Arthropod traits as proxies for abundance trends in the Azorean Islands

Human activities drive ecological transformation, impacting island
ecosystems from species diversity to ecological traits, mainly through
habitat degradation and invasive species. Using two unique long-term
datasets we aim to evaluate whether species traits (body size, trophic
level, dispersal capacity, and habitat occupancy) can predict temporal
variations in the abundance of endemic, Indigenous (endemic and native
non-endemic), and exotic arthropods in the Azores Islands. We found that
body size is crucial to predict arthropod abundance trends. Small-bodied
herbivorous arthropods showed a decrease in abundance, while large-bodied
indigenous arthropods increased in abundance, mainly in well-preserved
areas. Also, large-bodied exotic arthropods increased in abundance across
the entire archipelago. Moreover, endemic canopy dwellers increased in
abundance, while endemic ground dwellers decreased in abundance.
Simultaneously, exotic arthropods showed the opposite result, increasing
abundance in the ground while decreasing abundance in the canopy. Finally,
habitat influenced both endemic and exotic spider abundance trends.
Endemic spiders that occupy solely natural habitats experienced a decline
in abundance, while exotic spiders in the same habitats increased in
abundance. Our study underscores the significance of arthropod species
traits in predicting abundance changes in island ecosystems over time, as
well as the importance of monitoring species communities. Conservation
efforts must extend beyond endangered species to protect non-threatened
ones, given the increased extinction risk faced by even common species on
islands. Monitoring and restoration programs are essential for preserving
island ecosystems and safeguarding endemic arthropod populations.