Effect of human nuisance on the social organisation of large mammals: group sizes and compositions of seven ungulate species in Lake Mburo National Park and the adjacent Ankole Ranching Scheme

摘要

Most ungulates in East African savannahs experience some form of human disturbance, such as direct pursuit (e.g. hunting and poaching), habitat degradation and competition with livestock. In many studies, the impact of human activities on wildlife is assessed through census counts, i.e. by estimating population sizes or densities, but also the social organisation of gregarious species can be affected. Using seven species of ungulates occurring in the Akagera Ecosystem, we compared grouping patterns (i.e. group sizes and compositions) of different group types (e.g. bachelor, all-female and mixed-sex groups) between sites situated inside a protected area, i.e. Lake Mburo National Park in Uganda and the adjacent Ankole Ranching Scheme (ARS), an unprotected area with intense human pursuit. Differences in group sizes were detectible in only a few cases, e.g. bachelor group size in common eland Tragelaphus oryx pattersonianus increased in the ARS, which may be advantageous due to increased vigilance. However, we found pronounced differences in group compositions in numerous species and for different group types, for example, in eland and waterbuck Kobus ellipsiprymnus defassa (i.e. in all group types), and topi Damaliscus lunatus jimela, oribi Ourebia ourebi and warthog Phacochoerus aetiopicus (all-female and mixed-sex groups). We discuss that continuous monitoring of grouping patterns of these (and other) species may be a valuable approach to detect ‘subtle’ effects of human nuisance even before an overall population decline can be observed.