Sarah J. Sapsford, Angela J. Brandt, Kimberley T. Davis, Guadalupe Peralta, Ian A. Dickie, Robert D. Gibson II, Joanna L. Green, Philip E. Hulme, Martin A. Nuñez, Kate H. Orwin, Anibal Pauchard, David A. Wardle, Duane A. Peltzer
Many species of plants, animals and microbes have been introduced to new ecosystems, either accidentally or deliberately. In either case, these introduced species are non-native and can damage individuals, communities and ecosystems that are native to that area. Non-native species can spread widely and impact economic productivity (e.g., weeds in crops or forests), human health (e.g., carry pathogens), and biodiversity (e.g., by causing declines of native species). With global trade and travel accelerating, there are increased risks of non-native species being introduced and spreading into new environments. However, predicting how destructive a non-native species will be in its new environment and its impact on native species remain poorly understood.
We developed a conceptual framework that will help to predict the impacts of non-native species. Impacts of non-native species are not fixed but can be changed by both biotic factors (e.g., pathogens, microbes) and abiotic factors (e.g., temperature, moisture); we call this context dependence of impacts. We consider four main variables and their context-dependence that are needed to predict the impacts of non-native species: 1) Impacts of non-native species depend on their density or the number of individuals per unit area; 2) Impacts can be influenced by per capita effects or the effects of each individual; 3) Time since a non-native species arrived in their new environment can drive both density and per capita impacts and changes in biotic and abiotic variables; 4) Non-native species can exert legacy effects whereby their impacts persist even after they have been removed. By taking all four components into consideration, we should be able to more accurately predict the impacts of non-native species and more efficiently manage introductions of these species.