COS 83-9
Demographic mechanisms underlying invasive spread: Comparison of two invasive plants and their native ecological analogs
Knowledge of a species' range limit is important when triaging for non-native invasive species management. With invasive species, we often have limited data at the early stages of invasion as species are not at equilibrium. These species may be beyond eradication or control by the time enough demographic data are collected. Inferring population dynamics based on current locations of invasive populations may under- or over-estimate population growth rates and, thus, potential spread. Understanding how environmental variation affects demographic parameters is important in determining species range limits and to providing a mechanistic basis for understanding invasions. Mechanistic models increase our confidence when extrapolating population level patterns to a new set of conditions or novel landscape. We investigated establishment dynamics of two non-native invasive species; the woody Berberis thunbergii and the monocarpic biennial Alliaria petiolata, as well as two native ecological analogs. We used integral projection models (IPMs) to predict potential establishment risk across an environmental gradient found in New England for all species. The IPMs allowed us to combine multiple, relatively short-term data sets to estimate demographic patterns.
Results/Conclusions
We highlight conditions where natives and invasives perform similarly and where the invasives clearly outperform the natives. In general, the invasive species are less sensitive to climatic factors and are primarily limited by local habitat factors such as canopy closure. The mechanistic understanding allows us to scale up the geographic distribution to a regional level and to project potential population expansion to novel regions outside the current distribution of the species. As both invasive species are predicted to establish outside of their current distributions, these results provide evidence that B. thunbergii and A. petiolata are dispersal limited and have the ability to survive, grow, and reproduce in these areas.
Sensitivity analysis for both invasive species suggests that management techniques may need to vary by region based on the environmental conditions found. This method allows us to take a mechanistic approach and use data available on non-native species to highlight potential areas of concern for both researchers to collect more data and for land managers to design specific management plans.