Sympatric herbivores experience similar environmental conditions but can vary in
their population trends. Identifying factors causing these differences could
assist conservation efforts aimed at maintaining fully functional ecosystems.
From 1996–2013, tsessebe and wildebeest populations in the Okavango Delta,
Botswana, declined by 73% and 90%, respectively, whereas zebra populations
remained stable. These sympatric, medium sized herbivores are exposed to similar
natural and anthropogenic pressures, but apparently differ in their responses to
those pressures. To identify factors that could cause these differences, we
fitted GPS-enabled collars to six zebra, eight tsessebe and seven wildebeest in
the Moremi Game Reserve, Botswana. We calculated utilisation distributions (UDs)
from GPS data, and used 95% isopleths to compare seasonal home range size
between species. We calculated utilisation intensity (UI) from the UDs and
generated spatial layers representing resources and disturbances, and then used
model averaging to identify factors affecting UI for each species. We calculated
second and third order habitat selection ratios to determine whether species
were habitat specialists or generalists. Zebra occupied larger home ranges than
tsessebe and wildebeest, showed weaker responses to spatial variables and
displayed no third order habitat selection; zebra social systems are also more
fluid, allowing for information exchange between stable harems. Herbivore
species that are sedentary, occupy small home ranges, are habitat specialists
and exist in relatively isolated groups are likely to be less resistant and
resilient to the rapid pace of environmental change forecast by climate change
scenarios. Resources contained within existing protected areas are unlikely to
maintain populations of such species at sufficiently high levels, potentially
leading to functional extinction. Special precautions may be needed to ensure
that such species can persist in the wild, such as buffer zones around existing
protected areas, which would allow greater potential for adaptive movement
should current environmental conditions change.