Spiders in the context of agricultural land abandonment in Greek Mountains: species responses, community structure and the need to preserve traditional agricultural landscapes

Agricultural land abandonment is a major conservation issue when it comes to remote Mediterranean mountainous ecosystems. Although its impact on taxa such as birds or butterflies is well known, knowledge remains poor for less studied invertebrate taxa such as spiders. We sampled ground spiders (Gnaphosidae, Liocranidae, Miturgidae and Corrinidae) in 20 randomly selected sites (1 km × 1 km; 15 pitfall traps) that well depicted a land abandonment gradient, in terms of four forest encroachment classes. Our results showed a negative effect of land abandonment on ground spider species richness and diversity (Simpson index), pinpointing that forested habitats with more than 75 % woody vegetation cover are relatively poor. We also provide evidence for the beneficial role of low intensity grazing (0.4–4 livestock units/km2) for ground spider abundance. Community analysis revealed four distinct clusters of co-occurring species, while Generalized Linear Models at cluster and species level showed the definitive role of forest encroachment, and secondarily of other environmental factors such as humidity, elevation and longitude, in regulating species distribution patterns. Conservation measures for ground spider diversity maintenance should focus on promoting traditional agricultural practices, including small-scale cultivation and mild livestock grazing in order to preserve open and semi-open rural mosaics.