Character Variation and Adaptation in European Sparrows

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Abstract
The phenetics of European sparrows, Passer domesticus, P. hispaniolensis, and their hybrids, are here examined by univariate and multivariate statistics to determine the nature and direction of phenetic variation and the possible adaptive significance of this variation. There seems to be a close relationship of dimensional and color characters with climatic and other environmental variables; most instances of character variation are strictly clinal, with longer individuals occuring in southerly localities and shorter individuals at northerly localities. Thicknesses of bony elements tend not to vary geographically, so longer-limbed individuals are relatively thinner. Regression analyses suggest a persistent positive relationship between summer temperature and bone lengths, such as is subsumed by Allen's “ecogeographic rule.” There is sexual dimorphism in the size of wing and sternal elements, but not of other dimensional characters, meaning that females are proportionally larger in the head and legs than males. Probable causes for this complex dimorphism lie in (1) selection for large body size in males as advantageous in display and fighting, (2) selection for small body size in females for thermoregulatory advantage in closed nests, and (3) common use by both sexes of a single food resource. Results of multivariate cluster analyses are such that specimen localities show regularity in clustering occurrence when grouped by 33 male specimen characters, by 27 female specimen characters, or by 37 mean monthly climatic characters. Such coincidence suggests that at least part of the character variation used to construct infraspecific classifications of these sparrows is elaborated by finely-graded climatic differences.

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