Comparing biotic resistance with species richness and biotic interactions across latitudes and ecosystems

Background/Question/Methods

Modern definitions of biotic resistance include the degree to which native species can limit the further spread and establishment of established invaders. We can better understand the forces behind biotic resistance by examining studies across a wide range of systems.  We can also consider how local and regional diversity patterns and the strength biotic interactions vary across systems and across regions.  These changing patterns of diversity and interaction strength may potentially contribute to the observed patterns of biotic resistance across systems and across regions.  We use an extensive meta-analysis to ask how the strength of biotic resistance varies across different ecosystem types (terrestrial, marine) as well as across different trophic levels (producers, consumers) and different regions (temperate, tropical) in marine systems.  We then use these results to ask two additional questions.  First, how might the forces that determine local diversity influence the strength of biotic resistance between marine and terrestrial systems?  Second, how might the overall strength of biotic interactions across latitudes in marine systems compare influence patterns of biotic resistance across latitudes.

Results/Conclusions

Our meta-analysis revealed the strength of biotic resistance is greater in terrestrial systems relative to marine systems particularly for invasive producers.  Also, biotic resistance in marine systems is greater for invasive producers relative to invasive consumers, and greater at lower versus higher latitudes.  When we compared biotic resistance across systems with the relative influences of local vs. regional species pools, we find an interesting parallel.  Recent literature syntheses show that influence of regional species richness (RSR) relative to local species richness (LSR) on local processes is greater in marine systems. This suggests the possibility that local interactions influencing biotic resistance may also be less important in marine relative to terrestrial systems.  When we compare biotic resistance in marine systems across latitudes with biotic interactions, we also find an interesting concordance.  Recent literature surveys show that biotic interactions are more intense in the tropics relative to temperate regions.  We conclude that more intense biotic interactions could help explain increased biotic resistance at lower latitudes.   We discuss the assumptions and limitations of these explanations, but discuss how these ideas may contribute to a broader understanding of when and where biotic resistance may be important.