Matrix transformation alters species-area relationships in fragmented coastal forests
Ecological theory suggests that large habitat fragments should harbour more species than small fragments. However, this may depend on the surrounding matrix. Matrices in fragmented landscapes may either amplify or reduce area effects, which could influence predicted extinctions based on species-area relationships (SARs).
To determine the influence of matrix type on SARs.
We surveyed birds within 59 coastal forest fragments in two matrix types, anthropogenic (South Africa) and natural (Mozambique). We classified species as forest specialists or habitat generalists and fitted species-area models to compare how SAR slopes differed among matrix types. We also calculated nestedness and evenness to determine if these varied among matrix type and used logistic regressions to identify species-specific responses to matrix type.
For habitat generalists, SARs were weak within both matrices, while for forest specialists it was strong in the anthropogenic but weak in the natural matrix. In the former, the SAR was similar to those recorded for real islands within archipelagos. Forest specialist assemblages were nested by area within anthropogenic, but not natural matrices. Matrix type did not influence evenness. Area only affected the occurrence of one species when the matrix was natural, compared to 11 species when it was anthropogenic.
Forest specialist bird species conformed to island biogeographic predictions of species loss in forest fragments embedded in anthropogenic, but not natural matrices. Extinctions from small forest fragments might be prevented by conserving natural- or restoring anthropogenic matrices, as well as by increasing forest area.
KeywordsBirds Extinction Forest specialists Habitat generalists Island biogeography Nestedness Anthropogenic habitats
The MOZAL Community Development Trust, BHP Billiton HSC, National Research Foundation, Conservation Ecology Research Unit, Richards Bay Minerals, the Department of Trade and Industry and the University of Pretoria funded the study. Pieter Olivier was supported by an Innovation post-doctoral grant from the National Research Foundation. We also thank the field assistants who assisted with fieldwork and Thomas Matthews for valuable discussions around nestedness metrics.
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