Finite time, labor, and financial resources available to land managers can restrain invasive plant species management efforts and engender a need for a decision framework in which to prioritize management decisions.  Habitat suitability or probability of occurrence (PO) models, generated from environmental variables, can be used to estimate or predict the realized geographic distribution of a weed species and can be used as a tool for targeted sampling, monitoring, and management at a landscape scale.  In practice, however, these models are rarely employed to assess management strategies to reduce invasion rates (metapopulation growth rates).  A modified incidence function (MIF) simulation model was developed to explore the spatial metapopulation dynamics for an invading plant species using PO as a driving variable.  Our objective was to use the MIF to simulate the influence of management efficacy on metapopulation dynamics. We measured the response of the metapopulation growth rate over a 20 year time period starting from randomly distributed source populations by varying the probability of source patch mortality as a result of management. Several driving variables were manipulated to determine their relative impact on the success of management at reducing the invasion rate.   

Results/Conclusions

The primary goal of this study was to assess implications of management to develop methods for field experiments aimed at asking how management efficacy relates to PO.  Consequently, it is important to understand how metapopulation growth rates are affected by increasing management-induced mortality rates of source patches across a gradient of PO values.  In the absence of management, invasion rates, increased with increasing PO.  When the number of source patches managed each year was held constant, management efficacy had less effect on the metapopulation mean geometric growth rate as PO increased. Our results imply that higher levels of management-induced mortality targeted at populations occupying areas of lower PO might have more influence on invasion and extinction rates than management prioritized in favor of high PO areas. We are currently investigating how changes to numbers of source patches treated each year and how density and rates of emigration from source patches affect invasion rates.  The MIF model allowed us to use a theoretical framework to address an applied problem.