FACTORS AFFECTING SPECIES NUMBER AND DENSITY OF DABBLING DUCK GUILDS IN NORTH EUROPE

We addressed how species number and pair density in guilds of co-exist ing species is related to habitat structure, and to the abundance and diversity of food resources. using the assemblage of seven species of dabbling ducks (genus Anas) breeding in 60 lakes distributed over six regions in temperate north Europe. Partial correlation and multiple re gression revealed that species richness was best predicted by habitat structural diversity as indexed by a principal component analysis base d on 18 vegetation and lake characteristics, and by the abundance of a quatic and emergent prey. We found no effect of lake size or prey size diversity on species richness. Pair density was correlated with the p ercentage of shoreline with horsetails (Equisetum), by habitat structu ral diversity and by the abundance of emergent invertebrate prey. Neit her prey size diversity nor abundance of aquatic prey correlated with pair density. Species richness and pair density in North European duck guilds vary both with habitat structure and prey availability.