Intra-specific abundance-distribution relationships

Mechanisms that have been proposed to explain the relationship between abundance (mean abundance at occupied sites) and distribution (proportion of sites occupied) have been based on (1) differences among species that affect either their ability to exploit resources or their ability to move through the landscape, (2) differences in species' landscapes that affect rates of successful dispersal of individuals, or (3) statistical arguments. Existence of an intra-specific abundance-distribution relationship where species differences cannot be a factor would provide evidence that differences in species' landscapes likely contribute to the inter-specific abundance-distribution relationship. We examined the intra-specific relationship between abundance and distribution for 20 species of boreal forest songbirds. Abundance and distribution were calculated for each species in 52 to 119 locations over an area of 300 km x 100 km of northwestern Ontario. Based on separate regressions, 16 of the species demonstrated significant positive relationships between abundance and distribution at alpha = 0.05. The weighted mean partial correlation for all species combined was greater than zero (P < 0.05). Meta-analysis indicated that there is no significant variation in the abundance-distribution correlation among species. This study provides evidence that amount of habitat within a landscape contributes to a positive intra-specific abundance-distribution relationship and therefore suggests that this factor could also contribute to the positive abundance-distribution relationship that is commonly found among species within an assemblage.