Drivers of Spider (Arachnida:Araneae) Biodiversity in an ‘Olive Grove Ecosystem’ in North-Western Anatolia (Çanakkale and Balıkesir, Turkey)

Olive plantations cover vast areas on the Aegean coast of Turkey, and the southern foothills of Kaz Mountains is no exception. Olive trees dominate the terrestrial vegetation to such an extent that they form anovel ‘ecosystem’. The olive grove ecosystem is shaped by agricultural management, while impacts on biodiversity are largely unknown. We sampled spider communities living on soil surface and vegetation (understory herbaceous & tree canopy) microhabitats, alongside with various environmental variables linked to management or local habitat features in organic and conventional olive groves, as well as in relict patches of natural habitats, then used multivariate statistics to interpret associations within community composition (NMDS, CCA, RDA models) and compared diversity statistics (ANOVA, ANOSIM and permutation tests). 288 spider (morpho-) species of 14,252 adult specimens and >200 sampling units (plot based communities) were collected and standardized by sample coverage through rarefaction and extrapolation. Community composition differed by habitat type and by microhabitat. Olive groves and mixed forests had richer communities compared to maquis and pine stands. Soil surface was more species rich and diverse than vegetation. Difference between “organic” or “conventional” management types could not be distinguished well at the community level, whereas impact of soil management (tillage or herbicide use) and vegetation cover (tree/shrub vs. herb) were significant on the community. Our results may serve as evidence for a moderately strong species composition - environment relationship for spider communities