Optimal resource allocation for invasive species control: Two decision criteria for site prioritization

Invasive species management is often guided by the implicit assumption that minimizing the invaded population will concurrently minimize the economic and ecological damages it causes. However, this alignment is challenged when damages are spatially heterogeneous, raising a critical question for environmental managers: should limited control budgets prioritize sites to minimize invasion state or damage? This paper defines and compares two simple cost-effective decision criteria for site prioritization: an invasion-minimization criterion, which targets sites based on their per-unit-cost contribution to future invasion spread, and a damageminimization criterion, which targets sites based on their per-unit-cost contribution to future damages. We solve analytically the two optimization problems and derive the restrictive theoretical conditions under which these criteria yield identical rankings. Applying these criteria to the management of Primrose willow (Genus Ludwigia) in the Brière Regional Park in France, we demonstrate that for a realistic budget, the two criteria lead to starkly different spatial allocations of effort. The damage-minimization criteria concentrates resources in a few high-value, highly invaded areas, while the invasion-minimization criteria spreads effort across many more, less valued areas to curb overall invasion state. Our analysis reveals that the common managerial practice of prioritizing population reduction may not align with damage reduction objectives unless damages are uniform or dispersal networks are trivial. This work provides clear, operational decision rules and highlights the need for explicit consideration of management objectives and spatial heterogeneity in the economics of biological invasions.