Adapting to realistic constraints of eradications: an ‘action-portfolio’ framework that improves ecological benefit and reduces cost

This post by Melissa Wynn, discusses the recent paper by Kate Helmstedt, Justine Shaw, Michael Bode, Aleks Terauds, Keith Springer, Susan Robinson and Hugh Possingham ‘Prioritizing eradication actions on islands: it’s not all or nothing

Melissa is a PhD Candidate in the Fenner School of Environment and Society, at the Australian National University, (Twitter: @melissalwynn)

One of the greatest threats facing Australia’s unique fauna today is the invasion of pest species. Offshore islands create small, isolated refuges for a diverse range of unique fauna and flora, but unfortunately these refuges also allow island species to be more susceptible to extinction, particularly by the accidental introduction of invasive predators.

The current influx of invasive species threatening Australia’s biodiversity means that unless sufficient funding is allocated, it is no longer realistic to assume that all islands can be returned to their initial, pristine state. With the announcement of the 2016 Federal Budget, we can be sure that research funding in Australia is indeed ‘going south’ and consequently, biodiversity conservation is being starved of what little funding there is. This means that, within the limited budget set aside for conservation research and pest management, in order to achieve the most beneficial outcome, it’s time we prioritize our actions to get the most out of the resources we have.

Previous model-based methods of prioritizing eradication of invasive mammals on islands have been constrained by the assumption that managers must remove just a single species (‘rank-and-sort’ method), or eradicate all invasive mammals, or do nothing (‘all-or-nothing’ method). Certain elements such as feasibility, cost and complex ecological responses, are often omitted from these prioritization strategies but are crucial to accurately represent the complex decisions facing managers today.

Helmstedt et al. suggest a novel, more flexible, framework to prioritize portfolios of eradication actions; rather than relying on a restrictive, ‘all-or-nothing’ strategy. They used case studies of 23 distinct portfolios of actions on four uninhabited Australian islands that have all recently undergone successful vertebrate eradications (Faure, Tasman, Hermite and Macquarie), to parameterize the model with realistic values.

Workshops were used to elicit population estimates from experts for each island, and predictive statistical models calculated cost, feasibility and outcomes of all ‘action portfolios’ of vertebrate eradications, often with reference to the most recent report: Eradications of vertebrate Australian pests: Review and guidelines for future best practice, produced in 2014 by the Invasive Animals Cooperative Research Centre as part of the PestSmart series.

Helmstedt et al. show how the  ‘action portfolio’ strategy can more effectively gain a higher conservation benefit within the realistic constraints of management resources.  Specifically, the authors concluded that under budgetary constraints, it can be more efficient to intentionally leave some invasive species on islands, and suggest that managers focus efforts instead on those more destructive species that can be more feasibly eradicated.

A simplified example of Helmstedt et al.’s ‘action portfolio’ framework is a hypothetical island with feral cats and sheep (Figure 1). If nothing is done to eradicate these species (Figure 1A) there will be no ecological benefit, but all money will be saved. Alternatively, if all cats and sheep are eradicated using the ‘all-or-nothing’ method (Figure 1B), ecological benefit will be high, but so will cost, resulting in no funding left for either follow-up eradications (should they fail), or consequential management of trophic cascades. The ‘action portfolio’ method  (Figure 1C) would feasibly eradicate cats (the more destructive of the two pests), intentionally leaving sheep on the island and improving almost all the ecological benefit, but allowing for 60% of the funding to be kept aside for future use.


Advantages of the ‘action portfolio’ framework:

  • Outperformed simpler methods for almost 80% of all the budgets considered, (providing a 27% higher ecological benefit than the ‘all-or-nothing’ strategy, and always outperforming the ‘rank-and-sort’ method).
  • It is flexible; benefiting those budget scenarios where not all invasive vertebrates can be eradicated.
  • Considers and accounts for complex ecological processes that occur with eradications (i.e. trophic cascades).
  • Applicable to a more realistic range of options available to managers under current financial limitations.
  • Could be applied to ‘inland islands’ such as sanctuaries with predator-proof exclosures, with the requirement of additional modelling.

This novel framework by Helmstedt et al. bridges a critical gap by adapting modern prioritization techniques to fit the constraints of severe underfunding faced by managers on the ground; reducing some of the uncertainty about important conservation decisions.

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