The importance of semi-natural landscape structures in an agricultural landscape as habitats for stenotopic spiders

The development of agricultural landscapes during the last decades has been characterized by an increase in management intensity, and a consequent decrease in the number and size of natural and semi-natural habitats. As a result, isolation of populations of stenotopic species of forests, shores, heathers, etc., has increased. This is a serious problem, especially for smaller invertebrates with low dispersal ranges like snails, wingless insects (Mader, 1979; Mader et al., 1990) and spiders without ballooning behaviour. For these species linear or patchy natural and semi-natural landscape features may be important as guidelines or stepping-stones between habitats. Therefore the incorporation of habitat considerations within landscape planning and other nature conservation activities is considered very important in Germany. To this end, a large number of hedges and other linear or patchy landscape features have been introduced by a range of different organizations. However, little has been known until now about the ecological function of such landscape features as guidelines, stepping-stones or refuge zones within agricultural landscapes. This study on spiders forms part of the longterm project “Habitat and species protection in the cultivated landscape”, carried out by the Federal Agency for Nature Conservation. The main aim of this project is to analyse the function of different habitats and landscape features for more or less specialized animals belonging to different taxa (birds and mammals: Blab et al., 1989; amphibians and reptiles: Blab et al., 1991; Syrphidae: Ssymank, 1993). The results presented in this paper form part of a series of studies on epigeic arthropods (Carabidae: Riecken & Ries, 1993a,b; Riecken & Raths, 1996). I have focused on the following questions: (1) which spider species inhabit the different biotopes and landscape features within an agricultural landscape; (2) are there any specialists (stenotopic) species; (3) to what extent are supposed eurytopic species eurytopic; and (4) which landscape features (e.g. semi-natural The importance of semi-natural landscape structures in an agricultural landscape as habitats for stenotopic spiders