Wednesday, August 5, 2009 - 4:20 PM

OOS 28-9: Demographic models as a tool to understand and manage invasive plant species

Satu M. Ramula and Yvonne M. Buckley. University of Queensland


Population declines of invasive species may be achieved by focusing control on demographic processes (survival, growth, fecundity) with the greatest impact on population growth rate. However, we often have little demographic information on recent invasive populations and density-dependent processes in older and more established invasions. Matrix population models provide a tool for identification of the demographic processes with the greatest impact on population growth rates, enabling a better understanding of the population dynamics and potential management strategies for invasive plant species. We compared population dynamics between invasive and native species using published matrix population models for 21 invasive and 179 native plant species. We examined whether the population growth rate responsiveness to survival, growth and fecundity perturbations varied between invasive and native species, and determined which demographic processes of invaders to target for reductions in population growth rate when population dynamics are density-independent. Using multiple manipulated density levels for a short-lived weed (Senecio madagascariensis), we examined how population density affects management recommendations.


Invaders had higher population growth rates (λ) than natives, resulting in differences in demographic processes. Perturbations of growth and fecundity transitions (elasticities) were more important for population growth of invaders, whereas perturbations of survival had greater importance for population growth of natives. For rapidly growing populations of short-lived invaders, growth and fecundity transitions should be prioritised as control targets over survival transitions. For long-lived invaders with high adult survival, simultaneous reductions in more than one demographic process, preferably survival and growth, are usually required to ensure population decline. These general guidelines can be applied to rapidly growing recent plant invasions and at the invasion front where detailed demographic data on invasive species are lacking. However, different management strategies are usually required for more established and density-regulated invasive populations. Management conducted after the density-dependent process driving population dynamics best curbed density-regulated weed populations, with reductions in seed production having a negligible effect for our model species. Our results emphasise the importance of understanding the timing of density-dependent processes for the management of more established invasive plant populations.