A Test of the Area of Refuge Hypothesis in Indo-Pacific Marine Biogeography
Many hypotheses have been proposed to explain the marine biogeographic patterns of species richness of the Indo-Pacific. One of these hypotheses suggests that available habitat area is the main predictor of species richness. This is the basis for the area of refuge hypothesis that attempts to explain the global maxima of species richness found in the Coral Triangle, the area encompassing mostly the Philippines, Indonesia, and Malaysia. This species-area effect also has habitat heterogeneity as a potential component. The purpose of this study is to test the effects of habitat availability predictors, such as shallow water area and coastline length as proxy to area, and the effects of habitat heterogeneity, such as a habitat diversity index and patch density, as predictors of species richness. Problems of analytical scale and centroid location first had to be tested using grids of different sizes (small, medium, large, and Universal Transverse Mercator coordinate system (UTM); with the position of the UTM grid also shifted (UTMnorth/south, UTM east/west, and (UTMnortheast/southwest). An alternative to grid analysis was also tested using 1000, 500, and 100 equal area sections (EAS) of shallow water area to a depth limit of 200m. A total of 7,859 species distribution maps were generated and used to calculate patterns of species diversity. An epicenter of marine biodiversity within the Coral Triangle, in the center of the Philippines and eastern Indonesia is confirmed. The greatest extent of available shallow water habitat area can be found in the Arafura and Sunda shelves, while the highest concentration of coastline length is concentrated in the Philippines and eastern Indonesia. Habitat availability explains more variation in species richness than habitat heterogeneity. The availability and heterogeneity of habitats in the Coral Triangle significantly explains variation in species richness. However, the low regression coefficients associated with these parameters suggests that there are other major factors that contribute to shaping the marine biogeographic pattern of the Coral Triangle.
Refuge hypothesis, Indo-Pacific, Marine biogeography, Coral Triangle, Ecology and Evolutionary Biology, Geographic Information Sciences, Marine Biology, Natural Resources and Conservation, Oceanography
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