Conservation of arthropod diversity in montane wetlands: effect of altitude, habitat quality and habitat fragmentation on butterflies and grasshoppers.
The patterns of arthropod diversity were investigated in 24 montane wetlands in Switzerland. These differed in altitude, management regime (cattle-grazing vs. mowing), vegetation structure (index combining vegetation height and density) and degree of habitat fragmentation. The general arthropod diversity was determined by net sampling at 10 sampling points per site. The diversity of grasshoppers and butterflies was measured by counting species richness at the site and species density (species richness per unit area) on transects. The species richness of grasshoppers and butterflies was more sensitive to the geographical attributes of the site whereas species density was more affected by the habitat quality. Grasshopper diversity decreased within the observed altitudinal range (800-1400 m) and was higher at grazed sites, whereas butterfly diversity was higher at mown sites. Arthropod diversity but not abundance of arthropods was positively related to the vegetation structure. The species richness of butterflies was negatively influenced by the degree of habitat fragmentation: both the size of habitat as well as the area of wetland habitats within 4 km were related positively to the number of specialist wetland butterflies. Late mowing as well as low-density cattle-grazing are appropriate management actions to maintain arthropod diversity in montane wetlands. In order to establish site-specific management plans, the biology of the present target species as well as the historical context should be considered. It is suggested that the best protection for the species examined in this study would be a network of wetland sites managed using a variety of traditional, non-intensive methods. This can only be achieved by coordinated planning of conservation measures among sites.