Ecological character displacement occurs when competition among coexisting species results in the evolution of greater differences in resource use, and in phenotypic features associated with resource use, between sympatric populations than between allopatric ones. Despite the prominence of character displacement in ecological theory, most examples supporting the occurrence of character displacement rest on correlational data. Thus, it is often difficult to establish whether and how interspecific competition causes character evolution. Organisms that display polyphenism, where alternative phenotypes are produced from a single genotype in response to different environmental stimuli, are well-suited for studies of character displacement. Such systems are ideal, because a causal link between the presence or absence of competitors and character change can be unequivocally established if by removing or adding competitors the polyphenic species differentiates or not into multiple morphs. This research will explore character displacement by continuing and developing and ongoing investigation of trophic polyphenism in two desert spadefoot toads. The specific goals of the research would be to (1) use laboratory experiments to determine whether the presence of heterospecifics influences the production of carnivores, and if so, how, (2) employ a common garden experiment to determine if there are greater differences between species in carnivore morph production in sympatric populations than in allopatric ones, and (3) use field experiments to determine the evolutionary cause of character displacement by establishing if southern spadefoot toads are competitively inferior to plains spadefoot toads. Together, these studies will add to our understanding of how resource competition may promote phenotypic divergence. Spadefoot toad tadpoles are ideal for investigating how and why alternative phenotypes exist, which is among the most challenging issues facing modern biologists.
