Species traits modulate ecological release in island red devil spiders (Araneae: Dysderidae)

Abstract Ecological release, defined as the expansion of range, habitat and/or resource usage by an organism following a reduction in competitors, is ubiquitous in oceanic islands. Species colonising recently formed islands, whose ancestors evolved in highly competitive environments, may experience relaxed selection because of reduced diversity of not only competitors, but also predators and parasites. Indeed, factors other than competition may also be involved in determining the species' ability to expand their niche. Ecological specialisation, for instance, has been frequently considered an irreversible change, preventing the reversal to more generalist states. Here, we integrate geometric morphometric methods, stable isotope analyses and species distribution models using the spider genus Dysdera as a model organism to explore the implications of different cheliceral morphotypes related to different trophic adaptations on the species' ability to undergo ecological release. Contrary to our expectations, species with morphotypes associated with a more specialised diet tend to expand their trophic niche, increase their spatial range and modify their phenotype more similarly across the same area of morphospace when compared to generalist species. This outcome might be explained by their ability to feed on isopods, a prey typically rejected by most predators, along with other arthropods. This specialisation may have been crucial in expanding their ecological niche compared to generalist species. Our study constitutes one of the first examples of using a multidisciplinary approach to better understand the effects of ecological release on colonising species with supposed different trophic preferences.