Effects of habitat fragmentation on the distributional patterns of small mammals in a tropical forest in Thailand

The fragmentation, loss and disturbance of tropical forests by human activities has led to unprecedented losses of biodiversity. These losses have been particularly severe in South-East Asia where rates of deforestation are among the highest in the world. A major concern of conservation biologists and reserve managers is to understand how habitat fragmentation leads to species loss. Knowing how rapidly and why species loss occurs may suggest how to best conserve the species which are left after fragmentation has run its course.; There have been few opportunities to monitor the collapse of biodiversity on tropical forest fragments. At Chiew Larn, Thailand, 100 islands of evergreen forest were created in 1987 when a valley was flooded for a hydroelectric project. Annual surveys of small non-volant mammals were conducted on twelve islands, ranging 0.7 to 109 hectares, during the years 5 through 7 post-fragmentation. Distributions of mammals across islands were compared with those at equivalent-sized control areas in continuous forest on the adjacent mainland.; Richness and diversity of native mammals has rapidly declined on islands (Chapter 1), especially on the smallest ones ({dollar}<{dollar}10ha). Individual species differed in the ways in which population densities and distributions were altered by fragmentation (Chapter 2). This variability has led to a pattern in which islands with fewer species are nested subsets of islands with larger species numbers. In most cases, the combined influences of vegetation changes within islands (local effects of fragmentation), and reductions in forest area and the isolation of these areas (changes in the landscape context of fragments) influenced the likelihood of finding a given species on an island. Changes in vegetation at forest edges have affected the distributions of native mammals (Chapter 4), further suggesting that habitat disturbance has contributed to the local extirpation of natives on islands.; Most forest reserves in Peninsular Thailand are smaller than 125 km{dollar}sp2,{dollar} and share similar histories of disturbance to the Chiew Larn forests. Despite their size, these reserves may still preserve complete or nearly complete assemblages of small mammals as long as logging and anthropogenic fire disturbances are reduced or eliminated.