Differential responses of small mammals to fragmentation in a Thailand tropical forest

Fragmentation of tropical forests has wide-ranging effects on wildlife communities, but the actual mechanisms of species impoverishment remain poorly understood. Small mammal assemblages on recent land-bridge islands at Chiew Larn, Thailand, were compared with nearby continuous forest from the fifth to seventh years following island creation. Assemblages on islands rapidly developed a nested structure, converging in composition and representing a depauperate subset of those in continuous forest. Among species that persisted on islands, many had altered abundances, with some increasing and others declining. A "random placement model" accounted for the observed distributions of species on mainland sites but not on islands, suggesting that nested island assemblages were generated both by changes in species distributions and abundances after fragmentation. Six species were prone to extinction on islands, whereas three increased in abundance, apparently because they were good over-water colonizers or favored disturbed habitats on islands. We conclude that the development of nested mammal assemblages in the Chiew Larn archipelago was caused both by differential vulnerabilities of species to local extinction and by varying abilities of species to colonize islands and to thrive in disturbed island habitats. (C) 1999 Elsevier Science Ltd. All rights reserved.