Phylogenetic insights into the invasion paradox

Adrienne R. Ernst, Plant Biology and Conservation, Northwestern University and Chicago Botanic Garden, Glencoe, IL, Rebecca S. Barak and Andrea T. Kramer, Negaunee Institute for Plant Conservation Science and Action, Chicago Botanic Garden, Glencoe, IL, Andrew L. Hipp, Herbarium, The Morton Arboretum, Lisle, IL, Daniel J. Larkin, Department of Fisheries Wildlife and Conservation Biology, Minnesota Aquatic Invasive Species Research Center, University of Minnesota, St. Paul, MN, Hannah E. Marx, Biology, University of New Mexico, Albuquerque, NM

Background/Question/Methods
The question of how native community characteristics shape invasion dates to Elton’s formal conception of the field. He posited that more native species would lead to higher niche-filling, thus conferring resistance to invaders. This hypothesis has primarily been tested by comparing the relationship between native species richness and invasion. Studies have found that the diversity-invasibility relationship can be positive or negative depending on the context in which it is studied—with particular differences by spatial scale and between experimental and observational studies. However, few studies have explored how phylogenetic and functional diversity, which should more faithfully represent niche space, influence community invasibility. We explored this question in Illinois grasslands by leveraging a large-scale, long-term observational dataset encompassing 150 sites across the state and by performing two invasion studies in experimentally restored plots established with different levels of phylogenetic and functional diversity.
Results/Conclusions
We found that phylogenetic diversity provided insights to the invasion paradox distinct from what has been found for species richness. From our observational dataset, we observed that more phylogenetically diverse communities had higher abundance of invasive species; however, when viewed longitudinally, phylogenetically diverse communities had lower abundance of invasive species over time. This suggests that both sides of the so-called paradox may be operating simultaneously reflecting that both site characteristics and native diversity shape invasion. From the experimental communities we found that the effect of phylogenetic diversity differed depending on the invader’s origin and invasion stage. Abundance of native invaders increased with increasing phylogenetic diversity. More phylogenetically diverse communities had greater increases in the abundance of non-native species over time, but also had higher mortality of non-native invaders.