Gábor Pozsgai, Pedro Cardoso, Simone Fattorini, François Rigal, Ana Santos, Robert J. Whittaker, Isabel R. Amorim, Mário Boieiro, Luís Borda‐de‐Água, Ricardo Costa, Luís C Crespo, Maria Ferreira, Abrão Leite, Sébastien Lhoumeau, Jagoba Malumbres‐Olarte, Thomas J. Matthews, Catarina Melo, Guilherme Oyarzabal, Fernando Pereira, José Alberto Quartau, Carla Rego, Sérvio Pontes Ribeiro, Alejandra Ros‐Prieto, Artur R. M. Serrano, Kostas A. Triantis, Rosalina Gabriel, Paulo A. V. Borges
Insect declines are of global concern, yet no long-term ecological studies (LTER) have confirmed this trend on islands. This study utilises the first available LTER data on island arthropods, targeting epigeal and canopy species from the Azores Archipelago (Portugal), and covering over 20 years in three distinct sampling events from 30 standard sites. We investigate changes in abundance, biomass, and species richness within native forest arthropod communities, focusing on the proportions of endemic and introduced species, and temporal patterns among single-island endemics and forest-dependent endemics. Results reveal significant temporal variability, but overall abundance, biomass, and species richness remain stable across endemic and native non-endemic taxa. Among the species studied, 28% declined, 17% increased, and 55% showed no significant differences. Exotic invasions and related extinctions appear minimal. Forest-dependent endemic species declined below anticipated levels, suggesting that the extinction debt for these species may be less severe than initially expected. Nonetheless, some forest specialists have declined significantly, and seven species, not seen over 20 years, are considered to be extinct. The three-decade-long conservation of Azorean native forests may have contributed to the stability of some populations, thus these findings underscore the need for continued and enhanced conservation efforts of insular forest-associated diversity.