Are invaders different: comparing performance metrics among some of the world’s worst invaders in their home and away range

Background/Question/Methods

Introduced species are widely considered invasive when they become abundant in their new ranges, displace native species, and cause economic damage.  However, it is unclear whether the success in demographic performance of many invasive species stems from a fundamental change in ecological or evolutionary interactions, or whether some species are ecological dominants that thrive both at home and away.  While conventional wisdom suggests that invaders are more prolific in their introduced range relative to where they are native, emerging studies are often equivocal.  Most data documenting the differential success of invasive species are restricted to particular taxa, anecdotal in nature, or equivocal across many species.  The lack of broad scale comparisons of invader performance in their home versus introduced ranges hinders our ability to detect the mechanisms driving invasion success and thus limits our ability to mitigate their damage.  Our main goal here is to test whether introduced populations of exotic species exhibit increased demographic performance relative to where they are native. As a conservative test of this hypothesis, we used the IUCN Global Invasive Species Programme’s 100 World’s Worst Alien Invaders list to compile a database on multiple performance metrics in the native and introduced ranges. 

Results/Conclusions

Suitable data to compare population densities, individual size and reproductive effort in native and introduced populations were available for only 32 of these 100 species. In most cases, the lack of relevant data from the native range was the primary limiting factor.  To compensate and expand our study to include other invasive species, we also gathered data for 16 additional species that had been studied in both the home and away range.  Overall, there was a trend for introduced species to be larger and have denser populations in their new ranges.  However, there was a considerable amount of variation even among species that are widely considered prolific invaders, and in many cases the world’s worst invasive species were actually performing worse in their new ranges.  Our results indicate that there are surprisingly little data to support one of the fundamental tenets of invasion biology.