Factors affecting frog species richness in the Solomon Islands

Abstract

Studies across large oceanic archipelagos often provide an opportunity for testing different processes driving patterns of species richness. Frogs are among the most abundant vertebrates in the Solomon Islands but little is known of the factors influencing their richness patterns. This study used modelling to determine important ecological and biogeographic factors affecting the species richness of frogs at multiple locations on major islands across the archipelago. Between March 2009 and August 2012, 16 frog species were recorded along 109 transects placed in coastal, lowland, ridge and montane forests across 13 islands. Mean species richness was higher in the North Solomon Islands arc (6.2 species) and decreased eastwards towards the New Georgia islands (4.7 species), and Malaita (3.2 species). A plausible explanation is that the North Solomon Islands arc is closest to New Guinea, a major centre of dispersal in the south-west Pacific. Coastal (4.6 species) and freshwater (4.8 species) forests had lower predicted species richness than lowland, ridge, and montane forest types (all with 6.2 species). In addition, more frogs were predicted in areas with thin leaf litter (6.2 species), dense shrub cover (7.7 species), and moist soils (7.7 species), which are characteristic of undisturbed forests. These results suggest that frog conservation activities in the Solomon Islands should target islands in the west with intact lowland, ridge, and montane forests. Specific knowledge of this nature is vital for amphibian conservation on tropical islands experiencing extensive habitat loss, habitat modification and widespread predicted climate change impacts.