An Intercontinental Analysis of Climate-Driven Body Size Clines in Reptiles: No Support for Patterns, No Signals of Processes
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Climatic gradients impose clinal selection on animal ecological and physiological performance, often promoting geographic body size clines. Bergmann’s rule predicts that body size increases with decreasing environmental temperatures given the need to retain body-heat through adjustments of body-mass-to-surface-area ratio. This prediction generally holds for endotherms, but remains controversial for ectotherms. An alternative interpretation, the ‘resource rule’, suggests that food abundance, primary productivity and precipitation (which, unlike temperature, do not necessarily correlate with geography), drive body size clines. We investigate geographic variation in body size within 65 species of lizards and snakes (squamates) based on an intercontinental dataset (6,500+ specimens belonging to 56 Israeli species, and multiple populations of nine Liolaemus species from Argentina and Chile). Bergmann’s rule is only rarely supported by our data (in four species, 6 %), whereas six species (9 %) follow its converse (hence, it is unsupported in 94 % of cases). Similarly, size increases with resource abundance in only 12 species (18 %). Therefore, although neither of the rules is supported, factors suggested by the resource rule are better predictors of body size than temperature. Surprisingly, we show that some measures of the extent of a species’ climatic envelope do not affect the likelihood of it showing a size-climate relationship. We conclude that negative size-temperature associations are an exception rather than a generality among squamates.
KeywordsMacroecology Bergmann’s rule Resource rule Climatic variability Geographic variation in body size Lizards Snakes Liolaemus
We thank Erez Maza for invaluable help resolving the correct geographic origin of species in the TAUM, and Anat Feldman and Stanislav Volynchic for valuable discussion. We are also grateful to referee’s and editor’s comments that greatly improved our manuscript. D.P.-D. thanks the Leverhulme Trust and a University of Lincoln Faculty Starting Funding for financial support. D.P.D. dedicates this paper to Natalia Feltrin, a young Argentinean ecologist, and a good friend, who devoted her career to the study of Liolaemus lizards, and who recently passed away in a road accident. Her life was interrupted on her way to her Ph.D viva. Natalia’s work will be greatly remembered and appreciated.
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