Use of forest fragments by animalivorous bats in French Guiana

Abstract

The effects of habitat fragmentation on animalivorous bats were studied on recent forest islands created in 1994, at the time of the filling of Petit Saut dam in French Guiana. A sampling strategy, including control sites located in a nearby forested area not fragmented during the who le study period (1993-1997) was designed. Modifications affecting animali vorous bat communities in a remote 28 ha island (island 2) and in 15 islets smaller than 6 ha more or less isolated from the nearby continuous forest were analysed. Results were compared to those obtained with the same methods for frugivorous and nectarivorous bats. One hundred and forty eight gleaning animalivores, 41 aerial insectivores and 28 bats belonging to other guilds (omnivore, sanguivore) were trapped during the whole study. Capture analyses showed that species richness and abundance sharply declined in islets and in the island 2 in 1995 and 1996. However no significant difference was found between islands and continuous forest in 1997. There was no difference either in species richness or in abundance between the island 2 and several islets of comparable isolation. On the contrary, indices were significantly lower in far islets situated at more than 1 50 rn from the continuous forest than in near ones. One possible explanation is the reluctance of understorey species to cross open water to reach far islands. Between 1994 and 1997, we failed to detect any difference in the relative proportion of aerial insectivores and gleaning animalivores between islands and the continuous forest. Among non-frugivorous species, gleaning animalivores represented 73 % of the total number of captures made in the two habitats. Similarly no habitat differences were found in the respective contributions of frugivores and animalivores to bat communities. Frugivores made up roughly 80 % of the total number of bats captured during the study. Within the gleaning animalivores guild, there was a positive relationship between abundance of a species in islands and its abundance in the control area. Moreover, a positive correlation was equally found between body size and abundance in all habitats. The contribution of our results to the understanding of the impact of habitat fragmentation on animalivorous bats is limited due to rarity and low detectability of a high number of species making up animalivorous bat communities in Neotropical forests. Therefore, additional methods to collect and analyse data that take into account these features should be implemented to evaluate more accurately the impact of habitat fragmentation on bat communities at Saint-Eugene