Prioritizing eradications on islands: Should we take it all or are there other options?

Background/Question/Methods

The eradication of invasive species from uninhabited islands presents an immense opportunity for conservation. Islands hold a disproportionate percent of global biodiversity, there has been historically less human intervention on island ecosystems, and the native species of islands have unique, divergent evolutionary histories.  Despite this, a high proportion of animal extinctions have occurred on islands due to invasive vertebrates.  Unfortunately, island conservation actions are unusually expensive, so it is imperative that the limited finances available are spent on eradications that maximise conservation benefits.  Therefore to ensure investments in invasive eradication are spent wisely, the cost-efficiency and feasibility of actions must be considered transparently and defensibly, with a rational treatment of uncertainties.

We propose a general method for prioritizing the eradication of multiple invasive species across multiple islands for a fixed budget. Rather than focusing on islands as management units, this method prioritises portfolios of eradication actions targeting different subsets of invasive species. This better reflects the variety of options available to managers, and the range of ecological dynamics that can result from perturbing an insular system.

Results/Conclusions

We present a case study prioritization of 23 potential action packages on four Australian islands:  Macquarie, Tasman, Faure and Hermite Islands.  By including the possibility to only eradicate a subset of invasive species on each island, we find that there are measurable increases in the total expected conservation benefit.  The optimal prioritization action for some budgets is to leave some invasive species present on one of the islands (often mice due to the high cost and low feasibility of eradication) in favour of eradicating a more ecologically harmful invasive species on another island.