Browsing by Subject "predation"

Now showing 1 - 6 of 6
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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.
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    Extinctions: Past and Present Week 2 - Development of jaws
    (2017-03-17) Miyashita, Tetsuto
    In this video, Canadian scholar Tetsuto Miyashita explains how the development of backbones set humans apart from other species. He then describes the Ordovician-Silurian extinction event and how it was around this time that vertebrates developed jaws and become the most successful predators.
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    Incorporating cannibalism and inter-species predation effects into the hake assessment model: Methods and some preliminary results
    (2013) Ross-Gillespie, Andrea; Butterworth, Doug S
    Hake cannibalism and inter-species predation is modelled explicitly using a Type II functional response. Because of the fast dynamics of predation compared to other processes, the standard hake assessment model is converted from a yearly to a monthly time-step. Convergence of model fits is difficult to achieve both because of providing good estimates for starting values and of the tendency of the model towards oscillating behaviour. Thus far satisfactory fits have been obtained only from a somewhat reduced level of predation compared to that thought to occur. These results suggest that both hake species are at higher levels relative to pristine than for the standard assessment.
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    Seals and Sharks
    (2014-09-12) O'Riain, Justin; Neary, Tim
    In this radio broadcast, Justin o' Riain discusses shark and seal interactions in the False Bay/Seal Island area, focusing on predator-prey interactions and predation behaviour. Additional topics discussed are the seals' response to aggressive predation behaviour, including travelling strategies and learning patterns among young seals. Ethology of seals and sharks, specifically focusing on predator-prey relations, avoidance and predation strategies. Image provided courtesy of Christopher under a Creative Commons Attribution 2.0 Generic license.
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    The efficacy of culling seals seen preying on seabirds as a means of reducing seabird mortality
    (2009) Makhado, Azwianewi B; Meÿer, Mike A; Crawford, Robert J M; Underhill, Les G; Wilke, Chris
    In the 2006/2007 breeding season of Cape gannets Morus capensis at Malgas Island, the removal of 61 Cape fur seals Arctocephalus pusillus pusillus that preyed on gannet fledglings when they left to sea significantly reduced the mortality rate of these fledglings. However, because seals learned to avoid the boat used for their removal, it was not possible to remove all the seals that killed gannet fledglings and some mortality continued. The seals inflicting the mortality were all sub-adult males, with an average age of <5 years. Sustained removal of these animals may reduce this feeding behaviour, which is at present having an adverse impact on several threatened seabirds in the Benguela ecosystem.
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    To prey or not to prey? Welfare and individual losses in a conflict model
    (2008) Wittenberg, M W
    We analyse a generalised form of the Hirshleifer-Skaperdas predation model. In such a model agents have a choice between productive work and appropriation. We suggest that such a model can usefully be thought of as a continuous form of the Prisoners' Dilemma. We present closed form solutions for the interior equilibria and comparative statics for all Cournot equilibria and analyse the social welfare losses arising from predation. We show that predation is minimised under two quite different regimes, one in which claiming is very ineffective and another in which one of the players becomes marginalised. The worst outcomes seem to arise when claiming is effective, but inequality in power is significant but not extreme. This, arguably, is the situation in a number of transition societies.