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Effects of rain forest disturbance and fragmentation: comparative changes of the raptor community along natural and human-made gradients in French Guiana

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A density index of every diurnal raptor species (Falconiformes) was obtained on 101 400 ha sample plots distributed among eight natural habitats and five man-made habitats arranged along gradients of increasing forest degradation and fragmentation. The most significant structural parameter affecting species distribution was the tall canopy forest cover. Species richness, diversity and density all decreased with this mature forest cover index. Individual species and overall community densities decreased along the deforestation gradient but the species richness 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 their 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 sensitive to forest disturbance and opening. The other two-thirds were upper canopy, gap or edge species more tolerant to forest fragmentation. The last twenty-one species were associated with various coastal habitats, from dense forest patches to mangrove and savanna. Again, one third of them were strictly restricted to their specialized habitats while the last two-thirds colonized human-altered habitats and progressively replaced primary forest species with increasing deforestation. The maintenance of large areas of every natural habitat was essential for the conservation of (1) the whole population of a third of the total raptor diversity and (2) optimal and presumably potential source populations of most other species surviving in human-modified habitats.

Document Type: Research Article


Affiliations: C.N.R.S.-URA 258, Laboratoire d»Ecologie, E.N.S., 46, rue d»Ulm 75230 Paris Cedex 05, France

Publication date: January 1, 1996


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