Accurately predicting the pattern and rate of spread of invading species is difficult, particularly for species that disperse long distances. Though relatively rare, and often stochastic, long-distance dispersal events increase the maximum rate and geographic extent of invasion. Human activities are responsible for the spread of many exotic species, particularly aquatic species such as the zebra mussel, which are primarily transported within North America by recreational boaters. We estimated spatial and temporal patterns of boating traffic among Wisconsin's inland waterbodies using results of a large, randomized survey of recreational boaters conducted by the Wisconsin Department of Natural Resources. Of the survey respondents, Ͼ90% of boaters traveled locally, within a county or to adjacent counties, 8.4% moved Ͼ50 km, and only 0.8% moved extreme long distances (Ͼ261 km, two standard deviations above the mean of intercounty travel). Extreme longdistance boater movements were correlated positively with greater numbers of registered boaters in source and destination counties, and with greater surface area and numbers of named lakes in destination counties. We compared the observed spatial and temporal patterns of the zebra mussel invasion to those estimated from recreational boater movement by simple diffusion models. Diffusion models underestimated the maximum rate and geographic extent of the zebra mussel invasion and overestimated the invasion of suitable habitats within this extent. Patterns of recreational boater activity in Wisconsin were a better predictor of the observed zebra mussel invasion pattern because they provided probabilistic estimates of invasion at finer spatial resolution. These estimates may be used to manage the spread of boater-dispersed aquatic invaders. To slow the spread of boaterdispersed aquatic invaders such as the zebra mussel, management efforts should target highfrequency, long-distance boater movements, and regions with the greatest volume of source and/or destination boater movement.

In regions with abundant and diverse freshwater resources, it is difficult and costly to survey all lakes at the level required to detect invasive plants. Effective allocation of monitoring resources requires tools that identify waterbodies where exotic species are most likely to invade. We developed and tested models that predict conditions in which Eurasian watermilfoil, Myriophyllum spicatum, is most likely to survive and successfully colonize. We used logistic regression to model the likelihood of M. spicatum presence or absence using a suite of biological, chemical, and physical lake characteristics which are easily obtainable from public databases. We evaluated model fit by the Aikake criterion and model performance by the percentage of misclassification errors as well as the costs associated with acquiring data for variables modeled. Several models fit our data well, misclassifying only 1.3–11.0% of the lakes where M. spicatum was observed, and used relatively inexpensive landscape variables (percent forest cover in a drainage basin, presence and type of public boat launch, and bedrock type) that typically exist as information layers in geographic information systems (GISs) or recreational atlases. We found that the most important factors affecting the presence or absence of M. spicatum were those that influence water quality factors known to impact M. spicatum growth, rather than factors associated with human activity and dispersal potential. In particular, the amount of forest cover in the lake watershed was consistently important and could control the level of dissolved inorganic carbon in lakes, one of the factors known to affect M. spicatum growth rates. Factors such as the number of game fish species and number and types of boat ramps or proximity to roads were generally less important lake characteristics. Our models can be useful tools for developing management strategies to prevent or slow the spread of M. spicatum and aquatic invaders, such as the zebra mussel, that can attach to it and thus be dispersed. Our models also exemplify a general approach for slowing or stopping the spread of other invading species.

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Accurately predicting the pattern and rate of spread of invading species is difficult, particularly for species that disperse long distances. Though relatively rare, and often stochastic, long‐distance dispersal events increase the maximum rate and geographic extent of invasion. Human activities are responsible for the spread of many exotic species, particularly aquatic species such as the zebra mussel, which are primarily transported within North America by recreational boaters. We estimated spatial and temporal patterns of boating traffic among Wisconsin’s inland waterbodies using results of a large, randomized survey of recreational boaters conducted by the Wisconsin Department of Natural Resources. Of the survey respondents, >90% of boaters traveled locally, within a county or to adjacent counties, 8.4% moved >50 km, and only 0.8% moved extreme long distances (>261 km, two standard deviations above the mean of intercounty travel). Extreme long‐distance boater movements were correlated positively with greater numbers of registered boaters in source and destination counties, and with greater surface area and numbers of named lakes in destination counties. We compared the observed spatial and temporal patterns of the zebra mussel invasion to those estimated from recreational boater movement by simple diffusion models. Diffusion models underestimated the maximum rate and geographic extent of the zebra mussel invasion and overestimated the invasion of suitable habitats within this extent. Patterns of recreational boater activity in Wisconsin were a better predictor of the observed zebra mussel invasion pattern because they provided probabilistic estimates of invasion at finer spatial resolution. These estimates may be used to manage the spread of boater‐dispersed aquatic invaders. To slow the spread of boater‐dispersed aquatic invaders such as the zebra mussel, management efforts should target high‐frequency, long‐distance boater movements, and regions with the greatest volume of source and/or destination boater movement.

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