RELATIONSHIPS BETWEEN SPECIES NUMBER, LAKE SIZE AND RESOURCE DIVERSITY IN ASSEMBLAGES OF BREEDING WATERFOWL

Breeding waterfowl, habitat diversity and food diversity were studied in 31 boreal lakes in Finland and Sweden. Lakes were 2-48 hectares in size, and had zero to eleven waterfowl species each. In all, sixteen s pecies of Gaviiformes, Podicipediformes, Anseriformes and Fulica were recorded. The observed species distribution deviated from the 'null' e xpectation derived from a model of random placement, indicating a low importance of lake area per se. However, lake area was found to be a b etter predictor of species number than was length of shoreline, and la ke area-species number regressions gave values between 0.255 and 0.345 . We further evaluated 'the area per se (sampling)' hypothesis and 'ha bitat diversity' hypothesis separately by multiple stepwise regression s, in which lake area explained most of the variation in species numbe r in species dependent on the lake for brood-rearing. Richness of more mobile species and of all species was best explained by the number of prey taxa encountered in the lake.