Comparative impacts of fragmentation on birds in two bioregions in a biodiversity hotspot, the Cape Floristic Region
Kieck, Marius Burger
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Habitat loss and fragmentation are two of the most pressing threats to biodiversity. Avifaunal diversity and integrity is under immense pressure from these two processes. We have made major advances in our understanding of avifaunal responses to habitat fragmentation, but mostly focus on either fragment scale and/or landscape scale influences of fragmentation on birds. A more comprehensive approach to assessing the impacts of fragmentation was used in this study. The avifaunas of two different geographical regions and bioregions were surveyed and a multiscale analysis of avifaunal responses to fragmentation was attempted. The study sites include the West Coast and East Coast Renosterveld Bioregions in the Cape Floristic Region, South Africa. Assemblage shifts, feeding guild compositional changes, species abundance variation and species persistence were examined at the three spatial scales. Time- and distance-restricted point counts were used to document birds that were directly dependent on the habitat fragments. Forty fragments were selected in each bioregion and a once-off snapshot of the avifaunal richness and diversity was obtained. Results indicate that the avifauna of the two bioregions responded differently to habitat fragmentation. In the East Coast Renosterveld Bioregion, the assemblages, guild composition and species abundances were most accurately predicted by landscape configuration. An assemblage shift occurred at 20 ha fragment area, compared to the 50 ha fragment area threshold of the West Coast Renosterveld Bioregion’s avifauna composition. In the West Coast Renosterveld Bioregion, fragment area was the better predictor of assemblage, guild composition and species abundances. However in both bioregions, the persistence of common species was equally sensitive to area and landscape scale effects.