UBC Theses and Dissertations
The mechanistic pathways of species interactions in an African savanna Ford, Adam T.
Quantifying the interactions that govern the abundance and distribution of large African mammals is an opportunity to understand the forces structuring ecological communities and a means to inform conservation practice in a changing world. I paired experimental manipulations with correlative observations taken over expansive scales to quantify the mechanisms shaping interactions between trophic levels in an African savanna. Chapter 2 addresses the non-consumptive effects of predation risk on the behavior of a small and territorial antelope, Guenther’s dik-dik (Madoqua guentheri). Studies have suggested that mobile prey avoid areas of heightened risk, but few such studies have been carried out on territorial organisms whose movement is constrained by their neighbors. My findings showed that use of familiar areas increased after exposure to a cue of risk, such that predators may reinforce rather than override territoriality in dik-dik. Chapter 3 unifies risk-avoidance behavior in a medium-sized antelope, the impala (Aepyceros melampus), and plant defense (thorns) to explain the spatial distribution of plant community structure. My findings showed that plants can persist in landscapes characterized by intense herbivory, either by defending themselves or by thriving in risky areas where carnivores hunt. Chapter 4 explores the cascading effects of wild dog recolonization (Lycaon pictus) on dik-dik and trees. Previous work has equated a positive correlation between plant and large carnivore biomass to a trophic cascade, thereby inferring mechanisms by which carnivores suppress herbivores which then releases plants from herbivory. My results showed suppression of herbivores by carnivores and of plants by herbivores, coupled with a positive correlation between carnivore and plant biomass that, together, did not give rise to a trophic cascade. There was no trophic cascade because the effect of herbivory, as measured by replicated herbivore exclosures, was the same in the presence and absence of wild dogs. Chapter 5 summarizes the main findings and limitations of this dissertation, and provides a framework for quantifying trophic cascades in systems dominated by large carnivores. Put together, this dissertation reinforces the vital role of a mechanistic approach to quantifying trophic interactions in large mammals.
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