Biological invasions are considered a key threat to global biodiversity, yet whether introduced plants can drive native species loss remains highly controversial. This controversy has been fuelled by a dearth of identified causal mechanisms that show how alien plant invasions can cause native plant extinctions.
Life history tradeoffs provide a key explanation for species coexistence in heterogenous environments. According to the universal tradeoff hypothesis (Tilman 2011), alien plant invasions should never cause native plant extinctions because all species, regardless of biogeographic origin, are constrained by the same fundamental tradeoffs. However, humans may inadvertently help plant invaders overcome life history tradeoffs, giving them an “ecological fitness” advantage by e.g. planting and dispersing alien species in high numbers, for pasture production for example, increasing their colonisation ability at no cost to their competitive ability. Introduced species could therefore break the rules of coexistence that allow diverse communities to persist.
Parameterized and tested with targeted empirical data from a broader research project (alienimpacts.com), this project will build on recent theoretical advances in invasion, (meta-) population, and (meta-) community ecology to develop mathematical models of invasion impacts (Catford et al. 2018; Hui & Richardson 2018). Key theoretical extensions include incorporating a three-way tradeoff between species’ competitive ability, colonisation rate and mortality, accounting for habitat destruction and large scale disturbances like fire and floods, and enabling niche pre-emption.¬ Such changes will enable more realistic predictions of the likely impacts of alien invasion with and without other forms of environmental change, and will test and extend community ecology theory.
Policy Impact of Research:
Given the accelerating rate of alien plant introductions and biodiversity loss, there is an urgent need to ascertain if, how and under what conditions alien plants drive native species extinctions. Ascertaining the mechanisms and quantifying the likely extent of invader-induced plant extinctions will inform biodiversity conservation, biosecurity and invasive species management.