The effects of tropical forest fragmentation on frugivorous and nectarivorous bats were studied on recent islands created by the flooding of a dam in French Guiana. Study sites include forest islands isolated by water, and control plots in nearby continuous forest. Studies began 1y before the onset of forest fragmentation and encompassed the first 3y after flooding. Forest fragmentation greatly modified the diversity and abundance of bats. Changes occurred more rapidly in the smallest fragments than in the largest one, and trends were remarkably similar among all the studied islands. Bat captures in islands were characterised by the scarcity of understorey frugivores. Differences in home range size and foraging strategies may explain why understorey fruit bat species are more sensitive to fragmentation than canopy ones. Changes in the frugivorous bat community may have indirect consequences on both the demographic and the genetic structures of plant populations inside forest fragments.

The impact of deforestation on the composition and dynamics of bat communities received close attention during a 15-year survey of the bats of French Guiana. Overall, deforestation lowers species richness: 48 of the 75 bat species from primary forest, mainly mature-forest phyllostomids, were not found in large areas that had been deforested for a long time. The 27 "rare" species, each represented by fewer than 6 of 8031 captures, had been apparently virtually eliminated from deforested areas. These altered habitats had been repopulated by a few opportunistic frugivorous phyllostomid species and by species belonging to the widespread insectivorous families Vespertilionidae and Molossidae. Habitats altered by humans harbor over four times as many individual bats as primary rain forest. This rise in both frugivorous and insectivorous bat populations in areas of degraded vegetation appears linked to the abundance of bat-dispersed pioneer' fruiting plant species available to phyllostomids and the multiplication of roosting sites for vespertilionids and molossids in human habitats. The species richness of local bat communities is positively influenced by the presence of forest corridors or the immediate proximity of a forest block.

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