Data from: Competition drives trait evolution and character displacement between Mimulus species along an environmental gradient

Closely related species may evolve to coexist stably in sympatry through niche differentiation driven by in situ competition, a process termed character displacement. Alternatively, past evolution in allopatry may have already sufficiently reduced niche overlap to permit establishment in sympatry, a process called ecological sorting. The relative importance of each process to niche differentiation is contentious even though they are not mutually exclusive and are both mediated via multivariate trait evolution. We explore how competition has impacted niche differentiation in two monkeyflowers, Mimulus alsinoides and M. guttatus, which often co-occur. Through field observations, common gardens, and competition experiments, we demonstrate that M. alsinoides is restricted to marginal habitats in sympatry and that the impacts of character displacement on niche differentiation are complex. Competition with M. guttatus alters selection gradients and has favored taller M. alsinoides with earlier seasonal flowering at low elevation and floral shape divergence at high elevation. However, no trait exhibits the pattern typically associated with character displacement, higher divergence between species in sympatry than allopatry. Thus, although character displacement was unlikely the process driving initial divergence along niche axes necessary for coexistence, we conclude that competition in sympatry has likely driven trait evolution along additional niche axes.亲缘关系密切的物种可通过原位竞争驱动的生态位分化，在同域分布（sympatry）中稳定共存，这一过程被称为性状替换（character displacement）。与之相对，异域分布（allopatry）下的既往演化已足以充分降低生态位重叠，从而允许物种在同域环境中建立种群，该过程被称为生态分选（ecological sorting）。尽管二者并非互斥，且均通过多变量性状演化介导，但二者对于生态位分化的相对重要性仍存在争议。我们以两种常同域分布的猴面花（monkeyflowers）——*Mimulus alsinoides*（米努草状猴面花）和*Mimulus guttatus*（斑点猴面花）——为研究对象，探究竞争对其生态位分化的影响。通过野外观测、同质园实验以及竞争实验，我们发现：米努草状猴面花在同域分布区域中仅局限于边缘生境；且性状替换对生态位分化的影响较为复杂。与斑点猴面花的竞争改变了选择梯度，在低海拔区域青睐于株高更高、花期更早的米努草状猴面花，而在高海拔区域则推动其花形发生分化。然而，并无任何性状呈现出典型的性状替换相关模式——即同域种群间的性状分化程度高于异域种群。因此，尽管性状替换不太可能是驱动物种共存所需生态位轴初始分化的过程，但我们推断，同域环境中的竞争已推动物种在额外的生态位轴上发生了性状演化。