Using Plant Island Extinctions to Evaluate Causes of Mainland Species Declines

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Supervisors: Ayesha Tulloch (Fenner, ANU) and Marcel Cardillo (RSB, ANU),
Collaborators: Sarah Comer (Western Australian Department of Parks and Wildlife), Angela Sanders/Jim Radford (Bush Heritage Australia)

Aims

  1. Review knowledge of historical and current plant distributions on Australian islands, including current and past flora surveys and historical records
  2. Conduct an empirical analysis evaluating the number of known island plant extinctions that have occurred since European settlement
  3. Model the historic distribution of target plant species thought to be declining on the mainland, to determine whether they might have previously occurred on islands.
  4. Evaluate possible reasons for known and predicted local island extinctions of species that persist on the mainland, including changed fire regimes. 

Background

Understanding extinction on islands is critical for biodiversity conservation. Islands contain 40% of all critically endangered species, and extinction rates are disproportionately greater on islands, with 80% of all known extinctions occurring on islands (Quammen 2012). There has been decades of research on extinctions of fauna on islands. Most losses of birds (78.7% of species and 63.0% of subspecies) have occurred on oceanic islands, with the first settlers of the Pacific islands causing a massive extinction of nearly 1000 flightless bird species (Szabo et al. 2012). For Australian continental islands the introduction of exotic predators has been the major factor in mammal extinctions (Burbidge and Manly 2002, Hanna and Cardillo 2014). In contrast, there has been very little work on flora extinctions on islands, despite nearly a quarter of the world’s plant species existing only on islands.

Not only are island species vulnerable due to the inability to recolonise once a perturbation causes local extinction, but also these populations can inform and potentially predict the vulnerability and likely extinction processes of mainland populations subject to fragmentation, isolation, and anthropogenic threats. For example, both islands and the mainland of Australia have experienced changed fire regimes (on islands mainly due to indigenous people not inhabiting them anymore, whereas on the mainland due to cumulative effects of loss of indigenous burning, and changed burning in areas that must be either protected from fire or burn more frequently due to human impacts). The result of changed fire regimes is eventually a change in the composition and structure of flora and fauna communities. This is due either to senescence and the inability to reproduce in fire-dependent species, or too-frequent fire leading to the inability to reach maturity, which can cause local extinctions.

This project seeks to explore whether local island extinctions have occurred for plant species vulnerable to fire in south-western Australia. A review of existing information on plant species occurrence on islands historically and today will fill important knowledge gaps in the importance of islands for a range of Australian flora and allow an evaluation of evidence for plant extinctions from islands (e.g. Burbidge and Manly 2002, Hanna and Cardillo 2014). Species distribution models parameterized using historic occurrence records and hypotheses about plant-environment relationships will then be built to explore the possibility of additional local/regional extinctions that might have occurred on islands but been undetected due to no historical surveys being conducted. The results will be used to evaluate the vulnerability of mainland isolated plant populations to local extinction given changed fire regimes, fragmentation leading to patch isolation, and senescence (Tulloch et al. in review).

Methods

  1. Conduct a review of the scientific literature and plant species databases to list species on islands that are known or suspected to have gone extinct since European settlement.
  2. Evaluate possible reasons for plant species extinctions on islands based on known changes to vegetation cover, fire regimes, and invasive herbivores (e.g. goats).
  3. Run historical species distribution models for a set of target flora that may occur both on the mainland and on islands (including predicted distribution on islands).
  4. For islands predicted to have flora species that do not currently occur there, incorporate known drivers of extinctions (from step 2) to evaluate whether historical changes in land management and condition predict species distributions (and associated extinctions) on islands.

Key References

  • Burbidge, A. A., and B. F. J. Manly. 2002. Mammal extinctions on Australian islands: causes and conservation implications. Journal of Biogeography 29:465-473.
  • Hanna, E., & Cardillo, M. (2014). Island mammal extinctions are determined by interactive effects of life history, island biogeography and mesopredator suppression. Global Ecology and Biogeography, 23(4), 395-404. 
  • Quammen, D. (2012). The song of the dodo: island biogeography in an age of extinctions. Random House.
  • Sax, D. F., and S. D. Gaines. 2008. Species invasions and extinction: The future of native biodiversity on islands. Proceedings of the National Academy of Sciences 105:11490-11497.
  • Szabo, J. K., N. Khwaja, S. T. Garnett, and S. H. M. Butchart. 2012. Global Patterns and Drivers of Avian Extinctions at the Species and Subspecies Level. PLoS ONE 7:e47080.
  • Tulloch, A. I. T., J.-B. Pichancourt, C. R. Gosper, A. Sanders, and I. Chadès. in review. Fire management strategies to safeguard species across a fragmented landscape of contemporary extremes in fire intervals. Ecological Applications.

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