title: Interspecific interactions and co-existence in dabbling ducks: observations and an experiment.
abstract: We studied the possible role of resource limitation and interspecific competition in assemblages of dabbling ducks on breeding lakes in Finland and Sweden with observational and experimental data. After initial vegetation mapping and yearly censuses of ducks in 1985-1990, we collected observational data in 1991-1994 from 28 lakes with natural populations of mallard Anas platyrhynchos and teal A. crecca. Mallard and teal co-occur over vast areas in the Holarctic and they are the only breeding dabbling ducks on many oligotrophic lakes. Both species are migratory in our study regions, teal arriving later in spring than mallards. Log-linear model analysis of observational presence/absence data revealed a positive, not a negative, association between the species. This association was independent of habitat diversity as well as of lake size. Mallard-teal interaction was also studied in a cross-over introduction experiment in 32 other lakes in two years. Wing-clipped mallards were introduced to breeding lakes before the arrival of teal to induce resource limitation and interspecific competition, hypothesized to reduce lake use by teal. The density of mallard pairs on experimental lakes was 2.9-8.0 times higher than on controls, but there was no negative response by teal to the treatment. This is the first combined observational-experimental demonstration of lack of interspecific competition in waterfowl. Our results indicate that heterospecific attraction may affect species co-existence in dabbling ducks.
authors.affiliation: Department of Animal Ecology, Swedish University of Agricultural Sciences, S-901 83 Umeå, Sweden, , , , , , SE.
authors.forename: Johan
authors.initials: J
authors.lastname: Elmberg
authors.affiliation: Finnish Game and Fisheries Research Institute, Evo Game Research Station, Kaitalammintie 75, FIN-16970 Evo, Finland, , , , , , FI.
authors.forename: Hannu
authors.initials: H
authors.lastname: Pöysä
authors.affiliation: Department of Animal Ecology, Swedish University of Agricultural Sciences, S-901 83 Umeå, Sweden, , , , , , SE.
authors.forename: Kjell
authors.initials: K
authors.lastname: Sjöberg
authors.affiliation: Department of Applied Zoology, University of Helsinki, P.O. Box 27 (Viikki, C), FIN-00014 University of Helsinki, Finland, , , , , , FI.
authors.forename: Petri
authors.initials: P
authors.lastname: Nummi
keywords: Heterospecific attraction ; Key words Resource limitation ;  Anas crecca;  Anas platyrhynchos ;  Competition 