Resource selection by sympatric wild equids in the Mongolian Gobi.
Historically, the overlap zones of wild equids were small in Africa but extensive for Przewalski's horses Equus ferus przewalskii and Asiatic wild asses Equus hemionus in Asia. Currently, the Great Gobi B Strictly Protected Area in south-western Mongolia is the only place where sympatric, free-ranging populations of these equids occur. This provides a unique opportunity to test the hypothesis that Przewalski's horses are primarily adapted to mesic steppes and Asiatic wild asses to arid desert steppes and semi-deserts. Understanding the spatial needs and habitat requirements of these little-studied species is a pre-requisite for setting aside and managing protected areas and planning future re-introductions. From 2001 to 2005, we followed nine Przewalski's horses and seven Asiatic wild asses using satellite telemetry and direct observations to assess differences in their resource selection strategies and social organization. Przewalski's horses had non-exclusive home ranges of 152-826 km2, selected for the most productive plant communities and formed stable harems groups. Asiatic wild asses had non-exclusive home ranges of 4449-6835 km2, showed little preferences for any plant community and seemed to live in fission-fusion groups. Synthesis and applications. Our results provide evidence for different resource selection strategies in two sympatric equid species. Our findings indicate that the Gobi areas provide an edge, rather than an optimal habitat for Przewalski's horses. Consequently, only small and isolated pockets of suitable habitat remain for future re-introductions. Asiatic wild asses, on the other hand, need access to large tracts of land to cope with the unpredictable resource distribution of the Gobi. Managers should be aware that protecting habitat where Asiatic wild asses occur does not necessarily benefit Przewalski's horse restoration, whereas setting aside habitat for the conservation of Przewalski's horses will only locally benefit Asiatic wild asses.