INDIVIDUALS–AREA RELATIONSHIPS: THE RELATIONSHIP BETWEEN ANIMAL POPULATION DENSITY AND AREA

Abstract

We compiled studies that report data on the relationship between animal population density and patch or island area for 287 individual species and 21 faunas. We tested the assumption of the equilibrium theory of island biogeography that population densities are independent of area by performing a meta-analysis using the linear correlation coefficient,r, as a measure of the effect of area on population density. We fit meta-analyses that used a random-effects model to these data to test for the effects of taxa, habitat, latitude, spatial scale, and overall population density. We also fit meta-analyses that used a fixed- effect model to the same data to estimate the repeatability of measurements of the correlation between population density and area within species. Contrary to the equilibrium theory of island biogeography, our results indicate that, on average, animal population densities are positively correlated with area, which suggests that density compensation may be uncommon. This result was found for individual species, but not for faunas. We found taxonomic differences in the correlation between population density and area, with insects and birds having on average large or moderately large positive correlations, respectively, and mammals having correlations near zero. Observations within individual species showed considerable repeatability. The observed overall positive cor- relation between the population density of individual animal species and area is best ex- plained in the context of the resource concentration hypothesis. Our results imply that the regional abundance and persistence of animal populations may depend strongly on the presence and continued persistence of a few large patches of suitable habitat, rather than on a regional network of small and large habitat patches.