The role of plant fidelity and land-use changes on island exotic and indigenous canopy spiders at local and regional scales

Understanding the processes that lead to successful invasions is essential for the management of exotic species. We aimed to assess the comparative relevance of habitat (both at local and at regional scale) and plant features on the species richness of local canopy spiders of both indigenous and exotic species. In an oceanic island, Azores archipelago, we collected spiders in 97 transects belonging to four habitat types according to the degree of habitat disturbance, four types of plants with different colonisation origin (indigenous vs. exotic), and four types of plants according to the complexity of the vegetation structure. Generalised linear mixed models and linear regressions were performed separately for indigenous and exotic species at the local and regional landscape scales. At the local scale, habitat and plant origin explained the variation in the species richness of indigenous spiders, whereas exotic spider richness was poorly correlated to habitat and plant structure. The surrounding landscape matrix substantially affected indigenous spiders, but did not affect exotic spiders, with the exception of the negative effect exerted by native forests on the richness of exotic species. Our results revealed that the local effect of habitat type, plant origin and plant structure explain variations in the species richness observed at a regional scale. These results shed light on the mechanistic processes behind the role of habitat types in invasions, i.e., plant fidelity and plant structure are revealed as key factors, suggesting that native forests may act as physical barriers to the colonisation of exotic spiders.Financial support for field work was provided by projects: BALA—Direcção Regional dos Recursos Florestais (Proj. 17.01-080203—1999–2002); INTERFRUTA and INTERFRUTA II (INTERREG III B, 2000–2006); “Consequences of land-use change on Azorean fauna and flora—the 2010 Target” (DRCT-M.2.1.2/I/003/2008). We are also grateful to Direcção Regional da Ciência, Tecnologia e Comunicacões (DRCT) for supporting the fellowship of M.F. (M3.1.7/F/002/2011), which is currently funded by the Conselho Nacional de Desenvolvimento Científico e Tecnológico—CNPq (401045/2014-5), program Ciência sem Fronteiras. AMCS was supported by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) (SFRH/BPD/70709/2010), co-funded by the European Social Fund POPH-QREN and a Marie Curie Intra-European Fellowship (IEF 331623 ‘COMMSTRUCT’). FR was supported by the FCT project PTDC/BIA-BIC/119255/2010