Threats and conservation status of the endemic terrestrial arthropods of the Azores

Abstract

Insular ecosystems are disproportionately threatened by human activities, leading to an unprecedented decline in species diversity, particularly on remote archipelagos like the Azores. However, the impacts of humans on arthropods, which typically represent a big proportion of island biotas, remain poorly documented. We present an assessment of threats affecting different groups of species, examining the relationship between species occupancy, IUCN threat categories and trophic interactions for arthropods in the Azores (Macaronesia). We compiled data on endemic arthropods from published lists and IUCN assessments, including extinction risk, direct threats, and geographical ranges, to identify key pressures on species. Using network analyses, we examined the association between extinction risk and number of species, also estimating the IUCN Red List Index (RLI) for each island conservation status. We found that some of the Azorean endemic arthropod species have already gone extinct and more than half are classified as threatened by the IUCN Red List. Of these, predatory beetles (Coleoptera) and spiders (Araneae) have the highest numbers of threatened species, mainly due to habitat degradation, the spread of invasive plant species, and climate change. The RLI differs greatly among islands, being the lowest in Santa Maria, which concentrates a large number of critically endangered (CR) single-island endemic species, and higher in islands with larger and better-preserved native forest fragments, such as Terceira. A comprehensive approach integrating habitat protection, invasive species management and conservation measures is essential to ensure the long-term survival of Azorean arthropod endemic species in particular and island biota in general.