Comparative value of habitat biodiversity: an experimental system based on spider community analysis

Awareness of global environmental change gives some priority to the study of biodiversity and i ts maintenance (Blandin, 1986; Bridgewater & Walton, 1997). In the evaluation of biodiversity, invertebrates take an important place (New, 1995; Herrenschmidt, 1996; Cranston & Trueman, 1997), and spiders provide an interesting model to represent invertebrates. Numerous authors are aware of the qualities of spiders: they are predators and thus integrate some of the characteristics of food webs; they colonize all parts of the biotope; the species are not too numerous; and often the immatures can also be identified (Maelfait & Seghers, 1986; Maelfait & Baert, 1987, 1988; Mullhauser, 1990; Pinault, 1992; Furst et al., 1993; Neet, 1995; Churchill, 1997). The requirements of habitat managers are often precise: they need to test the relative quality of communities; they want to know the general actions required to maintain or restore biodiversity; and they need help to estimate the effects of their biotope management. The answers should not be understandable by specialists alone, they must be simple, comparable, and relevant to the initial question. Spiders have already given answers for biotope management (Marc et al., in press), but only a few authors (e.g. Růžička, 1986, 1987; Růžička & Boháč, 1994; Gajdoš & Sloboda, 1995) have attempted to test spider communities with a general index. Material and methods