Why Close Relatives Make Bad Neighbors: Phylogenetic Conservatism in Niche Preferences and Dispersal Disproves Darwin's Naturalization Hypothesis in the Thistle Tribe
Daniel S. Park1,* andDaniel Potter2
1Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA
2Department of Plant Sciences, University of California, Davis, CA
* Correspondence should be addressed to:
Daniel S. Park
Department of Organismic and Evolutionary Biology, HUH 22 Divinity Ave. Harvard University, Cambridge, MA 02138.
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/mec.13227
invasive species;phylogenetics;Cardueae; niche modeling;
dispersal;Darwin's Naturalization Hypothesis; biological invasions; thistles
The number of exotic plant species that have been introduced into the United States far exceeds that of other groups of organisms, and many of these have become invasive. As in many regions of the globe, invasive members of the thistle tribe, Cardueae, are highly problematic in the California Floristic Province, an established biodiversity hotspot. While Darwin's Naturalization Hypothesis posits that plant invaders closely related to native species would be at a disadvantage, evidence has been found that introduced thistles more closely related to native species are more likely to become invasive. In order to elucidate the mechanisms behind this pattern, we modeled the ecological niches of thistle species present in the Province and compared niche similarity between taxa and their evolutionary relatedness, using fossil calibrated molecular phylogenies of the tribe. The predicted niches of invasive species were found to have higher degrees of overlap with native species than non-invasive introduced species do, and pairwise niche distance was significantly correlated with phylogenetic distance, suggesting phylogenetic niche conservatism. Invasive thistles also displayed superior dispersal capabilities compared to non-invasive introduced species, and these capabilities exhibited a phylogenetic signal. By analyzing the modeled ecological niches and dispersal capabilities of over a hundred thistle species, we demonstrate that exapted preferences to the invaded environment may explain why close exotic relatives may make bad neighbors in the thistle tribe.
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