FINNISH BIRD FAUNA - SPECIES DYNAMICS AND ADAPTIVE CONSTRAINTS

The adaptive response of Finnish birds to the limits imposed by specie s dynamics, biological constraints, and environment is described by ex amining the patterns and underlying mechanisms in the relationships be tween the number of species, body size, population density, and geogra phical range size. In the total breeding avifauna the frequency distri bution of species with respect to body size was bimodal, while various subsets of species showed unimodal distributions significantly skewed toward the larger body size categories. Abundance distributions of la rger sets of species usually followed the canonical lognormal distribu tion with no significant skewness, while minor groups in general were not normally distributed and exhibited significant left-skewness. The variances of abundance were somewhat higher than the variances of biom ass, suggesting that biomass and energy use were more equitably distri buted among species than indicated by their abundance. Relatively more large than small species winter in Finland. So, from the energetic po int of view, the differences between the summer and winter bird commun ities were not as great as suggested on the basis of the number of ind ividuals. The average density of birds decreased significantly with in creasing body size, but the slope of the relationship was shallower (- 0.52) than expected for the energetic equivalence of the species. The Finnish range size of species tended to decrease with increasing body size, partly because the ranges of many larger species have been reduc ed by human impact. The width of the range increased with density in t he total set of species as well as in most of the ecological groups co nsidered, indicating the progress and success of colonization.