Long-term ecological changes influence herbivore diversity and abundance inside a protected area in the Mara-Serengeti ecosystem

Abstract

Protected areas in sub-Saharan Africa are fast becoming islands on which to conserve biodiversity as surrounding human populations grow exponentially, rangelands become urbanized, and natural habitats are fragmented. The Masai Mara National Reserve in the Mara-Serengeti ecosystem in Kenya is renowned for having one of the highest densities and diversities of large mammals in the world, but may be experiencing negative effects from anthropogenic disturbances (e.g., illegal livestock grazing) within Reserve boundaries. We monitored changes in the diversity and abundance of resident and migratory herbivores in response to temperature, rainfall, the size of the local pastoralist population, the burgeoning infrastructure for tourism, and the number of livestock grazing inside Reserve boundaries in the eastern portion of the Masai Mara over a 26 year period (1988–2013). Using hierarchical models fit in a Bayesian framework, we found that overall diversity and abundance of resident and migrant herbivores declined between 1988 and 2013 in the Talek region, which lies in the northeastern portion of the Reserve. The habitual grazing of livestock within the Reserve's boundaries, as well as both human population growth and the development of tourism infrastructure beside the Reserve, had strong negative correlations with herbivore diversity and with the size of resident and migrant herbivore populations in the Talek region. We also found that rainfall was negatively correlated with the numbers and diversity of resident herbivores, and that temperature was positively correlated with numbers of resident herbivores. We expect herbivore diversity and abundance to continue to decline if current trends in livestock grazing and tourism development continue in the eastern Masai Mara.