Spiders in Galapagos – diversity, biogeography and origin

Abstract

Abstract The Galapagos archipelago is an ideal location for studying species differentiation on oceanic islands due to its isolation and geological youth. Spiders, as early colonisers, are good model organisms to understand these processes. The aim of this study is to update the list of spiders found in Galapagos and investigate the current distribution patterns of these species in relation to their probable origin. The updated checklist now comprises 159 species, with half of these species being endemic to Galapagos, 24% cosmopolitan in distribution, and 26% of the species originating from continental America. Although in most cases it was difficult to determine the mode of arrival of these species, at least 16 species are likely to have been introduced accidentally by humans. High elevation islands inhabited by humans harbour the highest number of species and also a higher percentage of cosmopolitan species. The geographical range of most species is small, with 76% of the species occurring on fewer than five islands. Given that many endemic species are restricted to one or a few islands, we recommend additional studies to evaluate their distribution and determine if there are species that should be classified as at risk from extinction.