Title

Fire and the reasons for its influence on mammalian herbivore distributions in an African savanna ecosystem

Date of Award

2010

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Advisor(s)

Mark E. Ritchie

Keywords

Fire, African savanna, Herbivores, Predator-prey interactions

Subject Categories

Biology

Abstract

Fire is an abiotic factor which has long played a role in savanna and grassland ecosystems. Fire causes reductions in plant vegetation height and biomass and increases in plant nutrient content. Mammalian herbivores are attracted to post-fire burned areas and this attraction has largely been attributed to increases in plant nutrient content. However, because of the reduction in vegetation height and subsequent increase in sighting distance that fire causes, burned areas might also be safer habitats from predators. This dissertation investigates how fire influences the distribution of herbivores and carnivores in the post fire landscape. The results show that generally smaller sized herbivores prefer burned areas while larger sized herbivores do not. Both vegetation nutrient quality and vegetation height play a role in explaining this preference for burned areas. The role of predator avoidance as one possible explanation for herbivore preference of burned areas is further supported by data showing that lions ( Panthera leo ) do not prefer burned areas and do not kill more in burned areas despite increases in prey availability in these areas. To further investigate the potential impact of predators on herbivore use of burned areas, field studies were conducted on the vigilance behavior of Thomson's gazelles ( Gazella thomsonii ) in burned and unburned areas before and after exposure to a model cheetah ( Acinonyx jubatus ). Prior to cheetah presentation there was no difference in vigilance between the two habitats. However, right after cheetah presentation and removal vigilance levels were lower in burned areas than in unburned areas, indicating that Thomson's gazelles perceive burned areas to be safer habitats. Lastly, this dissertation explores three alternative hypotheses for herbivore preference of burned areas; (1) to avoid disease carrying and behavior changing invertebrates, (2) because burned areas are warmer microclimates, or (3) to obtain minerals from the ash. Of these three hypotheses only the ingestion of ash to obtain minerals is supported as a reason for herbivore preference of burned areas, but this would only be for time periods shortly after burning. The results from this dissertation contribute to our understanding of how and why fire influences herbivore distributions.

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