TEMPORAL VARIATION IN THE WETLAND WATERFOWL COMMUNITIES OF THE FINNISH LAKE DISTRICT

Variation in the waterfowl community structures of wetland habitat typ es were studied in the northern part of the Finnish lake district duri ng two decades (1970-1990). Mixotrophic and eutrophic lake types were identified on the basis of DCA ordinations of waterfowl assemblages. T he community gradients of these lake types were distinguished also on an annual scale. The communities were found to be fairly stable across time. Total waterfowl densities fluctuated most (CV% 13-14), and the number of species (CV% 5-7) and species diversity (CV% 1-3) the least. The between-year component for total diversities was only 1-2% and th e number of species 12-13%. The two lake types showed different dynami cs of species populations. CV% of pair numbers of the three most abund ant species were 12-29% in mixotrophic lakes and 30-36% in eutrophic o nes. Gradients of community structure and long-term dynamics seem to b e primarily connected with habitat, indicating that the lakes are in d ifferent phases of ecological succession.