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Katherine E. Eisen, Digest: Trait variation in Mimulus provides new evidence for the joint action of ecological sorting and character displacement, Evolution, Volume 71, Issue 5, 1 May 2017, Pages 1425–1427, https://doi.org/10.1111/evo.13233
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Understanding how closely related species coexist in communities is one of the oldest goals of ecology and evolutionary biology. One long-standing hypothesis is that the evolution of key differences in species’ niches or ecological requirements (a process known as niche differentiation) can minimize competition and promote coexistence.
Two processes are often invoked as contributing to niche differentiation: ecological sorting and character displacement. Traditionally, these processes have been considered in isolation, given that ecological sorting results from trait change in allopatry, while character displacement is produced by in situ evolution in sympatry.
In this issue, Kooyers et al. (2017) challenged this way of thinking by empirically demonstrating how both of these processes contributed to the co-occurrence of two Mimulus species (Fig. (1)A and B). To determine whether the species’ niches were differentiated in sympatry, the authors analyzed climatic variables and measured soil depth in replicated sympatric and allopatric populations across an elevation gradient. They then conducted common garden and competition experiments using seeds from these populations to determine whether phenotypic differences were genetically based, and whether competition affected trait evolution. Results from the field study indicated that the species occupied patches with distinct soil types in sympatry, which suggested that niche differentiation initially resulted from ecological sorting (habitat partitioning).
