Is spatial variation in food availability an explanation for aBergmannian size pattern in aNorthAmerican hibernating, burrowing mammal? An information‐theoretic approach

Abstract

AbstractPredictable empirical patterns of variation in body size along spatial and environmental gradients have been documented within many species of mammals. Four main hypotheses, heat conservation, heat dissipation, primary productivity and seasonality, have been proposed to explain these patterns of variation in body size. In this study, we reported an analysis of geographic variation in body size of Richardson's ground squirrelsUrocitellus richardsonii, aNorthAmerican hibernating, burrowing mammal. Firstly, we evaluated whether aBergmannian size pattern was exhibited by Richardson's ground squirrels. Secondly, we used an information‐theoretic approach to test which of the four main hypotheses best explain(s) geographic variation in body size of Richardson's ground squirrels or to assess whether, as proposed byMcNab's ‘resource rule’ orHuston andWolverton's ‘eNPPrule’, the primary productivity hypothesis is the only explanation.Richardson's ground squirrels exhibited a pattern of increasing body size towards the colder areas, that is, more productive and seasonal centralAlberta and foothills of the southernAlbertaRockyMountains, indicative of aBergmannian size pattern. Plant productivity and seasonality in plant productivity were likely the primary underlying factors generating the observed pattern of geographic variation in body size. Thus, our results supported primary productivity and seasonality hypotheses. From these results, we see thatMcNab's ‘resource rule’ orHuston andWolverton's ‘eNPPrule’ (i.e. spatial variation in food availability) is an explanation for aBergmannian size pattern inRichardson's ground squirrels, but not the only explanation.