Predicting plant invasions

Invasive species are a global problem. Managing them once they have become established is extremely costly and usually only marginally successful. But most introduced species never become established in their new homes, and only a small proportion of those that become established ever become troublemakers. The best way to manage invasive species is to prevent them from becoming established in the first place. But the challenge is to distinguishpotential invaders from innocuous introductions. In a paper published in the January issue of the Journal of Ecology, Angela Moles, Monica Gruber and Stephen Bonser have proposed a new framework for trying to identify potential invaders.

In trying to identify potential invaders, most people tend to look for classic weeds. Species which mature quickly and produce large quantities of readily dispersed seed seem to be ideal candidates for invasion. However, actual studies of invasive species have shown them to be highly idiosyncratic – a non-native species that is invasive in one context may be benign in another context.

Non-native species often do well in habitats that are not a normal part of the system. This is unsurprising – if the native species have not evolved with certain niches, they are likely to be competitively inferior to non-native species that have evolved in area where those conditions occur. Moles and colleagues developed a framework for identifying the species that are likely to be invasive in a given type of habitats.

Our approach can be applied to ecosystems where the environmental conditions and/or disturbance regime have recently changed, to predict the range of trait space occupied by (i) native species at risk of local extinction, (ii) native species that can persist under the present conditions, and (iii) successful invaders. Our approach can also be used to identify unoccupied viable trait space (i.e. vacant niches) that might be at risk of invasion.

Their framework looks interesting. Unfortunately, it depends on the existence of the sort of massive databases which are only now starting to be widely available. They point out that

For instance, we have seed mass data for around 13 000 species
(Moles et al. 2005b), genome size data for around 5000 species (Beaulieu
et al. 2007) and specific leaf area data for over 2000 species (Wright
et al. 2004).

These are major achievements, but this is still a tiny proportion of the 350-400,000 species of plants that are thought to exist. It’s a great start, but it points to the need for a lot of basic research data.

Moles, A.T., Gruber, M.A., Bonser, S.P. (2008). A new framework for predicting invasive plant species. Journal of Ecology, 96(1), 13-17. DOI: 10.1111/j.1365-2745.2007.01332.x