Aspects of condition in captive and free-ranging dolphins
- Authors: Young, Deborah Dione
- Date: 1999
- Subjects: Dolphins -- Physiology Dolphins -- Behavior
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5799 , http://hdl.handle.net/10962/d1006117
- Description: Aspects of morphological and physiological condition of captive and net-caught dolphins were studied with respect to age, diet, reproduction and seasonal changes in environmental factors. These investigations aimed to provide base-line data on marine mammal physiological and morphological condition indices and to expand the knowledge of condition assessment of small cetaceans. By examining the interactive nature of animal condition and growth, diet and the environment, the study investigated the potential usefulness of animal condition indices to assess and monitor habitat quality. Base-line values for haematological and blood chemistry parameters were established for five captive bottlenose dolphins (Tursiops truncatus), using monthly blood samples, collected between 1992 and 1995, and corresponding measures of body weight and blubber thickness; feeding, dietary energy intake, water temperature and behavioural and medical records. Curves of best fit were used to interpret trends between leukocytic, haematological and blood chemistry parameters and morphology, diet and water temperature. WBC's and WBC differential cell types were related more distinctly to clinical changes in health, than to condition. RBC, HB and PCV were useful as short-term indicators of nutritional condition, with enhanced haematological status associated with greater food intake and improved diet quality. Weight was a more effective long-term indicator of nutritional status. The importance of blubber thickness measurements as a morphological index of condition was reinforced, with relationships between blubber thickness and haematology highlighting interactions between morphological and physiological condition. The complex interactions between haematology, diet, temperature and weight emphasised the need to account for all influential factors when considering haematological condition. The blood chemistry parameters of serum creatinine, BUN, BUN:creatinine and serum albumin provided the best indication of nutritional condition and diet quality in captive dolphins. Creatinine and BUN:creatinine also reflected changes in morphological condition. Reduced ALP was associated with nutritional stress but was more effectively used as an indication of metabolism and growth activity. LDH and CPK were highly variable and fluctuated with changing activity levels, limiting their use as condition indices. Serum sodium was an important indication of diet quality and hydration status. Many of these parameters effectively illustrated that physiological condition is compromised outside of the thermoneutral zone of the species. Bottlenose and common (Delphinus delphis) dolphins, incidentally caught in shark nets, were used to investigate the condition of free-ranging dolphins. Blood samples, taken as soon as possible after capture from drowned animals, were used to analyse physiological parameters. Dissections provided morphological data. Age and dietary status were assessed using growth layer groups in teeth and stomach content analyses, respectively. Morphological measures of net-caught dolphins reflected important interactions with diet, water temperature and reproductive status. Weight, girth and blubber thickness were valuable indicators of condition, although blubber thickness and proportional blubber weight were the best indicators of nutritional status. Condition of net-caught dolphins was difficult to assess in terms of leukocytic and haematological parameters. Stress- and post-mortem-associated changes, and variable data, reduced the usefulness of some parameters. WBC counts reflected on immunological status and served to emphasise changes in health, which may lead to deterioration in condition. WBC's showed potential as indicators of habitat quality, in terms of parasite load and/or pollution. Interactions between RBC, HB, PCV, MCV and dietary, morphological and environmental factors proved valuable in the short-term. Several haematological parameters were related to morphological condition, with weight, girth and blubber thickness, showing potential as non-invasive predictors of haematological status. Relationships between haematology and water temperature implied that dolphins have physiological and environmental "zones of comfort", within which condition is optimised. LDH and CPK were elevated by capture stress and post-mortem changes. Serum sodium and plasma glucose were good indicators of short-term nutritional status, but were altered by stress, which reduced their usefulness as condition indicators. BUN, albumin, globulin, albumin:globulin, total cholesterol and triglycerides appeared to be little affected by these changes and are potentially valuable indicators of condition in net-caught and/or free-ranging dolphins, particularly with respect to nutritional condition, and associated changes in morphology. Although data were limited, these parameters show the greatest potential as physiological indicators of animal condition and environmental health. The limitations of this study are recognised, however, results highlight the feasibility of using net-caught specimens to monitor the condition of free-ranging marine mammals, and the marine habitat as a whole. Relationships established in this study will be used to elucidate further on the interactive nature of marine mammal condition and aid in the development of a non-invasive condition assessment technique.
- Full Text:
- Date Issued: 1999
Aspects of reproduction in the four-striped field mouse, Rhabdomys pumilio
- Authors: Jackson, Claire
- Date: 2000
- Subjects: Microtus , Mice , Mice -- Reproduction
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5637 , http://hdl.handle.net/10962/d1005319 , Microtus , Mice , Mice -- Reproduction
- Description: Rhabdomys pumilio, in the Eastern Cape of South Africa, does not use short day length as an inhibitory cue for reproductive activity, and, despite previous records indicating that these mice are strictly seasonal in their reproduction, litters have been found during the winters of some years,both in the Eastern Cape and in the Western Cape. This led me to believe that the reproductive activity of Rhabdomys pumilio is more opportunistic and that the cue or cues used to control reproduction are less predictable and, or more variable than the photoperiod cue used by many seasonally reproducing rodents. Two experiments were conducted, investigating the influence of low ambient temperature (15⁰C)and reduced food availability on the reproductive activity of both male and female four striped field mice. Mice were maintained in one of four conditions (food restricted at 15⁰C, food restricted at 26⁰C, ad lib. food at 15⁰C, and ad lib. food at 26⁰C) for 4 (males) and 8 weeks (females)(photoperiod 12L:12D, humidity 40%). Results indicated that the males reduced their reproductive activity slightly when exposed to either low temperature or low food availability and that maximum inhibition of reproduction occurred when mice were exposed to both low temperature and low food availability. However, female reproductive activity was inhibited when exposed to low food availability, irrespective of the temperature. Both sexes of mice showed varying abilities to resist fat loss and, in the males, the size of the fat store had a significant effect on reproduction. This varying ability to resist fat loss could be related to levels of activity and in the females (where activity was quantified), high activity scores were significantly associated with reproductive inhibition. These results support the hypothesis that reproduction in Rhabdomys pumilio is opportunistic and controlled by the availability of energy. I propose that the females will be more sensitive to reproductive inhibition due to their far greater post-fertilization responsibilities, where the reproductive activity of the females is rapidly inhibited by a reduction in food availability, while the males are less readily inhibited by low food availability or low temperature, unless the change in the controlling factors is severe enough, or prolonged, at which stage their reproductive activity will cease. The significance of opportunistic reproduction in the seasonal but unpredictable climate of the study area is discussed.
- Full Text:
- Date Issued: 2000
Aspects of the biology and ecology of some intertidal Holothurians (Echinodermata) along the Eastern Cape coast of South Africa
- Authors: Foster, Gregory George
- Date: 1994
- Subjects: Echinodermata , Echinodermata -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5638 , http://hdl.handle.net/10962/d1005320 , Echinodermata , Echinodermata -- South Africa
- Description: Four species of dendrochirote holothurians, Roweia stephensoni John, Pseudocnella sykion Lampert, Aslia spyridophora Clark, Roweia frauenfeldi frauenfeldi Ludwig, and one aspidochirote holothurian, Neostichopus grammatus Clark, are common inhabitants of the intertidal regions of the eastern Cape rocky shores of South Africa. All five species are sympatric for most of their geographical distribution. The intertidal distributions, densities and biomasses of R. stephensoni, P. sykion and N. grammatus were examined at six sites from Port Elizabeth to East London in the eastern Cape. At all sites the three species showed similar overlapping zonations with R. stephensoni and P. sykion reaching their highest maximum mean densities and biomasses (drained wet weight) in the lower mid-shore region (401m² and 684g/m², 181m² and 269g/m², respectively at Port Elizabeth), whilst N. grammatus in the low-shore region (61m² and 72g/m², at Port Elizabeth). The highest densities and biomasses of all three species were recorded on boulder shores that had minimal sand inundation. Seasonality of reproduction of R. stephensoni, P. sykion and N. grammatus was compared at Port Elizabeth, using gonad index values, gonadal tubule diameters, egg diameters and spermatozoon content in tubules from January 1992 until August 1993. All three species are dioecious and did not deviate from a 1: 1 sex ratio. Sizes at first sexual maturity were 2.5-2.9 cm³ for R. stephensoni and P. sykion, and 3.0-3.9cm³ for N. grammatus. The gonads of R. stephensoni and P. sykion consist of a bunch of unbranched tubules of equal diameter, with males having more tubules of a smaller diameter than females. By contrast, the gonad of N. grammatus consists of two tufts of multiple branched tubules. All three species followed annual reproductive cycles, and in R. stephensoni and P. sykion gametogenesis occurred from March 1992 until August/September 1992, and maturity was maintained until the main spawning event in January 1993. By contrast, in N. grammatus gametogenesis occurred from July 1992 until September 1992, and maturity was maintained until the main spawning event in December 1992/January 1993. Unlike R. stephensoni and P. sykion the reproductive cycle of N. grammatus was more pronounced, in that the gonad regressed after spawning. Aspects of the feeding biology of R. stephensoni, P. sykion, A. spyridophora, R.ffrauenfeldi and N. grammatus were compared, using the gross buccal tentacle morphology, type and size range of ingested food particles, and gut lengths. Scanning electron microscopy revealed that the buccal tentacles of R. stephensoni, P. sykion and A. spyridophora could be classified as dendritic, branching numerous times with the tips terminating in numerous nodes covered with discs of papillate projections. The buccal tentacle structure of R. f frauenfeldi deviated from the typical dendrochirote dendritic form. The tentacles are stout with few branches which terminate in large bulbous nodes lacking discs of papillate projections. Neostichopus grammatus possesses buccal tentacles that could be classified as peltate, terminating in large nodes which also lacked discs of papillate projections. Roweia stephensoni, P. sykion and A. spyridophora are suspension-feeders, ingesting food particles mostly <53μm in size. Roweia f frauenfeldi was classed as a "heavy" suspension-feeder, ingesting food particles mostly between 250μm-1.18μm, while N. grammatus is a deposit-feeder, ingesting benthic sediments mostly between 106-500μm. The gut lengths of the dendrochirote holothurians were found to be significantly longer than that of the aspidochirote, and may be attributed to the nature of the food ingested.
- Full Text:
- Date Issued: 1994
Aspects of the biology of aestivation in Bulinus (Physopsis) africanus (Krauss) (Gastropoda, Pulmonata)
- Authors: Heeg, J. (Jan)
- Date: 1973
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:21054 , http://hdl.handle.net/10962/6178
- Description: Aestivation, a period of dormancy during hot, dry conditions, is known to occur in both the Prosobranchia and the Pulmonata among freshwater Gastropoda. While there have been numerous accounts, mainly by field ecologists concerned with bilharziasis control, of the survival value of aestivation in the Gastropoda, little is known of its underlying physiological mechanisms. Results of investigations into the physiological basis of aestivation in the freshwater Prosobranchia, confined to the family Ampulariidae, have been conflicting, fundamental differences having been shown to exist between different species of the genus Pila . Only a single comprehensive study, that by von Brand and his coworkers on the planorbid snail Australorbis glabratus*, forms the basis of our knowledge of the aestivation process in the aquatic Pulmonata. In view of the conflicting results obtained in investigations on freshwater Prosobranchia, the general applicability of the findings for Australorbis glabratus to other freshwater Pulmonata was open to question. The present investigation on the planorbid snail Bulinus (Physopsis) afriaanus, a species known to be a successful aestivator, was prompted by the obvious need for a further comprehensive study on an aquatic pulmonate species . The results presented here show that aestivation in this species is a definite physiological state, characterised by a depression of the metabolic rate, which not only aids in husbanding the snails I metabolic resources. during the enforced starvation which must necessarily accompany aestivation, but also constitutes a form of resistance adaptation to the transient high temperatures which aestivating snails are bound to encounter. Loss of body water is shown to be important in initiating aestivation, but it is also the factor most likely to prove lethal during the course of aestivation. The results confirm and extend the earlier findings for Australorbis glabratus. The results are discussed in the context of our present knowledge of aestivation in other Gastropoda, both aquatic and terrestrial, and also in relation to other forms of resistance adaptation. As expected, the investigation raises more questions than it answers, thus directions for further research, arising out of the present findings, are suggested.
- Full Text:
- Date Issued: 1973
Aspects of the biology of Boophilus decoloratus (Koch, 1844) (Acarina : ixodidae)
- Authors: Londt, Jason G H (Jason Gilbert Hayden), 1943-
- Date: 1973
- Subjects: Ixodidae -- Development Ticks -- Development Boophilus -- Development
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5817 , http://hdl.handle.net/10962/d1007202
- Description: 1. The external morphology of all stages in the life cycle of B. decoloratus is described with the aid of scanning electron micrographs. 2. The biological activities of B. decoloratus during its parasitic cycle are examined with special reference to the course of feeding of all stages, and to the influence of the pharate nymph and adult conditions in accelerating the completion of the cycle. 3. The pattern of dropping of replete females is considered in relation to their weight and their time of drop-off. 4. The adult male population structure is described. Two distinct weight groups are reported and the taxonomic significance of these is discussed. 5. The preoviposition period duration of B .decoloratus was studied under laboratory conditions and found to be temperature dependent and humidity independent. Female size, as implied by their engorged weights, influenced the duration of the oviposition period: ticks weighing less than 20 mg possessed longer preoviposition periods. 6. The preoviposition period of B.decoloratus females under fluctuating macroclimatic conditions was studied and found to be long in duration. The implications of this are discussed in relation to laboratory findings and the summer build-up of this species in nature. 7. The duration of the oviposition period of B. decoloratus and the number of eggs produced during this period were studied under laboratory and field conditions. Both these parameters were found to be temperature dependent and uninfluenced by humidity. The significance of a temperature dependent oviposition period is discussed. 8. The minimum amount of 'blood' required by female ticks for oviposition of eggs was found to be approximately 16 mg. under laboratory conditions. 9. The oviposition behaviour of B. decoloratus females has been described and the water relations of ovipositing and non-ovipositing females were examined and discussed . 10. The effects of handling female ticks during their oviposition period was studied and females which were handled were found to produce significantly fewer eggs. The significance of this is discussed. 11. During preliminary experiments on the incubation period of B. decoloratus it was found that the viability of eggs laid during the first half of the oviposlting period was greater than for eggs laid in the second half of the period. The critical temperature of the 'wax' coating of eggs was found to be 42⁰C while the critical humidity was approximately 70% R.H. (7,53 mmHg) at 26⁰C. The implications of these findings are discussed. 12. The development of eggs, traced throughout the incubation period by monitoring the build-up of guanine spectrophotometrically, was studied under different humidity conditions . Successful development was found to be dependent on the water content of the eggs at the time of laying. As eggs were also found to be unable to take up water vapour from the atmosphere this finding is important evidence to support the suggestion that the survival of the egg stage largely determines the spacial distribution of larvae in the field. 13. Results of work done at constant, alternating and naturally fluctuating temperatures and humidities demonstrated that the duration of the incubation period of B.decoloratus is temperature dependent and humidity independent. The significance of this is discussed in relation to the findings of previous workers and to the biology of the species. 14. Egg viability (percentage hatch) was found to be humidity dependent and temperature independent. The implications of these findings are discussed. 15. Some of the problems associated with the assessment of the effects of climatic conditions on ticks are discussed. Special reference has been made to the advocation of using saturation deficit instead of relative humidity as the parameter indicative of environmental humidity in any biological study involving fluctuating humidity conditions. 16. The problems associated with having three variables (e.g. temperature, saturation deficit and incubation period duration) are discussed and reasons given for why contour diagrams have been used in this investigation. 17. A model of the interactions between the main abiotic factors of the environment (temperature and humidity) and the biological parameters studied during the second part of this investigation is presented. 18. The effects of climatic conditions on the life cycle and distribution of B.decoloratus are discussed. Special reference has been made to the available evidence explaining the summer build-up in tick numbers known to occur in nature and the way in which the present findings have helped in an understanding of the spacial distribution of B.decoloratus in the field.
- Full Text:
- Date Issued: 1973
Aspects of the biology of the infaunal bivalve Mollusc Solen cylindraceus (Hanley) in the Kariega estuary
- Authors: De Villiers, Casper Johannes
- Date: 1990
- Subjects: Mollusks -- South Africa -- Eastern Cape Bivalves -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5639 , http://hdl.handle.net/10962/d1005321
- Description: Solen cylindraceus is an infaunal filter-feeding bivalve inhabiting the intertidal mud banks of many southern African estuaries. It is particularly abundant in the Kariega estuary (33°41'S; 26°42'E) where it reaches densities of 400m⁻² (192g shell-free dry wt. m⁻²). The Kariega is a permanently open, marine dominated estuary about 18km in length, and S. cylindraceus is most abundant in its middle and upper reaches. Some physical characteristics of the estuary (temperature, salinity, sediment and water turbidity) are described, and the possible role of these factors in determining the density and distribution of S. cylindraceus within the Kariega estuary, is discussed. The structure of the alimentary system, gills and labial palps of S. cylintfraceus is described, all of which showed no major variation from the "typical" eulamellibranchiate form. Solen cylintfraceus was found to be a euryhaline osmoconformer with a salinity tolerance range of 15-65%. When animals were removed from their burrows, osmotic equilibration of the haemolymph was rapid (1-2 hours). By contrast, in animals left undisturbed in their burrows, osmotic equilibration was retarded (72-204 hours). It is suggested that the observed decrease in the rate of change of haemolymph osmolarity for animals in their burrows is linked to the stability of the interstitial salinity. A temperature tolerance range of 5-44°C was determined for S. cylintfraceus (in situ), in which prolonged exposure to 5°C and 40-45°C (12-36 hours respectively) resulted in a decreased burrowing ability, coma and death. Animal burrowing responses were not affected by temperatures in the range 15-35°C. Field experiments were carried out over several tidal cycles, in which the measurement of crystalline style volume was used as a means of assessing extracellular digestive activity. No major variation in style volume was recorded and it appeared that S. cylindraceus did not exhibit any cyclical pattern of style dissolution and regeneration. It is suggested that S. cylindraceus feeds continuously from the water column during high tide and possibly within its burrow, at or below the water table, during low tide. At a suspensoid concentration of 5Omg l⁻¹, S. cylindraceus was found to filter water almost continuously (90-95% of the time). Time spent filtering dropped to 68% at 100mg l⁻¹ and 32% at 500mg l⁻¹. Filtration rates for summer collected animals (25°C) were 22.86 ± 4.36ml min.⁻¹, some 3ml min.⁻¹ greater than that recorded for winter (16°C) collected animals. Filtration rate may be expressed as a function of shell length by the equations: y=0.247x¹̇⁰⁶⁶ (winter) and y=0.758x⁰̇⁸²⁶ (summer). Solen cylindraceus was capable of acclimating its filtration rate to both high and low temperatures under laboratory conditions. Filtration rate exhibited a thermal optimum in the range 15-35°C, declining at higher and lower temperatures. Q₁₀ values of filtration decreased rapidly from greater than 4 to less than 2, when the thermal optimum was reached. Maximum rates generally occurred at approximately 5°C above the temperature to which the animal had been acclimated. Optimal filtration rates (19-23ml min.⁻¹) were recorded in the salinity range 15-45%. When subjected to abrupt changes in salinity, filtration rates were immediately depressed. The extent and duration of these decreased filtration rates were dependent upon the magnitude and direction of salinity change, and were always less in animals exposed to hyper- than hyposaline conditions. Animals exposed to increased temperature and simultaneous elevated or unchanged salinity, showed a slight increase in filtration rate followed by rapid acclimation. A decrease in both temperature and salinity resulted in an initial decrease in filtration rate and a longer acclimation period. The ability of S. cylindraceus to acclimate fully within a wide temperature and salinity range, and to filter maximally in hypersaline conditions may, in part, explain its unusually high abundance in the Kariega estuary, despite it being close to the southernmost limit of the animal's geographical distribution. No significant difference in flItration rate was recorded at suspensoid concentrations of 5-100mg 1⁻¹. However, at 250 and 500mg l⁻¹ filtration rates decreased significantly, and coincided with increased levels of pseudofaecal production. Solen cylindraceus retained particles down to 2.5-3.0µm with great efficiency (ca. 60-90% efficiency). Below this particle size, retention efficiency decreased rapidly and a net production of particles was recorded below 1.51µm. Particle retention was independent of temperature (15 and 25°C) and salinity (15 and 35%). Use was made of stable carbon isotope analyses (¹³C/¹²C ratios) in an attempt to determine the important food sources of S. cylindraceus within the Kariega estuary. The results obtained demonstrated an enrichment in δ¹³ values for S. cylindraceus from the upper (-27.9%) to the middle (-25%c) and lower (-21.6%o ) reaches of the estuary, with no seasonal variation apparent. The bivalve was substantially more depleted in ¹³C relative to the dominant aquatic macrophytes Zostera capensis (-9.1 to -15.6%o) and Spartina maritima (-12.5%o). The use of δ¹³ alone, however, to unequivocally "pin point" specific food sources of a filter feeder in a predominantly detritus based food web, is limited. It is suggested that in the Kariega estuary, riparian litter and other terrestrially derived vegetation contribute to the carbon pool. A possible contribution of ¹³C depleted food sources via chemoautotrophic and/or anaerobic pathways, to the diet of S. cylindraceus, is suggested.
- Full Text:
- Date Issued: 1990
Aspects of the biology, thermal physiology and nutritional ecology of Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae), a specialist herbivore introduced into South Africa for the biological control of Chromolaena odorata (L.) King and Robinson (Asteraceae)
- Authors: Uyi, Osariyekemwen
- Date: 2015
- Subjects: Chromolaena odorata , Chromolaena odorata -- Biological control -- South Africa , Arctiidae
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5936 , http://hdl.handle.net/10962/d1017916
- Description: Chromolaena odorata (L.) King and Robinson (Asteraceae) is an invasive weedy shrub native to the Americas that has proven to be a significant economic and ecological burden to many tropical and sub-tropical regions of the world where it impacts negatively on agriculture, biodiversity and livelihoods. A distinct biotype of C. odorata was first recognised as naturalized in KwaZulu-Natal (KZN) province, South Africa, in the 1940s and has since spread to other climatically suitable provinces. Pareuchaetes insulata (Walker) (Lepidoptera: Erebidae: Arctiinae) was released in KZN, South Africa, as a biological control agent against the weed between 2001 and 2009. Although the moth did establish at one out of some 30 release sites, its population level is generally low in the field. This thesis attempts to unravel the reasons for the poor performance of P. insulata in South Africa.Studies of life history traits of P. insulata in the laboratory indicated that the moth possess good biological attributes such as low mortality, high fecundity, egg hatchability and high female mating success. Overall, adult female moths eclosed before their male counterparts suggesting the presence of protogyny. Beyond the contribution of this study to our understanding of the life history traits of erebid moths, it hypothesized that the absence of protandry might have contributed to the low population levels of the moth in the field. To determine if a degree of agent-host plant incompatibility is culpable for the poor performance of P. insulata, insect performance metrics were compared on two distinct C. odorata plants (one from Florida and another from South Africa) in laboratory experiments. Pareuchaetes insulata performance metrics were similar on both plant forms; there were no significant differences in total leaf area consumed, egg and larval development, immature survival rates, feeding index (FI), host suitability index (HSI), growth index (GI), and fecundity between the Floridian and southern African C. odorata plants. In sum, there was no evidence to demonstrate that differences in plant forms in C. odorata are culpable for the poor performance of P. insulata in South Africa.The effects of temperature on the developmental and reproductive life history traits, locomotion performance and thermal tolerance range of P. insulata were studied in order to elucidate the possible role of temperature on the poor performance of the moth. The results showed that at temperatures below 25 °C, mortality increased and development time was prolonged. Fecundity and egg hatchability were negatively affected at a constant temperature of 15 °C. Results futher showed that third instar larvae were unable to initiate movement at 6 °C and locomotor abilities were significantly reduced at 11 °C. In sum, it is hypothesized that both direct and indirect negative impacts of low temperature may partly explain the poor performance of P. insulata in South Africa. Theeffects of seasonal and spatial variations in the leaf characteristics of C. odorata on the performance of P. insulata were investigated. Foliar nitrogen and magnesium concentrations were higher in shaded plants during winter due to low temperatures. Leaves of C. odorata plants growing in the shaded habitat (relative to full sun) and leaves of plants during autumn (relative to winter) were more nutritionally balanced and suitable for herbivore performance. Consequently, P. insulata developed faster, had heavier pupal mass and increased fecundity when reared on shaded leaves (relative to full sun) or when reared on autumn leaves compared to leaves growing in winter. This study demonstrates that low winter temperatures can indirectly affect insect herbivore performance by changing the phytochemistry of host plant and hypothesized that excess nitrogen and possibly magnesium may have detrimental effects on the insect herbivore performance.A cross-feeding experiment was conducted to determine P. insulata response to a change in the diet of offspring due to a shift in plant quality in shaded versus full sun habitats. The results showed that a ‘negative switch’ in herbivore diet (i.e. when progeny from parents reared on shaded leaves were fed on full sun leaves) resulted in high (40%) mortality, prolonged development time and reduced fecundity. Thus full sun foliage is an inferior diet for P. insulata offspring. In laboratory experiments, foliar nitrogen was positively correlated with the performance of P. insulata. From this study, it is demonstrably evident that the poor performance of P. insulata on C. odorata in South Africa is caused by multiple factors such as low temperatures as well as spatio-temporal variations in the leaf characteristic of C. odorata leaves. This study shows the complexity of determining the causes of low populations and apparent low impact of biological control agents and herbivorous insects generally, in the field. The implications of this research to the biological control programme against C. odorata and the direction of future research for the control of C. odorata are discussed.
- Full Text:
- Date Issued: 2015
Aspects of the ecology and biology of the isopod, Exosphaeroma hylocoetes, (Barnard, 1940) in three temporarily open/closed southern African estuaries
- Authors: Henninger, Tony Oskar
- Date: 2009
- Subjects: Estuaries -- South Africa -- Eastern Cape Estuarine ecology -- South Africa -- Eastern Cape Isopoda -- South Africa -- Eastern Cape Estuarine biology -- South Africa -- Eastern Cape Ruppia maritima
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5640 , http://hdl.handle.net/10962/d1005322
- Description: Temporarily open/closed estuaries (TOCE’s) are the numerically dominant type of estuary accounting for ≈ 70 % of all estuaries along the South African coastline. Despite their numerical dominance, aspects of the biology of organisms within these systems, particularly macrocrustacea remain poorly understood. This study firstly assessed the abundance and biomass of the most common isopod, Exosphaeroma hylocoetes, in three Eastern Cape TOCE’s, (the West Kleinemonde, East Kleinemonde and Kasouga Estuaries), and their response to mouth breaching events. This study was followed by aspects of the biology of the isopod including their utilisation of submerged macrophytes as a refuge from predation and/or possible food source, as well as the growth rates of the isopods in the laboratory under different environmental conditions. Mean isopod abundances and biomasses ranged between 0 and 4 791 ind. m⁻² and 0 and 9.65 mg dwt. m⁻² in the West Kleinemonde Estuary and between 0 and 108 ind. m⁻² and 0 and 0.318 mg dwt. m⁻² in the nearby East Kleinemonde Estuary. In the Kasouga Estuary, the values ranged between 0 and 3 650 ind. m⁻² and 0 and 5.105 mg dwt. m⁻². Temporal and spatial changes in the abundance and biomass of E. hylocoetes within the three systems was primarily linked to mouth phase, with populations declining when the mouth was open and to a lesser extent, seasonality. In all three estuaries maximum isopod abundances and biomasses were recorded in their middle and upper reaches, which could be ascribed to the presence of submerged macrophytes particularly Ruppia maritima, in two of the estuaries. Males (5.71 ± 0.41 mm) were significantly larger than females (3.99 ± 0.26 mm), but the sex ratios were skewed in favour of females, (a common feature in many isopod populations). Females were found carrying brood throughout the study, releasing offspring directly into the water column, to allow recruitment to the populations. The larger the female, the larger the brood carried (up to a maximum of 72 embryo/mancas). Results of laboratory experiments indicate that the close association of Exosphaeroma hylocoetes with submerged macrophytes is a result of the plant stands providing a refuge against predation by selected ichthyofauna. However stable carbon isotope and fatty acid analyses indicate that E. hylocoetes made use of ephiphytic algae and detritus on the stems of R. maritima, rather than the submerged macrophyte itself. There were no significant differences in the growth rates of male and female isopods at combinations of temperature (15 and 25 °C) and salinity (15 and 35 ‰). Laboratory growth studies revealed that males lived longer than females (25.77 ± 3.40 weeks vs 21.52 ± 3.00 weeks), and therefore achieved larger overall size. Females, however, reached sexual maturity (at 2.5 mm) at a faster rate (two to four weeks) than males (5.5 mm after 6.5 to 11 weeks), dependent on temperature. Exosphaeroma hylocoetes with its association with submerged macrophytes, early maturity, its growth rates and longevity, female-biased sex ratios and year-round breeding, all contribute to its success in temporary open/closed estuaries.
- Full Text:
- Date Issued: 2009
Aspects of the ecology and reproductive biology of the limpet, Helcion pruinosus (Gastropoda : prosobranchia)
- Authors: Henninger, Tony Oskar
- Date: 2000
- Subjects: Prosobranchia , Limpets -- Reproduction , Limpets -- Ecology , Prosobranchia -- Ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5641 , http://hdl.handle.net/10962/d1005323 , Prosobranchia , Limpets -- Reproduction , Limpets -- Ecology , Prosobranchia -- Ecology
- Description: Helcion pruinosus, the rayed limpet, is found in the midshore region of the intertidal zone, (i.e. the Balanoid zone) of rocky shores, from Saldanha Bay to Sodwana Bay along the coast of South Africa. At Gonubie (32°57'S/25°01'E) this species of limpet was found under boulders, (when not feeding), and could reach average densities of 85/ m². The limpets prefer smooth boulders, avoiding those encrusted by coralline algae or boulders with a rough texture. There was no habitat segregation between adult and juvenile H. pruinosus, i.e. there was no sign of up-shore migration by larger individuals. Males out-numbered females by, on average 1.4 : 1, which was a similar sex ratio to that of the congeneric species, H. pectunculus (Gray, 996). Unlike H. pectunculus, there were no differences in shell lengths between males and females (p = 0.946 at Gonubie, south-east coast and p = 0.961 at Kommetjie, south-west coast; t-test). Shell height could also not be used as a criterion to differentiate between the sexes. The average maximum shell length of H. pruinosus at Gonubie and Kommetjie was 25 mm, but the maximum shell lengths found were 30 mm, (one individual in each case), on both the southeast coast and west coast. Growth occurred most rapidly in the first year of life, with individuals reaching 15 mm after 1 year. In the second year limpet growth slowed to only 7 mm. Sexual maturity was reached at a shell length of between 11 to 14 mm (at an age of 8 months to 1 year). The life-span of H. pruinosus was determined at 2.55 years on the south-east coast and 2.9 years on the south-west coast. Micro-growth bands were produced tidally. Growth occurred allometrically, i.e. shell length increased at a faster rate than shell height. The limpets foraged during low tide, at night, presumably feeding on epilithic algae on the boulders. A second smaller peak of limpet activity was often recorded during the day, when low tide coincided with dawn). More limpets (up to ten times more) were active at spring tides compared to neap tides. Limpet activity was greatest during the spring tides of autumn. During all seasons limpet activity peaked 30 minutes before low water, after which numbers decreased rapidly. All limpets had retreated beneath the boulders before being covered by the flooding tide. It was concluded that the limpets were responding to both endogenous and exogenous cues, but the actual stimulus for retreat could not be determined. The limpets did not return to a fixed scar nor did they return rigidly to a home site. H. pruinosus was found to be gonochoristic. Sexes could be separated, on dissection, according to the colour of their gonads (males had white gonads, whilst that of the females was olive-green). Gonads were present throughout the year in most individuals, i.e. totally spent animals were never observed. Reproductive seasonality was similar in west coast and south-east coast animals. The gonad indices of the west coast limpets were higher, (maximum of 35%), compared to that on the southeast coast, (25%). The animals were probably trickle spawners, with some individuals liberating gametes throughout the year. There was however synchrony in gametogenesis between male and female limpets on both the west coast and south-east coast lines. Gonad indices peaked in the summer months (October to December) with a second minor peak in April/May. These peaks occurred before the release of the gametes in spawning events. The gonad index was lowest in winter, (July). The ovaries were full of mature eggs (oocytes having a diameter of 200 to 250 ~) prior to spawning. The acinal wall thickness had been decreasing prior to spawning. After spawning there was an increase in previtellogenic eggs « 100 μm) in females, and an increase in the acinal wall thickness to indicate spermatogenesis. The two populations are subjected to different environmental conditions and the actual cue for stimulating the release of gametes could not be determined. Finally, a table of differences between H pruinosus and its sister species, H pectunculus was created to show the life-style of H pruinosus.
- Full Text:
- Date Issued: 2000
Aspects of the ecology of leopards (Panthera Pardus) in the Little Karoo, South Africa
- Authors: Mann, Gareth
- Date: 2014
- Subjects: Leopard -- South Africa -- Little Karoo Leopard -- Monitoring -- South Africa -- Little Karoo Leopard -- Ecology -- South Africa -- Little Karoo Wildlife monitoring -- South Africa Wildlife conservation -- South Africa Animal populations -- South Africa -- Little Karoo Leopard -- Conservation -- South Africa -- Little Karoo
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5855 , http://hdl.handle.net/10962/d1012241
- Description: Leopards (Panthera pardus) are the most common large predators, free roaming outside of protected areas across most of South Africa. Leopard persistence is attributed to their tolerance of rugged terrain that is subject to less development pressure, as well as their cryptic behaviour. Nevertheless, existing leopard populations are threatened indirectly by ongoing transformation of natural habitat and directly through hunting and conflict with livestock farmers. Together these threats may further isolate leopards to fragmented areas of core natural habitat. I studied leopard habitat preferences, population density, diet and the attitudes of landowners towards leopards in the Little Karoo, Western Cape, South Africa, an area of mixed land-use that contains elements of three overlapping global biodiversity hotspots. Data were gathered between 2010 and 2012 using camera traps set up at 141 sites over an area of ~3100km², GPS tracking collars fitted to three male leopards, scat samples (n=76), interviews with landowners (n=53) analysed in combination with geographical information system (GIS) layers. My results reveal that leopards preferred rugged, mountainous terrain of intermediate elevation, avoiding low-lying, open areas where human disturbance was generally greater. Despite relatively un-fragmented habitat within my study area, the leopard population density (0.75 leopards/100km²) was one of the lowest yet recorded in South Africa. This may reflect low prey densities in mountain refuges in addition to historical human persecution in the area. Currently local landowners are more tolerant of leopards than other wildlife species with incidents of conflict involving leopards being rare relative to black-backed jackals (Canis mesomelas), baboons (Papio hamadryas), caracals (Caracal caracal) and porcupine (Hystrix africaeaustralis). Although current levels of conflict between leopards and stock farmers are low, leopards do depredate livestock, which constitute 10-15% of their diet. Improved livestock husbandry measures and co-operation between conservation authorities and farmers are necessary to mitigate such conflict and balance economic security with biodiversity conservation in the region. Leopards are the only remaining top predators throughout much of the Little Karoo and the Western Cape and as such are predicted to play a critical role in ecosystem structure and the survival of other species. Current high levels of connectivity between areas of suitable leopard habitat bode well for the conservation status of leopards within this region and future conservation efforts need to ensure that narrow corridors linking such habitat are preserved. The potential for leopards to serve as both an umbrella and a flagship species for biodiversity conservation suggests that long term monitoring of this population would be a conservation priority for the Little Karoo.
- Full Text:
- Date Issued: 2014
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
Aspects of the ecology of the shrimp Palaemon pacificus (Stimpson) (Decapoda,Palaemonidae) in the Bushmans river estuary
- Authors: Robertson, Wendy Daryl
- Date: 1984
- Subjects: Shrimps -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5815 , http://hdl.handle.net/10962/d1007184 , Shrimps -- South Africa
- Description: The recruitment of Palaemon pacificus to the Bushmans River estuary was studied over a 12 month period. The dynamics of a population of shrimps in a small, tidal channel in the lower reaches of the estuary was investigated over a similar time span. Temperature and salinity tolerances of various stages and sizes of shrimps were compared in controlled experiments and are discussed in the light of the distribution and general ecology of the shrimp. Stage 6 zoeae and post-larvae entered the estuary on nocturnal flood tides throughout the year with peak recruitment occurring in March/April. The population of shrimps in the study site was predominantly juvenile for most of the year, with peak sub-adult numbers occurring in midsummer. The sex ratio was female-biased throughout the year except for short bursts of male predominance in February and April. Average growth rate was 0,043 mm carapace length per day. Maximum residence time in the study site was estimated to be four months and in the estuary at least six months. Flooding of the estuary resulted in a considerable reduction in juvenile numbers in the study site and some loss of sub-adults. Shrimps tolerated a temperature range of 4,3 to 30,9⁰C for 144 hours. Their long term tolerance range is probably narrower (10 to 28⁰C) because of the effects of temperature related factors such as starvation and disease. Their distribution in South Africa (Olifants River to Kosi Bay ) is consistent with this tolerance range. Sub-adults tolerated salinities of 1 to 79 ‰ and post-larvae 2 to 60 ‰ at 15⁰C for 144 hours. Low moulting success (low and high salinities ) and starvation (high salinities) would probably reduce these tolerance ranges to 2 to 56 ‰ (sub-adults) and 4 to 56 ‰ (post-larvae). Higher and lower temperatures (10 and 20⁰C) reduced the tolerance of post-larvae to low salinities, but sub-adults were only affected at 30⁰C. Stages 4 and 5 and stage 6 zoeae were intolerant of salinities below 14 ‰. The development of salinity tolerance with age is consistent with the retention of a marine breeding phase. It also explains the high loss of juveniles from the study site following the flood. It is postulated that recovery of the population after a flood would be fairly rapid except in extreme cases when estuarine vegetation is severely affected.
- Full Text:
- Date Issued: 1984
Aspects of the population ecology, habitat use and behaviour of the endangered Knysna seahorse (Hippocampus capensis Boulenger, 1900) in a residential marina estate, Knysna, South Africa: implications for conservation
- Authors: Claassens, Louw
- Date: 2018
- Subjects: Endangered species -- South Africa -- Knysna , Sea horses -- Behavior -- South Africa -- Knysna , Sea horses -- Habitat -- South Africa -- Knysna , Sea horses -- Ecology -- South Africa -- Knysna
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/54789 , vital:26616
- Description: The Knysna seahorse Hippocampus capensis is South Africa’s only endemic seahorse species, and is found in only three adjacent estuaries along the southern coast. The conservation of this endangered species is important on a national and international level. This study presents the first research on this species within the Knysna estuary since 2001 and specifically focuses on aspects of its ecology within a residential marina estate (Thesen Islands Marina). The physico-chemical and habitat features of the marina were described and the population ecology, habitat use, and behaviour of the Knysna seahorse were investigated. Physico-chemical conditions within the western section of the marina, characterised by high water current velocities, were similar to that of the adjacent estuary. The eastern section of the marina was characterised by lower water current velocities and higher turbidity. Four major habitat types were identified within the marina canals: (I) artificial Reno mattress (wire baskets filled with rocks); (II) Codium tenue beds; (III) mixed vegetation on sediment; and (IV) barren canal floor. Seahorse densities within the marina were significantly higher compared to densities found historically within the estuary. Highest seahorse densities were specifically found within the artificial Reno mattress structures and within the western section of the marina. Seahorse density varied spatially and temporally and the type of habitat was an important predictor for seahorse occurrence. An experimental investigation found that H. capensis chooses artificial Reno mattress habitat over Zostera capensis when given a choice. GoPro cameras were used successfully to investigate daytime seahorse behaviour within the Reno mattress habitat. Seahorses were more active during the morning, spent most of their time (> 80 %) feeding, and morning courting behaviour for this species were confirmed. However, during the summer holiday period (mid-December to mid-January) few seahorses were observed on camera, which suggests that the increase in motor boat activity and the related increase in noise had a negative effect on H. capensis feeding and courting behaviour. The marina development, and in particular the Reno mattresses, created a new habitat for this endangered species within the Knysna estuary. In addition to the protection and restoration of natural habitats in which H. capensis is found, the conservation potential of artificial structures such as Reno mattresses should be realised.
- Full Text:
- Date Issued: 2018
Aspects of the structure and function of some gastropod columellar muscles (Mollusca)
- Authors: Frescura, Mandy
- Date: 1991
- Subjects: Gastropoda -- Research Mollusks -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5642 , http://hdl.handle.net/10962/d1005324
- Description: The columellar muscle of both limpets and coiled shell gastropods is of the paramyosin smooth type. Collagen forms an integral part of the musculature constituting about 35% of the tissue. In limpets, muscle organisation is typical of a muscular hydrostat. Tightly packed blocks of muscle, dense arrays of cross-linked collagen, large muscle cells (9 µm diameter) and thick filaments (70 nm diameter, 30 µm long) produce a tough, relatively rigid but powerful muscle. In coiled shell gastropods, muscle organisation is intermediate between a muscular and a fluid hydrostat. Finer muscle cells (6 µm diameter), thick filaments (60 nm diameter) and a loose intercellular network of collagen interspersed with fluid vesicles are features of a more pliable and extensible muscle. In addition, ultrastructural differences, such as larger numbers of mitochondria and sarcolemmal invaginations distinguish the tarsal from the columellar muscle in both limpets and coiled shell gastropods. About 25% of muscle cells in most species examined, contain a novel arrangement of thin filaments with periodic electron-dense regions. These are similar in appearance to intrafusal cells and stress-fibres of non-muscle cells. Structural analysis of isolated filaments, optical diffraction and SDS gel electrophoresis confirm the, large dimensions and the paramyosin nature of the thick filaments. Microdensitometry of the gel proteins confirms the high proportion of collagen present. No significant differences in muscle ultrastructure were found between limpets from different tidal heights. Muscle attachment areas are shown to be species-specific and positively correlated to tenacity and wave exposure. The muscle attachment mechanism is similar to that described for other molluscs. It consists of a special epithelial layer and a mucous-like material at the muscle-shell interface that possibly has an adhesive function. Although the ultrastructure of Patella is very similar to that of the anterior byssus retractor of Mytilus, its mechanical behaviour is not. The muscle has a narrow working range where maximum tensions and "catch-like" contractions develop. This narrow length range is co-incident with the in situ length at which clamping occurs. It is suggested that the large component of collagen has an important influence over the mechanical behaviour of the muscle during clamping, by cross-linking in a manner similar to that described for some echinoderm connective tissues.
- Full Text:
- Date Issued: 1991
Aspects of the thermal ecology of six species of carcass beetles in South Africa
- Authors: Midgley, John Mark
- Date: 2008
- Subjects: Forensic entomology , Diptera -- South Africa , Beetles -- South Africa , Burying beetles , Burying beetles -- South Africa , Beetles -- Effect of temperature on
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5643 , http://hdl.handle.net/10962/d1005325 , Forensic entomology , Diptera -- South Africa , Beetles -- South Africa , Burying beetles , Burying beetles -- South Africa , Beetles -- Effect of temperature on
- Description: The forensic application of entomology is well known, but it is generally a field which concentrates on Diptera. Many Coleoptera also have forensic application, but are generally neglected by forensic entomology researchers. Necrophilic Coleoptera are diverse and therefore have application in estimating Post-Mortem Interval (PMI) by community composition, but they are also valuable in estimating PMI by development. In addition, Coleoptera are more common in stored product cases. Six species of forensically important Coleoptera were studied, three from the family Dermestidae (Dermestes haemorrhoidalis, D. maculatus and D. peruvianus) and three from the family Silphidae (Silpha punctulata, Thanatophilus micans and T. mutilatus). The effect of killing method and storage time on larval length was investigated in T. micans. Coleopteran larvae were shown not to behave in the same way as dipteran larvae. In contrast to dipteran larvae, it is recommended that coleopteran larvae be killed using ethanol. A development model is presented for T. micans. This represents the first statistically robust development model for forensically important Coleoptera, and the first development model for forensically important Silphidae. The model offers a method of estimating PMI which can be used once Diptera are no longer present on a corpse. Upper lethal temperature limits for four species of carcass beetle were determined. A comparison between species shows distinct differentiation between families and species. This differentiation accounts for microhabitat differences which these species show on carcasses. Bioclimatic models for the six species showed contrasting distributions, with both widespread and localised species. These models allow forensic investigators to assess whether the absence of a species from a corpse is forensically significant, or a result of the species distributions. Moisture-related variables were shown to be more important in predicting species distributions than temperature at a regional scale. Forensic entomology standards can be adjusted based on the findings of this study. Length was again shown to be an inferior measurement of larval age. Coleopteran development has been shown to be useful, and should be given greater consideration in future work. T. micans has been shown to be capable of locating and ovipositing on carcasses promptly after death, making it a good forensic indicator. Further work is needed for the full potential of necrophilic Coleoptera to be realised.
- Full Text:
- Date Issued: 2008
Assessing invasive alien aquatic plant species, phytoremediation effects using biological indicators in the Swartkops River system
- Authors: Tshithukhe, Getrude
- Date: 2020
- Subjects: Aquatic weeds -- Biological control -- South Africa -- Eastern Cape , Alien plants -- Biological control -- South Africa -- Eastern Cape , Phytoremediation -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/167665 , vital:41501
- Description: Pollution effluents in freshwater ecosystems are becoming increasingly ubiquitous as a result of cumulative anthropogenic activities, such as wastewater treatments works, and industrial, agricultural and mining activities. These activities are more noticeable in urban river atchments where there is greater human population densities and industrial developments. The ecological effects of anthropogenic activities on freshwater ecosystems include: excessive deposition of contaminants such as nutrients, pharmaceuticals, microplastics and other chemicals, which change physicochemical properties, causing a decline in aquatic biodiversity. These effects, impact negatively on the resilience of freshwater, making the systems vulnerable to invasion by alien aquatic plants. Ultimately, the loss of local biodiversity associated with the invasive alien aquatic plants (IAAP) results in a loss of some ecosystem goods and services. The Swartkops River system, Eastern Cape Province, drains most of the neighbouring formal and informal settlements, agricultural lands and industries, and hence is exposed to water pollution from human activities along the river catchment. Various water quality assessments are needed to evaluate the extent of pollutants and their impacts on the river ecosystem. Phytoremediation is one approach employed internationally for removing harmful nutrients and chemicals in freshwater ecosystems. Most studies measure the success of phytoremediation through measuring the reduction of contaminants in water or soil chemistry in mesocosm settings, which may not take into account all the important environmental factors that exist in the field. The present study assesses the phytoremediation potential of Pontederia (Eichhornia) crassipes and Salvinia molesta by evaluating water and sediment chemistry, periphyton and aquatic macroinvertebrate community recovery along seven field sites (excluding IAAP species mats sites) located upstream and downstream IAAP species mats on the Swartkops River between April and September 2018. Water and sediment samples were collected once monthly on ten seven field sites, including the IAAP species mat sites. Periphyton and aquatic macroinvertebrates were collected on seven sites, excluding the IAAP mat sites. Pontederia crassipes and S. molesta infestation in Swartkops River showed positive phytoremediation results and improved some water and sediment chemistry in the downstream treatments as compared to upstream treatments. Although there were some fluctuations with some variables, important water and sediment chemistry were reduced downstream. By contrast, biological assessment results did not show any response to the presence of IAAP species and phytoremediation. Periphyton and aquatic macroinvertebrates diversity and community assemblages were more influenced by water quality. Although IAAP species did provide improvement in water and sediments chemistry, multiple effluent point and non-point sources in Swartkops outpaced phytoremediation. Taxa evenness and relative taxa abundance showed significant differences between the upstream and downstream sites, however taxa richness and Shannon’s diversity showed no significant differences, indicating no relative recovery in biodiversity for either periphyton or aquatic macroinvertebrates. Similarly, the upstream and downstream sites showed similar periphyton and aquatic macroinvertebrates assemblages structure, all dominated by pollution tolerant taxa, thus indicating no functional diversity improvement down river; because of improvement in water chemistry downstream sites, it was expected that periphyton and aquatic macroinvertebrates assemblage structure would also improve at these downstream sites.It is possible that the phytoremediation process is outpaced by effluent discharges, given the multiple sources and distance between upstream and downstream mat sites. The study showed phytoremediation potential but the results were not indicated by biological indicators. A replica study conducted on a moderately disturbed river system is recommended to measure the success and recovery of biological indicators and assemblage composition following IAAP species phytoremediation; a moderately disturbed river compared to a largely disturbed river will broaden findings and look at differences for a wider application of phytoremediation.
- Full Text:
- Date Issued: 2020
Assessing the density and distribution of spotted hyaenas (Crocuta crocuta) in Hluhluwe–iMfolozi Park, KwaZulu-Natal, South Africa
- Authors: Roberts, Peter Jean
- Date: 2022-04-06
- Subjects: Spotted hyena Home range South Africa Hluhluwe Game Reserve , Spotted hyena Habitat South Africa Hluhluwe Game Reserve , Animal population density South Africa Hluhluwe Game Reserve , Scouting cameras , Home range (Animal geography) , Spatially-explicit mark recapture (SECR)
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/292681 , vital:57006
- Description: Protected areas are becoming increasingly isolated refugia for large carnivores and are critical for their survival. Spotted hyaenas (Crocuta crocuta) have, for centuries, been ‘managed’ as problem causing animals and their conservation has been largely overlooked. To preserve a population, it is paramount to understand its distribution and abundance through reliable and cost-effective monitoring techniques. My study estimated the density of spotted hyaenas and their use of space in Hluhluwe–iMfolozi Park (HiP), South Africa. I compared camera trap by-catch data and call-up surveys between 2013–2018 to assess spotted hyaena densities. The camera trap data estimated an average of 16.72 (SD: ±2.22) hyaenas per 100 km2 between 2013–2018, with an annual estimated high of 19.01 in 2018 and a low of 12.77 in 2015. The call-up surveys consistently produced lower estimates than those obtained from the camera trap data. These results highlight the importance of calibrating the response probability factor for call-up surveys to maintain precision. The space use of spotted hyaenas was analysed using the photo-capture data obtained during the same six-year period, to produce individual 100% Minimum Convex Polygon’s (MCPs). Seven clan territories were identified from individual female home ranges that overlapped by more than 66% of their MCPs. Territory sizes were similar to historical estimates for the park, with averages of 13.96 (SD: ±6.48) km2 in Hluhluwe and 34.61 (SD: ±23.87) km2 in iMfolozi. My study successfully used by-catch camera data to calculate annual density estimates and investigate the spatial use patterns for spotted hyaenas in HiP. I demonstrate that this approach is cost-effective and reliable for calculating density estimates. Conservation practitioners should take heed of the advancements in technology and analytical capacity now available to them to improve monitoring efforts. My study specifically calls for collaborative efforts to use existing camera trap data to improve regional estimates and population trends of spotted hyaenas across their range. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-04-06
Assessing the impact of climate change on mangrove crabs: the role of ontogenetic macrophysiology and settlement in the persistence of central and marginal populations
- Authors: Mostert, Bruce Petrus
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/826 , vital:19994
- Description: After a brief respite in the mid to late 20th century, macro physiology has come to the fore in elucidating large scale ecological patterns and processes as physiological assumptions often form the backbone of many predictive theories associated with species distributions. Critically, macro physiological patterns are valuable in explaining physiological variation across multiple scales and provide insights into the effects of climate change on populations spanning a wide range of latitudes. This can assist in predicting possible distribution expansions, contractions or shifts in light of current climate change scenarios. From this perspective, investigating intra- and inter-specific physiological responses to environmental stress may contribute to better understanding and predicting the effects of climate change on geographical ranges. Further, investigating the physiological effects to environmental stresses across ontogenetic stages allows for the identification of weak links within the lifecycle of a species. Additionally, determining settlement characteristics along a latitudinal cline provides integrated indications of the sustainability of populations, highlighting vulnerable regions in terms of repopulation of viable habitats. In this context, the present study aimed at establishing how temperature, in a physiological context, may affect reproductive biology of two species of mangrove crab, Perisesarma guttatum and Uca urvillei at the centre (Kenya) and edge (South Africa) of their distributional range along the east coast of Africa and highlight possible consequences for range distributions. A third species, Neosarmatium africanum, only in South Africa, was included to provide additional interspecies comparisons. Furthermore, settlement characteristics of brachyuran populations at the centre and edge of their distributional range were considered in order to determine how settlement may contribute to population persistence. Physiological investigations at the centre and edge of distributional range and across ontogenetic stages (larvae, stage 2 and 4 embryos, non-gravid and gravid females) under the concept of oxygen and capacity limitation of thermal tolerance (OCLTT), revealed that, for both species, populations at the centre of their distribution (Kenya) were generally more robust to increasing temperatures and generally displayed greater physiological stability with increasing temperatures compared to their conspecifics in South Africa. Variability in physiological robustness between regions, did however, differ among ontogenetic stages and species but, overall, were evident throughout. Within and between regions, adaptation to oxygen extraction in both milieus (air or water) was displayed for present temperature conditions but aerial respiration largely alleviated increased thermal stress due to overcoming the limitations of reduced oxygen availability and diffusiveness in water for all bimodal ontogenetic stages. Brooding eggs proved to be a physiologically critical process with either heighted oxygen consumption for gravid females or collapse of physiological processes demonstrated by supressed oxygen consumption. The physiological cost of brooding eggs, referred to as maternal costs, was reflected in in both Perisesarma guttatum and Uca urvillei where, in most cases, maternal costs were negative. Again, aerial respiration was able to alleviated increased thermal stress, as shown by positive maternal costs indicating sustained maternal care, but this mechanism was species and regionally specific. Settlement patterns differed between the edge and centre of distribution of the species studied. This difference was predominantly driven by zonal preference within the mangal and/or effects of new and full moon (lunar phase). Overall, settlement dynamics were more widely variable in South Africa, both spatially and temporally, than in Kenya. Finally, empirical physiological data from ontogenetic stages present during the reproductive process (early and late stage embryos) and from non-gravid and gravid females were used in conjunction with data mined from the existing literature to parameterise an individual based model designed to simulate reproductive output at the centre and edge of distribution of Perisesarma guttatum. Physiological data indicate that, in terms of reproductive output across increasing temperatures, populations based at the centre of their distribution presently outperform their counterparts at the edge of the species’ distribution, but reproductive output stagnated as temperature rose. Edge of distribution populations consistently increased reproductive output with increasing temperatures to eventually outperform centre of distribution populations at higher simulated temperatures. Overall, results of the physiological and settlement studies suggest that with increased climate change there may be a contraction of distributional range of the study species from high latitudes to low latitudes, contrary to general poleward shifts/migrations seen in most species, with possible contractions of the entire ecosystem mirroring the disappearance of keystone mangrove macrofauna.
- Full Text:
- Date Issued: 2016
Assessment of pheromone specificity in Thaumatotibia leucotreta (Meyrick) populations with focus on pest monitoring and the regional rollout of the sterile insect technique in citrus
- Authors: Joubert, Francois D
- Date: 2018
- Subjects: Cryptophlebia leucotreta , Pheromone traps , Citrus -- Diseases and pests -- South Africa , Cryptophlebia leucotreta -- Contol , Cryptophlebia leucotreta -- Biological control
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/60665 , vital:27812
- Description: False codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae) is considered the most important indigenous pest of citrus in southern Africa. It is recognized by several markets as a phytosanitary organism and the efficient control of this pest is now more important than ever. The pheromone communication between the male and female moths has been exploited in order to control FCM through the sterile insect technique (SIT). The sterilized males used for all SIT programmes across South Africa come from a colony that originates from wild material collected from the Citrusdal area of the Western Cape Province. The aim of this study was to determine if any differences in attractiveness of females to males exist between different geographical populations of FCM and if so what impact this would have on the male’s ability to locate females from other populations via the volatile sex pheromone released by the female. Laboratory trials with Y-tube olfactometers and flight tunnels tested the attraction of male moths to virgin females, but did not yield any consistent results. Field experiments were conducted with sterile male Citrusdal moths released and recaptured in yellow delta traps in two separate trials. For one trial, the traps were baited with live virgin females from five different geographical populations including Addo, Nelspruit, Marble Hall, Citrusdal and the Old colony, which is a mixture of several populations. For the other trial traps were baited with various synthetic pheromone blends including three regional blends which included South Africa, Ivory Coast and Malawi and three commercial blends including Pherolure, Isomate and Checkmate. For the virgin female trial the Citrusdal males showed a significant preference for females from their own population. There was also a significant difference in the recaptures from the different synthetic pheromones. The South African blend was the most attractive of all the regional and commercial blends. A cross-mating trial was also conducted under laboratory conditions in petri dishes with five different FCM populations including Citrusdal, Addo, Marble Hall, Nelspruit and Old (mixed origin). Females produced more eggs when mated with males from the same population for the Addo, Marble Hall, Nelspruit and Old (mixed origin) populations. The only case in which this was statistically significant was for the Marble Hall population. All the crosses produced viable eggs and the origin of the male or female did not influence egg hatch. The results from this study may lead to improvements in both the control and monitoring of FCM populations. The control methods include mating disruption, attract-and-kill and SIT. Tailoring these methods for a specific growing area with a pheromone blend originating from the area or releasing sterile moths from a colony that originates from the area may optimize the available monitoring and control options.
- Full Text:
- Date Issued: 2018
Augmentative releases of Dactylopius austrinus De Lotto (Dactylopiidae; Hemiptera) for biological control of Opuntia aurantiaca Lindley (Cactaceae), in South Africa
- Authors: Mulateli, Thifhelimbilu
- Date: 2019
- Subjects: Opuntia aurantiaca -- Biolotical control -- South Africa , Invasive plants -- Biolotical control -- South Africa , Dactylopius austrinus De Lotto -- South Africa , Dactylopius -- South Africa
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/92931 , vital:30765
- Description: Opuntia aurantiaca Lindely (Cactaceae) is an invasive alien cactus which has detrimental effects on agroecosystems and indigenous biodiversity in South Africa. Dense infestations over large areas reduce grazing capacity and indigenous biodiversity. Despite the release of a biological control agent, the cochineal insect Dactylopius austrinus De Lotto (Dactylopiidae), the weed is still considered a major problem in many parts of the country. Biological control has relied heavily on classical biological control, with little augmentative biological control implemented. This study investigated the outcome of mass-rearing and augmentative releases of D. austrinus for the control of O. aurantiaca. Augmentative releases are thought to improve the level of control by increasing agent densities in the field and thus increasing the level of damage inflicted to the plants. All data were collected with the intention to optimize release strategies so that the maximum benefit from the biological control agent could be achieved. An impact study was conducted using potted plants in a greenhouse to quantify the efficacy of multiple releases of the agent on the target weed. All three of the release treatments showed consistently higher proportion of cochineal than the controls, as well as the insect exclusion treatments, and these differences were statistically significant. The number of cladodes per plant increased significantly for the insect exclusion and control treatment over the period of the study, whilst all three release treatments decreased steadily over the same period. This study indicated that the agent is damaging to O. aurantiaca and that a single release event was beneficial but that multiple releases did not result in greater levels of control. A post-release evaluation was carried out to quantify the impact of releases of D. austrinus on O. aurantiaca in the field. Plots where the agent was excluded were compared with those where the agent was left at natural field densities and three treatments where agent populations were augmented to varying degrees through releases. The percentage of cochineal infested cladodes for all treatments decreased over time from the initiation of the experiment in October 2017 until the end of the experiment in October 2018. Opuntia aurantiaca densities also decreased over time for all treatments. The insect exclusion treatment had the greatest number of plants for the duration of the study, but this was not significantly different from other treatments. Dactylopius austrinus was damaging to O. aurantiaca, but climatic conditions in the field limited the efficacy of releases. Although O. aurantiaca density decreased during the experiment, it was evident that the reduced number of plants was not due to augmentation of the cochineal populations from the releases that were conducted. The experiment was conducted over a very dry period, when cochineal was particularly effective, so although augmentative releases did not improve the level of control, the natural population of cochineal was high and very damaging to O. aurantiaca over the course of the experiment. Releasing during wet periods, when the agent is less effective, could augment agent populations at a time when natural populations would be low, and hence improve levels of control further. Although this study was limited to a short period of two years, the results of this study suggest that the number of releases is less important than the timing of releases. Releasing immediately after periods of high rainfall is likely to be beneficial, while releasing during dry periods, or during winter when temperatures are low, is less effective. Dactylopius austrinus populations should be constantly monitored so that releases can be conducted when cochineal populations are low and the climatic conditions are correct. If the timing of release events is appropriate, then the over level of control of O. aurantiaca using D. austrinus could be improved.
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- Date Issued: 2019