On the relationship between distribution and abundance in birds breeding on Finnish mires: the effect of habitat specialization

Abstract

We tested Brown's (1984) explanation of the generally observed positive relationship between distribution and abundance of species. The hypothesis states that generalized species are widely distributed and locally common, and that specialized species are narrowly distributed and locally rare . The analysis is based on 327 censuses covering almost the whole north-south range of Finland, i.e ., ca. 1100 km. The censused habitats cover 19 peatland habitat types, ranging from open flark fens to forested peatlands. The relationship between distribution and abundance was positive for the total avifauna, and also for wader and for passerine species. Since the number of observations may affect the number of peatland types where the species is observed, we used two indices to measure habitat amplitude (a rarefaction estimate and Hurlbert's (1978) B'). The species that were able to inhabit several mire types had large geographical ranges, but were not locally abundant. Thus, in general, the species with a wide habitat amplitude are regionally widespread, but not locally abundant. The results do not fully support Brown's explanation of the distribution-abundance relationship .