Amphibian phenotypic variation along a gradient in canopy cover: species differences and plasticity


J. Van Buskirk, Inst. of Evolutionary Biology and Environmental Studies, Univ. of Zürich, CH–8057 Zürich, Switzerland. E-mail:


The distributions of many freshwater organisms correlate with a gradient in canopy cover, ranging from sunny wetlands to closed woodland ponds. Little is known about mechanisms that exclude species from some sections of the gradient while allowing persistence in others. I addressed this question by manipulating shading in 740-l outdoor mesocosms and measuring several ecologically-relevant traits in three species of amphibian larva (Rana temporaria and Triturus alpestris, generalists occupying the entire gradient; and Hyla arborea, a specialist in open habitats). Shading caused delayed development, but had no effect on survival and increased the growth rate of R. temporaria. Body and tail color were darker in the shade. Plasticity in morphological shape, consisting of reduced gut width and increased tail size under shaded conditions, may reflect poor food availability and low dissolved oxygen. The canopy generalist R. temporaria increased activity in the shade, spent more time basking in shallow water, and maintained high larval performance. Unexpectedly, the specialist H. arborea was also highly plastic. These results describe extensive phenotypic plasticity induced by shade, and highlight traits that may influence performance along the canopy gradient.