Abstract
Ecological character displacement--trait evolution stemming from selection to lessen resource competition between species--is most often inferred from a pattern in which species differ in resource-use traits in sympatry but not in allopatry, and in which sympatric populations within each species differ from conspecific allopatric populations. Yet, without information on population history, the presence of a divergent phenotype in multiple sympatric populations does not necessarily imply that there has been repeated evolution of character displacement. Instead, such a pattern may arise if there has been character displacement in a single ancestral population, followed by gene flow carrying the divergent phenotype into multiple, derived, sympatric populations. Here, we evaluate the likelihood of such historical events versus ongoing ecological selection in generating divergence in trophic morphology between multiple populations of spadefoot toad (Spea multiplicata) tadpoles that are in sympatry with a heterospecific and those that are in allopatry. We present both phylogenetic and population genetic evidence indicating that the same divergent trait, which minimizes resource competition with the heterospecific, has arisen independently in multiple sympatric populations. These data, therefore, provide strong indirect support for competition's role in divergent trait evolution.
Highlights
Ecological character displacement comes about when individuals most dissimilar from the average resourceuse phenotype of another species are selectively favoured, thereby causing the species to diverge in resource use and associated traits (Slatkin 1980; Taper & Case 1992)
Because selection to diverge from a heterospecific competitor acts only in areas where the two species co-occur, character displacement should produce a distinctive pattern in which potential competitors are more dissimilar in sympatry than in allopatry, and in which sympatric populations within each species differ from conspecifics in allopatric populations (Brown & Wilson 1956; Grant 1972; Endler 1986; Schluter 2000a; but see Goldberg & Lande 2006)
We evaluated whether variation among populations in trophic morphology is significantly correlated with variation in the competitive environment, even after controlling for either shared phylogenetic history or genetic distance between populations
Summary
Ecological character displacement comes about when individuals most dissimilar from the average resourceuse phenotype of another species are selectively favoured, thereby causing the species to diverge in resource use and associated traits (Slatkin 1980; Taper & Case 1992) Because this process has long been seen as crucial in explaining how closely related species are able to coexist in the same habitat (Brown 1995), considerable effort has gone into documenting character displacement in natural populations (Brown & Wilson 1956; Grant 1972; Schluter 2000a; Dayan & Simberloff 2005). Resource competition with S. bombifrons—has arisen independently in multiple sympatric populations
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