What feeds on Quercus ilex L.? A biogeographical approach to studying trophic interactions in a Mediterranean keystone species

Abstract

Aim: Holm oak (Quercus ilex L.) is regarded as a keystone plant species. Trophic interactions may affect the distribution and abundance of phytophagous species, but the number of arthropod species that use holm oak as a food resource and their levels of host specificity are not yet known. Here, we aimed to quantify these species, their feeding strategies and conservation status, the taxonomic relatedness in each trophic guild and their degree of host specificity on holm oak. Location: Our study covered the whole distribution area of Q. ilex in the central-western Mediterranean Basin. Methods: We reviewed the existing literature and compiled information about all arthropod species that feed on Q. ilex, as well as their feeding strategies and conservation status. We also investigated the relationships between trophic guilds and the taxonomic relatedness of species, and assessed the degree of climatic niche overlap with holm oak. Results: We found that 605 species feed on seven different parts of the holm oak plant (i.e. feeding strategies). More than 90% of these species lack a conservation status assessment, and eight are threatened by human activities, either as vulnerable, endangered or critically endangered. A significant phylogenetic relationship was found between taxonomic relatedness and groups of arthropods that feed on the same part of the plant (i.e. trophic guilds). Twenty per cent of the species had similar niches, thereby indicating the potentially high host dependence of these species. Main conclusions: This study highlights the significance of a keystone tree species for arthropod conservation and the need for further research into the distribution and conservation status of arthropod species in Mediterranean holm oak woodlands.