The diversification and evolution of niche breadth across spatial scales in western North American monkeyflowers

<p><span>Species show remarkable variation in ecological niche breadth, but the directionality of niche breadth evolution remains a question for niche axes across spatial scales. Testing the association between niche breadth evolution and the process of diversification could shed light on the role of ecology in the formation and maintenance of biodiversity. Here we applied Cladogenetic State change Speciation and Extinction models in western North American monkeyflowers (</span><em>Mimulus</em><span> sensu lato), with two states of niche breadth (generalist and specialist). We aimed to estimate the effects of niche breadth along broad-scale bioclimatic and local-scale microhabitat axes on diversification rate, and the evolutionary trend and mode of niche breadth. We found opposite patterns across spatial scales, with higher speciation rates detected for generalists along broad-scale bioclimatic axes and for specialists along local-scale microhabitat axes. Furthermore, we found weak trends towards specialization for bioclimatic niche breadth, but generalization for microhabitat niche breadth. Both cladogenetic and anagenetic changes were comparable and thus important in the evolution of niche breadth in this group. Together, these findings suggest that the underlying mechanisms of niche breadth evolution might differ across spatial scales, and that change in niche breadth could be tightly associated with the diversification process.</span></p>