EFFECTS OF RAIN-FOREST DISTURBANCE AND FRAGMENTATION - COMPARATIVE CHANGES OF THE RAPTOR COMMUNITY ALONG NATURAL AND HUMAN-MADE GRADIENTS IN FRENCH-GUIANA

A density index of every diurnal raptor species (Falconiformes) was ob tained on 101 400 ha sample plots distributed among eight natural habi tats and five manmade habitats arranged along gradients of increasing forest degradation and fragmentation. The most significant structural parameter affecting species distribution was the tall canopy forest co ver. Species richness, diversity and density all decreased with this m ature forest cover index. Individual species and overall community den sities decreased along the deforestation gradient but the species rich ness was partly maintained by species turnover. Six groups of species were identified according to their natural habitat preferences. Their distribution along the deforestation gradient was correlated with thei r natural habitat selection pattern. Thus the community composition of each vegetation or landscape type was predictable. Fifty-six percent of the regional assemblage of species had their optimal density in the primary forest. A third of them were interior forest species highly s ensitive to forest disturbance and opening. The other two-thirds were upper canopy, gap or edge species more tolerant to forest fragmentatio n. The last twenty-one species were associated with various coastal ha bitats, from dense forest patches to mangrove and savanna. Again, one third of them were strictly restricted to their specialized habitats w hile the last two-thirds colonized human-altered habitats and progress ively replaced primary forest species with increasing deforestation. T he maintenance of large areas of every natural habitat was essential f or the conservation of (1) the whole population of a third of the tota l raptor diversity and (2) optimal and presumably potential source pop ulations of most other species surviving in human-modified habitats.