Large mammals on small islands : short term effects of forest fragmentation on the large mammal fauna in French Guiana

Abstract

In this study, we present data on species richness of large mammals (mostly with body mass > 1 kg) in two contiguous areas at Saint-Eugène, French Guiana, before and after forest fragmentation by flooding. Assessment realized in 1993-94, i.e. before and during flooding, showed similar species richness and composition in the two studied areas. Before fragmentation, the large mammal community at Saint-Eugène was comparable to that recorded from a site of pristine forest in French Guiana. After forest fragmentation, one of these zones became isolated (medium-sized island) while the second one remained as a continuous forest. As a consequence, the number of species present on that newly isolated patch decreased of 30 % while it seemed non-affected in the continuous forest. This loss in species richness on the fragmented area was confirmed by a survey conducted in 1995-99 at three additional medium-sized islands (>20ha), 22 small-sized islands (1-10 ha) and 11 islets (< 1 ha). Occurrence status of the 32 large mammal species observed at Saint-Eugène is drawn up for all studied sites, and preliminary results on their overall abundance are presented for nine sites. The number of species present in a site was positively correlated to its area, but seemed not to be correlated to its isolation distance from the nearest larger landmass. Islands of less than 10 hectares had a mammal community that was rapidly impoverished and imbalanced in comparison to the one observed on medium-sized islands. The latter presented a mammal community that was richer and more complex, including all trophic guilds, despite it appeared affected in comparison to the continuous forest. Large mammal community on small and medium islands typically included species with small home ranges, and mostly generalist or herbivorous / granivorous feeding habits : armadillos (Dasypus spp.), acouchi (Myoprocta acouchy), agouti (Dasyprocta leporina), kinkajou (Potos flavus), sloths (Choelopus didactylus and Bradypus tridactylus), and squirrels (Sciurus aestuans and Sciurillus pusillus). However, species with larger home range, as felids, tapir (Tapirus terrestris), peccaries (Pécari tajacu and Tayassu pécari) and brocket deers (Mazama spp.) still frequented islands, at least temporarily. We thus discuss the role that fragments may potentially have in connecting larger landmasses.