Search

The extensive impact of invasive species has motivated a growing field of research combining ecological and economic models to find cost-effective management strategies. Ecological systems are rarely perfectly observable, meaning decision-makers are usually uncertain about the current extent of an infestation and even whether an invasive species is present or absent. We show how to account for this uncertainty when providing decision support for invasive species management., We constructed the first partially observable model to analyse the trade-off between all three facets of invasive species management: quarantine, surveillance and control. We use a partially observable Markov decision process ( POMDP) to determine how to allocate resources between these actions when the extent of an invasion is uncertain. We use a case study of potential black rat Rattus rattus invasion on Barrow Island, Western Australia., Our model shows it is often better to manage based on an uncertain belief in species presence than to spend money trying to confirm the presence or absence through surveillance. While it was never optimal to invest solely in surveillance to reduce uncertainty, it was often optimal to combine surveillance with quarantine or control. These mixed strategies, where multiple actions are implemented simultaneously, were more often optimal than for similar decision models where the extent of the infestation is known, suggesting an element of risk spreading., Optimal investments in each action were driven by their estimated efficacy, and the difference in the estimated impact of a localized and widespread invasion. For example, in our case study, it was often optimal to invest solely in control due to the low estimated efficacy of quarantine and the relatively small impact of a localized incursion., Synthesis and applications. Our analysis shows that the cost of reducing uncertainty through surveillance is not always accompanied by an improvement in management outcomes. By carefully analysing the benefits of surveillance prior to implementation of invasive species management strategies, managers can avoid wasting resources and improve management outcomes. [ABSTRACT FROM AUTHOR]

Finding efficient ways to manage the threat of invasive species helps make the most of limited resources. Different management actions reduce the impact of invasions differently: preventing invasion eliminates impacts entirely, surveillance can facilitate early detection and eradication, and removing individuals can reduce future impact. Few studies have examined the trade-off between all three facets of invasion management. Using a simple model of island invasion, we find how resources should be allocated to each action to minimise the total cost of management and impact. We use a case study of black rat (Rattus rattus) invasion on Barrow Island, Western Australia. The optimal amount to invest in each management action depends on the effectiveness of each action, and the magnitude of impact caused by different stages of invasion. If the pest is currently absent, it is more cost-effective to prevent impacts through prevention or surveillance. If the pest is already widespread, it can sometimes be cost-effective to give up rather than attempting eradication. This model of invasion can provide useful decision support by identifying the trade-offs inherent in each candidate management strategy, the thresholds that alter optimal strategies, and the parameters for which we need more information. [Copyright &y& Elsevier]