Size matters: Scale mismatch between space use patterns of tigers and protected area size in a Tropical Dry Forest

Abstract

India harbours the largest wild tiger population in the world and Tropical Dry Forest areas constitute the largest habitat for them. Recent extinctions, however, from two high profile tiger reserves, highlight the vulnerability of tiger in this habitat. Our examination of historic range areas for tigers shows that populations are disappearing at a faster rate in Tropical Dry Forest (64% sites suffering local extinction in 100years) than in any other suitable habitat in India. Focusing on data from the Tropical Dry Forest of Panna Tiger Reserve in central India, we examine the spatial ecology of the tiger population prior to its local extinction. We analyse home range sizes, overlaps and shifts, as well as the range expansion and contraction of radio-collared tigers between 1996 and 2005. In this reserve, the average annual home range sizes for both males (n=2) and females (n=4) were three to four times larger than those reported so far from other tropical habitats in India — male: mean 179.3±11.8km2 (95% Fixed kernel; n=7); female: mean 46.6±3.7km2; (95% Fixed kernel; n=16). Adult female home ranges were exclusive and overlapped little with neighbouring female ranges (3±1.46%, n=6). Male home ranges were not exclusive: resident floater males shared space with territorial males and mated with resident females. Home ranges of all breeding radio-collared tigers extended beyond the protected area boundary and were exposed to edge effects that exist at the periphery and outside. With such spatial use patterns, security and management measures provided within the boundary are unlikely to be very successful in protecting the population. Protected Areas in Tropical Dry Forest across India are relatively small (366.92±422.12km2 SD) and historical trends point towards a scale-mismatch that exists between the size of Protected Areas and the space use requirements of tigers. This scale mismatch adds to the vulnerability of existing small populations and perhaps explains why tiger populations in Tropical Dry Forest have disappeared at a faster rate than in any other tiger habitat of the sub-continent.