ABUNDANCE AND SPECIES RICHNESS PATTERNS OF PREDACEOUS DIVING BEETLES (COLEOPTERA, DYTISCIDAE) IN SWEDISH LAKES

Abundance and species richness of dytiscid water beetles were estimate d with activity traps in ten lakes each in south, central and north Sw eden. Partial least square regression models with two significant comp onents explained 76.5% and 55.8% of the total variance in dytiscid abu ndance and species richness, respectively. For abundance as well as sp ecies richness, component 1 had its highest positive loadings for stru ctural complexity of vegetation and abundance of Asellus and Diptera i mmatures, and high negative loadings for relative shore depth. Compone nt 2 had its highest positive loadings for fish abundance, number of d ipterans in emergence traps and relative shore depth, and high negativ e loadings for lake area. Both the number of dytiscid individuals and species were higher in the northern lakes than in the two other region s. Smaller species were not more abundant in the traps than larger one s. Species mean abundance was positively correlated with number of lak es occupied.