| This thesis is an investigation of the poorly understood underlying mechanisms of biological invasions. The spread of Lythrum salicaria is often attributed to high rates of growth and seed production. I tested these hypotheses by studying the demography of two floodplain populations in Wellington County, Ontario, Canada, over three years. Demographic parameters were estimated for 12 stages and analyzed using projection matrices to calculate population growth rates, lambda (lambda), for two time intervals and the sensitivity of lambda to perturbations at different size classes. Lambda exceeded one in both intervals and at both sites. At equilibrium, expected distribution differed from observed distribution. Comparison of the lambda's (purple loosestrife versus five other wetland species) revealed no significant difference. Survival rather than reproduction had the largest effect on lambda. These results dispute two major hypotheses regarding invasiveness in L. salicaria and provide insight into the causes and control of its spread. |
