Masters Degrees (Ecology)

Permanent URI for this collectionhttps://hdl.handle.net/10413/7488

Browse

Now showing 1 - 20 of 56

Comparative water relations of Protea nitida seedlings and sprouters after fire.
(1990) Smith, Rosemary Elizabeth.; Pammenter, Norman William.
This study was undertaken to determine the effect of vegetation structure (the ratio of re-seeding to re-sprouting plants) on post-fire catchment water yield. Plant communities are the only components of mountain catchments which can be manipulated to augment water supplies on any practical scale. Burning, which is one of the options available to catchment managers, reduces plant biomass and increases water yield by reducing transpiration and interception losses. Communities dominated by re-seeding species tend to recover more slowly after fires than when sprouters predominate. The rate of vegetation recovery will determine the rate at which streamflow returns to pre-fire levels. Sprouters may use more water than seeders in the early post-fire period by virtue of their greater leaf area, which both increases interception and transpiration losses. Leaf area development could be used as a simple determinant of post-fire water yield if transpiration losses per unit leaf area are similar in seedlings and sprouters. In this study, a comparison was made of the transpiration rates of seedlings and sprouters of Protea nitida after a fire in Swartboskloof (Cape Province) in 1987. Plant water potentials were determined (index of the degree of stress) and leaf stomatal conductances were measured. Results indicate that transpiration rates are similar throughout the year except during the short summer drought period when the seedlings have comparatively low transpiration rates (< 1 mmo1 m-2 s-1 compared to 2-3 mmo1 m-2 s-1 of the sprouter), and i immediately after the first winter rains where the seedlings have comparatively high rates (approxi.mately 4 mmol m-2 s-1 compared to 2 mmol m-2s-1.) The 1ow summer rates are thought to be the result of drought stress induced by limited water supply and the shallow root systems of the seedlings. The higher winter rates suggest that the shallow surface roots of the seedlings respond quickly to increased surface moisture. Differences in root structure (Le. shallow seedling roots and well-developed deep sprouter roots) rather than regeneration mode appear to be responsible for the marginal differences observed in transpiration rates. These differences are expected to disappear as seedling roots develop and occupy the profile. Leaf area could therefore, be used as a determinant of catchment water yield.
Behaviour of bottlenose dolphins : inference for dolphin tourism off Durban, South Africa.
(2008) Mahomed, Maleeha.
During long-term studies of dolphins, the number of individuals in the population being studied are constantly monitored using the technique of photo-identification. This constant monitoring makes use of different researchers over time. Therefore, measurement of photographic quality and individual distinctiveness for photo-identification analyses was incorporated in this dissertation to provide an additional data set for analysis. Researchers with differing levels of experiences did not obtain the same information from the same photograph and were unable to reliably quantify variables of photo quality and individual distinctiveness, but experienced researchers were found to be more adept than inexperienced researchers in counting notches on the dorsal fin of bottlenose dolphins. These results highlight the necessity for researchers to be trained in photo-identification techniques prior to carrying out their study. This study theodolite tracked dolphins off Durban from June 2004 to Feb 2005 to assess habitat utilization of bottlenose dolphins (Tursiops aduncus) in the Durban bay region. Dolphins were seen in all months surveyed and throughout the survey area. Temporal distribution of dolphins was skewed with 91% of dolphins seen before midday and 98% of sightings observed in water depths less than 30m. Six behavioural categories were recorded, including: social, fast travel, slow travel, feeding, resting and milling. The most dominant behaviour exhibited by dolphins was slow travel (46%) followed by feeding (27%). Resting was not observed at all. Of the feeding behaviour 88% occurred in the southern end of the bay whereas other behaviours occurred randomly throughout the survey area. Additional theodolite tracks were conducted during experimental boat approaches (before, during and after boat approaches) to determine potential short-term reactions of dolphins to dolphin watching boats. Two speeds of approach (slow ~ < 5 km/hr and fast ~ > 40 km/hr) and two distances of approach (20m and 80 m) were tested. The bottlenose dolphin groups did not change their behaviour in response to boat approaches during any of the periods of experimentation. Short-term changes in group speed, group size and spread were not statistically significant. Dolphin groups continued with their ‘normal’ behaviour and spent the same amount of time in the bay when compared to their distribution and behaviour in the absence of the experimental boat. These findings indicate that the experimental boat did not affect the behaviour of dolphins at either a slow or fast approach and even at a close distance. This is interpreted as being as a result of habituation of the dolphins due to their residency in a busy port. This work is crucial in developing guidelines for the development of a sustainable dolphin watching industry off Durban.
The ecological implications of sea-level rise and storms for sandy beaches in KwaZulu-Natal.
(2008) Harris, Linda R.
The aesthetic appeal of beaches has made coastal properties prime sites for development. However, this development has been mismanaged and is within the littoral active zone. Beaches retreat landwards as sea levels rise, but with current development trends, beaches are trapped in a coastal squeeze. Climate-change predictions include an increase in frequency and heightened intensity of storms, which can cause significant erosion. This study aimed to determine the ecological implications of sea-level rise and storms for beaches in KwaZulu-Natal (KZN), using geographic information systems (GIS) and beach sampling methods. The beaches were mapped in terms of physical and biological attributes. Spatial trends in these attributes showed that the coastline can be split into three – the northern, central and southern regions. Although 25 % of the coastline is protected by marine reserves, these are located in the Delagoa bioregion: 28 macrofauna species in the Natal bioregion are not protected. Storm impacts for beaches can be heterogeneous, depending on local coastal features, e.g., nearshore reef and sand dunes, and represented a temporary disturbance to macrofauna communities. A GIS-based coastal recession model was derived from Bruun’s rule, and applied for different scenarios of sea-level rise and coastal development. Coastal squeeze is concern, particularly in the southern region. Further, the 10-m elevation contour was not completely effective as a setback line, even for a low sea-level rise scenario. The coastal recession model was validated using data from a real event in KZN, where sea level rose temporarily by ~1.0 m. The model performed well, although the calibration possibly did not span a wide enough range of beach morphodynamic types, and under-predicted retreat for dissipative beaches. It was concluded that the Natal bioregion needs marine reserves, and that higher resolution spatial data are required for accurate beach modeling and the south coast railway line should be relocated proactively. Guidelines for sandy beach systematic conservation planning were outlined, and seated in a conceptual framework of managing beaches for resilience. Application of the proposed recommendations and frameworks could aid in determining a way forward in integrated coastal zone management for KZN, in the face of the uncertainties associated with climate change.
What drives the seasonal movements of african elephants (Loxodonta africana) in Ithala Game Reserve?
(2013) Muller, Kayleigh.; Ward, David Mercer.; Shrader, Adrian Morgan.
The changes in plant quality and availability in space and time present a substantial problem to mammalian herbivores. As a result, these herbivores need to alter their foraging behaviour to maximize their energy gain at both small (plant level) and large (landscape level) scales. A megaherbivore, the African elephant (Loxodonta africana), has been shown to be selective in its foraging choices at both of these scales. Furthermore, the ratio of palatability:defences (e.g. fibre and total polyphenols) has been highlighted as an important determinant of habitat selection in elephants. The elephants in Ithala Game Reserve (IGR) frequently leave IGR during the wet season and forage outside the reserve. However, they predominantly feed on the low-nutrient granite soils of the reserve and return to a high-nutrient area with dolerite soils during the dry season. In an attempt to understand these seasonal movements, I focused on how the small-scale foraging decisions of the elephants lead to large-scale seasonal movements in IGR, KwaZulu-Natal. Plant availability was determined seasonally for seven target species across four areas in the reserve. Crude protein, fibre, energy and total polyphenols as well as the ratios of palatability:digestion-reducing substances were analysed in the wet and dry seasons. All factors and their interactions were significant in a MANOVA. Consequently, I employed a dimension-reducing Principal Components Analysis (PCA) to better understand the factors of greatest importance. The PCA highlighted four of the six most important factors to be the ratios of palatability:digestion-reducing substances. The other two important variables were total polyphenols (negative effect) and crude protein (positive effect). At small spatial scales, I found that the elephants were selective in their decisions, especially during the dry season. For example, the increased inclusion of the principal tree species Acacia nilotica from 2.9% in the wet season to 39.3% during the dry season appears to be a result of a decline in total polyphenols and fibre during the dry season. At large spatial scales, the elephants moved back into IGR from the low-nutrient granite soils in the east in response to an increase in forage quality in the west as the quality declined in the east at the same time. However, it is unclear as to why the elephants are leaving the reserve during the wet season. Some possible explanations for this are discussed.Key-words: acid detergent fibre, crude protein, Loxodonta africana, neutral detergent fibre, total polyphenols, plant part quality.
Changes in adult female white rhino seasonal home ranges in relation to variation in food quality and availability.
(2013) Hebbelmann, Lisa.; Shrader, Adrian Morgan.; Ward, David Mercer.
As the dry season progresses across southern Africa, the availability and quality of food declines for large herbivores. Female white rhinos compensate for these declines by expanding and/or shifting their home ranges. These changes may be to incorporate habitat types that contain high quality food or quite simply more food. To determine the factors that drive these seasonal changes in home ranges, I focused on dry season changes in the availability and quality of grass in habitats utilised by white rhinos in the Ithala Game Reserve, South Africa. I expected that if food quality was the main driver, white rhinos would follow optimal foraging principles and incorporate habitat types with the highest nutritional quality into their dry season home ranges. Alternatively, due to their large body size (>1000 kg) and thus ability to survive on low quality food, they may rather incorporate habitat types with high food availability. In contrast to previous studies, I found that during the dry season female white rhinos did not increase the size of their home ranges, but rather shifted their home range boundaries. This resulted in individuals increasing the amount of Bushveld and decreasing the amount of Wooded Grasslands within their dry season home ranges. When I explored the different factors that could explain these patterns, I found that changes in the crude protein content of grass was the key factor driving the incorporation and exclusion of habitat types in the home ranges. During the dry season, white rhinos incorporated the habitat that had the smallest seasonal reduction in crude protein content, while excluding the one with the largest decrease in crude protein. As a result, my results suggest that the search for high quality best explains the seasonal home range shifts of female white rhinos in the Ithala Game Reserve.
The ecology of black-backed jackal (Canis mesomelas) on farmlands in the Midlands of KwaZulu-Natal, South Africa.
(2014) Humphries, Bruce David.; Downs, Colleen Thelma.; Ramesh, Tharmalingam.; Hill, Trevor Raymond.
Agricultural development is progressively being attributed as a cause of biodiversity loss. Despite this development, some species do successfully inhabit these transformed habitats and benefit from increased food and resource availability. Therefore it is important to understand how and why species persist in those altered landscapes to conserve remaining biodiversity. Black-backed jackals are an abundant mesopredator with an apparent success to these changing agricultural environments. An understanding of their ecology in agricultural areas can provide important ecological information on the species and elucidate possible reasons why this mesopredator is capable of adapting and surviving in agricultural lands. From 2013 to 2014, a study was conducted on the ecology of the black-backed jackal Canis mesomelas in the Midlands of KwaZulu-Natal, South Africa. The study examined the home range, habitat use and diet of the species. In addition species characteristics and conflict of black-backed jackal from a landowner’s perspective were determined. It was found that rodents comprised the most consumed item of prey by black-backed jackal, followed by domestic livestock. There was a significant diversity of prey species in the diet indicating the opportunistic and generalist nature of the species. The home range movements of the species were relatively large compared to previous studies on the species and juveniles generally had larger home ranges than adult males and females. Habitat selection within home ranges indicated jackals preferred bushlands in winter and spring, and croplands in summer and autumn. Landowner’s reported regular predation on livestock by the species and suggest the increasing intensity of agriculture provides a greater food source of jackals. Some farmers used mitigation strategies in an attempt to prevent livestock losses, however, 32 % of farmers confessed to having poor disposal techniques for dead animals. This study provides important ecological information on black-backed jackal as a mesopredator species. Information on the spatial movement and diet of jackals in this study highlighted the variability in ecology of the species, providing information on the species’ persistence and success in agricultural areas. Furthermore, feedback from farmers emphasised the importance of having collaboration between farmers to control jackal predation and reduce human-wildlife conflict.
Aspects of fruit digestion and selection in selected Southern African avain frugivores.
(2014) Zungu, Manqoba Moses.; Downs, Colleen Thelma.
Fruit-frugivore interactions play a central in maintaining the structure and diversity of ecosystems through their effects on seed dispersal. Because fruit selection and thus fruit removal represents the first stage in the seed dispersal process, understanding factors affecting fruit selection can play an important role in the formulation of sound conservation efforts especially light of the on-going habitat change. However, to date, the research is inconclusive as to factors affecting fruit selection as results have revealed inconsistent and controversial with a huge variation in fruit selection patterns between species and within individuals of the same species. The huge inter- and intra-specific variation in fruit selection patterns precludes any generalizations on fruit selection notwithstanding the research effort addressing the issue. One factor that could be attributed to this pattern is that most studies on fruit selection patterns in frugivorous birds have studied fruit attributes or physiological adaptations of frugivores to fruits in isolation. Because fruit profitability is affected by both pre- and post-ingestional factors, studying these factors in isolation deprives us of fresh insights into the fruit-frugivore interaction. Therefore by relating the physiological aspects of frugivores to fruit characteristics, this study aims to provide a link between the physiology of birds and their feeding ecology. Cape white-eyes (Zosterops virens), red-winged starlings (Onychognathus morio) and speckled mousebirds (Colius striatus) were used for this study. In the first part of this thesis, transit times and digestive efficiencies of birds fed equicaloric glucose and sucrose artificial fruit diets of varying concentrations were determined. Three concentrations were used: low (6.6%), medium (12.4%) and high (22%). Digesta transit times of birds increased with an increase in concentration for all diets but were generally higher on glucose diets. This finding has been widely reported in other similar studies. The increase in digesta transit times with an increase in sugar concentration may be due to high nutrient density on high concentration diets which require a longer processing time. Intake rates, on the other hand, decreased with an increase in sugar concentration. The inverse relationship between food intake and nutrient levels has often been attributed to compensatory feeding which posits that birds respond to nutrient dilution by increasing intake to allow a constant flux of assimilated energy. Indeed, speckled mousebirds and Cape white-eyes maintained a constant assimilated energy intake on sucrose diets by modulating food intake rates. The apparent assimilation efficiencies of glucose diets for all species were comparable and typical of those found in other frugivorous birds. However, red-winged starlings displayed low assimilation efficiencies for sucrose diets and lost significant body mass on all sucrose diets. The lack of significant sucrase activity in this species was attributed to this finding. This study showed the importance of digestive physiology in explaining fruit selection patterns in frugivorous birds. The second part of this thesis assessed the deterrence effects of tannins which are ubiquitous secondary compounds in plant material and are known for their ability to bind to protein which reduces nitrogen availability in the diet. In this study, birds were fed artificial fruit diets containing varying levels of tannins (0%, 2.5% and 5%) in paired choice tests. It was predicted that tannins would have no effect at low concentrations but at higher concentrations would act as deterrents although the levels at which they would become deterrents would differ among species. Red-winged starlings preferred the control diet, were indifferent to the medium tannin diet and were deterred by the high tannin diet whereas speckled mousebirds and Cape white-eyes were not deterred at all concentrations. The discrepancy in the results was attributed to differences in taste sensitivity, tolerance levels and detoxification mechanisms of secondary compounds between species. Occasional geophagy and consuming a broad diet were also implicated in producing the results obtained. Plant secondary compounds in fruits are diverse and their effects are similarly diverse and there is a possibility that different groups of secondary compounds generate disparate effects. Similar studies on other types of secondary compounds may thus contribute towards a broader understanding of the role of secondary compounds in mediating fruit-frugivore interactions. Overall, this study showed how diet affects ability to handle secondary compounds in fruits. The third part of this thesis addressed the influence of ethanol concentration on fruit selection in frugivorous birds. Because ethanol is ubiquitous in fruits and its concentration is positively correlated to fruit sugars, it has been suggested that because frugivores could use its odour to locate fruiting plants, they should select fruit with high ethanol concentrations. The aim of this study was to test this hypothesis by determining whether frugivorous birds show a preference for fruit laden with alcohol at levels equivalent to those of over-ripe fruits. Birds were provided with two artificial fruit diets in pairwise choice tests: an experimental diet containing 1% ethanol and an artificial fruit diet with no ethanol. For all species, there were no significant differences in the amount of fruit consumed between the two food types. These findings provided corroborating evidence to the suggestion that birds are unlikely to prefer over-ripe fruits compared to ripe fruits due to the negative impacts associated with ingesting ethanol at high concentrations. However, it could be possible that the lack of preference observed in this study was because the ethanol concentrations used were too low to be detected. Overall, this study suggests that at high concentrations, ethanol in fruits acts as a deterrent rather than an attractant. The last part of this thesis was conducted to determine the use of taste and olfaction by red-winged starlings in making foraging decisions. To determine whether they use taste in fruit selection, they were concurrently offered a control artificial fruit diet with another artificial fruit diet flavoured with different concentrations of ethanol and various fruit essences. To test whether they were able to use olfaction to locate food, they were provided with two choices: artificial fruit suspended over either banana and orange fruit essences and ethanol of varying concentrations or a control artificial fruit (without essence). It was hypothesized that (1) red-winged starlings have tasting ability which helps them in selecting fruits to feed on and that (2) red-winged starlings use olfaction to locate food. Results were consistent with the first hypothesis but inconsistent with the second one. Thus, red-winged starlings use taste when selecting fruits to feed on but do not use olfaction to locate fruit sources. The latter was unexpected because birds with olfactory bulb sizes similar to theirs exhibit advanced olfactory abilities. It was speculated that the lack of olfactory abilities in starlings could be attributed to the fact that this study was conducted outside of this species’ breeding season when olfactory abilities were likely to be lowest and also to that olfactory abilities may not have been important at the scale investigated in this study. Overall, the study showed that the sense of taste in birds plays an important role in making foraging decisions than currently appreciated. Overall, this thesis demonstrated the value of relating physiological attributes of frugivores to fruit attributes in acquiring deeper understanding of fruit-frugivore interactions. One particular advantage of the methodology employed in this study was that it controlled for covariance among fruit characters and also removed the confounding effects of as seed size and secondary compound composition. The shortcoming of this approach is related to the applicability of the results to the field conditions. Therefore an approach combining laboratory and field observations may produce results that may be important in informing us about how to manage our ecosystems.
Evolution of wind pollination in Leucadendron (Proteaceae) : experimental evidence and floral trait shifts.
(2014) Welsford, Megan Rae.; Johnson, Steven Dene.
Evolutionary transitions from insect to wind pollination are thought to have occurred many times during the angiosperm radiation. This transition is commonly associated with a suite of distinctive floral traits such as reduction of flower size and a transition to dry pollen. In the dioecious genus, Leucadendron (Proteaceae), evolutionary shifts from insect to wind pollination have been postulated based on floral morphology features. In this study, I aimed to experimentally test the potential for wind versus insect pollination in several Leucadendron species and document a variety of floral traits (pollen size, inflorescence size, scent, colour, etc.) in order to determine their functional significance whilst utilizing phylogenetic comparative methods to test the statistical significance of evolutionary associations between particular floral traits and pollination systems. Fifteen representative Leucadendron species were investigated to verify insect and wind pollination in as many clades as possible. Insect exclusion experiments confirmed that five Leucadendron species, L. rubrum, L. salicifolium, L. dubium, L. coniferum and L. teretifolium are indeed wind-pollinated. Pria cinerascens (Nititulidae) was found to be the main pollinator of the insect-pollinated Leucadendron species due to their abundance, high stigmatic contact and relatively pure Leucadendron pollen loads. Overall, however, the abundance of insects visiting inflorescences was not significantly different between insectand wind-pollinated species, which highlights the importance of conducting insect exclusion experiments to evaluate whether a species is wind- or insect-pollinated. From the previously determined pollination systems of 17 Leucadendron species, floral traits associated with the shift to wind pollination were investigated to determine whether transitions from insect to wind pollination were accompanied by modifications of pollination-relevant floral traits. In a wind tunnel, pollen grains of wind-pollinated species were found to be more motile than those of insect-pollinated species. Phylogenetic analyses suggest that transitions from insect to wind pollination occurred at least four times during the diversification of Leucadendron and that, compared to insect-pollinated cogeners, wind-pollinated Leucadendron species are characterized by increased production of smaller pollen grains, higher inflorescence density, less attractive visual and olfactory cues, and a greater degree of sexual dimorphism for these visual and olfactory cues. In conclusion, this study experimentally confirms that there were several shifts from insect to wind pollination in Leucadendron and identifies floral traits that were evolutionarily modified during these shifts.
Aspects of the ecology of feral cats (Felis catus) in urban Pietermaritzburg, KwaZulu-Natal, South Africa.
(2015) Pillay, Kerushka Robyn.; Downs, Colleen Thelma.
With changing land use such as urbanization, certain species thrive and are successful despite changes in the modified landscapes. Therefore, study of the ecology, adaptations and survival of these species in an urban context is warranted. Often these species include alien invasive species. An example is the feral cat (Felis catus). The negative effects caused by feral cats generally include impacts on native species of wildlife because of their highly predatory nature and their ability to spread zoonotic diseases. Furthermore, it often becomes a public nuisance occurring at high densities in urban areas. Consequently the aspects of the ecology of feral cats were studied from March 2014 to June 2015 in an urban mosaic in Pietermaritzburg, KwaZulu-Natal, South Africa. The research was also undertaken to propose and assist with an effective management strategy that was deemed necessary to control high densities of feral cats existing in urban Pietermaritzburg. Feral cats were trapped and fitted with GPS-GSM-UHF tracking collars in order to determine their home and core range sizes within the urban mosaic containing varying degrees of green and urban areas. Additionally, the disease prevalence in feral cats was also documented by collecting blood samples from feral cats occurring in many areas of the greater Pietermaritzburg area. The information gained in this study allowed compilation of feral cat management recommendations and strategies in order to control the increasing feral cat communities already established in Pietermaritzburg. Feral cat telemetry data showed that availability and abundance of food resources were the primary influencing factors affecting feral cat home range size and distribution as core areas contained at least one supplemental feeding site. There was considerable overlap of feral cats within the core areas. Overall home range size of feral cats was small but varied with individual cats. There was considerable overlap between and within the sexes. There were no significant differences in range size between sexes nor between day and night. However, diurnal ranges were generally smaller than nocturnal range sizes. Generally male feral cats had larger home ranges than female feral cats and nocturnal activity was higher across genders. Feral cats used urban areas more than green areas suggesting that the urban environment supports larger numbers of feral cats. The disease prevalence in feral cats tested was generally low. However, some tested positive for Feline Leukaemia Virus (FeLV) (28.6%) and for Feline Immunodeficiency Virus (FIV) (7.1 %). There was no occurrence of Feline Corona Viruses (FCoV) in feral cats tested in Pietermaritzburg. The location of feral cats within the city had a significant effect on prevalence of FeLV infection in feral cats tested. The findings of this study of feral cats in the urban mosaic of Pietermaritzburg showed that feral cats’ habitat use and home range were mainly affected by supplemental food resources. Furthermore, disease prevalence in feral cats tested was generally low. Thus efficient, cost-effective and realistic methods need to be implemented to control high densities of feral cats in this urban area require the use of a low-key supplemental feeding programme with a combined sterilization programme. This proposed strategy should be adopted and sustained with involvement of all concerned stakeholders to ensure that the welfare and population of the cats is well managed and humanely controlled particularly as this is an alien, invasive species. Additionally, all cats that test positive for any disease should be removed from the population to stop the spread of diseases to other feral or domestic cats in urban areas of Pietermaritzburg.
Aspects of Nile crocodile (Crocodylus niloticus) population ecology and behaviour in Pongolapoort Dam, KwaZulu-Natal.
(2015) Summers, Mark Kai.; Downs, Colleen Thelma.
Pongolapoort Dam is one of the largest dams in South Africa by volume. It is also home to a breeding population of Nile crocodiles (Crocodylus niloticus). Crocodiles are keystone species which play an important ecological role in their aquatic habitats but are under threat globally. Consequently the aims of this project were to investigate the population number, nesting ecology, and behavioural aspects of gaping in Nile crocodiles at Pongolapoort Dam. Data were captured from July 2014 to August 2015, where there was a marked decrease in water levels in Pongolapoort Dam due to a drought occurring throughout KwaZulu-Natal. An estimated 549 Nile crocodiles occurred in Pongolapoort Dam in 2015, an increase in population from a conservative estimate of 273 individuals in 2010. The majority (80%) of the Nile crocodile population occurred in the inlet section of the dam, and with dropping water levels, the crocodiles congregated in large numbers in the Croc Bay region of the inlet. The population structure changed from 2010 when the majority occurred in the juvenile class to the majority of the crocodiles occurring in the sub-adult and adult size class in 2014/2015. The reproductive output of a population can be an indicator of population health. Consequently nesting ecology of Nile crocodiles was investigated at Pongolapoort Dam for the 2014/2015 nesting season. A total of 38 Nile crocodile nests were found over four nesting sites in the river section of Pongolapoort Dam. Nest effort decreased from 73% in 2009/2010 to 43% in 2014/2015, with a density of 4.9 nests per kilometre in the river section. All nests were found in alluvial deposits where Phragmites australis was the dominant vegetation. Some nests were predated by water monitors (Varanus niloticus); however, two nurseries were found containing hatchlings, while many nests showed signs of being dug up by the nesting females. The N2 Bend and Buffalo Bend floodplain were the most important nesting grounds, and this was attributed to the presence of suitable nesting conditions. Gaping behaviour in Nile crocodiles has received little attention as there are conflicting ideas as to why gaping occurs. The majority of literature suggests that gaping is a thermoregulatory response aimed at cooling the head of the crocodile. We aimed to identify other possible behaviours associated with gaping, at a basking bank in Pongolapoort Dam during winter. Preliminary results suggest that gaping may be a communicative or behavioural posture brought on by the following factors; position of the crocodile relative to the water, total length of the crocodile, time of gape, degree of gape, nearest neighbouring crocodile and number of neighbouring crocodiles. Further research is needed to help understand this behaviour of Nile crocodiles and its importance in their ecology and behaviour. The study showed that the population of Nile crocodiles in Pongolapoort Dam is increasing and remains in a healthy state compared with other population in South Africa. Insights into their behaviour may be applicable to other crocodilian taxa.
Eco-physiological aspects of invasive common myna.
(2015) Senoge, Ntaki Donald.; Downs, Colleen Thelma.
Abstract not available.
Population dynamics and relocation success of the oribi antelope (Ourebia ourebi) in KwaZulu-Natal, South Africa.
(2015) Patel, Tamanna.; Shrader, Adrian Morgan.; Stears, Keenan.; Little, Ian Tchagra.
In South Africa, oribi (Ourebia ourebi) antelope are listed as vulnerable. The lack of understanding of their population dynamics makes it difficult for oribi conservation. To address these gaps, I used the Oribi Working Groups’ long-term survey database to determine 1) the trends (increasing, decreasing, stable) in oribi populations across KwaZulu-Natal, 2) the spatial distribution of these trends across the province, and 3) the factors influencing these trends. The overall oribi population trend for KwaZulu-Natal was linked with the number of survey returns submitted. This highlights the importance of landowners submitting consistent returns, resulting in more accurate population estimates. The majority of oribi populations across the province had decreasing population trends. I found that initial population size and the amount of suitable habitat available significantly affected oribi population growth rates. These growth rates increased when the availability of suitable habitat increased. In addition, grazing regime influenced growth rates. However, the variance observed was high, signifying that there may be other factors that are also responsible for driving these growth rates. Dog hunting was non-significant, however, because it is illegal, it was difficult to accurately measure its effect on oribi populations and thus should not be dismissed as a potential threat. Relocating oribi has been used as a conservation tool over the past 16 years. However, the success of these relocations has been poorly documented. To address this, I determined 1) the success rate of previous oribi relocations in KwaZulu-Natal, 2) the factors driving the success/failure of the relocations, and 3) whether relocation is a successful tool for the conservation of oribi in South Africa. I found a relocation success rate of only 10% (N = 1). Moreover, I found that following basic relocation criteria (e.g. the removal of threats (such as predators) or long-term post-release monitoring) was important in assuring relocation success. In all instances where relocations failed, key criteria were not considered prior to the relocation. This was in contrast to the one successful relocation, where all the criteria were considered and followed. Similar to my first study, I found that oribi population size, the availability of suitable habitat, and stocking rates of other large herbivores influenced growth rates, and ultimately, relocation success. Moreover, I found a significant interaction between suitable habitat available and stocking rates and their influence on population growth rates. Ultimately, this study highlights key factors that must be considered in any conservation or management decisions for oribi. In addition, prior to a relocation, landowners need to follow the basic criteria for successful relocations.
The potential overlap in habitat space of caracal (Caracal caracal) and blue duiker (Philantomba monticola) in KwaZulu-Natal, South Africa : an environmental niche modelling approach.
(2016) Jones, Amanda Lyn.; Schoeman, Marthinus Cornelius.
According to the mesopredator release hypothesis, when apex predators disappear from an ecosystem, the number of mesopredators increase and thus predation of prey species increases. Since the extermination of large predators in KwaZulu-Natal (KZN), South Africa, the caracal (Caracal caracal), a feline mesopredator, is presumed to have spread throughout the province. At the same time, populations of the rare blue duiker (Philantomba monticola), a small forest antelope, have markedly declined; probably due to habitat loss and degradation, yet possibly also by increasing numbers of mesopredators. As forest patches become smaller and more isolated, the blue duiker’s ability to disperse and find refuges becomes limited. Any additional predation threats due to increased probability of encounters between blue duiker and caracal could drive local populations to extinction. However, quantitative data on current broad-scale distribution ranges and habitat requirements of both species are scant. The aim of this study was to use an environmental niche modelling approach to test the hypotheses that the caracal has expanded its distribution range; that its suitable habitat space (i.e. Grinnellian niche) overlaps considerably with that of the blue duiker; and that human impact affects suitable habitat space. I compiled a comprehensive occurrence database for caracal and blue duiker using historical data, recent sightings and survey responses from conservancies and protected areas throughout KZN. I then used niche-based environmental models (Maxent) to map the potential suitable habitat space of caracal and blue duiker, based on the occurrence data and different combinations of environmental and human impact variables. I calculated two niche overlap indices to quantify habitat niche overlap and compared these to 1000 expected overlap indices in a null model to test for niche equivalence. After spatial filtering, my database comprised 94 caracal and 90 blue duiker occurrence points for 1994 to 2013. For both species, vegetation biome, specifically forests, was the most important variable, with rainfall second most important. Approximately two-thirds of KZN was moderate to highly suitable habitat for caracal and one third was moderate to highly suitable habitat for blue duiker. The potential suitable habitat maps matched mostly with published distribution ranges for both species. Nonetheless, occurrence data within comparably lower habitat suitability, suggest caracal may have expanded their range further towards the north east of the province. The niche overlap scores were considerably high (D = 0.683 and I = 0.924), yet the caracal and blue duiker niche models were not identical, which can be expected of a generalist carnivore with a broad niche compared to the narrow niche of a specialist herbivore. At the highest threshold of habitat suitability the overlap between caracal and blue duiker covered 7% of KZN with 20% of the overlap occurring in 70% of the forest biome. The overlap consisted primarily of a large region in the midlands, smaller regions in the south and forest patches throughout KZN. Human impact variables contributed much less to the models than environmental variables and although the negative impact was mostly < 10%, the effect was widespread over ~60% of KZN for both species. My results confirm that the caracal distribution range has expanded historically from the western highlands to the south coast of KZN and thus overlaps considerably with the blue duiker distribution range in the midlands and southern coastal forests. Although the proportion of blue duiker in caracal diet reported in studies elsewhere is low (5% or less), any new threat to a blue duiker population already under pressure from a variety of other threats, could lead to an irrecoverable decline. Thus further studies investigating the effects of the expanding caracal population on the diminishing blue duiker population and other vulnerable prey species are warranted.
Niche requirements and breeding system of Hypericum pseudohenryi, an invasive plant species in South Africa.
(2016) Smith, Carryn Leigh.; Jürgens, Andreas.; Johnson, Steven Dene.
Invasive alien species threaten ecosystems throughout South Africa through alteration of the habitat and loss of biodiversity. Emerging invasive alien plants are those that have small populations, but have the potential to spread and cause widespread damage in the future. One of these emerging invasive alien plants, Hypericum pseudohenryi, came from China as an ornamental plant, and has invaded the KwaZulu-Natal Drakensberg and Midlands and mountains of the Eastern Cape. There is little published information about H. pseudohenryi, both in the native range and the invaded range. To help create better management plans for H. pseudohenryi in the future, experiments were done to determine whether the species is self-compatible and to determine the potential spread of the species across South Africa. Breeding system experiments found that H. pseudohenryi is self-compatible and is able to produce small numbers of seeds via autogamous self-fertilisation. This indicates that there is a high risk of new populations being formed from a single founder individual. Climate niche modelling using current climatic conditions revealed that H. pseudohenryi has not yet realised its full climatic niche in South Africa. As the climate changes in the future, climate niche modelling showed that the range of climatically suitable habitat of H. pseudohenryi is contracting into high altitude areas of the Drakensberg. These findings suggest that H. pseudohenryi requires intense management, especially in the Drakensberg area, to contain the spread of this emerging invasive species.
Assessing the success of red-billed oxpecker translocations as a conservation tool in KwaZulu-Natal, South Africa.
(2016) Jordaan, Maryna.; Downs, Colleen Thelma.; Combrink, Leigh.
There are numerous factors that contribute to a bird species becoming threatened and in need of increased conservation efforts in order to survive. Compared with fossil records, current extinction rates are much higher than expected, which emphasizes the need for conservation. Conservation translocations aim to increase the survival of threatened species by ameliorating their possibility of extinction, and contribute either to educational, scientific or supportive purposes in this. Reintroductions or translocations are a well-established method for increasing a species’ distribution and for restoring their historical range. Translocations are defined as human-mediated movements of organisms from one area and released in another. A translocation is only considered successful when a population is self-sustained through breeding of the released individuals and does not require intervention. Oxpeckers are African passerines from the starling lineage. Historically, red-billed oxpeckers (Buphagus erythrorhynchus) had a distributional range that extended from Eritrea to Somalia, through south-eastern Sudan to Zimbabwe and into the former Transvaal, Natal and Eastern Cape Provinces, South Africa. Oxpecker populations became threatened in South Africa in the early years of the 20th century. In southern Africa, red-billed oxpeckers became Near-Threatened as a result of cattle dips with substances toxic to the birds, and because of a significant decrease in their large game host species. Conservation efforts in the 1980s onwards have attempted to deal with the factors causing their demise. In 2002, The Endangered Wildlife Trust began translocating red-billed oxpeckers to areas where they had gone locally extinct, in an attempt to increase their current distribution and population in South Africa. Consequently, we documented and reviewed the various capture and quarantine methods, conducted since 1988 to the present, in the various translocations of red-billed oxpeckers. We also highlighted lessons learnt from these translocation events. To determine how successful these translocations were, we compared changes in the Southern African Bird Atlas Project (SABAP) reporting rate data and determined the presence or absence of red-billed oxpeckers at all the 24 translocation release sites in KwaZulu-Natal (KZN). In SABAP 1, data on species occurrences were collected at the Quarter Degree Grid Cell (QDGC) level. In SABAP 2, this was refined to pentads, where nine pentads are in one QDGC. Therefore, the reporting rate comparison was done at QDGC level. Prior to these translocations, red-billed oxpeckers were absent from all these sites. Specifically, we conducted transect surveys to determine red-billed oxpecker’s population estimates in Ithala Game Reserve (IGR) and Tembe Elephant Park (TEP). We also netted and ringed red-billed oxpeckers at these sites to obtain morphological and genetic data and to determine their breeding status. Furthermore, we distributed an online questionnaire to determine public perceptions on red-billed oxpecker’s range expansion in South Africa. We analysed the SABAP data using general linear modelling and the survey data using the Distance Programme in R Studio. There was a significant increase in reporting rates of red-billed oxpeckers in southern Africa since the end of SABAP1 in 1991 with several new areas where they had established. This was again confirmed from landowners reporting the first observation made of red-billed oxpeckers on their respective properties. Reporting rates at the specific translocated release sites had also increased. Twenty-four per cent of the QDGCs (n = 170) showed an increase in reporting rates in southern Africa, however, 36% of the QDGCs showed a decrease in reporting rates (n = 258). Fourteen per cent of the QDGCs (n = 100) showed new areas colonized by red-billed oxpeckers. In South Africa, red-billed oxpeckers had colonised several new areas, particularly near areas where reporting rates had increased. Twenty-six per cent of the QDGCs showed areas where red- billed oxpeckers were absent and had gone locally extinct (n = 187); however these areas were mostly in Botswana and Zimbabwe. We determined that habitat, host preference and host herd size were important factors when calculating population densities of red-billed oxpeckers. Detection probabilities for red-billed oxpeckers were highest in open bush habitat and where large herds were present. In IGR, red-billed oxpeckers were seen in 8% (n = 33) of the total of 391 observations made. In TEP, red-billed oxpeckers were observed in 6% (n = 24) of the total 378 observations made. In both IGR and TEP all red-billed oxpeckers we trapped and ringed had not been previously ringed and some had brood patches supporting their successful reproduction there. To date, a total of 24 reintroduction events and 13 population reinforcements have taken place, with a total of 1359 red-billed oxpeckers translocated in South Africa. The increase in reports of red-billed oxpecker sightings, especially at release sites and on nearby land, showed the importance of translocations for the conservation of oxpeckers. In addition, the placement of artificial nest boxes has increased the likelihood of red-billed oxpeckers breeding at their new translocated site. The recent down-grading of red-billed oxpeckers from Near Threatened to Least Concern, and the data collected in our study support the success of translocation as a conservation tool for this species. Translocations of red-billed oxpeckers in South Africa should be considered one of the more successful of such programmes as indicated by its success.
A biogeographic study of the KwaZulu-Natal sandstone sourveld patches within the eThekwini Municipal Area.
(2016) Drury, Charmaine Crystal.; Ramdhani, Syd.; Naidoo, Sershen.; Carbutt, Clinton.
KwaZulu-Natal Sandstone Sourveld (KZNSS) is an endangered vegetation type in South Africa. Approximately 68% of KZNSS is transformed, with remaining patches existing within an urban and suburban matrix. Fragmented patches of KZNSS found within the eThekwini Municipal Area (EMA) represent a conservation priority but are often not managed/ conserved appropriately as they are sometimes misclassified as Indian Ocean Coastal Grassland Belt (IOCGB) based on their close proximity to the latter vegetation type in a number of areas. This motivated the present study which involved characterising the flora of eight grassland patches within the EMA presently categorised as follows: three KZNSS sites (viz. Giba Gorge Environmental Precinct, Inanda Mountain and Springside Nature Reserve), three IOCBG sites (viz. Spyhill Open Space, Tanglewood Nature Reserve and Edgecliff Open Space) which are currently called Ecotonal given their close proximity to KZNSS, and two IOCGB sites (viz. New Germany Nature Reserve and Roosfontein Nature Reserve). Floristic surveys, which involved quadrats sampling were performed year round (c. 60% in the winter, 30% in the summer and the remaining quadrats performed in spring or autumn) until an 80% sampling effort was achieved. Additionally, transect sampling was performed monthly for a year at each site. Data from both methods were used to determine the vegetation composition and structure at each site. The below-ground flora of each site was also characterized by removing 30 – 35 soil samples after the two main flowering events (late November and early December as well as late April and early May) at each site and allowing germination to occur, with the resulting germinants being identified and quantified. Field observations on levels of disturbance and management practices at each were also considered. When data for quadrats and transects were pooled, 263 species were found to occur across the eight sites, with 110 of these being common to all three vegetation categories. Only one of the eleven endemic taxa characteristic of KZNSS were found across all three vegetation categories, while none of the endemic taxa associated with IOCBG were found, suggesting iv that identifying KZNSS or IOCBG based on endemic (i.e. diagnostic) species may be inappropriate at the sites investigated here. Further comparisons showed KZNSS and Ecotonal to contain more species than IOCBG, which were spread across more plant families (55 found in total), although IOCBG had one less site than KZNSS and Ecotonal. Diversity measures indicated that Ecotonal is more similar to KZNSS, with more species in common between KZNSS and Ecotonal than Ecotonal had with IOCBG. Additionally, diversity measures show very little differentiation between the dominant taxa of IOCBG from KZNSS. Cluster analyses and ordinations confirmed the current classification of Ecotonal sites as part of IOCBG, despite Ecotonal sharing more superficial similarities with KZNSS. Island biogeography theory‟s area and distance effects were not upheld – most likely due to the sites not being truly isolated from each other and a very localised spatial scale, the limited temporal scale (current status a result of the past 200 years), the lack of a true originating mainland and anthropogenic disturbance. Interestingly, the below-ground flora represented only c. 10% of the species found above-ground for all three categories, with Sørenson similarity index ranging from c. 15 – 22% as opposed to the 50% expected for southern African grasslands. This suggests that seedbank health and hence, regenerative potential may be poor at many of these sites and this may necessitate species reintroduction and habitat restoration at a number of these sites. Additionally, the effects of disturbance were evident across sites in all three vegetation categories, with disturbed sites (Edgecliff Open Space, Inanda Mountain and Roosfontein Nature Reserve) containing fewer species of conservation concern, fewer indigenous taxa in general and more alien plant taxa. Diversity indices also suggest that disturbed sites were more heterogeneous. However, disturbance agents such as herbivory appear to have had an enriching effect in term of the abundance of graminoids within the germinable soil seedbank. Alien taxa also occurred frequently in the below-ground flora but were not noted in the above-ground flora which suggests that given further disturbance/transformation, some of these sites are prone to alien plant invasion. The study suggests that IBT is not applicable to vegetation islands (grasslands in this case) with varying levels of transformation in urban matrices. The results confirm the high levels of transformation reported for sub-tropical grasslands within South Africa, specifically KZNSS, and highlight the need for floristic surveys to delimit different grassland types and in turn ensure their appropriate conservation and/or rehabilitation.
Movement, home range and habitat use in leopard tortoises (Stigmochelys pardalis) on commercial farmland in the semi-arid Karoo.
(2016) Drabik-Hamshare, Martyn.; Downs, Colleen Thelma.
Given the ever-increasing demand for resources due to an increasing human population, vast ranges of natural areas have undergone land use change, either due to urbanisation or production and exploitation of resources. In the semi-arid Karoo of southern Africa, natural lands have been converted to private commercial farmland, reducing habitat available for wildlife. Furthermore, conversion of land to energy production is increasing, with areas affected by the introduction of wind energy, solar energy, or hydraulic fracturing. Such widespread changes affects a wide range of animal and plant communities. Southern Africa hosts the highest diversity of tortoises (Family: Testudinidae), with up to 18 species present in sub-Saharan Africa, and 13 species within the borders of South Africa alone. Diversity culminates in the Karoo, whereby up to five species occur. Tortoises throughout the world are undergoing a crisis, with at least 80 % of the world’s species listed at ‘Vulnerable’ or above. Given the importance of many tortoise species to their environments and ecosystems—tortoises are important seed dispersers, whilst some species produce burrows used by numerous other taxa—comparatively little is known about certain aspects relating to their ecology: for example spatial ecology, habitat use and activity patterns. Understanding an animal’s use of an environment is important in learning more about certain ecosystem functions and offering information to guide future conservation management. We studied spatial ecology and habitat use of the Leopard Tortoise, Stigmochelys pardalis: the largest and most abundant species in the region. Ten Global Positioning System (GPS) transmitters were placed eleven adult tortoises (one was redeployed following death of one individual), providing a minimum of 12 months of bihourly movement data. We used these data to estimate home ranges, indicate important predictor variables to movement, and investigate differences in space use between seasons, sex, and time of day. Using modern home range estimation techniques—such as GPS telemetry and Kernel Density Estimation (KDE)—we provided evidence that Leopard Tortoises have very large home ranges (n = 9, mean ± SE: 121.86 ± 28.12 ha, range 40.53—258.52 ha), with no significant differences between males and females. This large home range size supports previous research in the region, and supports the theory that populations in more arid regions have larger home ranges than in regions of higher rainfall. However, we also found that some Leopard Tortoises do not hold a home range: site fidelity tests suggested that two individuals exhibited apparent nomadic behaviour (hence home range estimated for only 9 of 11 tortoises above). When investigating seasonal changes in home ranges with generalised linear mixed models (GLMMs), we found important individual (sex and body mass), and weather (temperature and rainfall) predictor variables. We also used GLMMs to investigate bihourly and daily movement in Leopard Tortoises. Several important predictor models were identified, including temperature, rainfall, habitat type, availability of water, time of year, and time of day. We found a negative association for movement with distance from water sources, indicating that tortoises are more likely to move larger distances when closer to these resources. We attributed this behaviour to tortoises’ ability to supplement much of their water intake from water-rich food resources (e.g. succulents, grasses and forbs), as shown in previous studies. In contrast, as tortoises are still required to drink water to maintain water balance and excrete electrolytes and nitrogenous wastes, tortoises that have knowledge of drinking water resources within their home range are likely to make regular long distance movements to these areas. Movement data suggests that some Leopard Tortoises make nocturnal movements, despite tortoises being strongly diurnal animals. As adult Leopard Tortoises are large enough to avoid predation, are subject to reasonable night-time temperatures, and are able to maintain core temperatures above ambient temperatures, visibility of surroundings may be the largest limitation to movement. Further research is required, but we found higher nocturnal movement associated with periods of higher lunar illumination: e.g. full moon phase vs new moon phase. As stated above, there is a great importance in learning more about tortoises and contributing to conservation. One of these areas is improving genetic contributions that assists in identifying species. However, previous genetic research using a common mitochondrial primer site—cytochrome c oxidase I (COI)—has shown poor success rates with respect to tortoises. Using all tortoise COI sequence information available on the Barcode of Life Database (BOLD), and six of our own Leopard Tortoise samples, we recommend primer sites for the production of a mini-barcode specific to tortoises. Such a mini-barcode can be used to improve success rates in identifying specimens based on DNA, and increase extraction success with degraded DNA: e.g. museum specimens or environmental DNA. Information from this study can be used to further understanding of environmental and weather conditions that influence movement and space use in tortoises. We have identified several important resources and predictor variables which can affect how a tortoise uses its environment. Given that environments continue to be fragmented, degraded, or lost, better understanding of potential impacts on tortoises is required. We make recommendations on future research into fracking in the region, as well recommendations for use of electric fencing, which has been shown to cause large numbers of mortalities in Leopard Tortoises.
Use of freshwater fish to evaluate the wellbeing of selected rivers in KwaZulu-Natal, South Africa.
(2017) Evans, Wesley Drayson.; Downs, Colleen Thelma.; O'Brien, Gordon Craig.
Freshwater makes up just 0.01 % of the total water on earth but the fish species inhabiting it make up around 20 % of all vertebrate species. For centuries, human settlements have relied upon freshwater fish for food, recreation and the ecosystem services they provide. As a watershort country, South Africa has been unable to keep up with the increasing water demands from the ever-growing population. This has resulted in increased abstraction from rivers and the construction of instream barriers such as dams. The impacts of these are relatively poorly known for most South African fish species. Fish species are good indicators of river wellbeing as they are relatively easy to collect and identify, they are responsive to changes in environmental quality and they are mobile and long living. Fish have globally been established as ecological indicators and scientists and managers use attributes of fish related to various levels of biological organisation from cellular to community level. The ecologically relevant evaluations of community structures of fish can be used to evaluate the condition of many determinant factors of riverine ecosystems. Numerous multi-variate statistical analysis techniques have been established to allow for a robust statistical evaluation of sifts in community structures of fishes and relate changes in associated ecosystem variables to characterise causality. Additional community metric measure tools such as the Fish Response Assessment Index (FRAI) is being used throughout South Africa successfully to evaluate the wellbeing of fish communities and identify causes of probable shifts in communities. The FRAI is based on fish species intolerances and preferences, and their response to drivers of change in riverine ecosystems. By comparing the community structure changes of fish communities to outcomes of community metric measures the lines of evidences can be used to validate outcomes and reduce uncertainty in the application of the approach for the region. Labeobarbus natalensis, locally known as the KwaZulu-Natal (KZN) yellowfish or scaly, is ubiquitous in KZN, South Africa. Populations that have historically been found in most rivers within the province but have apparently declined in response to increased use of water resources. Major determinants of their decline include habitat loss, altered water quality and quantity, and the establishment of barriers such as dams and weirs that hinders migrations. The probable occurrence of Labeobarbus natalensis in KZN rivers and environmental factors and anthropogenic determinants affecting their presence/absence were evaluated.Assessments were carried out at 40 sites on 23 river systems in KZN, South Africa. Four seasonal surveys were undertaken between January 2015 and April 2016. The rapid assessments included monitoring fish communities, water quality and habitat availability/conditions. Fish were collected using a range of sampling techniques appropriate to the habitats observed in the rivers. Sampling methods included the use of electrofishing and passive and active netting techniques. Fish collected were identified, measured to total length (TL) and then released alive at their capture location. The diversity, abundance and population structures of fishes were evaluated and compared with known historical distributions. Community structure analyses were carried out using multivariate statistical procedures for the fish community structures in relation to the drivers of community structure changes. In addition to the two community-based structure analyses which were done, a population-level analysis was carried where TL was used to assess the shape and wellbeing of populations. Outcomes includes significant shifts in fish communities between catchments and within catchments and between seasons. Many communities were observed to have been significantly correlated with water quality, quantity and habitat variability associated with different land use scenarios. The FRAI results varied representing communities in a largely natural to critically modified condition that were closely correlated to changes in community structures analysed statistically. The general reduction in the wellbeing of many communities throughout KZN were partially attributed to the drought that took place during the study period. Additional stressors identified included the increase in range of alien predators and competing fish species and a range of land use activities. The FRAI scores indicated that study sites where agricultural activities were the dominant land use type were of most concern, as the fish communities occurred in severely and critically modified conditions. Sedimentation impacts affecting instream habitats and water quality from poor agricultural practices likely resulted in shifts in the dominant substrate type from cobbles/gravel to sand/silt. It was found that the semi-rheophilic KZN yellowfish had a preference for fast flowing water and cobbles/boulders as a substrate type and as a cover feature. Furthermore, invasive fish, abstraction and industrial use all had negative impacts on the state of the rivers and the KZN yellowfish population wellbeing. The drought, which was impacting the northern parts of KZN the most, likely accelerated the decline in fish populations. The vulnerability of substrates such as gravel, cobbles, and boulders to sedimentation has the potential to result in a population shift, away from L. natalensis and towards species like Oreochromis mossambicus and Micropterus spp. The KZN yellowfish populations in the Mkuze and Mlazi River systems in particular were observed to be in a poor state with low abundances and poor population structures of the species in the Mkuze River and no yellowfish were observed in Mlazi River system. Contrastingly, the KZN yellowfish populations in the Thukela and uMngeni River systems in particular, were in good health. They showed good population structure and good recruitment. The overall wellbeing of KZN yellowfish populations in many river systems has declined in response to consistent increases in stressors observed in the province due to increasing use of water resources and expansion of alien fish distributions. Increased conservation efforts are required to curb the overall decline of the wellbeing of freshwater fishes in KZN observed during the study. The spread of alien species of fish is of particular concern, along with habitat loss which is of high ecological importance to native fish species. The river catchments which are situated in areas of high anthropogenic use were found to be the most impacted, followed by areas with intense agricultural utilisation. The drought during the study period likely exacerbated the aforementioned drivers of change, an area which requires further study. This study investigated specific threats and environmental driving factors that impact freshwater fish populations in KZN. The outcomes of the study include information on fish communities that can facilitate the identification of key conservation areas for local riverine conservationists and demonstrate the successful use of multiple lines of evidence to monitor and evaluate fish community wellbeing in KZN.
Pollination ecology and the functional significance of unusual floral traits in two South African stapeliads.
(2017) du Plessis, Marc Alexander.; Shuttleworth, Adam.; Johnson, Steven Dene.; Nicolson, Susan W.
Carrion and dung mimicking plants often exhibit unusual floral traits which are believed to attract necro- and coprophagous insects as pollinators. Our understanding of these unusual traits and their functions is very limited. Stapeliads (Apocynaceae: Asclepiadoideae: Stapeliinae) are a monophyletic group of some 400 species of stem-succulent plants, many of which emit foul odours and exhibit unusual morphological traits that have anecdotally been assumed to represent adaptations to enhance the flowers’ resemblance to carrion or dung. This study looked at the pollination biology of two stapeliads, Orbea variegata and Stapelia hirsuta var. hirsuta, and explored the functional significance of some of the floral traits commonly associated with carrion or dung mimicking flowers. Further, odours emitted by both species were compared to the odours of putative models to explore the chemical basis for the assumed mimicry. Orbea variegata attracted flies from the families Muscidae, Calliphoridae and Sarcophagidae (at sites near Scarborough and Clifton, Western Cape) and individuals from each of these families were found carrying pollinia. The scent of O. variegata flowers was found to be dominated by dimethyl disulphide, dimethyl trisulphide as well as phenol. The presence of both these compounds suggests mimicry of both carrion and dung, although an ANOSIM analysis indicated that the odour of O. variegata shared more similarities with dung. This suggests that O. variegata is fairly generalist and explains the attraction of various flies that are associated with carrion or faeces by the flowers of this species. In experiments testing the importance of black versus yellow colouring and the importance of patterning, flies were found to prefer black coloured models in the presence of O. variegata odour, whereas the presence and size of blotching on the corolla lobes had no significant effect on fly visits. The colours of the black blotching and yellow of the corolla lobes showed minimal chromatic contrast when interpreted using the Troje (1993) fly vision model, although background rocks showed chromatic contrast, suggesting flies can distinguish between the flowers and the background. In an experiment testing the importance of odour for attracting flies, significantly fewer flies were able to locate concealed flowers compared to visible flowers, suggesting an important role for visual cues for flies to locate the odour source. Stapelia hirsuta var. hirsuta was found to exhibit two floral colour morphs at Swellendam (Western Cape). The yellow morph was rarer than the maroon morph. These flowers attracted flies belonging to the Muscidae, Calliphoridae and Sarcophagidae families, although only Calliphoridae and Sarcophagidae were found to carry pollinia. The odour composition of these two morphs differed slightly, where the odour of the maroon morph was dominated by dimethyl disulphide, dimethyl trisulphide and p-cresol and the yellow morph was dominated by dimethyl disulphide, dimethyl trisulphide and limonene. The ANOSIM analysis of odours emitted by S. hirsuta var. hirsuta in relation to that of various fly oviposition substrates suggested that these flowers are dung mimics rather than carrion mimics, although the presence of sulphides suggests possible mimicry of both. The yellow morph had higher fly visitation rates than the maroon morph. In experiments testing the role of floral trichomes, the removal of floral trichomes significantly decreased the visitation rates to the flowers, as well as the amount of time visitors spend on the flowers. Again, visual cues were shown to be of importance, as visible flowers received more visits than concealed flowers. Analysis of colours of different floral morphs, using the Troje (1993) fly vision model, suggests that flies cannot perceive chromatic colour differences between morphs. In these studies, I have shown that O. variegata and S. hirsuta var. hirsuta are visited and pollinated by carrion associated flies, and the flowers emit odours associated with both carrion and dung. This work sheds light on some of the floral features that are often associated with carrion and dung mimicry by flowers and the roles they play in the attraction of flies.
Managing nesting hawksbill turtles (Eretmochelys imbricata) on a small tropical island.
(2018) Gane, Julie Alexandra.; Downs, Colleen Thelma.; Brown, Mark.
Although human impact has caused the hawksbill turtle (Eretmochelys imbricata) to be on the brink of extinction, conservation efforts are on the increase and management strategies are being re-defined to manage the species towards rapid population increases. Numerous conservation measures have been applied and tested, with varying levels of success, to minimize threats and increase hatchling recruitment success rates. Conservation management is imperative for the survival of this species and has been shown to be easiest and most feasible at the nesting and hatching stages. On Cousine Island where this study took place, a turtle monitoring and management program was initiated in 1994 to protect nesting females and incubating eggs at the nesting and hatching stages of the lifecycle. Controversial conservation measures such as the handling of eggs, relocating clutches and application of crab proof barriers, have been applied on an ad hoc basis to minimize the high levels of mortality from natural erosion and crab predation. The merit of these practices, such as the translocation of egg clutches and the implementation of these specific barrier methods has never to our knowledge been scientifically tested using controlled experimentation. The first aim of this study was to find the most effective crab barrier method for increasing hatchling recruitment success and minimising predation rates with limited negative consequences. The second aim was to decipher crab density trends in order to offer a proxy for the number of crabs a nest might be exposed to within an area and develop beach profiles along the entire nesting beach to provide an expression of beach morphology to minimise nest loses from erosion. Finally, we analysed 10 years of nesting ecology and hatching success data with the aim of providing nesting and hatching trends to inform management decisions on Cousine Island into the future. Results across this study indicated that management measures can have both positive and negative effects on the nesting ecology and hatchling recruitment success in particular. We found that hawksbill clutches incubating without crab barriers are susceptible to losing on average a third or more eggs to crab predation than those with a crab barrier in place. Nests which were protected with netting had significantly higher hatchling recruitment success rates and nests protected with fencing had significantly lower predation rates than control nests. The use of netting, however, had a substantial cooling effect which can potentially distort natural sex ratios. Results across the entire study indicated that spatial distribution and environmental variations have an effect on embryonic development, hatchling fitness, sex determination, hatching success and the risk of predation. The hatchling recruitment success on Cousine Island was also found to be affected by nest losses each season from seasonal beach erosion. Beach dynamics were also found to be cyclical and we discovered that the nesting beach is prone to higher levels of erosion than accretion which created significant changes to beach width across the season. This study showed that when focusing turtle conservation measures at the nesting site, hatchling recruitment success can be increased by minimising mortality at the egg and hatchling stage. The aim in the long-term is to assist with the analyses of local and global population dynamics, deciphering threats and minimising the threat of extinction.

Browse

Browsing Masters Degrees (Ecology) by Issue Date