Joint test of historical vs. contemporary biogeography supports abundant center hypothesis shaping spatial patterns of self-fertilization

What generates and maintains the amazing diversity in plant reproduction we see today? Two major competing hypotheses include the role of historical drivers---such as post-glacial range expansion---and the role of contemporary ecology---such as pollinator or mate availability---in structuring spatial variation in reproductive assurance or the ability of a plant to reproduce without conspecifics. Due to methodological constraints, historical drivers have remained a relatively understudied explanation compared to the role of contemporary ecology, and, as a result, rarely are the two hypotheses studied concurrently. Range expansion into new habitats after glacial retreat, where pollinators or mates were scarce, is hypothesized to favour plants with the ability to reproduce by making self-pollinated seeds or vegetative clones. Alternatively, contemporary biogeography---predicated on the assumption that population densities peak at the geographic center of a species range and decline towards the range edges---is hypothesized to favour self-fertilization or vegetative propagation with decreasing population density. Here, we test the hypothesis of historical range expansion against the alternative hypothesis that contemporary biogeography structures spatial variation in reproductive assurance. Overall, we find stronger support for the contemporary ecological hypothesis, where the probabilities of making autonomously selfed-seed increase with greater distance from today's estimated range center.