Watson, James E. M., Whittaker, Robert J. and Dawson, Terence P.
Avifaunal responses to habitat fragmentation in the threatened littoral forests of south-eastern Madagascar
Journal of Biogeography, 31, (11), . (doi:10.1111/j.1365-2699.2004.01142.x).
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Madagascar's lowland forests are both rich in endemic taxa and considered to be seriously threatened by deforestation and habitat fragmentation. However, very little is known about how these processes affect biodiversity on the island. Herein, we examine how forest bird communities and functional groups have been affected by fragmentation at both patch and landscape scales, by determining relationships between species richness and individual species abundance and patch and landscape mosaic metrics. Location?
Littoral forest remnants within south-eastern Madagascar. Methods?
We sampled 30 littoral forest remnants in south-eastern Madagascar, within a landscape mosaic dominated by Erica spp. heathland. We quantified bird community composition within remnants of differing size, shape and isolation, by conducting point counts in November-December in 2001 and October-November 2002. Each remnant was characterized by measures of remnant area, remnant shape, isolation, and surrounding landscape complexity. We used step-wise regression to test the relationship between bird species richness and landscape structural elements, after correcting for sampling effort. Relationships between bird species abundances and the landscape variables were investigated with Canonical Correspondence Analysis and binomial logistic regression modelling. Results?
Bird species richness and forest-dependent bird species richness were significantly (P?<?0.01) explained by remnant area but not by any measure of isolation or landscape complexity. The majority of forest-dependent species had significant relationships with remnant area. Minimum area requirements for area-sensitive species ranged from 15 to 150?ha, with the majority of species having area requirements >?30?ha. Surprisingly, there was no relationship between bird body size and minimum area requirement. Forest-dependent canopy insectivorous species and large canopy frugivorous species were the most sensitive functional groups, with >?90% species sensitivity within each group. The distribution of four forest-dependent species also appeared to be related to remnant shape where remnant area was <?100?ha. Main conclusions?
The majority of forest-dependent species, including many that are considered widespread and common, were found to have significant relationships with fragment size, indicating that they are sensitive to processes associated with habitat loss and fragmentation. As deforestation and habitat fragmentation remain serious problems on the island, it follows that many forest-dependent bird species will decline in abundance and become locally extinct. At the regional scale, we urge that large (>?200?ha) blocks of littoral forest are awarded protected status to preserve their unique bird community.
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