Abstract
The assumption of species richness models that patches of different size hold equal numbers of individuals within a taxonomic group per unit area is tested, and rejected for some bird communities. Often total density (all species combined) is negatively correlated with patch size at least up to a threshold. The null-hypothesis that the average population density and relative abundance of species is about the same in sets of small and large habitat patches is also tested and is rejected for a majority of the species in the communities examined. Among relatively common bird species breeding in 66 lakes in a South Swedish area, ten species never breed in small lakes (<30 ha), ten occur in significantly higher population densities in small lakes, and only one species has a population density that is unaffected by size of lake. Species with large area requirements in the lakes mainly feed on fish, and are less common and on average heavier than the other species. Among waterbirds the proportion of fish-eating birds increases with lake size. In temperate bird communities all species can apparently occupy large biotope patches, but many species do not occur in small patches. This seems to apply at least to forests, lakes and estuaries. Smaller patches, when compared to larger patches of the same biotope, are found to have a higher proportion of abundant generalists that are often the smaller species. Implications of the results, especially for species richness models and nature conservation, are discussed.
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