Let the right one in: reply to Hulme et al. and van Kleunen et al.

Abstract

Hulme et al. [1xDon’t be fooled by a name: a reply to Thompson and Davis. Hulme, P.E. et al. Trends Ecol. Evol. 2011; 26: 318Abstract | Full Text | Full Text PDF | PubMed | Scopus (16)See all References[1] and van Kleunen et al. [2xResearch on invasive-plant traits tells us a lot. van Kleunen, M. et al. Trends Ecol. Evol. 2011; 26: 317Abstract | Full Text | Full Text PDF | PubMed | Scopus (18)See all References[2] have responded to our recent letter [3xWhy research on traits of invasive plants tells us very little. Thompson, K. and Davis, M.A. Trends Ecol. Evol. 2011; 26: 155–156Abstract | Full Text | Full Text PDF | PubMed | Scopus (63)See all References[3] in TREE on traits of invasive plants. First, we want to say that we highly respect our colleagues, some of whom we count as personal friends. They have all had leading roles in the field of invasion biology. However, most of the arguments deployed in their responses have, at best, only tangential relevance to our basic thesis, which is that, in terms of their ability to thrive in the modern, human-dominated landscape, plants are essentially either ‘winners’ or ‘losers’, and that this dichotomy is largely unrelated to native or alien status.We would not, for example, dispute for a moment that many studies have found trait differences between native species and invasive aliens. Given that invasive aliens are (by definition) winners, whereas natives are, at best, a mixture of winners and losers, such differences are inevitable. Neither do we wish to downplay the importance of continuing to research into the best traits for determining the invasive potential of future introductions; in our world view, such screening becomes more important as non-native status itself becomes less useful as a predictor of invasiveness.It is no part of our argument that ‘native species will in due course adapt to these new [anthropogenic] pressures’ [1xDon’t be fooled by a name: a reply to Thompson and Davis. Hulme, P.E. et al. Trends Ecol. Evol. 2011; 26: 318Abstract | Full Text | Full Text PDF | PubMed | Scopus (16)See all References[1]; we make no assumptions or predictions about future adaptation. Hulme et al. [1xDon’t be fooled by a name: a reply to Thompson and Davis. Hulme, P.E. et al. Trends Ecol. Evol. 2011; 26: 318Abstract | Full Text | Full Text PDF | PubMed | Scopus (16)See all References[1] also claim that our approach ‘assumes that the native and alien species pools within a region are similarly adapted to the anthropogenic impacts’, but we make no such assumption. Indeed, the very suggestion illustrates one of the perils of basing potential threatening status on biogeographic origin. Viewed from New Zealand, a country whose unique history has led to a flora composed largely of ‘losers’, alien status looks like (and indeed is) a significant risk factor. The other side of this coin is that native New Zealand plants are unlikely to have the right traits to cause trouble in North America, Europe or Asia, but, in both cases, traits are the key, rather than native or alien status.Most invasive species (whether alien or native) owe their success to an ability to exploit human disturbance and eutrophication (i.e. they are passengers rather than drivers of change). However, we agree that a minority of species do bring with them genuinely new problems, such as altered fire frequency or nitrogen fixation to ecosystems previously lacking that trait. This observation points to where studies of traits really can make a difference, and illustrates the crucial distinction between success (in a purely ecological sense) and impact. There is nothing magic about success; most successful species (regardless of origin) share a well-defined syndrome of ‘winning’ traits that requires little further documentation. Instead, researchers need to focus on a search for traits that are, in themselves, likely to cause real problems for ecosystems. These are the traits, especially if allied to the ‘winning’ syndrome, that should be of real concern.In conclusion, we find little to disagree with in either reply to our letter, partly because neither really responded to our core argument. Neither do we find much reason to change our opinion that it is time we stopped obsessing about non-native status, as though that, in itself, told us anything useful.