Browsing by Author "Leighton, Gabriella"

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    Caracals as sentinels for metal exposure in a human-transformed landscape
    (2023) Parker, Kim; Bishop, Jacqueline; Leighton, Gabriella
    Urbanisation and associated anthropogenic activity release large quantities of metallic elements and metalloids into the environment. Due to their toxicity, environmental persistence and bioaccumulative nature, these chemical pollutants threaten wildlife and human health. As urbanisation increases and top predators are forced to utilise more urban spaces, they will likely be exposed to more toxic heavy metals and metalloids. As secondary and tertiary consumers, terrestrial carnivores may be at increased risk of metal exposure through biomagnification effects. Relatively little is known about this emerging threat to terrestrial carnivores persisting in human-transformed landscapes, especially in the Global South. To better understand the extent of this issue, I quantified the level of metallic element and metalloid exposure in a sentinel top predator, the caracal (Caracal caracal), inhabiting the rapidly-urbanising, primarily coastal metropole of the Greater City of Cape Town, South Africa. Whole blood samples (n = 67) from GPS-collared (n = 25) and opportunistically sampled (n = 31) individuals were collected. Using Redundancy Analysis (RDA) and mixed-effect models, I explored the relative influence of caracal demography, landscape use, and diet on levels of individual exposure to 11 metallic elements and metalloids: Aluminium (Al), Arsenic (As), Cadmium (Cd), Chromium (Cr), Cobalt (Co), Copper (Cu), Mercury (Hg), Manganese (Mn), Lead (Pb), Selenium (Se), and Zinc (Zn). Mean metal concentrations (including Al, Cd, Co, Cu, Hg, Mn, Pb, Se and Zn) were generally found to be below toxic thresholds, however, As and Cr are present at potentially sublethal levels in certain individuals. The results suggest that increased use of human-transformed landscapes in home ranges (particularly urban areas, roads, and vineyards) was significantly associated with increased caracal exposure to Al (P < 0.05), Co (P = 0.05) and Pb (P = 0.07). Home ranges closer to the coast (RDA, P < 0.05) and feeding within aquatic food webs (marine and wetland-adapted prey) were associated with higher blood levels of Hg (P < 0.05), Se (P < 0.01) and As (P < 0.05). Further, increased predation on seabirds and aquatic birds likely facilitates the transfer of metals from aquatic to terrestrial food webs. Overall, these findings highlight the importance of urbanisation and anthropogenic activity as major environmental sources of metal exposure in terrestrial wildlife, including more natural areas through long-distance transport of pollutants. Further, they contribute towards a growing global evidence base suggesting cities act as ecological traps for wildlife, threatening their long-term health and persistence in these landscapes. Therefore, it is crucial that cities work to reduce the large quantities of chemical pollutants released into their surrounding environment. In Cape Town, this effort could be focused on the urban edge, waste management, water treatments, roads and agricultural areas. Future research into a possible ecological trap for urban-adapted carnivores should focus on assessing metal exposure at different trophic levels and investigating the potential physiological responses of exposure in species. I argue that the caracal is a valuable sentinel for assessing metal exposure and should be used in tandem with other small and mediumsized carnivores and aquatic bird species in local and national pollutant monitoring programmes to mitigate further exposure and promote carnivore conservation in human landscapes. A charismatic species, with a well-established local platform of research and science communication, the caracal is centrally positioned to help promote greater public awareness and engagement in issues concerning environmental pollutant contamination and monitoring.
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    Driving giants: spatial and temporal variables influencing giraffe movements in a private protected area
    (2024) Allouchery, Zoe; Bishop, Jacqueline; Miller, Susan M; Leighton, Gabriella
    Spatiotemporal factors play important roles in shaping interactions between species within ecosystems, influencing their behavior and survival strategies. For predator/prey interactions, survival of the prey may rely heavily on spatial and temporal characteristics of the landscape together with species-specific behavioral strategies. The fear of predation prompts antipredator responses in prey which include vigilance behavior, grouping, and shifts in habitat selection. However, these responses may incur costs, impacting energy expenditure of prey and time allocation of prey activities such as foraging, sleeping, drinking, and fleeing predators. This study investigates spatiotemporal habitat use characteristics of southern giraffes (Giraffa giraffa) and lions (Panthera leo) within a small private protected area in South Africa where lions are the primary predator of giraffes. Giraffes are most vulnerable to predation when young, sick, or when in a splay-legged position while drinking water. In addition to direct predation risk, the presence of lions in the landscape may influence a ‘landscape of fear', triggering general antipredator behaviors. Giraffe movement and landscape use within the reserve may therefore be strongly influenced by the presence of lions, together with various environmental factors such as water accessibility, habitat preferences, and the need for sufficient food intake to meet their substantial daily energy requirements. This study uses GPS collar data collected over two years from simultaneously collared lions and giraffes in a private game reserve in South Africa's North West Province, the !Khamab Kalahari Nature Reserve. Using this data, t-LoCoH home ranges were calculated to identify patterns of seasonal change and overlap between lions and giraffes. Resource selection function models (RSFs) were then used to identify spatiotemporal variables that influence giraffe movement in a landscape with lions. Variables were resource proximity, including distance to waterholes, NDVI, land cover, landforms, a predation risk variable, and a temporal variables, seasonality and time of day. There was high overlap between all lion and giraffe home ranges (73.9 to 92.2%), suggesting a high probability of encounters between the two species in the reserve. RSFs revealed season, time of day, proximity to waterholes, NDVI, and land cover were significant predictors of giraffehabitat and resources use. Importantly, ‘distance to the closest lion' was also included as a significant variable in the best-fit model. The findings suggest that, within this reserve, giraffes select for areas of higher NDVI and those closer to waterholes. Their presence in the landscape also suggests some avoidance of lions, preferring sites further from lions. In terms of land cover, giraffes selected areas with woodland and transformed land despite their lower proportion on the reserve. Grasslands, the most abundant land cover type, exhibited neither preference nor aversion. Overall, this study identified four spatial variables and two temporal variables that influence giraffe movement within this fenced, semi-arid, small reserve. The insights gained are valuable for understanding how predators impact prey species in managed game reserves, where natural ecological processes may be disrupted to varying degrees and necessitate careful management. Furthermore, given the significance of giraffes as tourist attractions, understanding their ecological requirements is crucial for both their welfare and effective reserve management.