| Popis: |
Colours influence numerous aspects of an animal's ecology. One possibility is that colour helps make an animal cryptic against the background on which it is resting. We test this hypothesis for two different, geographically separated colour forms (dark forms and light forms) of the Western Terrestrial Garter Snake, Thamnophis elegans. We quantified crypsis of snakes, in terms of colour (chromatic crypsis) and brightness (achromatic crypsis), by using objective measures of spectral reflectance of snakes and the surrounding habitat. These data were visually modelled from the perspective of potential snake predators and human researchers. Overall, snakes of both colour forms selected basking sites that increased chromatic crypsis over that which would have been achievable on random backgrounds. Both colour forms of T. elegans appear to exhibit similar achromatic and chromatic crypsis when viewed by potential predators, such as mammals and birds. From the perspective of the human visual model, dark T. elegans were generally more chromatically cryptic than light T. elegans, contrary to our a priori subjective impression. The main contribution of the present study is that we provide one of the first objective comparisons of snakes and their backgrounds as a measure of crypsis. Although we found some evidence for crypsis as a factor in choice of basking sites for snakes, other factors (e.g. thermoregulatory opportunities) undoubtedly play important roles as well. We also have not addressed whether snakes involved in other activities are cryptic or whether there are differences between the sexes or between reproductive and nonreproductive females. The adaptive significance of colour variation has been studied in diverse taxonomic groups. Although the mechanisms are not straightforward, the opportunities to carry out further work in this area are enhanced by the availability of objective approaches. © 2013 The Linnean Society of London |
