Invasion success and threat status: two sides of a different coin?

The characteristics possessed by invasive species have been suggested to be the reverse of those possessed by species threatened with extinction, such that relationships of species’ traits to invasion success should be opposite in sign to relationships of the same traits to extinction threat. A recent study (Jeschke, J. M. and Strayer, D. L. 2008. Are threat status and invasion success two sides of the same coin? – Ecography 31: 124–130) found no evidence for this “two-sides-of-the-same-coin” hypothesis but compared characteristics of species in each taxon that were invasive to a control group consisting of all other species. A different view of the “two-sides-of-the-same-coin” hypothesis may be obtained if the characters of invasive species are compared to those of a control group consisting of species that have not invaded despite actually being introduced. Here, we show that changing the control group for comparison with invasive species does not change the lack of support for the “two-sides-of-the-same-coin” hypothesis but does change views about which specific traits are consistent with the hypothesis.