Age, growth, reproduction and sexual dimorphism of the striped dolphin, Stenella coeruleoalba, off the south-east coast of southern Africa
- Authors: Bishop, Amy Ruth
- Date: 2014
- Subjects: Striped dolphin -- Conservation -- Africa, Southern , Striped dolphin -- Development -- Africa, Southern , Striped dolphin -- Africa, Southern -- Reproduction , Striped dolphin -- Age determination -- Africa, Southern , Dolphins -- Conservation -- Africa, Southern , Dolphins -- Development -- Africa, Southern , Dolphins -- Africa, Southern -- Reproduction , Dolphins -- Age determination -- Africa, Southern , Dimorphism (Animals)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5848 , http://hdl.handle.net/10962/d1011600 , Striped dolphin -- Conservation -- Africa, Southern , Striped dolphin -- Development -- Africa, Southern , Striped dolphin -- Africa, Southern -- Reproduction , Striped dolphin -- Age determination -- Africa, Southern , Dolphins -- Conservation -- Africa, Southern , Dolphins -- Development -- Africa, Southern , Dolphins -- Africa, Southern -- Reproduction , Dolphins -- Age determination -- Africa, Southern , Dimorphism (Animals)
- Description: The striped dolphin, Stenella coeruleoalba, is an oceanic dolphin found worldwide in tropical to warm temperate waters. Globally populations are threatened through direct fishing, bycatch and pollution. Little is known about the life history of this species in South African waters and it is currently listed as ‘Data Deficient’ by the International Union for Conservation of Nature (IUCN). Critical to the conservation and management of this species is an understanding of basic life history parameters. For the present study, metadata and tissues from 101 stranded S. coeruleoalba along the south-east coast of southern Africa between 1969 and 2012 were analyzed to examine age and growth, male and female reproduction and sexual dimorphism. Age and growth were determined by counting the number of growth layer groups (GLG’s) present in their teeth. A von Bertalanffy growth curve gave the best fit to the data and indicated that physical maturity was reached around 21 years in males and 18 years in females. Additionally, asymptotic lengths were reached at 231cm and 224cm in males and females, respectively. The maximum ages obtained were 21 years for males and 20 years for females. Length at birth was estimated to be between 116cm and 119cm for males and between 112cm and 114cm for females. The reproductive status of the adult dolphins was assessed by histological and macroscopic analyses of gonadal tissue. Sexual maturity was attained before physical maturity in both sexes. The males reached sexual maturity between 8 and 12 years of age and between 209 and 224cm in total body length. The maximum combined testis weight comprised about 0.24% of the total body weight and sexual maturity was reached between a combined testis weight of 16 and 41g, a mean testis length of 8 and 10cm, and a mean seminiferous tubule diameter of 44 and 70μm. Females attained sexual maturity between 7 and 8 years of age and between 213 and 216 cm in total body length. The ovulation rate was 0.32 per year and the majority of ovulations occurred in the left ovary, with ovulations occurring in the right ovary only in individuals older than 10 years of age. The annual pregnancy rate was calculated to be 26%. Reproductive seasonality could not be established due to the small sample size and the absence of samples throughout the year. However, both conceptions and births appear to occur in both August and December/January. Additionally, testis weight and seminiferous tubule diameters appear to fluctuate throughout the year, which could suggest reproductive seasonality in this species. Sexual size dimorphism in mature adults was evident for a number of external measurements, however, sexual shape dimorphism was not present in this species. Mature males had significantly longer and wider pectoral fins, dorsal fins and flukes than females (p<0.05 in all cases). It was suggested that the larger appendages are required for male on male combat during intraspecific competition for females. Additionally, larger appendages aid in thermoregulation, propulsion and maneuverability. Females had a significantly greater distance between the tip upper jaw and the genital aperture and anus, which was expected due to differences in anatomy between male and female genital openings. Overall, S. coeruleoalba did not exhibit distinct sexual dimorphism and together with the relatively small testes in relation to the total body weight (0.24%) it was proposed that this species demonstrates a less extreme form of polygyny. Additionaly, the results of this study are important to the understanding of the basic biology of the species.
- Full Text:
- Date Issued: 2014
- Authors: Bishop, Amy Ruth
- Date: 2014
- Subjects: Striped dolphin -- Conservation -- Africa, Southern , Striped dolphin -- Development -- Africa, Southern , Striped dolphin -- Africa, Southern -- Reproduction , Striped dolphin -- Age determination -- Africa, Southern , Dolphins -- Conservation -- Africa, Southern , Dolphins -- Development -- Africa, Southern , Dolphins -- Africa, Southern -- Reproduction , Dolphins -- Age determination -- Africa, Southern , Dimorphism (Animals)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5848 , http://hdl.handle.net/10962/d1011600 , Striped dolphin -- Conservation -- Africa, Southern , Striped dolphin -- Development -- Africa, Southern , Striped dolphin -- Africa, Southern -- Reproduction , Striped dolphin -- Age determination -- Africa, Southern , Dolphins -- Conservation -- Africa, Southern , Dolphins -- Development -- Africa, Southern , Dolphins -- Africa, Southern -- Reproduction , Dolphins -- Age determination -- Africa, Southern , Dimorphism (Animals)
- Description: The striped dolphin, Stenella coeruleoalba, is an oceanic dolphin found worldwide in tropical to warm temperate waters. Globally populations are threatened through direct fishing, bycatch and pollution. Little is known about the life history of this species in South African waters and it is currently listed as ‘Data Deficient’ by the International Union for Conservation of Nature (IUCN). Critical to the conservation and management of this species is an understanding of basic life history parameters. For the present study, metadata and tissues from 101 stranded S. coeruleoalba along the south-east coast of southern Africa between 1969 and 2012 were analyzed to examine age and growth, male and female reproduction and sexual dimorphism. Age and growth were determined by counting the number of growth layer groups (GLG’s) present in their teeth. A von Bertalanffy growth curve gave the best fit to the data and indicated that physical maturity was reached around 21 years in males and 18 years in females. Additionally, asymptotic lengths were reached at 231cm and 224cm in males and females, respectively. The maximum ages obtained were 21 years for males and 20 years for females. Length at birth was estimated to be between 116cm and 119cm for males and between 112cm and 114cm for females. The reproductive status of the adult dolphins was assessed by histological and macroscopic analyses of gonadal tissue. Sexual maturity was attained before physical maturity in both sexes. The males reached sexual maturity between 8 and 12 years of age and between 209 and 224cm in total body length. The maximum combined testis weight comprised about 0.24% of the total body weight and sexual maturity was reached between a combined testis weight of 16 and 41g, a mean testis length of 8 and 10cm, and a mean seminiferous tubule diameter of 44 and 70μm. Females attained sexual maturity between 7 and 8 years of age and between 213 and 216 cm in total body length. The ovulation rate was 0.32 per year and the majority of ovulations occurred in the left ovary, with ovulations occurring in the right ovary only in individuals older than 10 years of age. The annual pregnancy rate was calculated to be 26%. Reproductive seasonality could not be established due to the small sample size and the absence of samples throughout the year. However, both conceptions and births appear to occur in both August and December/January. Additionally, testis weight and seminiferous tubule diameters appear to fluctuate throughout the year, which could suggest reproductive seasonality in this species. Sexual size dimorphism in mature adults was evident for a number of external measurements, however, sexual shape dimorphism was not present in this species. Mature males had significantly longer and wider pectoral fins, dorsal fins and flukes than females (p<0.05 in all cases). It was suggested that the larger appendages are required for male on male combat during intraspecific competition for females. Additionally, larger appendages aid in thermoregulation, propulsion and maneuverability. Females had a significantly greater distance between the tip upper jaw and the genital aperture and anus, which was expected due to differences in anatomy between male and female genital openings. Overall, S. coeruleoalba did not exhibit distinct sexual dimorphism and together with the relatively small testes in relation to the total body weight (0.24%) it was proposed that this species demonstrates a less extreme form of polygyny. Additionaly, the results of this study are important to the understanding of the basic biology of the species.
- Full Text:
- Date Issued: 2014
Macroinvertebrate community and species responses to chlorinated sewage effluent in the Umsunduze and Umbilo rivers, Kwa Zulu-Natal, South Africa
- Authors: Williams, Margot Lluttrell
- Date: 1997
- Subjects: Sewage -- Environmental aspects -- South Africa -- KwaZulu-Natal , Sewage -- Purification -- Chlorination -- South Africa -- KwaZulu-Natal , Baetis -- South Africa -- KwaZulu-Natal , Mayflies -- South Africa -- KwaZulu-Natal , Chlorine -- Environmental aspects -- South Africa -- KwaZulu-Natal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5727 , http://hdl.handle.net/10962/d1005413 , Sewage -- Environmental aspects -- South Africa -- KwaZulu-Natal , Sewage -- Purification -- Chlorination -- South Africa -- KwaZulu-Natal , Baetis -- South Africa -- KwaZulu-Natal , Mayflies -- South Africa -- KwaZulu-Natal , Chlorine -- Environmental aspects -- South Africa -- KwaZulu-Natal
- Description: Chlorine has a wide variety of applications in water treatment. Because of its disinfectant efficacy, it is used world wide for the treatment of potable water, sewage, swimming pools and for the control of nuisance organisms in cooling towers. A problem arises when such chlorinated water enters the natural environment, as chlorine's greatest advantage, i.e. its germicidal capacity, becomes its greatest disadvantage. In particular, the discharge of heated, chlorinated water from cooling towers and chlorinated, treated sewage into rivers have severe consequences for the riverine flora and fauna. This study focused on the effects of chlorinated, treated sewage effluent on the community structure of benthic macroinvertebrates in two rivers in KwaZulu-Natal viz. the Umsunduze River in the Pietermaritzburg area, and the Umbilo River in the Durban area. The study was conducted in three phases. The first two phases comprised a toxicological investigation of the effects of chlorine on a selected riverine macroinvertebrate, and the third phase comprised an ecotoxicological investigation of the effects of chlorinated treated sewage on benthic macroinvertebrate community structure. The first phase of the study involved the development of an artificial stream system which would be suitable for determining the response of a selected macroinvertebrate species to chlorine. Chlorine is both reactive and volatile, so this necessitated the development of a specialised flow-through system with apparatus which would allow continuous dosing of a sodium hypochlorite solution. The system was set up at the Process Evaluation Facility at Wiggins Waterworks, Durban, where raw water from lnanda Dam was used. The second phase involved the use of this artificial stream system to conduct acute 96 h toxicity tests. Baetid mayfly nymphs (Baetis harrisoni Barnard) were selected as the test organisms after a preliminary investigation found them to be suitable for survival under laboratory conditions. For comparative purposes, tests were run first on B. harrisoni from a relatively uncontaminated stream in a residential area of Westville, then on specimens from the severely impacted Umbilo River. The LC₅₀ of chlorine for organisms from both sources was found to be in the region of 0.004 mg/l (free chlorine). This value was well below the general effluent standard of 0.1 mg/l in effect at the time. The recommended acute environmental guideline is 0.001 mg/l. The third phase of the study involved field validation of the toxicity test results. It was hypothesised that since the LC₅₀ for free chlorine was 0.004 mg/l, B. harrisoni would not be found downstream from a point source of chlorinated effluent where the concentration of free chlorine ranged from 0.06 to 0.2 mg/l, and that the macroinvertebrate community structure would also be altered. In order to test these hypotheses, benthic macro invertebrate community structure was investigated at several sites up- and downstream from the outlets of the Darvill Wastewater Works in the Umsunduze River and the Umbilo Sewage Purification Works in the Umbilo River. In addition, in order to differentiate between the effects of chlorinated and unchlorinated treated sewage, a section of the Umbilo River (upstream from the chlorinated discharge) was exposed to unchlorinated, treated sewage. In this way, a limited "before and after" sewage and an "upstream and downstream" from sewage investigation could be carried out. Organisms were collected from riffles (and from pools in the Umbilo River) and the samples were then sorted and organisms were identified to species level, where possible, otherwise to genus or family. Changes in community composition were shown graphically as pie charts of relative proportions of organisms found at each site, graphs of the average number of taxa at each site; and graphs of the average number of individuals at each site; Data from the Umbilo River were also analysed using TWINSPAN (Two-way indicator species analysis). In both the Umsunduze and the Umbilo rivers, the deleterious effects of the chlorinated effluent were clearly evident. At Umsunduze Site 3 and Umbilo Site 5 (both immediately downstream from the chlorinated effluent) both the number of taxa and number of individuals were substantially reduced, sometimes to zero. Where organisms were found at the next sites downstream (Sites 4 and 6 respectively), the samples were dominated by Chironomus. In contrast, the unchlorinated effluent in the Umbilo River caused very little difference in community structure. As predicted, B. harrisoni was not found in downstream samples in which chlorine was present, yet appeared to be relatively unaffected by the unchlorinated effluent, suggesting that chlorine, rather than the effluent was responsible for its absence at downstream sites. In conclusion, it would appear that while treated sewage effluent certainly causes changes in macroinvertebrate community structure, chlorination of this effluent leads to large scale destruction of the riverine community. This in turn delays the recovery process of the river, rendering a longer stretch unfit for use. The consequences of this delayed recovery are that the failure to meet the water quality requirements of the natural environment results in those of the other water users (agriculture, industry, domestic and recreation) not being met. This reduces the natural capacity of the riverine community to process organic waste and recover from the discharge of sewage effluent. Chlorination increases the distance of impaired water quality and environmental integrity which result from organically enriched treated sewage effluent. The results of the study indicated that the draft water quality guidelines for aquatic ecosystems, derived from inadequate data, and calculated with a safety factor, were the correct order of magnitude. The approach followed in the study will be useful in the development and refinement of water quality guidelines for aquatic ecosystems.
- Full Text:
- Date Issued: 1997
- Authors: Williams, Margot Lluttrell
- Date: 1997
- Subjects: Sewage -- Environmental aspects -- South Africa -- KwaZulu-Natal , Sewage -- Purification -- Chlorination -- South Africa -- KwaZulu-Natal , Baetis -- South Africa -- KwaZulu-Natal , Mayflies -- South Africa -- KwaZulu-Natal , Chlorine -- Environmental aspects -- South Africa -- KwaZulu-Natal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5727 , http://hdl.handle.net/10962/d1005413 , Sewage -- Environmental aspects -- South Africa -- KwaZulu-Natal , Sewage -- Purification -- Chlorination -- South Africa -- KwaZulu-Natal , Baetis -- South Africa -- KwaZulu-Natal , Mayflies -- South Africa -- KwaZulu-Natal , Chlorine -- Environmental aspects -- South Africa -- KwaZulu-Natal
- Description: Chlorine has a wide variety of applications in water treatment. Because of its disinfectant efficacy, it is used world wide for the treatment of potable water, sewage, swimming pools and for the control of nuisance organisms in cooling towers. A problem arises when such chlorinated water enters the natural environment, as chlorine's greatest advantage, i.e. its germicidal capacity, becomes its greatest disadvantage. In particular, the discharge of heated, chlorinated water from cooling towers and chlorinated, treated sewage into rivers have severe consequences for the riverine flora and fauna. This study focused on the effects of chlorinated, treated sewage effluent on the community structure of benthic macroinvertebrates in two rivers in KwaZulu-Natal viz. the Umsunduze River in the Pietermaritzburg area, and the Umbilo River in the Durban area. The study was conducted in three phases. The first two phases comprised a toxicological investigation of the effects of chlorine on a selected riverine macroinvertebrate, and the third phase comprised an ecotoxicological investigation of the effects of chlorinated treated sewage on benthic macroinvertebrate community structure. The first phase of the study involved the development of an artificial stream system which would be suitable for determining the response of a selected macroinvertebrate species to chlorine. Chlorine is both reactive and volatile, so this necessitated the development of a specialised flow-through system with apparatus which would allow continuous dosing of a sodium hypochlorite solution. The system was set up at the Process Evaluation Facility at Wiggins Waterworks, Durban, where raw water from lnanda Dam was used. The second phase involved the use of this artificial stream system to conduct acute 96 h toxicity tests. Baetid mayfly nymphs (Baetis harrisoni Barnard) were selected as the test organisms after a preliminary investigation found them to be suitable for survival under laboratory conditions. For comparative purposes, tests were run first on B. harrisoni from a relatively uncontaminated stream in a residential area of Westville, then on specimens from the severely impacted Umbilo River. The LC₅₀ of chlorine for organisms from both sources was found to be in the region of 0.004 mg/l (free chlorine). This value was well below the general effluent standard of 0.1 mg/l in effect at the time. The recommended acute environmental guideline is 0.001 mg/l. The third phase of the study involved field validation of the toxicity test results. It was hypothesised that since the LC₅₀ for free chlorine was 0.004 mg/l, B. harrisoni would not be found downstream from a point source of chlorinated effluent where the concentration of free chlorine ranged from 0.06 to 0.2 mg/l, and that the macroinvertebrate community structure would also be altered. In order to test these hypotheses, benthic macro invertebrate community structure was investigated at several sites up- and downstream from the outlets of the Darvill Wastewater Works in the Umsunduze River and the Umbilo Sewage Purification Works in the Umbilo River. In addition, in order to differentiate between the effects of chlorinated and unchlorinated treated sewage, a section of the Umbilo River (upstream from the chlorinated discharge) was exposed to unchlorinated, treated sewage. In this way, a limited "before and after" sewage and an "upstream and downstream" from sewage investigation could be carried out. Organisms were collected from riffles (and from pools in the Umbilo River) and the samples were then sorted and organisms were identified to species level, where possible, otherwise to genus or family. Changes in community composition were shown graphically as pie charts of relative proportions of organisms found at each site, graphs of the average number of taxa at each site; and graphs of the average number of individuals at each site; Data from the Umbilo River were also analysed using TWINSPAN (Two-way indicator species analysis). In both the Umsunduze and the Umbilo rivers, the deleterious effects of the chlorinated effluent were clearly evident. At Umsunduze Site 3 and Umbilo Site 5 (both immediately downstream from the chlorinated effluent) both the number of taxa and number of individuals were substantially reduced, sometimes to zero. Where organisms were found at the next sites downstream (Sites 4 and 6 respectively), the samples were dominated by Chironomus. In contrast, the unchlorinated effluent in the Umbilo River caused very little difference in community structure. As predicted, B. harrisoni was not found in downstream samples in which chlorine was present, yet appeared to be relatively unaffected by the unchlorinated effluent, suggesting that chlorine, rather than the effluent was responsible for its absence at downstream sites. In conclusion, it would appear that while treated sewage effluent certainly causes changes in macroinvertebrate community structure, chlorination of this effluent leads to large scale destruction of the riverine community. This in turn delays the recovery process of the river, rendering a longer stretch unfit for use. The consequences of this delayed recovery are that the failure to meet the water quality requirements of the natural environment results in those of the other water users (agriculture, industry, domestic and recreation) not being met. This reduces the natural capacity of the riverine community to process organic waste and recover from the discharge of sewage effluent. Chlorination increases the distance of impaired water quality and environmental integrity which result from organically enriched treated sewage effluent. The results of the study indicated that the draft water quality guidelines for aquatic ecosystems, derived from inadequate data, and calculated with a safety factor, were the correct order of magnitude. The approach followed in the study will be useful in the development and refinement of water quality guidelines for aquatic ecosystems.
- Full Text:
- Date Issued: 1997
Geographic susceptibility of Helicoverpa armigera (Lepidoptera: Noctuidae) to insecticidal proteins in Bt-cotton in South Africa
- Van Jaarsveld, Martha Johanna
- Authors: Van Jaarsveld, Martha Johanna
- Date: 2004
- Subjects: Helicoverpa armigera , Noctuidae , Lepidoptera , Cotton -- Diseases and pests -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5701 , http://hdl.handle.net/10962/d1005387 , Helicoverpa armigera , Noctuidae , Lepidoptera , Cotton -- Diseases and pests -- South Africa
- Description: Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) (African bollworm) is a typical noctuid with a very catholic taste in food plants and whose larvae feed on a wide range of cultivated and wild plants. It has been identified as the most polyphagous and injurious pest in South Africa. Helicoverpa armigera is also a key pest of cotton in many parts of the world. This key pest requires extensive control as it adversely effects yield and has built up resistance to synthetic pyrethroid insecticides. Cotton is an important crop produced by commercial and small-scale farmers in South Africa. The local demand for cotton has not been exceeded yet, but to satisfy a demanding market, pest control costs play an important role in cotton production. The threat of an insect pest that has already shown resistance prompted the present study to investigate the possibility of resistance to Bt-cotton. Genetically engineered or Bt-cotton was introduced commercially in 1996 in South Africa. All Bt-cotton plants contain one or more foreign genes derived from the soil-dwelling bacterium, Bacillus thuringiensis (Berliner), which produces protein crystals. These crystals were isolated and transferred into the genome of a cotton plant resulting in the plant producing it’s own protein insecticide. In 1998, Monsanto (Pty) Ltd requested research into the geographic susceptibility of H. armigera to the insecticidal proteins in Bt-cotton in SA. Laboratory reared and field sampled populations of H. armigera were exposed to a diet mixed with various baseline concentrations of the Bt-gene Cry1Ac freeze dried protein. This study also determined the performance of H. armigera and Spodoptera littoralis (Boisduval) on different Bt-cotton field cultivars containing different Cry-protein genes. Results obtained indicated a significant difference in susceptibility in two field populations of H. armigera to the Bt-protein Cry1Ac, even though the LD50,s in the 2003 season did not indicate resistance. Bt-cotton cultivar 15985 BX controlled H. armigera and S. littoralis larvae, the best followed in descending order by cultivar 15985 X, 15985 B and DP50 B. Results on H. armigera also indicated that the Cry-proteins in the plant parts of the different cultivars did not diminish as the season progressed. The Bt-cotton cultivars induced retarded growth of larvae, due to either a repellent effect or lack of feeding by larvae. Widespread adoption of Bt-cotton by South African farmers led to regional declines in bollworm populations, reduced insecticide use, and increased yields. Genetically modified crops therefore contribute to a cost effective, sustainable, productive and efficient form of agriculture, with a resultant positive impact on the environment. As the market for commercial Bt-cotton in South Africa expands, it is recommended that a monitoring programme for potential resistant genes in H. armigera should be implemented at least every 2 - 3 years. This will ensure that effective resistance management strategies are utilised. Coupled with this are the Biosafety Risks regarding the effect of new proteins expressed in transgenic plants, which require further studies.
- Full Text:
- Date Issued: 2004
- Authors: Van Jaarsveld, Martha Johanna
- Date: 2004
- Subjects: Helicoverpa armigera , Noctuidae , Lepidoptera , Cotton -- Diseases and pests -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5701 , http://hdl.handle.net/10962/d1005387 , Helicoverpa armigera , Noctuidae , Lepidoptera , Cotton -- Diseases and pests -- South Africa
- Description: Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) (African bollworm) is a typical noctuid with a very catholic taste in food plants and whose larvae feed on a wide range of cultivated and wild plants. It has been identified as the most polyphagous and injurious pest in South Africa. Helicoverpa armigera is also a key pest of cotton in many parts of the world. This key pest requires extensive control as it adversely effects yield and has built up resistance to synthetic pyrethroid insecticides. Cotton is an important crop produced by commercial and small-scale farmers in South Africa. The local demand for cotton has not been exceeded yet, but to satisfy a demanding market, pest control costs play an important role in cotton production. The threat of an insect pest that has already shown resistance prompted the present study to investigate the possibility of resistance to Bt-cotton. Genetically engineered or Bt-cotton was introduced commercially in 1996 in South Africa. All Bt-cotton plants contain one or more foreign genes derived from the soil-dwelling bacterium, Bacillus thuringiensis (Berliner), which produces protein crystals. These crystals were isolated and transferred into the genome of a cotton plant resulting in the plant producing it’s own protein insecticide. In 1998, Monsanto (Pty) Ltd requested research into the geographic susceptibility of H. armigera to the insecticidal proteins in Bt-cotton in SA. Laboratory reared and field sampled populations of H. armigera were exposed to a diet mixed with various baseline concentrations of the Bt-gene Cry1Ac freeze dried protein. This study also determined the performance of H. armigera and Spodoptera littoralis (Boisduval) on different Bt-cotton field cultivars containing different Cry-protein genes. Results obtained indicated a significant difference in susceptibility in two field populations of H. armigera to the Bt-protein Cry1Ac, even though the LD50,s in the 2003 season did not indicate resistance. Bt-cotton cultivar 15985 BX controlled H. armigera and S. littoralis larvae, the best followed in descending order by cultivar 15985 X, 15985 B and DP50 B. Results on H. armigera also indicated that the Cry-proteins in the plant parts of the different cultivars did not diminish as the season progressed. The Bt-cotton cultivars induced retarded growth of larvae, due to either a repellent effect or lack of feeding by larvae. Widespread adoption of Bt-cotton by South African farmers led to regional declines in bollworm populations, reduced insecticide use, and increased yields. Genetically modified crops therefore contribute to a cost effective, sustainable, productive and efficient form of agriculture, with a resultant positive impact on the environment. As the market for commercial Bt-cotton in South Africa expands, it is recommended that a monitoring programme for potential resistant genes in H. armigera should be implemented at least every 2 - 3 years. This will ensure that effective resistance management strategies are utilised. Coupled with this are the Biosafety Risks regarding the effect of new proteins expressed in transgenic plants, which require further studies.
- Full Text:
- Date Issued: 2004
Aspects of the ecology of piscivorous birds of Lake Kyle Rhodesia
- Authors: Junor, F J R
- Date: 1969
- Subjects: Bird populations -- Zimbabwe , Water birds -- Zimbabwe
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5909 , http://hdl.handle.net/10962/d1015201
- Description: [From Introduction]. From an early period in the lake's history research was undataken to determine the potential of Kyle as a source of edible fish, In such a study, knowledge of the number and weight of fish consumed by piscivorous birds would seem to be an obvious consideration. Accordingly special investigation was undertaken into the food requirements of fish eating birds which live in the lake area. The method employed, on this occasion, to obtain the required information has differed radically from that more generally used by investigators working with similar objects in view. The common practise has been to examine the stomach contents of a considerable number of birds of the same species, which have been destroyed in order to make information available.
- Full Text:
- Date Issued: 1969
- Authors: Junor, F J R
- Date: 1969
- Subjects: Bird populations -- Zimbabwe , Water birds -- Zimbabwe
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5909 , http://hdl.handle.net/10962/d1015201
- Description: [From Introduction]. From an early period in the lake's history research was undataken to determine the potential of Kyle as a source of edible fish, In such a study, knowledge of the number and weight of fish consumed by piscivorous birds would seem to be an obvious consideration. Accordingly special investigation was undertaken into the food requirements of fish eating birds which live in the lake area. The method employed, on this occasion, to obtain the required information has differed radically from that more generally used by investigators working with similar objects in view. The common practise has been to examine the stomach contents of a considerable number of birds of the same species, which have been destroyed in order to make information available.
- Full Text:
- Date Issued: 1969
The parasite complex of the citrus psylla, trioza erytreae (Del Guercio) (Homoptera)
- Authors: McDaniel, J. R.
- Date: 1971
- Subjects: Psylla -- Regulation , Citrus , Biological control systems , Parasites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5865 , http://hdl.handle.net/10962/d1012866
- Description: 1. Fifteen parasite species comprising the T. erytreae complex in Salisbury are listed. 2. Detailed, illustrated accounts are given of the biology of two primary parasites, Tetrastichus Pradiatus Waterston and Psyllaephagus pulvinatus (Waterston ), and their main hyperparasite, Aphidencyrtus cassatus Annecke. 3. The biology of the remaining twelve less important hyperparasites is briefly described and illustrated. 4. Keys are given to the adults, pupae and pupal remains of the parasites. 5 . The population fluctuations of T. erytreae and its parasites, as determined from field studies in the Salisbury area, are reported . 6. The interrelationships between T. erytreae and its parasites are summarised and discussed. Summary, p. 89.
- Full Text:
- Date Issued: 1971
- Authors: McDaniel, J. R.
- Date: 1971
- Subjects: Psylla -- Regulation , Citrus , Biological control systems , Parasites
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5865 , http://hdl.handle.net/10962/d1012866
- Description: 1. Fifteen parasite species comprising the T. erytreae complex in Salisbury are listed. 2. Detailed, illustrated accounts are given of the biology of two primary parasites, Tetrastichus Pradiatus Waterston and Psyllaephagus pulvinatus (Waterston ), and their main hyperparasite, Aphidencyrtus cassatus Annecke. 3. The biology of the remaining twelve less important hyperparasites is briefly described and illustrated. 4. Keys are given to the adults, pupae and pupal remains of the parasites. 5 . The population fluctuations of T. erytreae and its parasites, as determined from field studies in the Salisbury area, are reported . 6. The interrelationships between T. erytreae and its parasites are summarised and discussed. Summary, p. 89.
- Full Text:
- Date Issued: 1971
An evaluation of Mimorista pulchellalis (Dyar) (Lepidoptera : Pyraustidae) as a biocontrol agent against jointed cactus in South Africa
- Authors: Nieman, Erik
- Date: 1984
- Subjects: Cactus -- South Africa , Weeds -- Biological control -- South Africa , Pyralidae -- South Africa , Moths -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5812 , http://hdl.handle.net/10962/d1007052 , Cactus -- South Africa , Weeds -- Biological control -- South Africa , Pyralidae -- South Africa , Moths -- South Africa
- Description: From the introduction: The work on Mimorista is divided into two sections: a laboratory orientated study which describes the biology and rearing techniques and a field orientated study where the establishment of the insect and its impact on jointed cactus populations are examined. In the final chapters the integration of this insect in the current control program are discussed and recommendations regarding its future in South Africa are given.
- Full Text:
- Date Issued: 1984
- Authors: Nieman, Erik
- Date: 1984
- Subjects: Cactus -- South Africa , Weeds -- Biological control -- South Africa , Pyralidae -- South Africa , Moths -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5812 , http://hdl.handle.net/10962/d1007052 , Cactus -- South Africa , Weeds -- Biological control -- South Africa , Pyralidae -- South Africa , Moths -- South Africa
- Description: From the introduction: The work on Mimorista is divided into two sections: a laboratory orientated study which describes the biology and rearing techniques and a field orientated study where the establishment of the insect and its impact on jointed cactus populations are examined. In the final chapters the integration of this insect in the current control program are discussed and recommendations regarding its future in South Africa are given.
- Full Text:
- Date Issued: 1984
Feeding dynamics of suspension-feeders in the nearshore marine environment adjacent to two contrasting estuaries in the Eastern Cape, South Africa
- Authors: Vermeulen, Ilke
- Date: 2012
- Subjects: Suspension feeders -- South Africa -- Eastern Cape , Suspension feeders -- Food -- South Africa -- Eastern Cape , Coastal organisms -- South Africa -- Eastern Cape , Streamflow -- South Africa -- Eastern Cape , Tetraclitidae -- South Africa -- Eastern Cape , Mexilhao mussel -- South Africa -- Eastern Cape , Polychaeta -- South Africa -- Eastern Cape , Estuarine health -- South Africa -- Eastern Cape , Estuaries -- Freshwater inflow -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5916 , http://hdl.handle.net/10962/d1016242
- Description: Coastal transition zones form important interlinking regions where marine ecosystems, rivers and estuarine environments significantly influence each other. Coastal rocky shores are key habitats that sustain a variety of primary producers and invertebrates and due to the dynamic nature of coastal ecosystems, suspension-feeders on rocky shores can be influenced by an array of autochthonous and allochthonous food sources. Fatty acid and stable isotope trophic markers were employed to distinguish between regional and temporal changes in the potential food sources to rocky shore suspension-feeders in the Eastern Cape Province of South Africa. The primary aim was to assess the spatial and temporal influences of contrasting river flows on the available food sources to three indigenous coastal suspensionfeeders, namely the volcano barnacle Tetraclita serrata, brown mussel Perna perna and tubebuilding polychaete Gunnarea capensis. This was done by examining the intra- and interspecific changes in the fatty acid and stable isotope signatures of the barnacles, mussels and polychaetes in the adjacent marine environment of a freshwater-restricted (Kariega) and freshwater-dominated (Great Fish) estuary during austral summer and winter. Multivariate and Kruskal-Wallis analyses of variance on the fatty acid and isotopic signatures, respectively, identified significant regional changes in the barnacles and mussels, while only stable isotopes distinguished between the Kariega and Great Fish polychaetes (P < 0.05). In addition, significant temporal changes were observed in consumer fatty acids and isotope values in both regions (P < 0.05). Bacterial sources, detritus and phytoplankton assemblages, which are influenced by hydrology and vegetation, differed between regions and were mainly responsible for the regional and temporal separations. Principal component analyses on the consumer fatty acid signatures distinguished between animals situated upstream (i.e. north) and downstream (i.e. south) of the Kariega Estuary mouth in summer. The north/south separation was mainly due to greater contributions of diatoms to northernlocated animals and dinoflagellates and detritus to southern-located consumers. In addition, the south-flowing Agulhas Current on the eastern shores of southern Africa appeared to influence the north/south separation in the Kariega region, as water leaving the estuary was probably entrained into the south-easterly flowing currents, thereby depositing estuarinederived detritus to southern populations. In general, diatoms and detritus were essential food sources to the filter-feeders in summer, and flagellates, diatoms, zooplankton and detritus were important in winter. Coastal macroalgae was a key food source in the Kariega and Great Fish regions during both seasons. Consistently large levels of diatom markers (16:1n-7 and 20:5n-3) and dinoflagellate markers (22:6n-3) in consumer tissues in the Kariega and Great Fish regions identified that phytoplankton was their dominant food source. The barnacles, mussels and polychaetes had similar fatty acid markers and a fairly narrow δ¹³C range (-16.5 to -14.4 ‰), suggesting that they probably consumed similar food. Carbon isotope analyses, however, separated the suspension-feeders into slightly depleted (barnacles; -16.5 to -16.1 ‰), intermediate (mussels; -15.8 to -15.0 ‰) and enriched (polychaetes; -15.0 to -14.4 ‰) consumers, but did not provide conclusive evidence of their preferences for specific phytoplankton. Conversely, fatty acid analyses highlighted that barnacles and mussels had greater proportions of dinoflagellate markers (22:6n-3; 7.0-15.3 % TFA), while polychaetes had larger diatom levels (20:5n-3; 15.1-22.2 % TFA). In addition, all three species had consistently large contributions from bacterial fatty acids (15:0, i-16:0, 17:0 and i-18:0; 4.2-13.6 % TFA) in summer and winter, and large proportions of saturated fatty acids (33.3-53.1 % TFA) including those with 14 to 18 carbons, indicating that bacterial and detritus food sources played an important role in their diets. Barnacles had small levels of terrestrial markers (18:2n-6 and 18:3n-3; <2.5 % TFA) and demonstrated increased omnivorous feeding compared with the other suspension-feeders [increased levels of 20:1n-11 and 20:1n-9, higher 18:1n-9/18:1n-7 ratios at ~2.1, enriched δ¹⁵N values at ~10.6 ‰; zooplankton (potentially including microzooplankton, larvae and protists) contribution of up to 61 % of the diet]. Mussels contained significant proportions of the terrestrial markers (18:2n-6 and 18:3n-3; >2.5 % TFA) and exhibited intermediate omnivory (intermediate levels of 20:1n-11 and 20:1n-9, intermediate 18:1n-9/18:1n-7 ratios at ~1.3, less enriched δ¹⁵N values at ~7.9 ‰; zooplankton contribution of 10-15 % of the diet). The more depleted nitrogen signatures in the mussels relative to the barnacles and polychaetes possibly illustrated a stronger preference for autotrophic food. Polychaetes mainly consumed plant food sources (i.e. microalgae, macroalgae and detritus; high levels of i-18:0, 18:1n-9, 18:4n-3 and 20:5n-3) and displayed little omnivory (low levels of 20:1n-11 and 20:1n-9, low 18:1n-9/18:1n-7 ratios at ~0.4, intermediate δ¹⁵N values at ~9.1 ‰; zooplankton contribution of <10 % of the diet). The barnacles, mussels and polychaetes are all suspension-feeders, originally presumed to consume the same food sources. The variations observed among the species, therefore, may result from differences in the proportional contributions of the various food sources to their diets as well as distinctions in metabolism. The distinct changes in the fatty acid and stable isotope signatures in all three filter-feeders in the Kariega and Great Fish regions are likely influenced by the diversity in regional vegetation and hydrology in the different systems, combined with interspecific differences in resource partitioning among the species.
- Full Text:
- Date Issued: 2012
- Authors: Vermeulen, Ilke
- Date: 2012
- Subjects: Suspension feeders -- South Africa -- Eastern Cape , Suspension feeders -- Food -- South Africa -- Eastern Cape , Coastal organisms -- South Africa -- Eastern Cape , Streamflow -- South Africa -- Eastern Cape , Tetraclitidae -- South Africa -- Eastern Cape , Mexilhao mussel -- South Africa -- Eastern Cape , Polychaeta -- South Africa -- Eastern Cape , Estuarine health -- South Africa -- Eastern Cape , Estuaries -- Freshwater inflow -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5916 , http://hdl.handle.net/10962/d1016242
- Description: Coastal transition zones form important interlinking regions where marine ecosystems, rivers and estuarine environments significantly influence each other. Coastal rocky shores are key habitats that sustain a variety of primary producers and invertebrates and due to the dynamic nature of coastal ecosystems, suspension-feeders on rocky shores can be influenced by an array of autochthonous and allochthonous food sources. Fatty acid and stable isotope trophic markers were employed to distinguish between regional and temporal changes in the potential food sources to rocky shore suspension-feeders in the Eastern Cape Province of South Africa. The primary aim was to assess the spatial and temporal influences of contrasting river flows on the available food sources to three indigenous coastal suspensionfeeders, namely the volcano barnacle Tetraclita serrata, brown mussel Perna perna and tubebuilding polychaete Gunnarea capensis. This was done by examining the intra- and interspecific changes in the fatty acid and stable isotope signatures of the barnacles, mussels and polychaetes in the adjacent marine environment of a freshwater-restricted (Kariega) and freshwater-dominated (Great Fish) estuary during austral summer and winter. Multivariate and Kruskal-Wallis analyses of variance on the fatty acid and isotopic signatures, respectively, identified significant regional changes in the barnacles and mussels, while only stable isotopes distinguished between the Kariega and Great Fish polychaetes (P < 0.05). In addition, significant temporal changes were observed in consumer fatty acids and isotope values in both regions (P < 0.05). Bacterial sources, detritus and phytoplankton assemblages, which are influenced by hydrology and vegetation, differed between regions and were mainly responsible for the regional and temporal separations. Principal component analyses on the consumer fatty acid signatures distinguished between animals situated upstream (i.e. north) and downstream (i.e. south) of the Kariega Estuary mouth in summer. The north/south separation was mainly due to greater contributions of diatoms to northernlocated animals and dinoflagellates and detritus to southern-located consumers. In addition, the south-flowing Agulhas Current on the eastern shores of southern Africa appeared to influence the north/south separation in the Kariega region, as water leaving the estuary was probably entrained into the south-easterly flowing currents, thereby depositing estuarinederived detritus to southern populations. In general, diatoms and detritus were essential food sources to the filter-feeders in summer, and flagellates, diatoms, zooplankton and detritus were important in winter. Coastal macroalgae was a key food source in the Kariega and Great Fish regions during both seasons. Consistently large levels of diatom markers (16:1n-7 and 20:5n-3) and dinoflagellate markers (22:6n-3) in consumer tissues in the Kariega and Great Fish regions identified that phytoplankton was their dominant food source. The barnacles, mussels and polychaetes had similar fatty acid markers and a fairly narrow δ¹³C range (-16.5 to -14.4 ‰), suggesting that they probably consumed similar food. Carbon isotope analyses, however, separated the suspension-feeders into slightly depleted (barnacles; -16.5 to -16.1 ‰), intermediate (mussels; -15.8 to -15.0 ‰) and enriched (polychaetes; -15.0 to -14.4 ‰) consumers, but did not provide conclusive evidence of their preferences for specific phytoplankton. Conversely, fatty acid analyses highlighted that barnacles and mussels had greater proportions of dinoflagellate markers (22:6n-3; 7.0-15.3 % TFA), while polychaetes had larger diatom levels (20:5n-3; 15.1-22.2 % TFA). In addition, all three species had consistently large contributions from bacterial fatty acids (15:0, i-16:0, 17:0 and i-18:0; 4.2-13.6 % TFA) in summer and winter, and large proportions of saturated fatty acids (33.3-53.1 % TFA) including those with 14 to 18 carbons, indicating that bacterial and detritus food sources played an important role in their diets. Barnacles had small levels of terrestrial markers (18:2n-6 and 18:3n-3; <2.5 % TFA) and demonstrated increased omnivorous feeding compared with the other suspension-feeders [increased levels of 20:1n-11 and 20:1n-9, higher 18:1n-9/18:1n-7 ratios at ~2.1, enriched δ¹⁵N values at ~10.6 ‰; zooplankton (potentially including microzooplankton, larvae and protists) contribution of up to 61 % of the diet]. Mussels contained significant proportions of the terrestrial markers (18:2n-6 and 18:3n-3; >2.5 % TFA) and exhibited intermediate omnivory (intermediate levels of 20:1n-11 and 20:1n-9, intermediate 18:1n-9/18:1n-7 ratios at ~1.3, less enriched δ¹⁵N values at ~7.9 ‰; zooplankton contribution of 10-15 % of the diet). The more depleted nitrogen signatures in the mussels relative to the barnacles and polychaetes possibly illustrated a stronger preference for autotrophic food. Polychaetes mainly consumed plant food sources (i.e. microalgae, macroalgae and detritus; high levels of i-18:0, 18:1n-9, 18:4n-3 and 20:5n-3) and displayed little omnivory (low levels of 20:1n-11 and 20:1n-9, low 18:1n-9/18:1n-7 ratios at ~0.4, intermediate δ¹⁵N values at ~9.1 ‰; zooplankton contribution of <10 % of the diet). The barnacles, mussels and polychaetes are all suspension-feeders, originally presumed to consume the same food sources. The variations observed among the species, therefore, may result from differences in the proportional contributions of the various food sources to their diets as well as distinctions in metabolism. The distinct changes in the fatty acid and stable isotope signatures in all three filter-feeders in the Kariega and Great Fish regions are likely influenced by the diversity in regional vegetation and hydrology in the different systems, combined with interspecific differences in resource partitioning among the species.
- Full Text:
- Date Issued: 2012
Mesoscale alongshore and cross-shore transport and settlement of invertebrate larvae on the south east coast of South Africa
- Authors: Dyantyi, Siphelele Buntu
- Date: 2019
- Subjects: Marine invertebrates -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Benthic animals -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Mexilhao mussel -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Mytilus galloprovincialis -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Oysters -- Larvae -- Dispersal -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/97007 , vital:31386
- Description: Pelagic larval stages of most marine benthic species are important in maintaining coastal populations of adults. Several physio-chemical factors such as currents, winds, larval behaviour and time have an influence on the dispersal and transport of larvae to the adult habitat but their role is however still poorly understood. The aim of this study was to investigate the alongshore and cross-shore transport and temporal delivery of invertebrate larvae at four sites (Kenton on Sea, Cannon Rocks, Schoenmakerskop and Cape St Francis) along the south east coast of Eastern Cape, South Africa. Larval distribution of several taxa was determined during two sampling periods, by collecting water samples at nearshore line transects (3 distances: 900m, 1500m and 2400m – perpendicular to the shore) and at three depths (surface, thermocline/middle, bottom), which ranged from 15m (inshore) to 50m (offshore). Physical properties (current speed and direction, dissolved oxygen, fluorescence, turbidity, temperature, salinity, pH, pressure, density and conductivity) were measured and coupled in order to further understand larval distribution. The larvae were analysed as both total abundance and separately as the abundances of a variety of taxa which were: Perna perna, Mytilus galloprovincialis, oysters, early and late nauplii and cyprids. Larval settlement and recruitment on the rocky shores were measured by monthly deployment and collection of 20 (10 each for barnacles and mussels) artificial collectors at each site, which were preserved in ethanol or frozen for further processing. Multiple Permutational Multivariate Analysis of Variance (PERMANOVA) analyses were used to test the effects of site, depth and distance from the shore for the nearshore larvae (taxa analysed separately). In addition, a distance based linear model (distLM) was performed to analyse the relationship between the total larval abundance and the above mentioned physical variables. Multiple two-way analyses of variance (ANOVA) were performed to test the effects of months and sites on the settlement and recruitment of the larvae (P. perna, M. galloprovincialis, other bivalves, cyprids and juvenile barnacles) arriving on the shore. For the nearshore larval distribution, results from the PERMANOVAs revealed that most taxa showed a significant site and depth interactions with the exception of ‘early nauplii’ taxon. Also nearly all taxa were found within the thermocline, besides ‘oyster’ and ‘cyprids’ which were located at thermocline or bottom. Larvae were also located at variable distances from the shore, with most occurring at the offshore stations. Furthermore, there was a geographical separation of larval abundance according to sites, with most larvae located at Cannon Rocks and Kenton on Sea and least at Schoenmakerskop and Cape St Francis. For the settlement and recruitment, most taxa showed a seasonal trend, with the highest abundance of settlers and recruits expectedly appearing during the summer months of the sampling period. Additionally there was a site effect for most taxa (P. perna, M. galloprovincialis, other bivalves and juvenile barnacles), where settlers and recruits were mostly found at Cannon Rocks. Significant differences in abundance of settlers and recruits amongst the four sites indicate spatial and temporal variability for the targeted 180km stretch of coast. Overall for this study, taxon and ontogenetic stage of larvae were important in the distribution and abundance of larvae. Throughout the time frame of nearshore and intertidal sampling, Cannon Rocks consistently resulted as a ‘hot spot’ for larval abundance, settlement and recruitment, while a broad west to east separation was also observed. These results hence highlight that within this stretch of c.180km coast, time, taxon, ontogeny and post-settlement factors influence early dynamics of benthic populations.
- Full Text:
- Date Issued: 2019
- Authors: Dyantyi, Siphelele Buntu
- Date: 2019
- Subjects: Marine invertebrates -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Benthic animals -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Mexilhao mussel -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Mytilus galloprovincialis -- Larvae -- Dispersal -- South Africa -- Eastern Cape , Oysters -- Larvae -- Dispersal -- South Africa -- Eastern Cape
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/97007 , vital:31386
- Description: Pelagic larval stages of most marine benthic species are important in maintaining coastal populations of adults. Several physio-chemical factors such as currents, winds, larval behaviour and time have an influence on the dispersal and transport of larvae to the adult habitat but their role is however still poorly understood. The aim of this study was to investigate the alongshore and cross-shore transport and temporal delivery of invertebrate larvae at four sites (Kenton on Sea, Cannon Rocks, Schoenmakerskop and Cape St Francis) along the south east coast of Eastern Cape, South Africa. Larval distribution of several taxa was determined during two sampling periods, by collecting water samples at nearshore line transects (3 distances: 900m, 1500m and 2400m – perpendicular to the shore) and at three depths (surface, thermocline/middle, bottom), which ranged from 15m (inshore) to 50m (offshore). Physical properties (current speed and direction, dissolved oxygen, fluorescence, turbidity, temperature, salinity, pH, pressure, density and conductivity) were measured and coupled in order to further understand larval distribution. The larvae were analysed as both total abundance and separately as the abundances of a variety of taxa which were: Perna perna, Mytilus galloprovincialis, oysters, early and late nauplii and cyprids. Larval settlement and recruitment on the rocky shores were measured by monthly deployment and collection of 20 (10 each for barnacles and mussels) artificial collectors at each site, which were preserved in ethanol or frozen for further processing. Multiple Permutational Multivariate Analysis of Variance (PERMANOVA) analyses were used to test the effects of site, depth and distance from the shore for the nearshore larvae (taxa analysed separately). In addition, a distance based linear model (distLM) was performed to analyse the relationship between the total larval abundance and the above mentioned physical variables. Multiple two-way analyses of variance (ANOVA) were performed to test the effects of months and sites on the settlement and recruitment of the larvae (P. perna, M. galloprovincialis, other bivalves, cyprids and juvenile barnacles) arriving on the shore. For the nearshore larval distribution, results from the PERMANOVAs revealed that most taxa showed a significant site and depth interactions with the exception of ‘early nauplii’ taxon. Also nearly all taxa were found within the thermocline, besides ‘oyster’ and ‘cyprids’ which were located at thermocline or bottom. Larvae were also located at variable distances from the shore, with most occurring at the offshore stations. Furthermore, there was a geographical separation of larval abundance according to sites, with most larvae located at Cannon Rocks and Kenton on Sea and least at Schoenmakerskop and Cape St Francis. For the settlement and recruitment, most taxa showed a seasonal trend, with the highest abundance of settlers and recruits expectedly appearing during the summer months of the sampling period. Additionally there was a site effect for most taxa (P. perna, M. galloprovincialis, other bivalves and juvenile barnacles), where settlers and recruits were mostly found at Cannon Rocks. Significant differences in abundance of settlers and recruits amongst the four sites indicate spatial and temporal variability for the targeted 180km stretch of coast. Overall for this study, taxon and ontogenetic stage of larvae were important in the distribution and abundance of larvae. Throughout the time frame of nearshore and intertidal sampling, Cannon Rocks consistently resulted as a ‘hot spot’ for larval abundance, settlement and recruitment, while a broad west to east separation was also observed. These results hence highlight that within this stretch of c.180km coast, time, taxon, ontogeny and post-settlement factors influence early dynamics of benthic populations.
- Full Text:
- Date Issued: 2019
The endocoprid dung beetles of southern Africa (Coleoptera: Scarabaeidae)
- Davis, Adrian L V (Adrian Louis Victor)
- Authors: Davis, Adrian L V (Adrian Louis Victor)
- Date: 1978
- Subjects: Dung beetles -- Ecology , Dung beetles -- Africa, Southern
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5845 , http://hdl.handle.net/10962/d1011030 , Dung beetles -- Ecology , Dung beetles -- Africa, Southern
- Description: The biology and ecology of the endocoprid dung beetles of the Aethiopian zoogeographic region has been studied in the field and laboratory. Work has centred mainly on Oniticellus planatus and O. formoaus although infomation has also been supplied on O. egregius, O. pictus and Tragiscus dimidiatus. The taxonomy of Onticellus (s.str.) and Tragiscus has been discussed with the recommendation that O. planattus and O. pseudaplanatus be synonymised. It has been suggested that endocoprid distribution is chiefly controlled by temperature, rainfall and the density of suitable large dung masses. On the basis of distribution it has been suggested that the taxonomic status of the subspecies of O. pictus should be reviewed. Endocoprids (genus Oniticellus (s.str.) are found throughout the warmer regions of Africa and Asia. Tragiscus is found only in Africa. Methods are described for monitoring endocoprids in the field, for distinguishing freshly emerged from older specimens, and for breeding endocoprids under laboratory conditions. It has been shown that endocoprids breed within or just beneath large dung masses unlike most other members of the Scarabaeinae which actively bury dung and construct the their broods at depth in the soil. It has been shown that there is a restriction of breeding sites available to endocoprids due to the removal of dung by the Scarabaeinae beetles and the limited space available within dung pads. This has resulted in low endocoprid population numbers, a disadvantage, which has been countered by highly specialised but opportunistic breeding habits. The requirements of dung plasticity have limited the time available for breeding activity by most endocoprids (excluding O. egresius) so that both the reproductive system and the reproductive behaviour (cf. O. planatus) are geared to rapid egg and brood production. Large numbers of follicles are able to be produced over a short period. In the probable absence of feeding, this has possibly been allowed by the involvement of a well developed fat body. The broods are tended by the parent female during larval development and the follicles are gradually resorbed, probably to prevent starvation. Ovarian recovery is rapid once feeding recommences. Behavioural mechanisms have developed which boost the number of broods constructed and the rapidity with which they are produced. The duration of endocoprid colonisation and the timing of arrival at dung is shown to be related to the rate of pad desiccation which is chiefly controlled by temperature and degree of dung removal by other dung beetles. Precipitation may also play a part. Predation by vertebrates and other insects has been noted and a number of mechanisms are described which are probably protective. Two insect parasitoids of O. formosus larvae have been recorded. The potential use of endocoprids in the Australian dung and fly control project has been discussed and it is recommended that their introduction be considered of low priority. It is suggested that the endocoprids evolved from Euoniticellus type ancestors and that their behaviour complex nidification developed in response to harsh environmental factors, chiefly the danger of desiccation and competition for dung with other dung beetles. From a consideration of brood and brood chamber construction it is suggested that O. egresius is a relatively unspecialised endocoprid which may retain dry season aestivation and has not evolved much further than its probable Euoniticellus type ancestor. The broods are coated in clay and abandoned soon after construction. Greater specialisation is shown by O. planatus and O. formosus which exhibit brooding behaviour, increasing longevity, more specialised brood protection, increased potential fecundity and continuous activity throughout the year. O. formosus shows greater specialisation in brood production than O. planatus. Greatest specialisation is found in T. dimidiatus which exhibits a precise brooding period and low egg production. Brood construction is of a similar degree of specialisation to that of O. formosus. Activity is also continuous throughout the year. The comparative biology of the five southern African endocoprids is summarised in Table 35. Summary, p. 129-131.
- Full Text:
- Date Issued: 1978
- Authors: Davis, Adrian L V (Adrian Louis Victor)
- Date: 1978
- Subjects: Dung beetles -- Ecology , Dung beetles -- Africa, Southern
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5845 , http://hdl.handle.net/10962/d1011030 , Dung beetles -- Ecology , Dung beetles -- Africa, Southern
- Description: The biology and ecology of the endocoprid dung beetles of the Aethiopian zoogeographic region has been studied in the field and laboratory. Work has centred mainly on Oniticellus planatus and O. formoaus although infomation has also been supplied on O. egregius, O. pictus and Tragiscus dimidiatus. The taxonomy of Onticellus (s.str.) and Tragiscus has been discussed with the recommendation that O. planattus and O. pseudaplanatus be synonymised. It has been suggested that endocoprid distribution is chiefly controlled by temperature, rainfall and the density of suitable large dung masses. On the basis of distribution it has been suggested that the taxonomic status of the subspecies of O. pictus should be reviewed. Endocoprids (genus Oniticellus (s.str.) are found throughout the warmer regions of Africa and Asia. Tragiscus is found only in Africa. Methods are described for monitoring endocoprids in the field, for distinguishing freshly emerged from older specimens, and for breeding endocoprids under laboratory conditions. It has been shown that endocoprids breed within or just beneath large dung masses unlike most other members of the Scarabaeinae which actively bury dung and construct the their broods at depth in the soil. It has been shown that there is a restriction of breeding sites available to endocoprids due to the removal of dung by the Scarabaeinae beetles and the limited space available within dung pads. This has resulted in low endocoprid population numbers, a disadvantage, which has been countered by highly specialised but opportunistic breeding habits. The requirements of dung plasticity have limited the time available for breeding activity by most endocoprids (excluding O. egresius) so that both the reproductive system and the reproductive behaviour (cf. O. planatus) are geared to rapid egg and brood production. Large numbers of follicles are able to be produced over a short period. In the probable absence of feeding, this has possibly been allowed by the involvement of a well developed fat body. The broods are tended by the parent female during larval development and the follicles are gradually resorbed, probably to prevent starvation. Ovarian recovery is rapid once feeding recommences. Behavioural mechanisms have developed which boost the number of broods constructed and the rapidity with which they are produced. The duration of endocoprid colonisation and the timing of arrival at dung is shown to be related to the rate of pad desiccation which is chiefly controlled by temperature and degree of dung removal by other dung beetles. Precipitation may also play a part. Predation by vertebrates and other insects has been noted and a number of mechanisms are described which are probably protective. Two insect parasitoids of O. formosus larvae have been recorded. The potential use of endocoprids in the Australian dung and fly control project has been discussed and it is recommended that their introduction be considered of low priority. It is suggested that the endocoprids evolved from Euoniticellus type ancestors and that their behaviour complex nidification developed in response to harsh environmental factors, chiefly the danger of desiccation and competition for dung with other dung beetles. From a consideration of brood and brood chamber construction it is suggested that O. egresius is a relatively unspecialised endocoprid which may retain dry season aestivation and has not evolved much further than its probable Euoniticellus type ancestor. The broods are coated in clay and abandoned soon after construction. Greater specialisation is shown by O. planatus and O. formosus which exhibit brooding behaviour, increasing longevity, more specialised brood protection, increased potential fecundity and continuous activity throughout the year. O. formosus shows greater specialisation in brood production than O. planatus. Greatest specialisation is found in T. dimidiatus which exhibits a precise brooding period and low egg production. Brood construction is of a similar degree of specialisation to that of O. formosus. Activity is also continuous throughout the year. The comparative biology of the five southern African endocoprids is summarised in Table 35. Summary, p. 129-131.
- Full Text:
- Date Issued: 1978
The roles of black-backed jackals and caracals in issues of human-wildlife conflict in the Eastern Cape, South Africa
- Authors: Murison, Megan Kate
- Date: 2015
- Subjects: Black-backed jackal -- South Africa -- Eastern Cape , Human-animal relationships -- South Africa -- Eastern Cape , Predatory animals -- Control -- South Africa -- Eastern Cape , Black-backed jackal -- Food -- South Africa -- Eastern Cape , Black-backed jackal -- Effect of human beings on -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5939 , http://hdl.handle.net/10962/d1018667
- Description: [Partial abstract]: Human-wildlife conflict is a widely observed phenomenon and encompasses a range of negative interactions between humans and wildlife. Depredation upon livestock and game species proves to be the prevalent form of this conflict and often results in the killing of carnivores. Within the South African context, despite intense lethal control, two sympatric mesopredators, the blackbacked jackal (Canis mesomelas) and the caracal (Caracal caracal), remain common enough to be considered a major threat to human livelihoods through depredation. Wildlife ranches and livestock farms dominate the landscape in the Eastern Cape Province. Moreover, human-predator conflict within the region is extensive as both the black-backed jackal and caracal are seen to be inimical by landowners. Understanding this conflict is essential for mitigating any potential adverse environmental reactions (i.e. range collapses or extinctions) and requires knowledge of anthropogenic, ecological and environmental factors. I interviewed 73 land owners across five municipal boundaries in the Eastern Cape to quantify perceptions of predator control methods.
- Full Text:
- Date Issued: 2015
- Authors: Murison, Megan Kate
- Date: 2015
- Subjects: Black-backed jackal -- South Africa -- Eastern Cape , Human-animal relationships -- South Africa -- Eastern Cape , Predatory animals -- Control -- South Africa -- Eastern Cape , Black-backed jackal -- Food -- South Africa -- Eastern Cape , Black-backed jackal -- Effect of human beings on -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5939 , http://hdl.handle.net/10962/d1018667
- Description: [Partial abstract]: Human-wildlife conflict is a widely observed phenomenon and encompasses a range of negative interactions between humans and wildlife. Depredation upon livestock and game species proves to be the prevalent form of this conflict and often results in the killing of carnivores. Within the South African context, despite intense lethal control, two sympatric mesopredators, the blackbacked jackal (Canis mesomelas) and the caracal (Caracal caracal), remain common enough to be considered a major threat to human livelihoods through depredation. Wildlife ranches and livestock farms dominate the landscape in the Eastern Cape Province. Moreover, human-predator conflict within the region is extensive as both the black-backed jackal and caracal are seen to be inimical by landowners. Understanding this conflict is essential for mitigating any potential adverse environmental reactions (i.e. range collapses or extinctions) and requires knowledge of anthropogenic, ecological and environmental factors. I interviewed 73 land owners across five municipal boundaries in the Eastern Cape to quantify perceptions of predator control methods.
- Full Text:
- Date Issued: 2015
Studies on certain aspects of the neuromuscular physiology of insects
- Authors: Moran, V. C. (V. Cliff)
- Date: 1963
- Subjects: Insects -- Physiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5866 , http://hdl.handle.net/10962/d1012879
- Description: It is well known that high potassium ion concentrations depolarize nervous tissue and it has been suggested that the nerve sheath surrounding the peripheral nerves of insects serves as a protective barrier for the exclusion of potassium ions, in the haemolymph, from the immediate environment of axons. Further it is known that the concentration of potassium ions in the haemolymph of phytophagous insects is far higher than that in predatory forms; this has led to the suggestion that the nerve sheath in plant feeding insects should be more highly developed than that of entomophagous insects. In this work the structure of the nerve sheath in phytophagous and predatory insects has been studied and this assumption has been shown to be groundles. However, preliminary experiments on the effects of ions and drugs on the peripheral nerves of phytophagous and predatory insects have shown that there is a definite difference in susceptibility between the nerves of these two forms and this has led to the postulate of a diffusion barrier beneath the level of the nerve sheath, which is more highly developed in phytophagous than in predatory forms. The properties of this second barrier are discussed. Part 1. , During the course of the work which has been described in Part 1- an outbreak of large saturniid moths Nudaurelia cytherea capensis Stoll.) occurred in the Grahamstown area. It was felt that an investigation into the properties of the flight motor of this moth, which has an extremely low wing beat frquency, might be rewarding as our knowledge of the flight motor in insects is limited to those with very much higher wing beat frequencies than that of this moth. The anatomy, innervation and histology of the flight muscles of Nudaurelia are described and it is shown that the flight motor of this moth is functionally different to that of other insects which have been investigated. Further, Nudaurelia shows a characteristic warm-up fluttering of the wings prior to flight - this phenomenon has also been examined in the following investigation. This study has yielded information about the location of a warm-up centre in the central nervous system of this moth. Part 2.
- Full Text:
- Date Issued: 1963
- Authors: Moran, V. C. (V. Cliff)
- Date: 1963
- Subjects: Insects -- Physiology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5866 , http://hdl.handle.net/10962/d1012879
- Description: It is well known that high potassium ion concentrations depolarize nervous tissue and it has been suggested that the nerve sheath surrounding the peripheral nerves of insects serves as a protective barrier for the exclusion of potassium ions, in the haemolymph, from the immediate environment of axons. Further it is known that the concentration of potassium ions in the haemolymph of phytophagous insects is far higher than that in predatory forms; this has led to the suggestion that the nerve sheath in plant feeding insects should be more highly developed than that of entomophagous insects. In this work the structure of the nerve sheath in phytophagous and predatory insects has been studied and this assumption has been shown to be groundles. However, preliminary experiments on the effects of ions and drugs on the peripheral nerves of phytophagous and predatory insects have shown that there is a definite difference in susceptibility between the nerves of these two forms and this has led to the postulate of a diffusion barrier beneath the level of the nerve sheath, which is more highly developed in phytophagous than in predatory forms. The properties of this second barrier are discussed. Part 1. , During the course of the work which has been described in Part 1- an outbreak of large saturniid moths Nudaurelia cytherea capensis Stoll.) occurred in the Grahamstown area. It was felt that an investigation into the properties of the flight motor of this moth, which has an extremely low wing beat frquency, might be rewarding as our knowledge of the flight motor in insects is limited to those with very much higher wing beat frequencies than that of this moth. The anatomy, innervation and histology of the flight muscles of Nudaurelia are described and it is shown that the flight motor of this moth is functionally different to that of other insects which have been investigated. Further, Nudaurelia shows a characteristic warm-up fluttering of the wings prior to flight - this phenomenon has also been examined in the following investigation. This study has yielded information about the location of a warm-up centre in the central nervous system of this moth. Part 2.
- Full Text:
- Date Issued: 1963
Post-release evaluation of the biological control programme against Cereus jamacaru De Candolle (Cactaceae), in South Africa
- Authors: Sutton, Guy Frederick
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7982 , vital:21330
- Description: Cereus jamacaru De Candolle (Cactaceae) is an environment-transforming weed of both agricultural and wildlife habitats in South Africa. Weed infestations reduce carrying capacity of the land, and pose a risk to livestock, wildlife and human safety due to the plant’s spiny thorns. The weed is considered to be under complete biological control in South Africa, due to its introduced control agent, Hypogeococcus festerianus Lizer y Trelles (Hemiptera: Pseudococcidae), although observational reports suggest that the level of success achieved is variable. In this thesis, a formal post-release evaluation of this biological control programme was conducted, specifically to determine the efficacy of H. festerianus as a biological control agent, and to identify factors which may limit or constrain the level of success achieved by the control agent. These data were collected with the intention of improving the control of C. jamacaru in South Africa. A field-based study of C. jamacaru population demographics investigated the efficacy of H. festerianus as a biological control agent of the weed, by integrating weed growth, fecundity and survival metrics with C. jamacaru population dynamics and demographic patterns from 8 sites where H. festerianus was present and 14 sites where the control agent was absent. The findings indicated that H. festerianus significantly reduced weed fecundity, which resulted in fewer seedling recruits, and that levels of plant mortality were greater at sites where H. festerianus was present. The reduction in weed fecundity and survival translated into negative population-level consequences for H. festerianus. Weed-population age frequency distributions in the absence of H. festerianus demonstrated a “reverse J-shaped” distribution, indicative of high recruitment rates and population stability, while C. jamacaru populations infected with H. festerianus were described by bell-shaped distributions, and were typified by limited recruitment, or a complete lack thereof. By constraining recruitment and inhibiting selfregeneration, H. festerianus appears to regulate populations of C. jamacaru. Predation and parasitism of H. festerianus was believed to be a limiting factor for the biological control programme against C. jamacaru in South Africa, although no formal evaluation of this claim had been undertaken. Accordingly, the assemblage of natural enemies acquired by H. festerianus in South Africa was identified by field-collections of infected H. festerianus gall-material. Further, timed point-count surveys of natural enemies associated with H. festerianus were performed and integrated with the data on the impact of H. festerianus on weed population dynamics to assess the impact of two prominent predaceous taxa on H. festerianus efficacy as a biological control agent. Although H. festerianus had acquired a diverse suite of novel natural enemies in South Africa, this has not prevented the biocontrol agent from having an impact on C. jamacaru populations, although other subtler effects cannot be ruled out. This study showed that biological control efforts employing H. festerianus for the management of C. jamacaru have been successful. Furthermore, these data demonstrated the utility of retrospective analyses in developing and improving the science of biological control, specifically how to improve candidate agent prioritisation, determining how many agents are required for successful biological control, and how to evaluate the success of biological control efforts. Improvements in our theoretical understanding of biological control will undoubtedly reduce costs of biological control programmes, improve success rates, and increase the predictability of biological control.
- Full Text:
- Date Issued: 2017
- Authors: Sutton, Guy Frederick
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/7982 , vital:21330
- Description: Cereus jamacaru De Candolle (Cactaceae) is an environment-transforming weed of both agricultural and wildlife habitats in South Africa. Weed infestations reduce carrying capacity of the land, and pose a risk to livestock, wildlife and human safety due to the plant’s spiny thorns. The weed is considered to be under complete biological control in South Africa, due to its introduced control agent, Hypogeococcus festerianus Lizer y Trelles (Hemiptera: Pseudococcidae), although observational reports suggest that the level of success achieved is variable. In this thesis, a formal post-release evaluation of this biological control programme was conducted, specifically to determine the efficacy of H. festerianus as a biological control agent, and to identify factors which may limit or constrain the level of success achieved by the control agent. These data were collected with the intention of improving the control of C. jamacaru in South Africa. A field-based study of C. jamacaru population demographics investigated the efficacy of H. festerianus as a biological control agent of the weed, by integrating weed growth, fecundity and survival metrics with C. jamacaru population dynamics and demographic patterns from 8 sites where H. festerianus was present and 14 sites where the control agent was absent. The findings indicated that H. festerianus significantly reduced weed fecundity, which resulted in fewer seedling recruits, and that levels of plant mortality were greater at sites where H. festerianus was present. The reduction in weed fecundity and survival translated into negative population-level consequences for H. festerianus. Weed-population age frequency distributions in the absence of H. festerianus demonstrated a “reverse J-shaped” distribution, indicative of high recruitment rates and population stability, while C. jamacaru populations infected with H. festerianus were described by bell-shaped distributions, and were typified by limited recruitment, or a complete lack thereof. By constraining recruitment and inhibiting selfregeneration, H. festerianus appears to regulate populations of C. jamacaru. Predation and parasitism of H. festerianus was believed to be a limiting factor for the biological control programme against C. jamacaru in South Africa, although no formal evaluation of this claim had been undertaken. Accordingly, the assemblage of natural enemies acquired by H. festerianus in South Africa was identified by field-collections of infected H. festerianus gall-material. Further, timed point-count surveys of natural enemies associated with H. festerianus were performed and integrated with the data on the impact of H. festerianus on weed population dynamics to assess the impact of two prominent predaceous taxa on H. festerianus efficacy as a biological control agent. Although H. festerianus had acquired a diverse suite of novel natural enemies in South Africa, this has not prevented the biocontrol agent from having an impact on C. jamacaru populations, although other subtler effects cannot be ruled out. This study showed that biological control efforts employing H. festerianus for the management of C. jamacaru have been successful. Furthermore, these data demonstrated the utility of retrospective analyses in developing and improving the science of biological control, specifically how to improve candidate agent prioritisation, determining how many agents are required for successful biological control, and how to evaluate the success of biological control efforts. Improvements in our theoretical understanding of biological control will undoubtedly reduce costs of biological control programmes, improve success rates, and increase the predictability of biological control.
- Full Text:
- Date Issued: 2017
The reproductive performance, demography and spatial ecology of an extralimital white rhinoceros population
- Authors: Truter, Anja
- Date: 2021-04
- Subjects: White rhinoceros -- South Africa -- Eastern Cape , White rhinoceros -- Effect of poaching on -- South Africa -- Eastern Cape , White rhinoceros -- South Africa -- Eastern Cape -- Reproduction , White rhinoceros -- Dispersal -- South Africa -- Eastern Cape , White rhinoceros -- Food -- South Africa -- Eastern Cape , White rhinoceros -- Behavior -- South Africa -- Eastern Cape , Spatial ecology -- South Africa -- Eastern Cape , Animal populations -- South Africa -- Eastern Cape , Endangered species -- South Africa -- Eastern Cape , Spatial behavior in animals -- South Africa -- Eastern Cape , Shamwari Game Reserve (South Africa)
- Language: English
- Type: thesis , text , Master , MSc
- Identifier: http://hdl.handle.net/10962/177975 , vital:42895
- Description: The white rhinoceros (Ceratotherium simum) (hereafter rhino) is under threat of becoming extinct due to continued poaching for its horns. In South Africa and elsewhere in Africa private landowners have, over the last few decades, contributed to the conservation of various species, including rhinos, even in areas where they have not occurred historically (i.e., where they are extralimital). Unfortunately, very few studies have investigated the conservation contribution of extralimital white rhinos on private reserves to the overall meta-population and/or their reproductive performance. The first aim of my study was therefore to determine whether or not the white rhinos introduced to a private game reserve in the Eastern Cape Province in 1992 have been successful from a reproductive perspective. I calculated inter-calving intervals, age at first calving, conception period, sex ratio, fecundity and fertility rates for white rhinos over this 28-year period. The average annual population growth rate for the rhinos was 10%, which is higher than the recommended 5% by the Rhino Management Group. Trends in density-dependent parameters such as age at first calving and inter-calving intervals also indicated that my study population is still well below carrying capacity for white rhinos and is contributing positively to white rhino conservation in South Africa. The second aim of my study was to investigate home range size and vegetation preferences of white rhinos. Home ranges were mostly larger for all age groups compared to rhinos in their native range. Previously cultivated lands (dominated by several grass species) were preferred by all rhino age groups. The rehabilitation of these previous agricultural-based pastures has likely contributed to the successful introduction of the white rhino as an extralimital megaherbivore in the Eastern Cape. I conclude that although extralimital white rhino populations in the Eastern Cape can be successful from a reproductive perspective, their potential impact on the indigenous biodiversity of the region should be a key future research priority. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-04
- Authors: Truter, Anja
- Date: 2021-04
- Subjects: White rhinoceros -- South Africa -- Eastern Cape , White rhinoceros -- Effect of poaching on -- South Africa -- Eastern Cape , White rhinoceros -- South Africa -- Eastern Cape -- Reproduction , White rhinoceros -- Dispersal -- South Africa -- Eastern Cape , White rhinoceros -- Food -- South Africa -- Eastern Cape , White rhinoceros -- Behavior -- South Africa -- Eastern Cape , Spatial ecology -- South Africa -- Eastern Cape , Animal populations -- South Africa -- Eastern Cape , Endangered species -- South Africa -- Eastern Cape , Spatial behavior in animals -- South Africa -- Eastern Cape , Shamwari Game Reserve (South Africa)
- Language: English
- Type: thesis , text , Master , MSc
- Identifier: http://hdl.handle.net/10962/177975 , vital:42895
- Description: The white rhinoceros (Ceratotherium simum) (hereafter rhino) is under threat of becoming extinct due to continued poaching for its horns. In South Africa and elsewhere in Africa private landowners have, over the last few decades, contributed to the conservation of various species, including rhinos, even in areas where they have not occurred historically (i.e., where they are extralimital). Unfortunately, very few studies have investigated the conservation contribution of extralimital white rhinos on private reserves to the overall meta-population and/or their reproductive performance. The first aim of my study was therefore to determine whether or not the white rhinos introduced to a private game reserve in the Eastern Cape Province in 1992 have been successful from a reproductive perspective. I calculated inter-calving intervals, age at first calving, conception period, sex ratio, fecundity and fertility rates for white rhinos over this 28-year period. The average annual population growth rate for the rhinos was 10%, which is higher than the recommended 5% by the Rhino Management Group. Trends in density-dependent parameters such as age at first calving and inter-calving intervals also indicated that my study population is still well below carrying capacity for white rhinos and is contributing positively to white rhino conservation in South Africa. The second aim of my study was to investigate home range size and vegetation preferences of white rhinos. Home ranges were mostly larger for all age groups compared to rhinos in their native range. Previously cultivated lands (dominated by several grass species) were preferred by all rhino age groups. The rehabilitation of these previous agricultural-based pastures has likely contributed to the successful introduction of the white rhino as an extralimital megaherbivore in the Eastern Cape. I conclude that although extralimital white rhino populations in the Eastern Cape can be successful from a reproductive perspective, their potential impact on the indigenous biodiversity of the region should be a key future research priority. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-04
A study of the Pycnonotus bulbul species complex in Southern Africa
- Authors: Lloyd, Penn
- Date: 1995
- Subjects: Bulbuls -- Ecology -- South Africa -- Eastern Cape , Songbirds -- Ecology -- South Africa -- Eastern Cape , Birds -- Ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5782 , http://hdl.handle.net/10962/d1005470 , Bulbuls -- Ecology -- South Africa -- Eastern Cape , Songbirds -- Ecology -- South Africa -- Eastern Cape , Birds -- Ecology -- South Africa -- Eastern Cape
- Description: The three Pycnonotus bulbuls endemic to Africa, P. barbatus, P. nigricans and P. capensis, occupy mutually exclusive distributions in southern Africa. These species are closely related and appear to occupy very similar ecological niches, only in different regions. Using a multifaceted approach, this study attempts to explain the ecology of this species complex. All three species show similar physiological responses to temperature extremes, and are therefore unlikely to be directly limited by environmental temperature. However, their distributions are highly correlated to a complex of environmental variables, particularly winter minimum temperatures, the coefficient of variation in mean annual rainfall, and the seasonality of rainfall. This combination of environmental parameters can be used to predict the distributions of at least one of the species, P. nigricans, accurately. An analysis of the vocalizations and behaviour of the three species revealed that, whilst P. capensis has a number of recognizably different vocalizations, those of P. barbatus and P. nigricans are very similar. The three have nearly identical behaviours, particularly courtship and pre-copulatory behaviours. The mate recognition systems of the three are therefore extremely similar. P. barbatus is territorial during the breeding season, and exhibits highly structured-variation in male territorial song at the level of the local neighbourhood. The literature pertaining to song dialects is reviewed, and a new hypothesis is postulated to explain song-matching in terms of neighbour/stranger discrimination and the possible existence of cooperative territory defence. A survey of the eastern Cape region, where all three species come into contact, showed that extensive hybridization is taking place between each species pair. Phenotypically, this hybridization is restricted to narrow hybrid zones, that are considered to be stable in both time and place. The evolutionary and ecological significance of these zones to the distributions of the species is discussed, and it is proposed that the zones are maintained by selection acting on differentially-adapted genomes along an environmental gradient.
- Full Text:
- Date Issued: 1995
- Authors: Lloyd, Penn
- Date: 1995
- Subjects: Bulbuls -- Ecology -- South Africa -- Eastern Cape , Songbirds -- Ecology -- South Africa -- Eastern Cape , Birds -- Ecology -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5782 , http://hdl.handle.net/10962/d1005470 , Bulbuls -- Ecology -- South Africa -- Eastern Cape , Songbirds -- Ecology -- South Africa -- Eastern Cape , Birds -- Ecology -- South Africa -- Eastern Cape
- Description: The three Pycnonotus bulbuls endemic to Africa, P. barbatus, P. nigricans and P. capensis, occupy mutually exclusive distributions in southern Africa. These species are closely related and appear to occupy very similar ecological niches, only in different regions. Using a multifaceted approach, this study attempts to explain the ecology of this species complex. All three species show similar physiological responses to temperature extremes, and are therefore unlikely to be directly limited by environmental temperature. However, their distributions are highly correlated to a complex of environmental variables, particularly winter minimum temperatures, the coefficient of variation in mean annual rainfall, and the seasonality of rainfall. This combination of environmental parameters can be used to predict the distributions of at least one of the species, P. nigricans, accurately. An analysis of the vocalizations and behaviour of the three species revealed that, whilst P. capensis has a number of recognizably different vocalizations, those of P. barbatus and P. nigricans are very similar. The three have nearly identical behaviours, particularly courtship and pre-copulatory behaviours. The mate recognition systems of the three are therefore extremely similar. P. barbatus is territorial during the breeding season, and exhibits highly structured-variation in male territorial song at the level of the local neighbourhood. The literature pertaining to song dialects is reviewed, and a new hypothesis is postulated to explain song-matching in terms of neighbour/stranger discrimination and the possible existence of cooperative territory defence. A survey of the eastern Cape region, where all three species come into contact, showed that extensive hybridization is taking place between each species pair. Phenotypically, this hybridization is restricted to narrow hybrid zones, that are considered to be stable in both time and place. The evolutionary and ecological significance of these zones to the distributions of the species is discussed, and it is proposed that the zones are maintained by selection acting on differentially-adapted genomes along an environmental gradient.
- Full Text:
- Date Issued: 1995
The biology of Acia lineatifrons (Naude) (Homoptera : Cicadellidae) on grapevines in the Western Cape
- Authors: Marais, Elleunorah
- Date: 1988
- Subjects: Homoptera
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5597 , http://hdl.handle.net/10962/d1002047
- Description: The leafhopper, Acia lineatifrons (Naude) was identified as a pest on grapevines near Tulbagh in 1978 and has since been reported on grapevines all over the South Western Cape. A. lineatifrons causes browning of the leaves which often results in the shedding of the discoloured leaves. Heavy defoliation before harvest can result in sunburn damage to the grapes, whilst premature leaf loss after harvest adversely affects the ripening of the canes and the accumulation of reserves. This project was aimed at obtaining basic information on the biology and population dynamics of A. lineatifrons as well as to identify priorities for future research. This information is needed to develop a reliable crop-linked predictive model, methods for monitoring pest populations as well as to develop efficient short- and long-term control measures and pest management strategies. The life cycle of A. lineatifrons was studied in the laboratory. At 26°C the mean incubation period of the eggs was nine to eleven days, the mean developmental period for the five nymphal instars was 15 days and the minimum pre-oviposition period five to ten days. This adds up to a mean generation time of 29 to 36 days at 26°C. At 20°C the mean nymphal development period was 25 days, confirming the strong influence of temperature on the development rate. Fecundity was determined in the laboratory as the number of nymphs produced per female. The mean of 8,5 nymphs per female recorded at 26°C is very low compared to that of other leafhopper species (see Appendix 2). The low fecundity measured was most likely due to sub-optimal environmental conditions in the laboratory, a reduction in the suitability of the host plant under these conditions and handling of the females. The seasonal occurrence of A. lineatifrons on grapevines was studied over three seasons. It was found that the leafhoppers overwinter in the adult stage on indigenous Rubus spp, and that they enter the vineyard from the end of October until the beginning of November. Peak populations occurred between the middle of February and the end of March after which the population declined steadily towards the end of the season as the vine leaves were shed. The sex ratio of the overwintering population on R. chrysocarpus was heavily female biased, possibly due to differential mortality of the sexes. During the growing season the sex ratio was slightly male biased and reached equality on several occasions, both on the Rubus and on the grapevines. The movement of A. lineatifrons between the Rubus and the grapevines was investigated, but no evidence of a directional migration from the Rubus to the grapevines was found. Furthermore, no evidence was found to indicate that morphologically distinct short- and long-distance fliers, as found in Cicadulina species by Rose (1972b), exist in the A. lineatifrons population. Host preference tests also showed that adult leafhoppers apparently have no significant preference for grapevines to Rubus or vice versa. It seems, therefore, that the leafhoppers' move onto the grapevines at the beginning of the growing season is not prompted by a host preference. Chaboussou (1971) suggested that certain organic fungicides may cause leafhopper outbreaks because they affect the suitability of the vines as host plants and alter leafhopper fecundity. The effect of Mikal-M (active ingredient Fosetyl AL/Mancozeb), a systemic dithiocarbanate fungicide, on A. lineatifrons was investigated. Laboratory experiments showed no significant effect on fecundity and leaf analysis of potted vines treated with Mikal-M indicated no significant difference in total leaf nitrogen compared to untreated control plants. However, the field experiment on the effect of Mikal-M on the population build-up of the leafhopper showed that significantly more leafhoppers occurred on the vines treated with Mikal-M than on those treated with a conventional inorganic fungicide, copper oxychloride. In view of the far-reaching implications this can have on the viticultural industry, further research on the effects of organic fungicides on leafhopper populations is recommended to confirm the generality of these results so that recommendations regarding the use of these fungicides may be made. The question as to why A. lineatifrons became a pest only recently was raised. Three possibilities were considered, namely (1) that A. lineatifrons is a species of tropical origin which moved down the continent and became established in the Western Cape only recently, (2) that is has been in the Western Cape at least as long as the grapevines, but required prolonged exposure to establish itself on the new host and (3) that is has been on the vines for some time, but was noticed only recently when outbreaks occurred. These outbreaks could have been caused by the introduction of organic fungicides or the depletion of natural enemies by insecticides used to control other insects in the vineyards. Due to the lack of evidence this question could not be answered conclusively. Other research priorities that were established are the development of methods for damage assessment and monitoring of leafhopper populations, determining if A. lineatifrons can transmit grapevine virusses, the development of an economic threshold level and the identification of natural enemies of A. lineatifrons to enable the development of efficient pest management strategies (Summary, p. 63-65)
- Full Text:
- Date Issued: 1988
- Authors: Marais, Elleunorah
- Date: 1988
- Subjects: Homoptera
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5597 , http://hdl.handle.net/10962/d1002047
- Description: The leafhopper, Acia lineatifrons (Naude) was identified as a pest on grapevines near Tulbagh in 1978 and has since been reported on grapevines all over the South Western Cape. A. lineatifrons causes browning of the leaves which often results in the shedding of the discoloured leaves. Heavy defoliation before harvest can result in sunburn damage to the grapes, whilst premature leaf loss after harvest adversely affects the ripening of the canes and the accumulation of reserves. This project was aimed at obtaining basic information on the biology and population dynamics of A. lineatifrons as well as to identify priorities for future research. This information is needed to develop a reliable crop-linked predictive model, methods for monitoring pest populations as well as to develop efficient short- and long-term control measures and pest management strategies. The life cycle of A. lineatifrons was studied in the laboratory. At 26°C the mean incubation period of the eggs was nine to eleven days, the mean developmental period for the five nymphal instars was 15 days and the minimum pre-oviposition period five to ten days. This adds up to a mean generation time of 29 to 36 days at 26°C. At 20°C the mean nymphal development period was 25 days, confirming the strong influence of temperature on the development rate. Fecundity was determined in the laboratory as the number of nymphs produced per female. The mean of 8,5 nymphs per female recorded at 26°C is very low compared to that of other leafhopper species (see Appendix 2). The low fecundity measured was most likely due to sub-optimal environmental conditions in the laboratory, a reduction in the suitability of the host plant under these conditions and handling of the females. The seasonal occurrence of A. lineatifrons on grapevines was studied over three seasons. It was found that the leafhoppers overwinter in the adult stage on indigenous Rubus spp, and that they enter the vineyard from the end of October until the beginning of November. Peak populations occurred between the middle of February and the end of March after which the population declined steadily towards the end of the season as the vine leaves were shed. The sex ratio of the overwintering population on R. chrysocarpus was heavily female biased, possibly due to differential mortality of the sexes. During the growing season the sex ratio was slightly male biased and reached equality on several occasions, both on the Rubus and on the grapevines. The movement of A. lineatifrons between the Rubus and the grapevines was investigated, but no evidence of a directional migration from the Rubus to the grapevines was found. Furthermore, no evidence was found to indicate that morphologically distinct short- and long-distance fliers, as found in Cicadulina species by Rose (1972b), exist in the A. lineatifrons population. Host preference tests also showed that adult leafhoppers apparently have no significant preference for grapevines to Rubus or vice versa. It seems, therefore, that the leafhoppers' move onto the grapevines at the beginning of the growing season is not prompted by a host preference. Chaboussou (1971) suggested that certain organic fungicides may cause leafhopper outbreaks because they affect the suitability of the vines as host plants and alter leafhopper fecundity. The effect of Mikal-M (active ingredient Fosetyl AL/Mancozeb), a systemic dithiocarbanate fungicide, on A. lineatifrons was investigated. Laboratory experiments showed no significant effect on fecundity and leaf analysis of potted vines treated with Mikal-M indicated no significant difference in total leaf nitrogen compared to untreated control plants. However, the field experiment on the effect of Mikal-M on the population build-up of the leafhopper showed that significantly more leafhoppers occurred on the vines treated with Mikal-M than on those treated with a conventional inorganic fungicide, copper oxychloride. In view of the far-reaching implications this can have on the viticultural industry, further research on the effects of organic fungicides on leafhopper populations is recommended to confirm the generality of these results so that recommendations regarding the use of these fungicides may be made. The question as to why A. lineatifrons became a pest only recently was raised. Three possibilities were considered, namely (1) that A. lineatifrons is a species of tropical origin which moved down the continent and became established in the Western Cape only recently, (2) that is has been in the Western Cape at least as long as the grapevines, but required prolonged exposure to establish itself on the new host and (3) that is has been on the vines for some time, but was noticed only recently when outbreaks occurred. These outbreaks could have been caused by the introduction of organic fungicides or the depletion of natural enemies by insecticides used to control other insects in the vineyards. Due to the lack of evidence this question could not be answered conclusively. Other research priorities that were established are the development of methods for damage assessment and monitoring of leafhopper populations, determining if A. lineatifrons can transmit grapevine virusses, the development of an economic threshold level and the identification of natural enemies of A. lineatifrons to enable the development of efficient pest management strategies (Summary, p. 63-65)
- Full Text:
- Date Issued: 1988
A study of coeval sibling cannibalism in larval and juvenile fishes and its control under culture conditions
- Authors: Pienaar, Anthony Graham
- Date: 1990
- Subjects: Fishes -- Behavior , Fishes -- Larvae , Fish culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5781 , http://hdl.handle.net/10962/d1005469 , Fishes -- Behavior , Fishes -- Larvae , Fish culture
- Description: The primary objective of this study was to examine environmental parameters thought to affect cannibalism in certain fish species. It was found that environmental, behavioural, genetic and physiological factors all affect cannibalism in the species exhibiting the phenomenon. The diversity of factors nfluencing cannibalism served to illustrate the complexity of this behaviour pattern. Feeding to satiation was found to suppress cannibalism in catfish, trout and koi carp. High population densities were found to increase the rate of cannibalism, thereby acting as a population regulation mechanism for catfish, trout and the common and koi carps. Live food, as compared with dry pelletized feed was found to significantly suppress cannibalistic aggression. Catfish grown in total darkness, provided with refuges and living in turbid conditions were found to exhibit lowered cannibalistic and territorial aggression. Various lines of evidence suggested that cannibalism has a genetic basis, as was shown by the differences in cannibalistic behaviour of the two strains of Cyprinus carpio, viz. common and koi carp, with cannibalism being higher in the latter. This finding substantiates the hypothesis that cannibalism is genetically controlled and therefore open to evolutionary change. It is concluded that cannibalism is adaptive in times of food limitation, but that it is merely a by-product of normal feeding behaviour when food is abundant. Since cannibalism is advantageous and thus adaptive, the question arises ai to whether selection is occurring at the individual or the population level (or both). It was concluded that it is acting at the individual level, and that any benefits accruing at the population level iv were simply the effect of the initial cause, viz. individual selection. One of the aims of this study was to determine whether cannibalistic tendencies in fish are influenced by differing life history style trajectories. Based on the results of this study it is hypothesized that cannibalism is an r-selected trait. wi th the understanding gained from the knowl edge of the fundamental principles governing cannibalism, certain recommendations for its control in fish culture could be made. It is, however, imperative that further intensive studies be carried out to understand more fully this complex subject. General "rules" for regulating cannibalism could be helpful for any given cannibalistic species. However, in considering the differing life-history styles of each species, it becomes evident that species-specific guidelines need to be worked out. Until then, any suggestions for cannibalistic control offered to the aquaculturist can only serve as unrefined tools.
- Full Text:
- Date Issued: 1990
- Authors: Pienaar, Anthony Graham
- Date: 1990
- Subjects: Fishes -- Behavior , Fishes -- Larvae , Fish culture
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5781 , http://hdl.handle.net/10962/d1005469 , Fishes -- Behavior , Fishes -- Larvae , Fish culture
- Description: The primary objective of this study was to examine environmental parameters thought to affect cannibalism in certain fish species. It was found that environmental, behavioural, genetic and physiological factors all affect cannibalism in the species exhibiting the phenomenon. The diversity of factors nfluencing cannibalism served to illustrate the complexity of this behaviour pattern. Feeding to satiation was found to suppress cannibalism in catfish, trout and koi carp. High population densities were found to increase the rate of cannibalism, thereby acting as a population regulation mechanism for catfish, trout and the common and koi carps. Live food, as compared with dry pelletized feed was found to significantly suppress cannibalistic aggression. Catfish grown in total darkness, provided with refuges and living in turbid conditions were found to exhibit lowered cannibalistic and territorial aggression. Various lines of evidence suggested that cannibalism has a genetic basis, as was shown by the differences in cannibalistic behaviour of the two strains of Cyprinus carpio, viz. common and koi carp, with cannibalism being higher in the latter. This finding substantiates the hypothesis that cannibalism is genetically controlled and therefore open to evolutionary change. It is concluded that cannibalism is adaptive in times of food limitation, but that it is merely a by-product of normal feeding behaviour when food is abundant. Since cannibalism is advantageous and thus adaptive, the question arises ai to whether selection is occurring at the individual or the population level (or both). It was concluded that it is acting at the individual level, and that any benefits accruing at the population level iv were simply the effect of the initial cause, viz. individual selection. One of the aims of this study was to determine whether cannibalistic tendencies in fish are influenced by differing life history style trajectories. Based on the results of this study it is hypothesized that cannibalism is an r-selected trait. wi th the understanding gained from the knowl edge of the fundamental principles governing cannibalism, certain recommendations for its control in fish culture could be made. It is, however, imperative that further intensive studies be carried out to understand more fully this complex subject. General "rules" for regulating cannibalism could be helpful for any given cannibalistic species. However, in considering the differing life-history styles of each species, it becomes evident that species-specific guidelines need to be worked out. Until then, any suggestions for cannibalistic control offered to the aquaculturist can only serve as unrefined tools.
- Full Text:
- Date Issued: 1990
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
Studies on the effects of microclimates on the distribution of larval ticks in the Eastern Cape Province
- Authors: Kraft, Mary Kay
- Date: 1962
- Subjects: Ticks -- South Africa -- Eastern Cape , Ticks -- Ecology -- South Africa -- Eastern Cape , Ticks -- South Africa -- Eastern Cape -- Geographical distribution , Ticks -- Control -- South Africa -- Eastern Cape , Ixodidae -- South Africa -- Eastern Cape , Microclimatology -- Research -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5898 , http://hdl.handle.net/10962/d1013469
- Description: 1. In studying the effects of micro-climates on the distribution of larval ticks in the Eastern Cape Province four species were considered, namely, Boophilus decoloratus (Koch), Rhipicephalus evertsi (Neu), Amblyomma hebraeum (Koch) and Ixodes pilosus (Koch). 2. Three types of investigation were made:- i) autumn and spring surveys of the distribution of larval clusters, which were assumed to be close to positions in which egg-masses had been laid. - (Four species); ii) observations on the survival and development of eggs and engorged female ticks in microclimatically distinct field plots. - (Four species); iii) observations on the behaviour of the larvae and of the engorged female ticks. - (B. decoloratus). 3. The survey and plot data suggest that in autumn larval clusters of I. pilosus were to be found only in well-shaded situations because more exposed places were micro-climatically unfavourable to the survival of earlier stages. 4. The surveys show that in spring 1957 larval clusters of I. pilosus were to be found in unshaded, as well as in shaded, situations. 5. The survey and plot data indicate that the winter of 1957 was not favourable to the development of larvae of B. decoloratus, and that in spring new larval clusters may be expected to appear first in the warmest situations and later in the generally cooler places. 6. The plot data show that during hot and dry periods exposed situations were unfavourable to tho engorged females and eggs of all four species considered, but that during such periods these stages could sometimes survive in well-shaded places. 7. The survey and plot data show that in autumn and in spring larval clusters of B. decoloratus and R. evertsi may be present in unshaded situations. 8. The plot investigations provide little information about the distribution of larval clusters of A. hebraeum, but the survey data suggest that it is not remarkably different from that of B. decaloratus and R. evertsi. 9. There is a discrepancy in the survey and plot data: the surveys show that larval clusters of R. evertsi, and B. decoloratus were rare or absent from well-shaded situations, whereas tho plot data suggest such situations were micro-climatically favourable to larval developmcnt during the months preceding Autumn. 10. The observations on the behaviour of larvae and engorged females of B. decoloratus provide information which suggests that the behaviour of those stages may account for the rarity of larval clusters in well-shaded places. 11. The relative density of larval clusters of B. decoloratus is evidently also affected by factors other than micro-climate . The dropping- off behaviour of engorged female ticks appears to be possibly important in this.
- Full Text:
- Date Issued: 1962
- Authors: Kraft, Mary Kay
- Date: 1962
- Subjects: Ticks -- South Africa -- Eastern Cape , Ticks -- Ecology -- South Africa -- Eastern Cape , Ticks -- South Africa -- Eastern Cape -- Geographical distribution , Ticks -- Control -- South Africa -- Eastern Cape , Ixodidae -- South Africa -- Eastern Cape , Microclimatology -- Research -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5898 , http://hdl.handle.net/10962/d1013469
- Description: 1. In studying the effects of micro-climates on the distribution of larval ticks in the Eastern Cape Province four species were considered, namely, Boophilus decoloratus (Koch), Rhipicephalus evertsi (Neu), Amblyomma hebraeum (Koch) and Ixodes pilosus (Koch). 2. Three types of investigation were made:- i) autumn and spring surveys of the distribution of larval clusters, which were assumed to be close to positions in which egg-masses had been laid. - (Four species); ii) observations on the survival and development of eggs and engorged female ticks in microclimatically distinct field plots. - (Four species); iii) observations on the behaviour of the larvae and of the engorged female ticks. - (B. decoloratus). 3. The survey and plot data suggest that in autumn larval clusters of I. pilosus were to be found only in well-shaded situations because more exposed places were micro-climatically unfavourable to the survival of earlier stages. 4. The surveys show that in spring 1957 larval clusters of I. pilosus were to be found in unshaded, as well as in shaded, situations. 5. The survey and plot data indicate that the winter of 1957 was not favourable to the development of larvae of B. decoloratus, and that in spring new larval clusters may be expected to appear first in the warmest situations and later in the generally cooler places. 6. The plot data show that during hot and dry periods exposed situations were unfavourable to tho engorged females and eggs of all four species considered, but that during such periods these stages could sometimes survive in well-shaded places. 7. The survey and plot data show that in autumn and in spring larval clusters of B. decoloratus and R. evertsi may be present in unshaded situations. 8. The plot investigations provide little information about the distribution of larval clusters of A. hebraeum, but the survey data suggest that it is not remarkably different from that of B. decaloratus and R. evertsi. 9. There is a discrepancy in the survey and plot data: the surveys show that larval clusters of R. evertsi, and B. decoloratus were rare or absent from well-shaded situations, whereas tho plot data suggest such situations were micro-climatically favourable to larval developmcnt during the months preceding Autumn. 10. The observations on the behaviour of larvae and engorged females of B. decoloratus provide information which suggests that the behaviour of those stages may account for the rarity of larval clusters in well-shaded places. 11. The relative density of larval clusters of B. decoloratus is evidently also affected by factors other than micro-climate . The dropping- off behaviour of engorged female ticks appears to be possibly important in this.
- Full Text:
- Date Issued: 1962
The ichthyofauna associated with Taylor's salt marsh, Kariega estuary (Eastern Cape), South Africa
- Authors: Booth, Tara Loren
- Date: 2009
- Subjects: Fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Salt marsh animals -- South Africa -- Eastern Cape , Eelgrass -- South Africa -- Eastern Cape , Gray mullets -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5710 , http://hdl.handle.net/10962/d1005396 , Fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Salt marsh animals -- South Africa -- Eastern Cape , Eelgrass -- South Africa -- Eastern Cape , Gray mullets -- South Africa -- Eastern Cape
- Description: The spatial and temporal patterns in the ichthyofaunal community composition and structure in Taylor’s salt marsh and adjacent eelgrass beds (Zostera capensis) in the Kariega Estuary, was investigated every two months between May 2006 and March 2007. Total ichthyofaunal abundances and biomass in the salt marsh ranged between 0.55 and 21.7 ind.10m-2 and between 0.03 and 1.9 g.wwt.10m⁻², respectively. There were no significant spatial patterns in the values evident (P > 0.05 in all cases) although seasonal trends were marked, with highest values consistently recorded during the warmer summer months. Investigations into the community structure showed that the ichthyofaunal community within salt marsh was composed almost exclusively of juveniles of estuarine dependant (category II) species, mainly juvenile Mugilidae (<20mm SL) that comprised up to 83% of all fish sampled. Hierarchical cluster analysis and multidimensional scaling did not identify any distinct spatial patterns in the ichthyofaunal community within the salt marsh. The absence of any spatial patterns in the community structure could be related to the absence of any significant spatial patterns in the physico-chemical (temperature, salinity and dissolved oxygen concentrations) and biological (water column and microphytobenthic algal concentrations) variables within the salt marsh (P > 0.05 in all cases). Temporal shifts in the ichthyofaunal community structure within the salt marsh were, however, evident largely reflecting the breeding cycles of individual species within the sub-region. Within the adjacent eelgrass beds, total ichthyofaunal abundances and biomass ranged between 8.4 and 49.4 ind.10m⁻² and between 2.9 and 94.5 g.wwt.10m⁻², respectively. Once again there were no distinct spatial patterns in the abundance and biomass values evident although seasonal patterns were marked. In contrast to the salt marsh, within the in the eelgrass community, there were a large number of adult individuals recorded. Again category II species, the estuarine dependent species, were numerically and gravimetrically dominant. The dominance of category II species reflects the marine dominance of Kariega Estuary. The remaining estuarine utilisation categories did not contribute significantly to abundance or standing stock totals. Hierarchical cluster analysis showed that the salt marsh and eelgrass beds represented two distinct habitats within the Kariega Estuary. Within the salt marsh, the family Mugilidae were numerically dominant contributing 83% of the total catch. Within the eelgrass beds, the sparid, Rhabdosargus holubi and representatives of the family Gobidae contributed 36.3% and 33.9% respectively to the total catch. Estuaries with a wide range of microhabitats have been demonstrated to support a more diverse ichthyofaunal community. Shallow water habitats in general are important areas for juvenile fish within estuaries. Taylor’s salt marsh provides an alternative shallow water habitat, occupied by a distinct ichthyofaunal community composition, with increased food availability and decreased predation pressure, for a wide range of fish species.
- Full Text:
- Date Issued: 2009
- Authors: Booth, Tara Loren
- Date: 2009
- Subjects: Fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Salt marsh animals -- South Africa -- Eastern Cape , Eelgrass -- South Africa -- Eastern Cape , Gray mullets -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5710 , http://hdl.handle.net/10962/d1005396 , Fishes -- South Africa -- Eastern Cape , Estuaries -- South Africa -- Eastern Cape , Fish communities -- South Africa -- Eastern Cape , Salt marsh animals -- South Africa -- Eastern Cape , Eelgrass -- South Africa -- Eastern Cape , Gray mullets -- South Africa -- Eastern Cape
- Description: The spatial and temporal patterns in the ichthyofaunal community composition and structure in Taylor’s salt marsh and adjacent eelgrass beds (Zostera capensis) in the Kariega Estuary, was investigated every two months between May 2006 and March 2007. Total ichthyofaunal abundances and biomass in the salt marsh ranged between 0.55 and 21.7 ind.10m-2 and between 0.03 and 1.9 g.wwt.10m⁻², respectively. There were no significant spatial patterns in the values evident (P > 0.05 in all cases) although seasonal trends were marked, with highest values consistently recorded during the warmer summer months. Investigations into the community structure showed that the ichthyofaunal community within salt marsh was composed almost exclusively of juveniles of estuarine dependant (category II) species, mainly juvenile Mugilidae (<20mm SL) that comprised up to 83% of all fish sampled. Hierarchical cluster analysis and multidimensional scaling did not identify any distinct spatial patterns in the ichthyofaunal community within the salt marsh. The absence of any spatial patterns in the community structure could be related to the absence of any significant spatial patterns in the physico-chemical (temperature, salinity and dissolved oxygen concentrations) and biological (water column and microphytobenthic algal concentrations) variables within the salt marsh (P > 0.05 in all cases). Temporal shifts in the ichthyofaunal community structure within the salt marsh were, however, evident largely reflecting the breeding cycles of individual species within the sub-region. Within the adjacent eelgrass beds, total ichthyofaunal abundances and biomass ranged between 8.4 and 49.4 ind.10m⁻² and between 2.9 and 94.5 g.wwt.10m⁻², respectively. Once again there were no distinct spatial patterns in the abundance and biomass values evident although seasonal patterns were marked. In contrast to the salt marsh, within the in the eelgrass community, there were a large number of adult individuals recorded. Again category II species, the estuarine dependent species, were numerically and gravimetrically dominant. The dominance of category II species reflects the marine dominance of Kariega Estuary. The remaining estuarine utilisation categories did not contribute significantly to abundance or standing stock totals. Hierarchical cluster analysis showed that the salt marsh and eelgrass beds represented two distinct habitats within the Kariega Estuary. Within the salt marsh, the family Mugilidae were numerically dominant contributing 83% of the total catch. Within the eelgrass beds, the sparid, Rhabdosargus holubi and representatives of the family Gobidae contributed 36.3% and 33.9% respectively to the total catch. Estuaries with a wide range of microhabitats have been demonstrated to support a more diverse ichthyofaunal community. Shallow water habitats in general are important areas for juvenile fish within estuaries. Taylor’s salt marsh provides an alternative shallow water habitat, occupied by a distinct ichthyofaunal community composition, with increased food availability and decreased predation pressure, for a wide range of fish species.
- Full Text:
- Date Issued: 2009
Investigation of the larval parasitoids of the false codling moth, Cryptophlebia Leucotreta (Meyrick) (Lepidoptera: Tortricidae), on citrus in South Africa
- Authors: Sishuba, Nomahlubi
- Date: 2004
- Subjects: Cryptophlebia leucotreta , Tortricidae , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Parasitoids , Citrus -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5918 , http://hdl.handle.net/10962/d1016267
- Description: The study examined the larval parasitoids of Cryptophlebia leucotreta (Meyrick) on citrus in South Africa and aimed to improve the existing rearing techniques of C. leucotreta with a view to mass rearing of biological control agents. The biological characteristics of Agathis bishopi Nixon (Hymenoptera: Braconidae) were studied, with an emphasis on parasitism rates in the field, host stage preference, developmental rate, life span and offspring sex ratios. Two larval parasitoids, A. bishopi and Apophua leucotretae (Wilkinson) (Hymenoptera: Ichneumonidae), and an egg parasitoid, Trichogrammatoidea cryptophlebiae Nagaraja (Hymenoptera: Trichogrammatidae), were recorded on C. leucotreta on citrus. A. bishopi was the more abundant of the larval parasitoids and exhibited density dependent parasitism. The highest parasitism rates were observed in December with up to 38% in Sundays River Valley and 34% in Gamtoos River Valley, at a time when the highest false codling moth infestations were observed. Agathis bishopi was recorded only in the Eastern Cape Province. The sex ratio of A. bishopi was biased towards females throughout the study (77% in Gamtoos River Valley and 72% in Sundays River Valley). Agathis bishopi is a solitary, koinobiont, larval-pupal endoparasitoid. The species showed a preference for 1st and 2"d instar hosts. Females regulate the sex of their progeny according to the size and larval stage of the host, ovipositing unfertilised eggs in younger, smaller larvae (1st instars) and fertilised eggs in older, larger larvae (2nd instars). The developmental rate of A. bishopi is in synchrony with that of the moth and adults emerge when adult moths that have escaped parasitism emerge. Agathis bishopi and T. cryptophlebiae compliment each other because they have different niches and strategies of attack. Integrating A. bishopi and T. cryptophlebiae into the management of citrus orchards has potential to suppress false codling moth. Larger rearing containers seemed ideal for large-scale rearing of false codling moth. A higher percentage of adults was obtained from larvae reared in larger containers than in smaller ones. The width of the sponges used as stoppers prevented escape of the larvae. Media prepared in larger containers are easier and simpler to prepare than in smaller ones, thus eliminating many precautions otherwise necessary to prevent contamination. Moth production was greatly reduced by the high concentration of Sporekill used for egg decontamination.
- Full Text:
- Date Issued: 2004
- Authors: Sishuba, Nomahlubi
- Date: 2004
- Subjects: Cryptophlebia leucotreta , Tortricidae , Cryptophlebia leucotreta -- Control , Pests -- Biological control , Parasitoids , Citrus -- Diseases and pests
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5918 , http://hdl.handle.net/10962/d1016267
- Description: The study examined the larval parasitoids of Cryptophlebia leucotreta (Meyrick) on citrus in South Africa and aimed to improve the existing rearing techniques of C. leucotreta with a view to mass rearing of biological control agents. The biological characteristics of Agathis bishopi Nixon (Hymenoptera: Braconidae) were studied, with an emphasis on parasitism rates in the field, host stage preference, developmental rate, life span and offspring sex ratios. Two larval parasitoids, A. bishopi and Apophua leucotretae (Wilkinson) (Hymenoptera: Ichneumonidae), and an egg parasitoid, Trichogrammatoidea cryptophlebiae Nagaraja (Hymenoptera: Trichogrammatidae), were recorded on C. leucotreta on citrus. A. bishopi was the more abundant of the larval parasitoids and exhibited density dependent parasitism. The highest parasitism rates were observed in December with up to 38% in Sundays River Valley and 34% in Gamtoos River Valley, at a time when the highest false codling moth infestations were observed. Agathis bishopi was recorded only in the Eastern Cape Province. The sex ratio of A. bishopi was biased towards females throughout the study (77% in Gamtoos River Valley and 72% in Sundays River Valley). Agathis bishopi is a solitary, koinobiont, larval-pupal endoparasitoid. The species showed a preference for 1st and 2"d instar hosts. Females regulate the sex of their progeny according to the size and larval stage of the host, ovipositing unfertilised eggs in younger, smaller larvae (1st instars) and fertilised eggs in older, larger larvae (2nd instars). The developmental rate of A. bishopi is in synchrony with that of the moth and adults emerge when adult moths that have escaped parasitism emerge. Agathis bishopi and T. cryptophlebiae compliment each other because they have different niches and strategies of attack. Integrating A. bishopi and T. cryptophlebiae into the management of citrus orchards has potential to suppress false codling moth. Larger rearing containers seemed ideal for large-scale rearing of false codling moth. A higher percentage of adults was obtained from larvae reared in larger containers than in smaller ones. The width of the sponges used as stoppers prevented escape of the larvae. Media prepared in larger containers are easier and simpler to prepare than in smaller ones, thus eliminating many precautions otherwise necessary to prevent contamination. Moth production was greatly reduced by the high concentration of Sporekill used for egg decontamination.
- Full Text:
- Date Issued: 2004