Diversitet hos jordlöpare (Col: Carabidae) i hävdade strandnära gräsmarker

Sammanfattning: The carabid community in moist seminatural grasslands was studied at three different sites in mid-Sweden. Pitfall trapping was carried out during six weeks in spring and early summer 2003. Eight transects, each containing seven pitfall traps, were placed in three different management regimes, either late or continous grazing, or meadow. The species composition was analysed by ordination analyses, i.e. DCA and CCA. Diversity was calculated both as species richness and as the Shannon diversity index. Most differences were found between the three study sites, mainly because of geographical differences. The same goes for size distribution among the carabids - there were more differences between the study sites than between management regimes. However, it seemed that the meadows had a different carabid community than the pastures. They had lower species diversity than pastures but at the same time more individuals of carabids. Higher numbers of especially medium-sized carabids in the meadows resulted in a much higher biomass of carabids in meadows. The data also suggest that the degree of isolation and the size of the area affect species richness in these areas. It appears that a larger area - with similar abiotic and biotic factors - contains a more specialised carabid community. That is, a large moist area contains a higher part of wetland species than does a smaller moist area. The distance to open water was not of great importance. In the wet grasslands diversity seemed to increase linearly with the variation in vegetation height. This could indicate a bottom-up-control system, not as dependent on plant species diversity as on structural heterogeneity. A high structural heterogenity is providing conditions for many niches. Most moisture dependent carabids show a similar life cycle. They are all adults at the same time of the season, in late spring. The season in moist areas may be shortened by a longer frozen period so that all species have to breed at the same time. This may be important for predators such as birds and small mammals because they will have a very limited period of using carabids as a food resource. The protection from the thicker adult carapace is probably also beneficial in moist areas where much ice is formed during the winter.