Browsing by Subject "savanna"
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Item Open Access Direct and indirect effects of fire on parasites in an African savanna(Journal of Animal Ecology, 2023-12-01) Donaldson, JE; Holdo, RM; Anderson, TM; Morrison, TA; Hopcraft, JGC; McIntyre, J; Devaney, E; Hempson, G; Senso, B; Trentinus, A; Ezenwa, VOFires in grassy ecosystems consume vegetation and initiate high-quality regrowth, which results in pyric herbivory when mammalian grazers concentrate feeding in recent burns. For environmentally transmitted parasites with transmission mechanisms linked to vegetation structure, fire should exert direct effects on parasites, as well as indirect effects resulting from subsequent enhanced herbivory, which can affect parasite input and exposure to environmental conditions. We combined an experimental manipulation with observational data in the Serengeti National Park to investigate the direct and indirect effects of fire on parasites. We assessed the direct effects of fire by measuring changes in parasitic nematode larvae in the grass layer before and after fire on paired experimental burned and control plots. To investigate indirect effects linked to pyric herbivory, we sampled herbivore dung, grass biomass, ground temperature and larval densities every month for 5 months following fire in seven pairs of burned and unburned monitoring plots. Finally, to assess if fire-driven changes to larval densities affected host infection burdens, we collected faecal samples from a key host, Grant's gazelle (Nanger granti), each month for 5 months to estimate within-host parasite burdens. Fire killed all larvae and increased grazer dung inputs by 40% for 2 months following fire. Dung inputs after fire led to larval parasite recolonization of burned patches, but intense herbivory kept grass short and larval densities were associated with changes in ground temperature linked to grass biomass and ambient temperature. Grant's gazelles had lower parasite burdens when sampled in areas with higher compared to lower burned area fraction. Fire and pyric herbivory change the densities of larval parasites in the environment and divide the landscape into burned and unburned regions with distinct infection risks for local herbivores. The indirect effects quantified here represent a novel finding with major implications for all grazing systems impacted by fire.Item Open Access The impacts of climate change and veterinary fencing on savanna ungulate populations, communities, and behaviors(2023) Swift, Margaret ElizabethAs global change pushes ecosystems past climate tipping points, southern African savannas will experience more heat waves and droughts. These ecosystems are home to 90% of the world’s large herbivore diversity, millions of livestock, and a rapidly growing human population expected to reach 2 billion by 2040. As a unique vestige of large Pleistocene-era herbivores and a burgeoning powerhouse of global population, it is necessary to understand how African savanna ecological communities will respond to global change. Especially concerning for these communities are increased heat loads that may overwhelm ungulate thermoregulatory systems; more frequent droughts that may dry up key surface water resources; and the expansion of veterinary fencing across the landscape, which currently restricts historic great migrations of millions of ungulates. Large herbivores regulate nutrient cycling and vegetation structure on African savannas in a way that cannot be replaced by smaller herbivores or livestock; therefore, their responses to these threats are of utmost importance to preserving savanna functioning for the future.
This dissertation addresses the effects of increasing heat, drought, and fencing on savanna ungulate communities from the individual to the metapopulation scale. In Kruger National Park, South Africa, we first address large-scale and long-term questions of drought impacts on rare antelope populations in the context of the full suite of large herbivores in the Kruger Park. We use forty years of harmonized aerial census data and a Bayesian Generalized Joint Attribute Model to understand how drought, and its interaction with other environmental covariates, drives herbivore community structure and rare antelope survival. In Khaudum National Park, Namibia, we then use a four-year dataset of 33 antelope fitted with GPS collars to answer questions on heat and fencing-induced behavioral changes on two species on opposite sides of a water-dependence spectrum. We investigate how these species differ in their reliance on surface water, cool microclimates, and shifting activity budgets when responding to higher temperatures. We then explore how they differ in their responses to veterinary fencing, and how these responses change seasonally. As climate change brings more drought and hotter temperatures to southern Africa, the findings of this dissertation indicate that the placement of artificial waterholes on the landscape will be key to rare antelope survival in the Kruger Park; that water dependence is a key factor in antelope responses to heat and fencing; and that the expression of thermoregulatory strategies for two savanna ungulates will intensify under higher temperatures. This dissertation adds these unique findings to the canon of savanna movement and fence ecology literature, and provides multiple points from which future research in this arena can improve on our expectations of savanna ungulate behavioral shifts under climate change.