DEPARTMENT OF MATHEMATICAL AND STATISTICAL SCIENCES
UNIVERSITY OF ALBERTA
PIMS-MITACS MATHEMATICAL BIOLOGY SEMINAR
MONDAY, November 22, 2004
3:00 - 4:00 p.m.
Dr. Marjorie Wonham
Department of Mathematical and Statistical Sciences
University of Alberta
Temporal increases in biological invasions: using models to distinguish among mechanisms
Biological invasion records reveal rapid and increasing changes in global biodiversity. Where recorded invasions appear to be increasing supra-linearly through time, proposed driving mechanisms include increasing introduction rates, invader survival, and detection. To distinguish among these hypotheses we develop a null model that describes temporal trends in the number of invasions as a function of introduction rate and species survival probability. Our model shows that even under constant species survival probabilities and introduction rates, an exponential distribution of introduction times is predicted. Model extensions show that simple temporal patterns in survival probabilities and introduction rates can generate apparently linear, quadratic, exponential, or sigmoid distributions of introduction times. We compared the model predictions to empirical data of new invaders per year from eleven marine, freshwater, and terrestrial datasets. A single best fit emerged in only a few cases, indicating that data are often insufficient to distinguish among models. Most datasets supported linear and exponential models, and fewer supported quadratic and sigmoid models. Even when the models can be distinguished, inferring the driving mechanisms requires further investigation.