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

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 specialization, 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 specialized
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 specialization 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 colonizing species with supposed different trophic preferences.