Ecological and behavioral correlates of coloration in artiodactyls: systematic analyses of conventional hypotheses

To test the generality of adaptive explanations for coat coloration in even-toed ungulates, we examined the literature for hypotheses that have been proposed for color patterns exhibited by this taxon, and we derived a series of predictions from each hypothesis. Next, we collected information on the color, behavioral, and ecological characteristics of 200 species of even-toed ungulates and coded this in binary format. We then applied chi-square or Fisher's Exact probability tests that pitted presence of a color trait against presence of an ecological or behavioral variable for cervids, bovids, and all artiodactyls. Finally, we reanalyzed the data by using concentrated-changes tests and a composite molecular and taxonomic phylogeny. Hinging our findings on whether associations persisted after controlling for shared ancestry, we found strong support for hypotheses suggesting even-toed ungulates turn lighter in winter to aid in concealment or perhaps thermoregulation, striped coats in adults and spotted pelage in young act as camouflage, side bands and dark faces assist in communication, and dark pelage coloration is most common in species living in the tropics (Gloger's rule). Whereas white faces, dark legs, white legs, dark tails, and white tails did not appear to assist in communication alone, legs and tails that were either dark or white (i.e., conspicuous) did seem to be linked with communication. There was moderate support for hypotheses that countershading aids concealment, that white faces are a thermoregulatory device, and that white rumps are used in intraspecific communication. There was weak support for spots in adults and stripes in young providing camouflage and for dark leg markings being a form of disruptive coloration. We found little or no evidence that overall coat color serves as background matching, that side bands are disruptive coloration devices, or that white rumps help in thermoregulation. Concealment appears the principal force driving the evolution of coloration in ungulates with communication, and then thermoregulation, playing less of a role.