Fire is an integral component of tropical grassland ecosystems and influences both the flora and fauna of these ecosystems. Previous studies have found that herbivores are attracted to burned areas, presumably because plant nutrient content is higher following fire. However, herbivores may also preferentially use burned areas to avoid predators because of increased sight distance. The relative benefits of plant nutrition and safety from predators maybe stronger for smaller herbivores that require more nutrient-rich diets and are more vulnerable to predation. This study was conducted in Serengeti National Park, Tanzania. The Serengeti is an ideal place in which to conduct this study due to its large abundance and diversity of herbivores and carnivores. In addition, controlled burning is conducted in the Serengeti, with up to a third of the ecosystem burning annually. Herbivores were counted bi-weekly for a year on 14 paired burned and unburned sites. Vegetation height, to be used as a proxy for predation pressure, and forage nitrogen content were collected bi-monthly. Lastly, field observations and a database of lion, Panthera leo, locations was obtained to assess predator distribution relative to fire.
Results/Conclusions
We found that overall, herbivores prefer burned areas (p = 0.002). When analyzed by species smaller herbivores, such as Thomson?s gazelles, Gazella thomsoni, preferred burned areas (p = 0.004) while larger herbivores, such as Cape buffalo, Syncerus caffer, did not (p = 0.05). Thomson?s preference for burned areas was evident during the dry season (p = 0.005), but disappeared during the wet season (p = 0.41). Grass nitrogen content was significantly higher in burned areas during the dry season (p < 0.001), but not during the wet season (p = 0.3). Vegetation height, and presumably predation risk, was significantly lower in burned areas during the dry season (p = 0.001), but not during the wet season (p = 0.7). Additionally, lions were sighted more often than would be expected by chance in unburned areas (p < 0.001). For smaller herbivores our data support the previously assumed hypothesis that attraction to burned areas is due to increased plant nutrient content. However, even more significantly, our data support the hypothesis that smaller herbivores are attracted to burned areas because of decreased predation risk. Our study is the first to test the role that predation risk plays in herbivore attraction to burned areas.
