Recovery of wild large herbivores following livestock decline in a tropical Indian wildlife reserve.
Resource competition is an important process governing the impact of livestock on native wild mammalian herbivores, an issue acknowledged to be of global conservation concern. Resource competition occurs between species when their resources (habitat and diet) overlap and are limiting. Yet the evidence that livestock compete with wild herbivores has remained weak because resource limitation is often difficult to demonstrate in the field. This 2-year field study at Bandipur National Park, India, examined livestock-mediated resource limitation among five wild herbivore species: wild pig Sus scrofa, chital Axis axis, sambar Cervus unicolor, gaur Bos gaurus and Asian elephant Elephas maximus, by comparing their distribution and densities in adjoining livestock-grazed and livestock-free areas before, and after, a 49% decline in livestock density. During 2001, mean densities of wild grazers, gaur (0.11 ha-1), chital (1.51 ha-1) and elephant (0.61 ha-1), were, respectively, 132, 11 and six times higher in the livestock-free area than in the adjacent livestock-grazed area. Densities of gaur, chital and elephant showed a sharp declining relationship with increasing livestock density, whereas no clear pattern was discernible with wild pig, a non-ruminant generalist, and the sambar, a forest browser. Preferred plant biomass also fell sharply with increasing livestock density. Following the decline in livestock density in the livestock-grazed area in 2002, the densities of gaur, chital and elephant increased by a factor of 57, five and two in the same area, respectively, whereas no changes were seen in the densities of wild pig and sambar or in the preferred plant biomass. Except for a decline in elephant density, the livestock-free area did not show changes in wild herbivore densities. Given the considerable overlap in habitat and dietary preference/requirements between livestock and wild herbivores in the study area, it is suggested that the recovery of gaur, chital and elephant densities following the livestock decline represents their release from livestock-mediated resource limitation. Synthesis and applications. These results indicate that resource competition may be intense between wild herbivores and grazing livestock, and if left unchecked could trigger declines of wild herbivores, particularly grazing ruminants and bulk feeders. These results also suggest that, where possible, interventions to reduce livestock grazing may rapidly benefit wild herbivores that have been competitively suppressed. This has important implications for the management of livestock grazing in India's wildlife reserves.