Ecologists utilize many approaches to assess risk of invasive
species establishment. We subscribe to an approach that first considers
introduction effort to identify which lakes are exposed to an invader,
following which the environmental suitability and ecological integration
ability are considered. We highlight this approach using all three steps for
the zebra mussel in Ontario. We
measured introduction effort using a 'gravity model', which linked invaded
source with noninvaded destination lakes via an array of human activities. Of
291 lakes, invasion status was accurately predicted for 80% using only gravity
scores in a Multivariate Adaptive Regression Spline
analysis; 69% of 48 lakes predicted to be invaded were invaded. Another MARS
model based upon physical and chemical parameters indicated that establishment
was correlated with two parameters: dissolved organic carbon (-) and pH (+). Of
lakes predicted to be invaded based upon introduction effort, 75% were
correctly classified with regard to invasion status when lake characteristics
were considered. Of these lakes, 94% predicted to be invaded were invaded.
Another MARS model used fish community composition for lakes predicted to be
invaded from the previous models; 30 of 35 lakes predicted to be invaded were
invaded. Establishment was negatively correlated with presence of whitefish, which
prey on Dreissena, and positively correlated with largemouth bass,
reflecting predation release from molluscivorous fishes by the bass. While this
approach is data and computationally intensive, it may provide the most
realistic assessment of where spreading nonindigenous species may colonize
successfully.