Preliminary conservation status and needs of an oceanic island fauna: the case of Seychelles insects

Abstract

Islands are generally reported to have much higher extinction rates and levels of threat than continental areas. This perception is based largely on studies of vertebrates. A recent assessment of the biodiversity of the Seychelles islands enables the status of a range of taxonomic groups to be compared. A high proportion of the fauna is found to be threatened, with Dictyoptera being the most threatened insect order (51% of 34 native species) followed by Orthoptera (47% of 68 species). Lower levels of threat are found in Diptera (28% of 562 species), Dermaptera (24% of 21 species) and Lepidoptera (21% of 517 species). Differences between the orders relate mainly to distribution patterns, with the most threatened orders having the highest proportions of endemic and restricted range species. The main threats for most orders are habitat deterioration due to invasion by introduced plant species, sea level rise and climate change. These threat factors are different from those reported to affect vertebrates, which are generally considered to be threatened by introduced predators resulting in critically low population sizes. These findings indicate that conservation sources would be more useful and cost effective for insect conservation if directed to habitat maintenance and restoration rather than to alien predator control.