Abstract
Deforestation and changes in land use have reduced the tropical dry forest to isolated forest patches in northwestern Costa Rica. We examined the effect of patch area and length of the dry season on nestedness of the entire avian community, forest fragment assemblages, and species occupancy across fragments for the entire native avifauna, and for a subset of forest dependent species. Species richness was independent of both fragment area and distance between fragments. Similarity in bird community composition between patches was related to habitat structure; fragments with similar forest structure have more similar avian assemblages. Size of forest patches influenced nestedness of the bird community and species occupancy, but not nestedness of assemblages across patches in northwestern Costa Rican avifauna. Forest dependent species (species that require large tracts of mature forest) and assemblages of these species were nested within patches ordered by a gradient of seasonality, and only occupancy of species was nested by area of patches. Thus, forest patches with a shorter dry season include more forest dependent species.
Highlights
Deforestation and change in land use are the primary factors causing habitat degradation and forest fragmentation in tropical regions (Jaeger, 2000; Lambin, Geist & Lepers, 2003; Azevedo-Ramos, De Carvalho Jr & Do Amaral, 2006; Joyce, 2006; Martínez et al, 2009)
Area did not explain the number of species found in these forest patches, which suggests that other factors, such as environmental heterogeneity, influenced the number and/or composition of species in fragments
Nestedness of the dry forest avifauna and forest dependent species is influenced by a gradient of seasonality and by fragment area (Fig. 2)
Summary
Deforestation and change in land use are the primary factors causing habitat degradation and forest fragmentation in tropical regions (Jaeger, 2000; Lambin, Geist & Lepers, 2003; Azevedo-Ramos, De Carvalho Jr & Do Amaral, 2006; Joyce, 2006; Martínez et al, 2009). These changes in natural landscapes may often reduce connectivity for species trying to move between fragments embedded in a matrix that consists of anthropogenic and seminatural habitats (Renjifo, 2001; Graham & Blake, 2001).
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