Overwintering waterfowl on Swiss lakes: how are abundance and species richness influenced by trophic status and lake morphology?
Mean waterfowl populations (1976–1987) on the 20 major Swiss lakes north of the Alps were analysed in order to identify lake characteristics which shape waterfowl populations. Abundance and species richness are linear (abundance) and power functions (species richness) of lake area or shore-length, according to waterfowl guild. The remaining variation can partly be explained by variables related to the available food (coarse fish yield for piscivorous species) or the suitability for foraging (shallow areas and percentage of natural, open shoreline for dabbling ducks). Reedbelts are not important per se. There are no unequivocal relationships with the trophic status, since lakes with low waterfowl densities or species numbers are found among all trophic levels. However, mean and maximum species richness increase with nutrient load. Maximum bird densities increase from oligotrophic to meso-/eutrophic lakes in all guilds. Hypertrophic lakes may also have high densities of fisheaters because of the large populations of Cyprinid fish present. Diving duck densities are much lower in hypertrophic than in less nutrient-loaded lakes, since their main food, the bivalve Dreissena polymorpha, prefers less eutrophicated lakes. Food abundance and availability seems to be the main factor governing lake choice by overwintering waterfowl, although other factors such as disturbance levels may not have been detected by this broad-scale analysis.
- 1 - sciences appliquees, technologies et medecines
- 2 - sciences biologiques et medicales
- 3 - sciences biologiques fondamentales et appliquees. psychologie
- 4 - ecologie animale, vegetale et microbienne