Spatial Differentiation of the Total Bird Population in a Definite Area

The spatial structure of the total bird population at the level of communities has been studied in a definite area at the boundary between northern open forests and forest-tundra. The boundaries of communities have been delimited by mapping out areas with a homogeneous species composition. The pattern of communities is shown to be as follows: the species-richest part of a local species assemblage (characteristic of a given landscape type) forms the basic community, which is surrounded by poorer communities of increasingly variable composition and configuration, depending on distance from the basic community. The most distant communities consist almost exclusively of abundant and widespread species. A group of borderline communities of mixed composition is located at the boundary between two landscape complexes. Mechanisms accounting for such a pattern are discussed.