Influence of stand-alone trees on epigeic spiders (Araneae) at the alpine timberline

Abstract

We studied community composition and activity densities of spiders around stand-alone Norway spruce at the alpine timberline with respect to three interrelated parameters: (1) relative distance from tree trunk, (2) branch-, and (3) vegetation cover. Pitfall traps were positioned in an inner distance range (close to tree trunk), a median, and an outer distance range (at the outer limit of branch cover). Community composition: Linyphiid species numbers increased significantly towards the tree trunks where the branch cover was high, whereas lycosid and gnaphosid species numbers increased towards the edge where branch cover was low. Activity densities: 11 out of 14 species were significantly correlated with the relative distance to the tree trunk, ten with the branch cover, and two with vegetation cover. Open-land species preferred the outer distance range and forest species the inner distance range. Caracladus avicula is probably a habitat specialist of the alpine timberline.