Abundance-distribution relationships on interacting trophic levels: the case of lake-nesting waterfowl and dytiscid water beetles

Aim To compare patterns in local abundance, regional distribution and body size in waterfowl and dytiscid beetles sampled from the same lakes. Location Thirty Swedish lakes, 56-63 degrees N. Methods Birds were censused repeatedly, at which time submerged activity traps were placed on the littoral to catch invertebrates. Avian patterns were analysed separately for four different selections of species, each motivated on functional or phylogenetical grounds. Patterns in dytiscid beetles have been described earlier in Nilsson, Elmberg & Sjoberg (1994). Results Although there were large differences between individual lakes, there was no significant latitudinal gradient at the lake level in either species richness or abundance in any of the bird groupings. Lakes which were rich in species and numbers of dytiscid beetles were also rich in species and numbers of all four waterfowl groups. Three of the four bird groups conform with the general pattern of widely distributed species being more abundant locally, as do dytiscid beetles in the same lakes. Body mass and local abundance were correlated in one of the four birds groups only, i.e. dabbling ducks, (Anas spp.). Main conclusions We find evidence for a similar and positive local abundance-distribution relationship in dytiscid beetles and waterfowl breeding in the same lakes, but no common general pattern in local abundance vs. body size.