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Cat removal is already underway, but there is concern that a decrease in the cat population could release predation pressure on rats, potentially leading to increased rat predation on red-tailed tropicbirds ( I Phaethon rubricauda i ) (Baker et al., 2020; Han et al., 2020). The metabolic demands of rats and cats (which included the mass of rats and cats) and the mass and energy of adult birds influenced the estimates of cat equivalence most strongly. For example, if reducing cat populations by 50% costs twice as much as reducing rats by 50%, but each cat is worth 77 rats, then our cat equivalence metric suggests that removing cats would be the most cost-effective strategy, but if cat equivalence is 30 then removing rats would be more effective. [Extracted from the article]

Reintroduction projects, which are an important tool in threatened species conservation, are becoming more complex, often involving the translocation of multiple species. Ecological theory predicts that the sequence and timing of reintroductions will play an important role in their success or failure. Following the removal of sheep, goats and feral cats, the Western Australian government is sequentially reintroducing 13 native fauna species to restore the globally important natural and cultural values of Dirk Hartog Island (DHI).We use ensembles of ecosystem models to compare 23 alternative reintroduction strategies on DHI, in Western Australia. The reintroduction strategies differ in the order, timing and location of releases on the island. Expert elicitation informed the model structure, allowing for use of different presumed species interaction networks which explicitly incorporated uncertainty in ecosystem dynamics.Our model ensembles predict that almost all of the species (~12.5 of 13, on average) will successfully establish in the ecosystem studied, regardless of which reintroduction strategy is undertaken. The project can therefore proceed with greater confidence and flexibility regarding the reintroduction strategy. However, the identity of the at‐risk species varies between strategies, and depends on the structure of the species interaction network, which is quite uncertain. The model ensembles also offer insights into why some species fail to establish on DHI, predicting that most unsuccessful reintroductions will be the result of competitive interactions with extant species.Synthesis and applications. Our model ensembles allow for the comparison of outcomes between reintroduction strategies and between different species interaction networks. This framework allows for inclusion of high uncertainty in dynamics. Finally, an ensemble modelling approach also creates a foundation for formal adaptive management as reintroduction projects proceed. [ABSTRACT FROM AUTHOR]

Many highly diverse island ecosystems across the globe are threatened by invasive species. Eradications of invasive mammals from islands are being attempted with increasing frequency, with success aided by geographical isolation and increasing knowledge of eradication techniques. There have been many attempts to prioritize islands for invasive species eradication; however, these coarse methods all assume managers are unrealistically limited to a single action on each island: either eradicate all invasive mammals, or do nothing., We define a prioritization method that broadens the suite of actions considered, more accurately representing the complex decisions facing managers. We allow the opportunity to only eradicate a subset of invasive mammals from each island, intentionally leaving some invasive mammals on islands. We consider elements often omitted in previous prioritization methods, including feasibility, cost and complex ecological responses (i.e. trophic cascades)., Using a case study of Australian islands, we show that for a fixed budget, this method can provide a higher conservation benefit across the whole group of islands. Our prioritization method outperforms simpler methods for almost 80% of the budgets considered., On average, by relaxing the restrictive assumption that an eradication attempt must be made for all invasives on an island, ecological benefit can be improved by 27%., Synthesis and applications. Substantially higher ecological benefits for threatened species can be achieved for no extra cost if conservation planners relax the assumption that eradication projects must target all invasives on an island. It is more efficient to prioritize portfolios of eradication actions rather than islands. [ABSTRACT FROM AUTHOR]

Fences that exclude alien invasive species are used to reduce predation pressure on reintroduced threatened wildlife. Planning these continuously managed systems of reserves raises an important extension of the Single Large or Several Small (SLOSS) reserve planning framework: the added complexity of ongoing management. We investigate the long-term costefficiency of a single large or two small predator exclusion fences in the arid Australian context of reintroducing bilbies Macrotis lagotis, and we highlight the broader significance of our results with sensitivity analysis. A single fence more frequently results in a much larger net cost than two smaller fences. We find that the cost-efficiency of two fences is robust to strong demographic and environmental uncertainty, which can help managers to mitigate the risk of incurring high costs over the entire life of the project. [ABSTRACT FROM AUTHOR]