Invasive species threaten habitat structure, biodiversity and ecosystem function of native communities. Understanding the mechanisms driving or allowing invasion may help prevent future invasions and perhaps provide clues to slowing or even remediating existing invasions and informing subsequent restoration. Substantial ecological theory has suggested that more functionally diverse communities should be more resistant to invasion, but this has not been thoroughly tested to date. Using three forests in southeast Michigan, we ask if functional diversity of native species can predict the relative abundance or number of species of invasive shrubs in these forests. Two levels of analysis were carried out – among the three forests, and among the quadrats within these three sites. Abundance data was collected for each quadrat within these sites, as were traits associated with the leaf economics spectrum – specific leaf area, leaf dry matter content, leaf nitrogen content, and delta 15N. These data for native species were used to calculate site and quadrat level functional diversity using Rao’s quadratic entropy, and then correlated with relative abundance and number of invasive species in each sampling unit.
Results/Conclusions
Results suggest a modest to moderate role for functional diversity in driving invasions, with an overall weak inverse relationship between functional diversity and relative abundance of invasive shrubs. There was no relationship with number of invasive species present, however, at the quadrat level (but a weak relationship at among site level). Interestingly, more heavily invaded sites showed significantly increased functional diversity when invasive species were included in calculation of Rao’s entropy compared to lightly invaded sites; considering the nature of most invasive species’ functional traits, this is perhaps unsurprising, since they are commonly demonstrating traits rather different from those native to a site.