Impacts of the invasive alien prickly pear, Opuntia stricta (Haw.) Haw., on natural communities of Mediterranean insular habitats

Opuntia spp. are important invasive alien plants threatening Mediterranean habitats, particularly in island ecosystems, but few studies have assessed their ecological impacts and relationships with invertebrate communities, focusing more on socio-economic impacts and loss of plant diversity. To fill this gap, we aimed to evaluate the impacts of Opuntia stricta (Haw.) Haw. on the native plant and invertebrate communities of Capraia, a small Mediterranean island of high naturalistic value in central Italy and particularly invaded by this species. We investigated the natural communities occurring in EU habitats of conservation interest, comparing the areas invaded by O. stricta with control one. To thoroughly evaluate the impacts of this species on biodiversity, we assessed multiple groups of organisms, specifically vascular plants, ants, and other soil microarthropods, by randomly sampling a total of 12 plots of 4 m2 (6 invaded and 6 control plots). Samples were also collected to analyze soil physico-chemical properties. We estimated the abundance of all the groups and analyzed diversity indices and community composition. O. stricta seemed to significantly impact only plant communities (pseudoF1,10 = 17.92, P = 0.01), with a decrease in species richness in the invaded areas, but not on soil properties or invertebrate communities. However, the remarkable changes in the vegetation structure of the island's maquis could threaten natural habitats and consequently alter other parameters related to plants (e.g., shelters or resources for animals). Therefore, further studies could assess the indirect impacts of this alien species and verify the presence of complex processes resulting from its invasion.