Spiders in Forest Ecoystems

Introductory paragraph: Spiders are a key component of forest ecosystems, occupying a unique position in food webs. As predators, they are important in the regulation of invertebrate populations, which include pest species, and as prey they provide food for other invertebrates and birds. This is notwithstanding the contribution they make to ecosystems in their own right. Currently, the known German spider fauna stands at 992 species from 38 families, which is approximately 25 % of the European count (van Helsdingen 2012). Additionally, almost half of these species are associated with forested habitats (Blick et al. 2013), demonstrating the significant role individual trees and whole forests play in supporting these important animals. Spiders are influenced by changing environmental conditions and can be used as indicators of habitat quality (Wise 1993). They are one of the most abundant groups of terrestrial predators, relatively easily sampled through methods like pitfall trapping (small plastic cups placed in the ground), and taxonomically well known in Europe compared to other invertebrate groups. In forested ecosystems, spiders have the added advantage of inhabiting all layers from the litter to the canopy, allowing comparisons of the fauna across the vertical strata of the forest. Furthermore, spiders are ecologically well studied and can be classified into guilds determined by their hunting strategy (e.g. active hunters, ambush predators, various types of web builders), which gives additional information on species habitat use.