Meta-analysis: Altered biotic interactions do not explain invasive species success

Background/Question/Methods

After over 50 years of intensive study on invasive species, there is still no consensus about the mechanisms that drive their success. When species are introduced to a new area, they leave behind their co-evolved communities and enter into new species interactions; these altered biological contexts may be one of the major drivers of invasive species success. While there is mounting evidence that invasive species interact with their invaded communities in novel ways, altered biotic interactions do not necessarily translate into increased performance and invasiveness. To date, there has been no meta-analysis that summarizes the effects of biotic interactions for native, exotic non-invasive, and invasive species across all major biotic interactions.

We conducted a meta-analysis to determine the fitness effects of biotic interactions during invasions, and to compare these to native and non-invasive exotic species. Our meta-analysis covers all major biological interactions including competition, predation, herbivory, mutualism, disease, and microbial interactions. We hypothesize that invasive species gain their competitive superiority through decreased interactions with antagonistic biotic interactors, compared to co-occurring native species or conspecifics in their native range.

Results/Conclusions

In our study we address the following questions: (1) Does the native community provide biotic resistance to exotic and invasive species? (2) Do biotic interactions differ for native, exotic non-invasive, and invasive species? and (3) Are altered biotic interactions a general mechanism for invasive species success? We found evidence for biotic resistance – the removal of predators and plant microbial communities benefitted exotic species, and the removal of insect herbivores, mammal browsers, and predators benefitted invasive species. However, the strengths of most biotic interactions did not differ between native, exotic non-invasive, and invasive species (p > 0.44) and therefore cannot explain the success of invasive species. Based on our results, we find that altered biotic interactions do not explain the success of invasive species.