Optimal spatial prioritization of control resources for elimination of invasive species under demographic uncertainty

Abstract

Populations of invasive species often spread heterogeneously across a landscape, consisting of local populations that cluster in space but are connected by dispersal. A fundamental dilemma for invasive species control is how to optimally allocate limited fiscal resources across local populations. Theoretical work based on perfect knowledge of demographic connectivity suggests that targeting local populations from which migrants originate (sources) can be optimal. However, demographic processes such as abundance and dispersal can be highly uncertain, and the relationship between local population density and damage costs (damage function) is rarely known. We used a metapopulation model to understand how budget and uncertainty in abundance, connectivity, and the damage function, together impact return on investment (ROI) for optimal control strategies. Budget, observational uncertainty, and the damage function had strong effects on the optimal resource allocation strategy. Uncertainty in dispersal probability was the least important determinant of ROI. The damage function determined which resource prioritization strategy was optimal when connectivity was symmetric but not when it was asymmetric. When connectivity was asymmetric, prioritizing source populations had a higher ROI than allocating effort equally across local populations, regardless of the damage function, but uncertainty in connectivity structure and abundance reduced ROI of the optimal prioritization strategy by 57% on average depending on the control budget. With low budgets (monthly removal rate of 6.7% of population), there was little advantage to prioritizing resources, especially when connectivity was high or symmetric, and observational uncertainty had only minor effects on ROI. Allotting funding for improved monitoring appeared to be most important when budgets were moderate (monthly removal of 13–20% of the population). Our result showed that multiple sources of observational uncertainty should be considered concurrently for optimizing ROI. Accurate estimates of connectivity direction and abundance were more important than accurate estimates of dispersal rates. Developing cost‐effective surveillance methods to reduce observational uncertainties, and quantitative frameworks for determining how resources should be spatially apportioned to multiple monitoring and control activities are important and challenging future directions for optimizing ROI for invasive species control programs.

An efficient method of evaluating multiple concurrent management actions on invasive populations

“…By using the approach we developed, managers can evaluate their control actions without diverting resources from additional control activities and show evidence of the impact of their actions for stakeholders. Additionally, our approach can be used to evaluate the effectiveness of management actions and be combined with economic approaches to determine the cost effectiveness of different management actions and optimal control strategies (Pepin et al, 2020).…”

Movement and mortality of invasive suckermouth armored catfish during a spearfishing control experiment

“…In other systems, including SAC in the San Marcos River, although control efforts successfully suppress populations, there appears to be a limit to suppression under existing programs (Pennock et al 2018 ; Blanton et al 2020 ). For ecosystems in which suppression has reached a limit, enhanced suppression will likely come from either increased effort, though it cannot be increased indefinitely (Pepin et al 2020 ), or by applying complementary methods that could be used in concert with the existing methods. One promising approach for ecosystems that cannot be dried is the use of Trojan genes , or phenotypically sex-reversed carriers of Y chromosomes for fishes with XY sex determination (Cotton and Wedekin 2007 ).…”

Integrated spatial model based evaluation methodology for optimal invasive species management: common ragweed in the Republic of Korea

“…Although studies using various perspectives are essential for comprehending and improving the efficiency of controlling invasive species, an integrated form of study that includes all the factors, such as the optimization of removal from a spatial perspective, is necessary for establishing a more practical and realistic policy (Pepin et al 2020). In addition, in terms of the evaluation, considering the fact that there is no standard framework, especially for comprehending the effects of a policy regarding adaptation to climate change (Hyun et al 2019), a methodology using an integrated spatial model approach for both quantitative and spatial analysis needs to be developed.…”