Global Scale Macroecology: Interactions between Population Size, Geographic Range Size and Body Size in the Anseriformes

Abstract

1. A large body of literature has addressed macroecological interactions between abundance, geographic range size and body size across species in animal assemblages. Studies have examined a variety of taxa, at a variety of spatial scales, using a variety of measures of the relevant variables, and with assemblages defined in different ways. Given this heterogeneity, it has been difficult to draw firm conclusions about the nature of these relationships. 2. Here we present an analysis of patterns in the abundance, geographic range size and body size of a monophyletic animal group, the Anseriformes (wildfowl), using data on global abundance and range size for almost all (probably) extant species and comparative methods to control for phylogenetic effects. As far as we are aware, this is the first study to examine these patterns for an entire group at this scale. 3. Population and range sizes are log-normally distributed in wildfowl, whereas the body mass distribution is positively log-skewed. There is a consistent relationship only between abundance and measures of geographic range size. Body size explains little variance in either of these two variables, but some variance in abundance unexplained by geographic range size can be accounted for by life-history traits relating to the rate at which offspring are raised. 4. Abundance, geographic range size and body size all show latitudinal variation, but this is not consistent between variables, and does not appear to affect the relationships observed between them. Wildfowl listed as threatened with extinction have smaller global population sizes and geographic ranges than species considered non-threatened, but it is population size, rather than range size, that seems to contribute most strongly to categorization as threatened or otherwise. 5. Phylogenetic and across-species analyses generally reveal the same patterns. 6. The results are discussed in relation to previous studies and to hypotheses concerning patterns in, and mechanisms structuring, animal assemblages.