I and II) of large secretory cells filled with product and some irregularly shaped support cells that surrounded a central lumen. The product of both cell types was produced by organelles confined to the bases of the cells. The entire gland was surrounded by a well developed layer of smooth muscle and collagen. Type I cells stained positively for neutral and sulphated mucins, and at the transmission electron microscope level the product had a reticulated appearance. By contrast type II gland cells stained very positively for acidic mucins and the secretory product was formed as large granular vesicles. The product from both types of cell, which appeared to be secreted by holocrine secretion, mixed in the lumen of the duct. Individuals of Siphonaria gigas had two types of lateral pedal glands, a large multi-cellular type and a tubular unicellular gland. The multi-cellular glands, which were surrounded by poorly developed muscle, contained one type of gland cell that stained for neutral and sulphated mucins only, as well as some support cells. The tubular glands contained a heterogeneous product that stained very positively for neutral and sulphated mucins. In addition two species of shell-less marine Systellommatophorans, Onchidella capensis and O. hildae, were examined. Onchidellids also posses large marginal, multi-cellular, epidermal glands that produce a repugnatorial secretion. Like the multi-cellular epidermal glands of siphonariids, those of onchidellids are surrounded by layers of smooth muscle. The muscular capsule was particularly well developed in both species of onchidellid, but more so in O. hildae. In addition, this study has shown that unlike siphonariids, muscle fibres run between the gland cells of O. capensis and O. hildae. Unlike siphonariids, onchidellids have a layer of epithelial cells lining the lumen of the gland. The well developed muscle layer and the strands of muscle running between the different gland cells indicates that the glands can be constricted to forcibly propel their secretions along the length of the duct and away from the body of the animal. Based on their product, glands of O. capensis were comprised of five different types of secretory cell and O. hildae only four. Histological and histochemical staining of the glands of showed that the secretory product is largely made up of acidic mucopolysaccharides and neutral and sulphated mucins. A single species from the order Eupulmonata, Trimusculus costatus, was examined and the glands were very different to the species from the siphonariids and onchidellids. Trimusculus costatus does not have large multi-cellular glands encapsulated in a well developed muscle layer, but based on their cell contents, three different types of large unicellular gland cell can be recognised. The glands of T. costatus gave positive results for acid, neutral and sulphated mucins, but negative results for carboxylated mucin. It is possible that the mucous secreted by T. costatus is also an anti-bacterial agent and whilst not totally eliminating bacteria may prevent the accumulation of epibionts on these sedentary limpets. The acidic or sulphated nature of the secretions may help in this role. The defensive mucous secretions of Siphonaria and Onchidella contain polypropionate derivatives, whilst the active ingredients of Trimusculus mucus have been identified as labdane diterpenes, similar to those produced by opisthobranchs. The structure of the glands thought to produce these repungnatorial secretions is very different, with the glands of T. costatus resembling those of the opisthobranchs.
- Full Text:
- Date Issued: 2010
Phylogeography and epifauna of two intertidal seaweeds on the coast of South Africa
- Authors: Mmonwa, Lucas Kolobe
- Date: 2009
- Subjects: Phylogeography -- South Africa , Marine algae -- South Africa , Red algae -- South Africa , Gelidium -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5738 , http://hdl.handle.net/10962/d1005424 , Phylogeography -- South Africa , Marine algae -- South Africa , Red algae -- South Africa , Gelidium -- South Africa
- Description: Southern African biogeographic boundaries delimit the phylogeographic distribution of some coastal and estuarine invertebrates. This study investigated the impact of these boundaries on the phylogeographic distribution of two intertidal red seaweeds, Gelidium pristoides and Hypnea spicifera using the mitochondrial Cox2-3 spacer and the nuclear ITS1 regions. G. pristoides spores have short distance-dispersal, while long distance-dispersal is more likely in H. spicifera via spores and drifting fertile thallus fragments. Both markers revealed a south-western and south-eastern lineage within G. pristoides but the breaks between lineages do not coincide with any recognised biogeographic limits. The Cox2-3 spacer revealed a boundary between the two lineages at the Alexandria Coastal Dunefield (ACD) and ITS1 at the Gamtoos-Van Stadens Dunefields (GVD) which is approximately 80km west of the ACD. The minor difference between the two markers regarding location of the phylogeographic boundary is probably due to the dating differences between the two dunefields. The ACD as developed currently is superimposed on the ancient dunefields which formed during the Pleistocene, coinciding with the Cox2-3 spacer sequences divergence which dates back 500,000 - 580,000 years. The GVD formed during the Holocene (6,500 - 4,000 years ago), coinciding with the ITS1 sequences divergence which dates 4,224 - 4,928 years ago. Thus, these phylogeographic boundaries probably appeared without the influence of biogeographic boundaries, but rather due to the lack of suitable habitat in the dunefields, coupled with short dispersal-distances of the spores. Analysis of the ITS1 and Cox2-3 spacer regions in H. spicifera revealed that the species is characterized by uniform genetic structure along the coastline. This reflects the species`s potential for long range expansion as it inhabits both the intertidal and subtidal zones; and this presumably leads to high gene flow among populations. The ITS1 sequences showed minimal genetic variation of one substitution between the gametophyte and tetrasporophyte generations within H. spicifera. This suggests the predominance of asexual reproduction, which reduces gene flow and fixes alleles between generations. ANOSIM and Bray-Curtis cluster analyses showed scale-dependant variation in the abundances of epifauna (mainly amphipod, isopod, mollusc and polychaete species) on G. pristoides. At small local (within site) and large (among sites) scales, there were weak and no structure in epifaunal abundances respectively. However, at larger, biogeographic scales, samples from the same biogeographic region tended to be clustered together. Thus, there was a group containing predominantly south coast samples and a group containing east coast samples mixed with the remaining south coast samples. Such scale-dependant variation in epifaunal abundances is probably due to the effects of factors driving species richness at small local (within site) scales (e.g. wave exposure, seaweed biomass) and at larger, biogeographic scales (e.g. surface sea temperature). Moreover, at very small (individual samples) scales; there was no correlation between epifauna composition and genotype of the seaweed. Seaweed samples characterized by distinct ITS1 or Cox2-3 spacer sequences did not show any significant differences in epifaunal composition. Although the distributional pattern of the epifaunal community observed at large biogeographic scale is not clear, it seems to be associated with the biogeographic regions. However, phylogeographic distribution of Gelidium pristoides is not connected to biogeographic regions. Thus, at larger, biogeographic scales, there is no correlation between phylogeographic distribution of G. pristoides and distribution of the associated fauna
- Full Text:
- Date Issued: 2009
- Authors: Mmonwa, Lucas Kolobe
- Date: 2009
- Subjects: Phylogeography -- South Africa , Marine algae -- South Africa , Red algae -- South Africa , Gelidium -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5738 , http://hdl.handle.net/10962/d1005424 , Phylogeography -- South Africa , Marine algae -- South Africa , Red algae -- South Africa , Gelidium -- South Africa
- Description: Southern African biogeographic boundaries delimit the phylogeographic distribution of some coastal and estuarine invertebrates. This study investigated the impact of these boundaries on the phylogeographic distribution of two intertidal red seaweeds, Gelidium pristoides and Hypnea spicifera using the mitochondrial Cox2-3 spacer and the nuclear ITS1 regions. G. pristoides spores have short distance-dispersal, while long distance-dispersal is more likely in H. spicifera via spores and drifting fertile thallus fragments. Both markers revealed a south-western and south-eastern lineage within G. pristoides but the breaks between lineages do not coincide with any recognised biogeographic limits. The Cox2-3 spacer revealed a boundary between the two lineages at the Alexandria Coastal Dunefield (ACD) and ITS1 at the Gamtoos-Van Stadens Dunefields (GVD) which is approximately 80km west of the ACD. The minor difference between the two markers regarding location of the phylogeographic boundary is probably due to the dating differences between the two dunefields. The ACD as developed currently is superimposed on the ancient dunefields which formed during the Pleistocene, coinciding with the Cox2-3 spacer sequences divergence which dates back 500,000 - 580,000 years. The GVD formed during the Holocene (6,500 - 4,000 years ago), coinciding with the ITS1 sequences divergence which dates 4,224 - 4,928 years ago. Thus, these phylogeographic boundaries probably appeared without the influence of biogeographic boundaries, but rather due to the lack of suitable habitat in the dunefields, coupled with short dispersal-distances of the spores. Analysis of the ITS1 and Cox2-3 spacer regions in H. spicifera revealed that the species is characterized by uniform genetic structure along the coastline. This reflects the species`s potential for long range expansion as it inhabits both the intertidal and subtidal zones; and this presumably leads to high gene flow among populations. The ITS1 sequences showed minimal genetic variation of one substitution between the gametophyte and tetrasporophyte generations within H. spicifera. This suggests the predominance of asexual reproduction, which reduces gene flow and fixes alleles between generations. ANOSIM and Bray-Curtis cluster analyses showed scale-dependant variation in the abundances of epifauna (mainly amphipod, isopod, mollusc and polychaete species) on G. pristoides. At small local (within site) and large (among sites) scales, there were weak and no structure in epifaunal abundances respectively. However, at larger, biogeographic scales, samples from the same biogeographic region tended to be clustered together. Thus, there was a group containing predominantly south coast samples and a group containing east coast samples mixed with the remaining south coast samples. Such scale-dependant variation in epifaunal abundances is probably due to the effects of factors driving species richness at small local (within site) scales (e.g. wave exposure, seaweed biomass) and at larger, biogeographic scales (e.g. surface sea temperature). Moreover, at very small (individual samples) scales; there was no correlation between epifauna composition and genotype of the seaweed. Seaweed samples characterized by distinct ITS1 or Cox2-3 spacer sequences did not show any significant differences in epifaunal composition. Although the distributional pattern of the epifaunal community observed at large biogeographic scale is not clear, it seems to be associated with the biogeographic regions. However, phylogeographic distribution of Gelidium pristoides is not connected to biogeographic regions. Thus, at larger, biogeographic scales, there is no correlation between phylogeographic distribution of G. pristoides and distribution of the associated fauna
- Full Text:
- Date Issued: 2009