ASSEMBLAGES OF DYTISCID PREDATORS AND CULICID PREY IN RELATION TO ENVIRONMENTAL-FACTORS IN NATURAL AND CLEAR-CUT BOREAL SWAMP FOREST POOLS

Assemblages of diving beetles (Dytiscidae) and mosquito immatures (Cul icidae) were studied during 1987-1988 in 40 small, more or less tempor ary, snowmelt pools in spruce swamp forest and clearings at the Arctic Circle in Sweden. Larger pools were warmer than smaller ones, and cle aring pools were warmer than forest pools. Temperature differences bet ween pools remained high until late July. Twenty-one dytiscid species, representing three guilds, occurred in the pools, and individual pool s had 1-13 species. Ten species occurred in both habitats. A few steno topic species of boreal swamp forests had in clearing pools apparently been replaced by some species with a preference for more productive, often man-made habitats. Six Aedes species were collected in the clear ing pools. Five of these were found in the forest pools, of which thre e had no mosquito larvae. Dytiscid assemblages in both habitats and cu licid assemblages in clearing pools showed strong nested patterns. Abu ndance and species richness of both culicids and dytiscids were higher in clearing than in forest pools with an area < 2 m(2) after that the effects of pool area had been accounted for (MANCOVA). In both habita ts, abundance and species richness of both culicids and dytiscids were strongly and positively correlated with a linear combination of pool area, depth and temperature (Canonical Correlation). Increasing drough t frequency of pools had a negative, less significant effect on the bi ota. In the clearing, the abiotic correlations with abundance were som ewhat weakened chiefly by the relatively low abundance values from the largest pool. Distribution and mean abundance of individual dytiscid species were positively related in the clearing pools. Flying dytiscid s were trapped in the larger (1.6 m(2)), but not in the smaller (0.07 m(2)) artificial pools, and the immigration rate was markedly higher o n clearings than in forest. Dug pools were colonized faster on clearin gs than in forest. Even the flightless Hydroporus melanarius colonized dug pools during the first year.