Ecology

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The comparative ecology of Natal's smaller estuaries.
(1983) Begg, George William.; Hanks, John.; Bowmaker, A. P.
Fifty one of Natal's 73 estuaries have been almost completely overlooked in terms of any scientific study, despite which a marine nursery function has commonly been attributed to each of them. In the knowledge that many of these systems were normally closed and others were in a seriously degraded state, this study was undertaken with the aims of examining their present day community structure in order to provide a basis upon which their future condition can be monitored and to provide a classification of these coastal resources. The study area incorporated 62 different systems extending over 240 km of the Natal coastline south of the Tugela River. During the three year study period (Sep 1979 - Nov 1982) 82 515 specimens, comprising an assemblage of 125 different species, were caught by means of a small beam trawl. These comprised 86 species of fish, 21 species of crabs and 18 species of prawns. The data obtained were correlated to abiotic variables such as mouth condition, salinity, temperature, dissolved oxygen, water transparency, depth, nature of the substratum and peripheral vegetation. Based on the ability of biota to synthesize environmental variables into one common response, multi-variate analysis is used to demonstrate the similarity in community structure between open and closed systems (for example) or between fresh and saline systems, and thereby resolve an age-old argument about estuary classification. The data also suggest that in their present day condition only six of the systems studied make a significant contribution to the recruitment of estuarine-dependent marine stocks (sensu stricto) principally because of their open mouth condition. Closed systems, deliberately classified as lagoons, have a different resource value, being utilized primarily by resident species that can complete their life cycle within the system. An appreciation of this salient difference helps to reinforce the critical need for an effective management strategy to be implemented to prevent Natal's dwindling estuarine resources from deteriorating any further. The term 'estuarine-dependence' is critically examined in this context to show that a species more dependent on estuaries than any other, is man. It is argued that man's continued abuse of these resources is shortsighted, and that the most serious threat of all is sedimentation, accelerated in this instance beyond the geological norm by catchment mismanagement. The practical application and value of classification to planning and management is demonstrated and a methodology proposed, based on community responses, for the monitoring of the future environmental condition of each estuary and lagoon in Natal.
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.
The ecology and parasitology of small mammals from selected sites in Swaziland.
(2007) Mahlaba, Themb'alilahlwa A. M.; Perrin, Michael Richard.
The study was initially a long term study of the ecology of small mammals at Mlawula Nature Reserve in the eastern part of Swaziland. Due to the drought and dwindling numbers of rodents in the reserve the study was redirected to determining the factors resulting in the low numbers. The impacts of food and cover and grazing by the larger ungulates were studied. In addition, the age class distribution and gastro-intestinal parasites of small mammals were studied. A study of the small mammals in the Siphiso Valley of Mlawula Nature Reserve was conducted over four years from August 2000. The population density, biomass and composition of the small mammal community in the area were studied. The community comprised of Mus minutoides A. Smith, 1834, Mastomys natalensis (A. Smith, 1834), Lemniscomys rosalia (Thomas, 1904), Crocidura hirta Peters, 1952, Steatomys pratensis Peters, 1846 and Graphiurus murinus (Desmarest, 1822). Mus minutoides was the dominant species with pregnant females caught from November to May. Species richness varied significantly with the time of the year. The biomass, density and numbers of small mammals were low and by the end of the second year of the study, small mammal density was close to zero. Mastomys natalensis from a Middleveld study site, Luyengo, Swaziland were used to study the age structure of the population by means of eye lenses. The eye lens to age (in days) curve determined by Leirs (1994) was applied. A large percentage of M. natalensis in winter (June) were 2 months old while in spring/summer (October to March) the population consisted mainly of 3 month old specimens. A very low number of specimens were older than 4 months. This suggests a high mortality/removal rate of the young especially in the winter months. The impact of grazing pressure and rainfall on small mammal densities were investigated. High grazing pressure by ungulates rendered the habitat unsuitable for small mammals as it removed cover and encouraged colonization by alien invasive plant species. This effect was exacerbated by diminishing and unpredictable rains, such that mild grazing pressure negatively impacted on small mammal communities and on individual species. When the small mammals disappeared from the study site, M. natalensis was reintroduced to determine the factors that led to the disappearance. Supplementary food resulted in the longest persistence of the reintroduced mice while the impact of additional cover was small. Predation was likely responsible for the rapid decline of the reintroduced mice. Small mammals were examined for ectoparasites and gut parasites as these were thought to negatively impact on their physiology and reproduction. Ectoparasites collected included the ticks Ixodes sp. and Boophilus sp., the mite Allodermanyssus sp. and another species of mite. The gastrointestinal tracts contained the helminths Syphacia sp., Heligmonina sp., Trichuris sp., Protospirura sp., two unidentified nematode species and different cestode species. A new species of heligmosomoid nematode is described and named.
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.
Ecology and evolution of the specialized hemipepsis-wasp (Hymenoptera : Pompilidae) pollination guild in South Africa.
(2011) Shuttleworth, Adam.; Johnson, Steven Dene.; Brothers, Denis John.
Pollinators are believed to have played a key role in the radiation of flowering plants. The Grant-Stebbins model of pollinator-mediated speciation, in which evolutionary shifts between pollinators result in phenotypic diversification and enforce reproductive isolation, is one of the most compelling hypotheses for the rapid diversification of angiosperms. A key principle in this model is that plant pollination systems tend towards specialization, resulting in convergent suites of floral traits (syndromes) associated with particular types of pollinators. However, the expectation of pollination system specialization is not always supported by ecological data and has also been questioned on theoretical grounds. In this thesis, I examine pollination by Hemipepsis spider-hunting wasps (Hymenoptera, Pompilidae, Pepsinae) and use this system to address questions about levels and proximal mechanisms of floral specialization, floral shifts and convergent evolution of floral traits. Specialized pollination by Hemipepsis wasps is a newly described pollination system within the angiosperms. I document pollination by these wasps for the first time in 15 South African grassland plant species, including two species of Eucomis (Hyacinthaceae) and 13 asclepiads (Apocynaceae: Asclepiadoideae). In one of the asclepiads, Xysmalobium undulatum, I describe a bimodal pollination system involving both Hemipepsis wasps and a cetoniine beetle. I also describe an unusual and potentially antagonistic pollination mechanism whereby wasps are systematically dismembered during the insertion of pollinia in the two asclepiads Pachycarpus asperifolius and P. appendiculatus. I have used these and previous case studies to establish the existence of a new pollination guild, consisting of at least 21 plant species (across 10 genera and three families), that are reliant on four functionally similar species of Hemipepsis wasp for pollination. Plants in the guild are distributed throughout the moist grasslands of eastern South Africa and flower from September through until early May, peaking in December/January. The Hemipepsis-wasp pollination guild is characterized by high levels of functional specialization (17 of the 21 known guild members are pollinated exclusively by Hemipepsis wasps), despite the absence of morphological adaptations to prevent non-pollinating insects from accessing nectar. I used field and laboratory based experiments to explore the function of floral traits in enforcing specialization. These showed that Hemipepsis wasps primarily use scent, rather than visual cues, to locate flowers, but I was unable to firmly identify specific compounds responsible for the attraction of these wasps (compounds that elicited antennal responses in preliminary GC-EAD experiments did not attract wasps in bioassays). The chemical composition of the floral scents of guild members was examined for 71 individuals representing 14 species in addition to previous studies, and found to comprise complex blends of volatiles (usually containing between 30 and 50 compounds), typically dominated by aliphatics and monoterpenes with small amounts of aromatics. I also showed that the floral colours of guild members are similar to background vegetation, suggesting that floral colours are adapted for crypsis to avoid detection by non-pollinating insects. Palatability choice experiments with honeybees showed that non-pollinating insects find the nectars of at least three of the asclepiad guild members distasteful. Plants in this guild thus appear to achieve specialization through biochemical filters (scent as an attractant and differentially palatable nectar) and cryptic coloration. Pollinator-mediated convergence in floral traits is the fundamental basis for pollination syndromes, but has seldom been rigorously analyzed. Flowers in the Hemipepsis-wasp pollination guild share several qualitative traits, including dull greenish- or brownish-white colour, often with purple blotches, exposed sucrose dominant nectar with a relatively high sugar concentration (typically over 50% sugar by weight) and a sweet/spicy fragrance to the human nose. To test for convergent evolution in guild members, I compared scent, nectar and colour traits of guild members to those of congeners with different pollinators. Although traits often differed between guild members and their congeners, I found little evidence for overall convergence in floral scent profiles and nectar properties, but floral colours in the guild were significantly closer to the colour of background vegetation than those of congeners. At this stage, the lack of knowledge about specific floral volatiles that influence Hemipepsis-wasp behaviour and secondary nectar constituents that limit non-pollinator visits makes it difficult to identify the extent of biochemical convergent evolution within the guild. The directions and functional traits involved in evolutionary transitions between pollination by Hemipepsis wasps and other vectors are currently difficult to ascertain as there is limited phylogenetic data for the plant families concerned. In the genus Eucomis, fly and Hemipepsis-wasp pollinated species are very similar in floral morphology and colour, but differ strongly in floral scent. Using manipulative field experiments in conjunction with detailed analyses of colour, scent and morphology, I was able to show that a shift between wasp and fly pollination could be induced simply by manipulating oligosulphides in the scent emission from inflorescences. When considered in combination with other experiments highlighting the importance of scent as a pollinator attractant for all guild members, this suggests that scent properties may have played a key role in the evolutionary transitions between pollination by Hemipepsis wasps and other vectors. This research has established that pollination by Hemipepsis spider-hunting wasps is more geographically and phylogenetically widespread than was previously known, and has confirmed that these wasps are important and consistent pollinators in southern African grassland ecosystems. I have shown that a distinct guild of plants is specialized for pollination by these wasps. The high levels of specialization within this guild highlight the effectiveness of biochemical filters and cryptic coloration in limiting the spectrum of flower visitors. The major challenge ahead will be to identify the floral volatiles that attract Hemipepsis wasps and the non-sugar constituents that make the nectars of some guild members differentially palatable. These would both contribute greatly to our understanding of floral specialization and the mechanisms involved in the radiation of the angiosperms.
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.
Spatial and reproductive ecology and population status of the Nile crocodile (Crocodylus niloticus) in the Lake St Lucia estuarine system, South Africa.
(2014) Combrink, Alexander Stanislou.; Downs, Colleen Thelma.
The Lake St Lucia estuarine system, Africa’s largest and oldest protected estuary, also contains the largest Nile Crocodile (Crocodylus niloticus) population in a single waterbody in South Africa. We investigated the species’ spatial and reproductive ecology as well as population status in order to make management recommendations. During the first decade of the 21st century, the St Lucia estuarine lake experienced a prolonged drought, streams ceased flowing and in 2006 more than 90% of the total water area evaporated. We conducted 10 aerial surveys from 2009 - 2013 and recorded the majority of crocodiles in the Narrows, a ~27 km low salinity channel south of the lake. Above average rainfall at the end of 2010 resulted in the refilling of the lake, and most crocodiles moved north to the lake. We estimated the sub-adult and adult population at 1005 ± 137 individuals. We investigated detailed movements and activity for 18 Nile Crocodiles using GPS-satellite transmitters. The overall activity level was 41.0 %, and it differed significantly throughout the day. There was a significant seasonal effect on activity, peaking during autumn (52.0 %), while crocodiles were most inactive in winter (30.5 %). Crocodile size and mobility were positively correlated with mean daily movement (1244 m). Adults moved more at night, but sub-adults were significantly more mobile during the day. There was a considerable seasonal variation in mobility, with the longest movements during autumn and the shortest in winter. About 60 % of total daily movements were < 1 km per day, but for sub-adults this calculation was 96 %. We recorded complex and varied home range patterns for 14 Nile Crocodiles, resulting from differences in size, sex, reproductive status and habitat. The median home range and core-use area of adults were significantly greater than sub-adults. Three size- related patterns of home range behaviour emerged for adult males; transient, (< 3.0 m TL), topographically confined (3.5 - 4.0 m TL) and “territorial” (> 4.0 m TL). Adult males revealed an inverse correlation between home range size and crocodile size, while the home range sizes of adult females were generally more homogeneous. All nesting females displayed an explosive increase in mobility and space-use subsequent to the nesting period, and all adults, except one female in the central lake, moved during winter in the drought period to large crocodile congregations south of the lake. Sub-adults occupied significantly smaller home ranges than adults, which were habitat specific with strict spatial partitioning. They remained in shallow vegetated areas adjacent to deep water, avoiding open deep water altogether. Nile Crocodile nests have been monitored since 1982, with mean nest abundance = 76.19 ± 6.42, range: 29 - 141. The macro-level heterogeneity of nesting habitats reflects the spatio-temporal diversity of the Lake St Lucia system, and is possibly unique within a single Nile Crocodile population. Changes in nest abundance and distribution were seemingly related to increased human disturbance and habitat transformation in the northern and southern parts of the lake. Hydrological variability, especially during droughts, combined with the state of the estuary mouth (i.e. open or closed), affected prey abundance/availability contributing to large variation (6.9 % - 56.4 %) in nest effort from 1982 - 2013. All nests were located close to freshwater streams or seepage areas. We confirmed the re-use of the identical nest-site by a female, while other females oviposited in nest-sites occupied by different females during previous years. Despite variable nest effort, the St Lucia nesting population remains the largest recorded nesting population in South Africa, and least vulnerable to flooding. The mean home range of nesting Nile Crocodile females (0.85 ha) was significantly smaller than non-nesting females (108.41 ha) during the nesting season. Activity levels and mean daily movements on the nest were 8.1 ± 2.5 % and 213 ± 64 m, respectively, and increased to 47.9 ± 11.7 % and 2176 ± 708 m during the post-nesting period. Overall levels of nest fidelity were 82.8 ± 11.7 %, which increased to 87.3 ± 7.8 % at night. The highest nest fidelity recorded during incubation was 99.7 % over a 96 day period. We investigated nest predation, hatchling liberation and nest-guarding activities of nesting Nile Crocodile females using remote camera traps. We captured 4305 photographs of 19 nest-guarding females over four years. Seven nests (36.8 %) were raided by the egg predators Water Monitors (Varanus niloticus) and Marsh Mongooses (Atilax paludinosus), on average 12.1 days ± 6.2 subsequent to trap camera employment. All females settled back on the nest following the first predation event and on average, females returned to their nests three times ± 0.8 between nest raids before finally abandoning the nest. Nest raids continued on average 5.9 days ± 1.6 while on average 18.8 ± 4.0 raids per nest were recorded. Five females were captured by trap cameras liberating hatchlings. During the day females were almost never photographed on the nest, but during the late afternoon or early evening females moved onto the nest and continued to stay there during the night. Females always defended their nests aggressively against non-human intruders. We investigated homing behaviour and specific movements using a GPS-satellite transmitter by translocating an adult female (2.7 m), with a known home range, ~50 km north (straight line distance) to the False Bay area of Lake St Lucia. Following release, the individual moved a total distance of 178.3 km over 136 days (mean daily movement = 1311 ± 207 m), compared with 60.4 km (mean daily movement = 444 ± 32 m) for the identical time period the previous year. Homing movement was not continuous, but characterised by periods of extensive and directed mobility followed by prolonged periods of inactivity associated with freshwater or low salinity habitats. The translocated crocodile displayed remarkable navigational abilities, even though this required negotiating complex habitat challenges including extensive areas of the lake that were either hypersaline or completely dry, resulting in frequent and extensive overland movements. On 14 September 2012, the individual returned to the same freshwater pool where it was captured 136 days previous. This is the first study to confirm homing behaviour for Nile Crocodiles, and supports growing evidence that crocodilians and other ectothermic taxa possess complex navigational abilities. Our study revealed numerous novel insights into the ecology and behaviour of Nile Crocodiles and some of the findings may be applicable to other crocodilian taxa. We hope the results will guide the management and conservation of this threatened species.
Flexibility in metabolic rate in a small Afrotropical bird Zosterops virens.
(2014) Thompson, Lindy Jane.; Downs, Colleen Thelma.; Brown, Mark.
The scientific literature contains hundreds of studies on avian basal metabolic rate (BMR), many of which assumed that BMR was fixed for each species. Yet those from the last few decades have shown avian BMR to be a flexible trait, changing temporarily and reversibly in response to numerous environmental variables. Given that birds from lower latitudes are relatively understudied compared with temperate and Holarctic species, and that seasonal trends in BMR of southern hemisphere birds are not well understood, we looked at seasonal variation in BMR of a small Afrotropical bird, the Cape white-eye (Zosterops virens), over two years, and found that small birds may reverse the direction and amplitude of seasonal change between years. We also looked at circannual rhythm in avian resting metabolism (RMR), and found that peaks and troughs in resting metabolic rate (RMR) may not necessarily correspond with peaks and troughs in ambient temperature, suggesting that some of the confusion regarding the direction and magnitude of seasonal change in avian BMR may be caused by timing of seasonal measurements. Since we were using captive birds for my work, and since captivity may have an effect on avian BMR, we compared the BMR of freshly wild-caught birds with that of long-term captives housed in outdoor aviaries. The captive birds had higher BMR, giving weight to the argument that some physiological data of captive birds should not be used as representative of wild conspecifics, however the direction of seasonal change was similar in freshly wild-caught and long-term captive birds. Along the same vein, acclimation to laboratory conditions, experimental procedure, and different thermal environments, may also affect avian BMR, and thus before we started the final experiment, Cape white-eyes were acclimated to two different thermal regimes, with no change in RMR over an eight-week period, although there was an increase in body mass over the first three weeks, presumably due to the captive diet being of higher quality than a wild one. These results suggested that in some instances, small birds that are freshly wild-caught may not need to be acclimated in terms of their metabolism, before respirometry trials begin. Finally, given that anthropogenic climate change is anticipated to eclipse all other threats to biodiversity, and since many current predictive models pay no heed to metabolic flexibility of birds, we investigated the effect of a 4°C increase in housing temperature on resting metabolism of the Cape white-eye. This temperature increase is equivalent to that predicted for the range of this species by 2080, and therefore gives an indication of the effect of a sustained increase in mean surface air temperature. The results showed only a marginal difference in various metabolic parameters, suggesting that these birds may cope with the mean temperature increase predicted for their range in the coming decades. Together, these results highlight the importance of considering phenotypic flexibility when studying avian resting or basal metabolic rate. This has special implications for seasonal studies that implicitly assume that summer and winter measurements provide snapshots of the maximum and minimum RMR of which birds are capable, and for comparative studies, which may incorporate metabolic data from both wild and captive populations, or from study birds that were acclimated for different periods.
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.
The ecology and conservation biology of Lilian's lovebird Agapornis lilianae in Malawi.
(2014) Mzumara, Tiwonge I.; Downs, Colleen Thelma.
Despite their popularity, parrots are the world’s most threatened birds. Lovebirds (Agapornis) are very popular pet and aviary birds and as ecologically specialised species in the wild, they are also among the most threatened group of birds. Lilian’s lovebird Agapornis lilianae is a mopane Colophospermum mopane woodland specialist. This study represents the first detailed investigation of the species ecology in the wild. The current distribution of Lilian’s lovebird in Malawi was explored. Furthermore, the extent of the largest resident population in Liwonde National Park (LNP) was investigated. Five new atlas records are reported; three within 40-56 km of the LNP population, and two were over 150 km south and north of LNP respectively. One of them in Kasungu National Park is about 66 km from the Lilian’s lovebird population in Luangwa Valley, Zambia. Lilian’s lovebirds occurred throughout LNP with the highest abundance in the central section. Seasonal movements to areas outside the park were recorded. A variety of vegetation types were used by the lovebirds. The strongest vegetation associations were with seasonally wet grasslands and not mopane woodlands. The abundance and density of the Lilian’s lovebird in LNP was investigated. The highest density estimates of 17 ± 4.8 lovebirds km-2 were recorded in LNP’s mopane woodland. However, number of observations per transect differed significantly. Waterhole counts had the lowest estimates (10 ± 3.5 lovebirds). Flyway counts had the intermediate estimate (14 ± 3.0 lovebirds). The total population of Lilian’s lovebirds in LNP is therefore estimated to be about 4000 individuals. The use of line transect counts at the end of the rainy season is recommended for continued monitoring of Lilian’s lovebirds abundance in LNP. Lilian’s lovebird is a secondary cavity user adapted to mopane woodlands. We investigated its roost characteristics and roosting behaviour. We quantified tree and roost site variables for roost and non-roost trees. Roosting behaviour was observed during the morning and late afternoon. Lilian’s lovebirds’ roosts were located in large tall mopane trees with a mean diameter at breast height (dbh) of 57.4 ± 1.64 m, a mean height of 16.5 ± 0.42 m, and with a mean cavity height of 10.0 ± 0.05 m. All roosts were located in mopane trees within mopane woodland with 10 – 50 % tree cover. Non-roost areas had significantly smaller trees (mean dbh = 39.4 ± 1.72 m) and were located significantly closer together. Human disturbance was low in both areas, however, evidence of elephant Loxodonta africana browsing was high with large areas of stunted mopane woodland recorded in non-roost areas. We recommend that the current LNP vegetation map be updated to highlight areas of stunted mopane woodland unsuitable for Lilian’s lovebird roosts. The impact of elephant browsing on large mopane trees should be assessed to understand its impact on the availability of suitable cavities for lovebirds and other tree cavity-reliant vertebrate species. Investigations into the diet and foraging behaviour of the Lilian’s lovebird revealed they fed on 30 different plant species. These occurred in six habitat types, two of which were outside LNP (agriculture fields and dambos). In the wet season majority of Lilian’s lovebirds (23 %) foraged in dambo areas, whilst in the dry season (August – November) the lovebirds mainly foraged in grasslands with tree cover (18 %). In mopane woodland feeding flock sizes differed significantly between the wet (mean = 20 ± 1.0 lovebirds) and dry season (mean = 34 ± 2.3 lovebirds). Grass seeds were their main food source from December to June. Lilian’s lovebirds diet was more diverse from July to November and included leaves, leaf buds, fruits, fruit seeds and herbs. Grass seeds fed on during the wet season had a high protein and energy content. The Lilian’s lovebirds foraging habitat is protected within LNP, however, early burning in areas outside the park needs to be monitored. The breeding biology of the Lilian’s lovebird was investigated. Data were collected through a combination of direct observations and infrared camera traps during three breeding seasons. Results show large similarities with the black-cheeked lovebird A. nigrigens in Zambia. The breeding season was from February to May. Lilian’s lovebirds nested mainly in south-east oriented deep cavities (≥ 1 m) located in large mopane trees (mean dbh = 57.6 ± 2.35 cm). Nests were located in loose clusters in the areas they roosted (mean distance to nearest nest = 24.2 m). Nest fidelity was observed. Clutch size ranged from 3 – 6 eggs, (mean 5.0 ± 0.22). We recorded 49 % hatching success and 69 % fledging success. Results suggest a low breeding success mainly due to the loss of eggs to predation. The use of poison to kill wildlife is a threat to biodiversity. In LNP illegal hunters poison naturally occurring waterholes to catch mammals and birds for food. Lilian’s lovebirds are among the victims at these poisoned waterholes. Lilian’s lovebird population in LNP represents about 20 % of the global population. The drinking habits of the Lilian’s lovebird, the availability of natural waterholes and the occurrence of poisoning incidents in LNP were investigated. Results showed Lilian’s lovebirds congregate at waterholes in the dry season with flock sizes ranging from 1 to 100 individuals. Significantly larger flock sizes were seen in the dry season compared with the wet season. The number of poisoning incidents/year ranged from 1 to 8. The dry season had the highest numbers of poisoning incidents. Lilian’s lovebirds were killed at approximately four poisoning incidents each year between 2000 and 2012. The number of lovebirds found dead at a poisoned pool ranged from 5 to 50 individuals. A list of other species affected by the poisoning is provided. There is need for increased efforts in preventing this lethal activity in the park. Avian diseases are considered to be one of the key threats to bird conservation. Psittacine beak and feather disease (PBFD) is the most significant infectious disease in psittacines. It is caused by the beak and feather disease virus (BFDV) and currently has no cure. PBFD threatens the survival of wild populations of endangered parrots in Africa. The occurrence of BFDV was investigated in wild populations of Lilian’s lovebird. In addition, evidence of blood parasites presence was also investigated to determine their general health. All samples (n = 48) tested negative for BFDV. Blood parasites were observed in 13 of the 48 samples (27 %). Investigation of virus occurrence in other known populations of the species is recommended to assess the conservation risk faced. Lilian’s lovebirds (n = 55) were mist-netted and ringed in LNP. Measurements showed that females were significantly larger than males. About 50 % of the birds ringed in October were half way through their primary moult indicating that moulting starts in earlier months possibly just after the breeding season in April. This study highlights three of the key threats (waterhole poisoning, habitat loss and predation) to the conservation of Lilian’s lovebirds in LNP and provides proposed actions to address these threats.
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.
Urban ecology of the crowned eagle stephanoaetus coronatus in KwaZulu-Natal, South Africa.
(2015) McPherson, Shane Cameron.; Downs, Colleen Thelma.; Brown, Mark.
Urban environments comprise a complex and dynamic landscape, and urban sprawl is irreversibly transforming large areas of land globally. Increasingly, the need for incorporating ecosystem services into urban landscapes provides opportunities for green-space to benefit biodiversity and indigenous wildlife. Enhancing urban green-space maximises indigenous biodiversity and provides conservation value, and can also benefit people by enriching their experience and awareness of nature. Large charismatic species can stimulate awe and interest as emblematic representatives of the wilderness. As the global population becomes ever more urban, this enriches the human experience. The crowned eagle (Stephanoaetus coronatus) is a large predatory raptor and a threatened species that is increasingly known to inhabit the Durban Metropolitan Open Space System (D’MOSS), within eThekwini municipality, KwaZulu-Natal (KZN), South Africa. This research investigated the ecology of the crowned eagle in the urban environment and suggests opportunities for enhancing the urban landscape for conservation benefits. Globally, dramatic land use change typical of urbanisation negatively affects biodiversity, especially for top predators. The D’MOSS design faces the challenge of conserving biodiversity in a regional hotspot in the face of rapid urban growth in one of Africa’s major commercial hubs. Understanding habitat use of keystone and apex species provides urban planners with an opportunity to integrate biodiversity in a growing city. Consequently, we investigated habitat use and nest site selection of crowned eagles on various spatial scales within this urban mosaic. Unexpectedly the inter-nest distances were small in this human-dominated landscape. However, breeding sites were not evenly distributed through the landscape and were closely associated with natural forest, while nest trees were most frequently in patches of exotic large riverine Sydney blue gum (Eucalyptus saligna, Smith 1797) within the D’MOSS planning zones. Crowned eagles showed a strong tendency to avoid informal settlement areas, however they were tolerant of proximity to established formal settlements and occupied dwellings. Further, home range and habitat selection were investigated with GPS telemetry, albeit with a limited sample size (n =5) due to the limitations of abundance and dispersion of this apex predator. The 350 km2 urban core study area comprised a matrix of mainly formal settlements (44%), and DMOSS green space areas (29%). The study area was occupied by up to 22 active breeding pairs of crowned eagles. We documented a mean (n = 4) annual home range of 13 km2 (hull100%) containing 6.3 km2 of territory per pair (LKDE HLSCV 95%). These relatively small home ranges for a large eagle included shared territorial boundaries. Rapid replacement of vacancies at breeding sites suggests a saturated population. Habitat selection within the home range, thresholds of critical habitat, exotic trees, and correlation with DMOSS show the importance of pockets of indigenous forest in this urban mosaic landscape. These forests are fragmented and fragmentation increases the available edge habitats and landscape heterogeneity, potentially enhancing resource availability for crowned eagles in a highly modified landscape. The presence of remnant patches of mature Eucalyptus was more preferred than monotypic timber plantation stands. Consequently, continued protection of the D’MOSS system, and a considered approach to management of Eucalyptus are required for the persistence of the crowned eagle in this landscape The study of diet is pivotal in understanding a species, particularly for quantifying a predatory raptors’ economic niche and potential for human-wildlife conflict. In close association with urban development, the local population of crowned eagles has the potential to be a concern to the safety of domestic stock and pets. Time-lapse cameras were positioned at urban nest sites (n = 11) to identify the prey composition during breeding, particularly in regards to taxa with human associations. This was the first use of this technique for this species. The numerical proportion of avian prey, particularly hadeda ibis (Bostrychia hagedash) pulli, was several times greater than any previous diet description. The methodology used and the abundance of hadeda ibis in these urban environments are potential contributing factors. Rock hyrax (Procavia capensis) was the primary prey and where hyrax were unavailable, the diet composition was broader and included more vervet monkeys (Chlorocebus pygerythrus). Domestic stock comprised only 6% of the identifiable prey. Contrary to popular belief, no dogs (Canis familiaris) and few cats (Felis catus) were delivered to the nest by breeding eagles in this study. In situ pet attacks are most frequently attributed to juvenile and immature crowned eagles in winter and spring. Attacks on pets by crowned eagles, especially on small dog breeds, although relatively rare have a substantial influence on human-wildlife conflict and public perceptions. Pet attacks are generally attributed to juvenile and immature crowned eagles during periods of limited resources, particularly winter and during dispersal in the juveniles’ first spring. Negative social perceptions have resulted in persecution (n = 5), one of the main causes of recorded injury and mortality to crowned eagles in the region. Gunshot persecution, electrocution and collisions with anthropogenic structures have the greatest impact on juvenile and immature survival in the region. We provide management recommendations regarding various categories of crowned eagle human-wildlife interactions. Collaboration of wildlife authorities with NGO’s and public stakeholder input creates an environment for successful crowned eagle conservation and management of human-wildlife conflicts. Public awareness is an important aspect to the sustainability of the urban crowned eagle population. This study demonstrates that urban mosaic landscapes can provide conservation benefits for the crowned eagle. The land planning strategies enacted in Durban can guide urban expansion in tropical forest biomes to enhance indigenous biodiversity in urban mosaic landscapes in Africa, and globally.
Key factors driving the foraging ecology of Oribi : fear, cattle and the quality and quantity of food.
(2015) Stears, Keenan.; Shrader, Adrian Morgan.
Body size and digestive physiology are two factors that influence herbivores foraging behaviour, habitat use and potential to compete with other animals. The aim of this study was to determine how seasonal changes in grass quality, interactions with cattle, and perceived predation risk influenced oribi (Ourebia ourebi) foraging and landscape use. Oribi are one of the smallest pure grazing ruminants. As a result, they should select high quality vegetation. In line with this, I found that throughout the study oribi fed selectively over multiple spatial scales ranging from plant parts to habitats. By focussing on green grass within these different scales, oribi were able to maintain their crude protein intake needed for maintenance. Throughout South Africa, oribi frequently interact with cattle. Due to their differences in body size and nutritional requirements, there should be sufficient resource partitioning to avoid competition. However, I found that the nature of the interspecific interactions (i.e. competition or facilitation) between these species depended on season and cattle stocking rates. During the wet season, cattle facilitated oribi by providing high quality regrowth. However, at high stocking rates, cattle indirectly competed with oribi during the dry season via the impacts of their wet season grazing. Specifically, intense wet season grazing by cattle reduced the availability of high quality grass for oribi in the dry season. This was not the case at low and intermediate stocking rates. Differences in food availability and predation risk across habitats can influence how herbivores utilise landscapes. I found that predation risk greatly affected oribi foraging behaviour, with oribi preferring to feed in safer rather than riskier habitats. However, when food availability increased in these risky habitats, oribi increased their risk-taking behaviour at both small- and large-scales within these risky areas. Ultimately, this suggests that oribi trade-off between predation risk and food availability. Finally, to link my results to the management and conservation of this vulnerable antelope, I applied the knowledge I gained from the above research to a case study.
Ecosystem carbon change of shrub-encroached grasslands across a precipitation gradient in South Africa.
(2015) Mureva, Admore.; Ward, David Mercer.
Abstract available in PDF file.
Morphometrics, ecotoxicology and stable isotope ecology of Nile crocodiles (Crocodylus niloticus) in KwaZulu-Natal, South Africa.
(2015) Warner, Jonathan Kirk.; Downs, Colleen Thelma.; Myburgh, Jan.
Abstract available in PDF.
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.

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