Predicting future damage costs of non-native species using combined dynamical and cost-density equations

Danish A. Ahmed, Corey J.A. Bradshaw, Noor Tahat, Emma J. Hudgins, Pierre Courtois, Philip E. Hulme, Yuya Watari, Ali Serhan Tarkan, Ismael Soto Almena, Paride Balzani, Ross N. Cuthbert

Biological invasions threaten biodiversity, economic stability, and public health, and are exacerbated by intensive global trade and transport. The economic costs of these invasions have reached US$ trillions globally and are expected to continue increasing. However, while past invasion costs have been described across various contexts, there are few robust projections of future costs, limiting effective management planning. We developed a mathematical framework for predicting future economic damage caused by biological invasions, combining cost-density relationships with a density-time function based on logistic population growth. We tested the model on five non-native mammal species with wide-ranging negative impacts on biodiversity, agriculture, health, and infrastructure globally, using country-specific data from Japan: Pallas’ squirrel Callosciurus erythraeus, small Indian mongoose Herpestes javanicus (synonym Urva auropunctata), nutria Myocastor coypus, masked palm civet Paguma larvata, and raccoon Procyon lotor. All species-specific impacts followed a similar S-shaped, high-threshold cost curve over time, characterised by time lags between low impact at low densities and subsequent exponential cost growth and saturation, with varying intrinsic growth rates and sensitivities to resource availability. Our model returned accumulated costs up to 2050 varying over several orders of magnitude, from $0.43 million (H. javanicus) to $88 million (P. larvata), with the highest rates of increase for P. larvata (up to 55%) and H. javanicus (78%). Under business-as-usual management, our approach identifies thresholds beyond which damages escalate rapidly — for all species, costs begin to surge 40 to 80 years after the first record of the species, with 90% of expected long-term damages incurred within 10 to 20 years — except for H. javanicus, which takes approximately 35 years. For managers, these results highlight the importance of timely interventions, underscoring the need for tailored management strategies considering species-specific dynamics, socio-economic contexts, and the speed of cost escalation. We demonstrate that cost dynamics can be reliably forecasted even at early-stage invasions before economic impacts surge. Therefore, early-stage cost dynamics can predict future trajectories of existing and emerging invasions, helping inform proactive management prioritisation. Our predictions equip policymakers and resource managers with improved foresight to anticipate and mitigate future economic burdens of non-native species.