DEPARTMENT OF MATHEMATICAL & STATISTICAL SCIENCES
UNIVERSITY OF ALBERTA
MONDAY, NOVEMBER 18, 2002
Dr. Brian Leung
Department of Biological Sciences
University of Notre Dame
Biological Invasions: Predictions, Risk, and Action
Ecological forecasting and risk analysis are exciting intellectual frontiers where the science of ecology meets critical public policy needs. As the recent National Invasive Species Management Plan (National Invasive Species Council 2001) and other reports (CENR 1999) have recognized, ecological guidance and quantitative risk analyses are crucial to respond to many environmental challenges, including those posed by nonindigenous species (NIS). Nonindigenous species are one of the top causes of biodiversity loss in many ecosystems. In addition, they can cause large ecosystem changes, and interact strongly with many other drivers of global environmental change. The financial cost of nonindigenous species to the US alone has been roughly estimated at $137 billion/yr. Clearly, it is important to determine which areas are at risk of invasion to focus prevention effort. It is likewise important to determine reasonable actions, both in terms of prevention before and control after an invasion. I have developed a model to forecast the location of new invasions, using propagule pressure, gravity models, and population dynamics in terms of Allee effects. Then, I use bioeconomic risk analysis for decision formulation, with stochastic dynamic programming as its mathematical basis. These models are applied to zebra mussel invasion of inland lakes. For forecasting invasions, I demonstrate that Allee effects are present and that, using a validation data set, we can correctly predict up to nine times as many invasions as the null (random) model. Further, the Allee model assigned average probabilities 4.5 times higher for lakes that became invaded compared to uninvaded lakes, whereas the non-Allee model only predicted probabilities two times as high. Thus, this model improves predictions of future invasions, and demonstrates the importance of considering the Allee effect. For determining appropriate actions, I use cost-benefit analyses and show that society would benefit by spending up to $324,000 USD/yr to reduce invasions of zebra mussels into each lake with a power plant. In sharp contrast, US Fish & Wildlife Services spent $825,000 in FY2001 to manage all aquatic invaders for all lakes. Thus, greater investment in prevention appears warranted.