Phylogenetic relatedness and invader colonization: An experimental approach of Darwin’s naturalization conundrum

Background/Question/Methods Darwin’s naturalization conundrum states that invader species closely related to natives should be successful because of a shared affinity for local environmental conditions, but that close relatives often compete the most, limiting niche opportunities for the invaders. Previous studies have generally considered these two ‘opposing’ hypotheses as mutually exclusive, yet evidence for both of them abounds. However, there is a dearth of experiments examining both mechanisms simultaneously. Meanwhile, little attention has been paid in previous studies to colonization, which is an early but very important stage that all invaders have to experience. Here, we present the first experimental evidence that both environmental filtering and competitive interaction influenced invader colonization success within a community, by assessing effects of phylogenetic relatedness on colonization of an invader, Ambrosia artemisiifolia.

Results/Conclusions We found that the probability of invader establishment declined with phylogenetic distance between the invader and its recipient communities. The strong filtering effect observed in communities composed of distantly related species was likely linked to two soil enzymes, which exhibited a significant phylogenetic signal. On the other hand, the average size of invader individuals increased with the phylogenetic distance, suggesting strong competition interactions between the invader and its closely related resident species. Taken together, our results highlight that closely and distantly related species of invaders in recipient communities may represent distinctive mechanisms influencing their colonization success, thus shedding some light on the long-standing debate on the roles of phylogenetic relatedness in determining invader success.