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Island eradications: Approaches and assessment of success

Island eradications: Approaches and assessment of success. Biodiversity Bonanza Dean Anderson Landcare Research. Central question:. How can we determine whether an eradication effort has been successful?. Answer is important:. Influence management practice Funders want to know outcome

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Island eradications: Approaches and assessment of success

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  1. Island eradications: Approaches and assessment of success Biodiversity Bonanza Dean Anderson Landcare Research

  2. Central question: How can we determine whether an eradication effort has been successful?

  3. Answer is important: • Influence management practice • Funders want to know outcome • If fail, want to know sooner rather than later.

  4. Assessing success • Establish relationship between search effort and probability of detection. • Actively search for survivors • Collect spatial and temporal data on search effort

  5. Key relationship 1 Probability of detection 0 Search effort

  6. Probability of detection and success 1 Probability of eradication success Probability of detection 0 Search effort

  7. Probability of detection and success 1 Threshold Probability of eradication success Probability of detection 0 Search effort

  8. Probability of detection and success 1 Probability of eradication success Probability of detection 0 Search effort

  9. How do we get this “key” relationship? 1 Probability of detection Depends on eradication method 0 Search effort

  10. Carcasses collected Pigs on Santa Cruz Island, USA - (Ramsey et al. 2009) • Goats on Guadalupe Island, Mexico • Luciana Luna, Conservacion de Islas Stoats on Resolution Island, NZ DOC

  11. Catch – effort model:(knock-down phase) Helicopter Ground Helicopter Goats dispatched Helicopter Hunting hours

  12. Probability of detection and success 1 Probability of eradication success Probability of detection 0 Search effort

  13. No carcasses: Rat Eradication with single toxin drop

  14. 2 Approaches when missing carcasses • Wait and see • Easy • Takes time • If fail, the problem is big • Actively search • Requires data and statistics • If fail, survivors may be very localised

  15. Mexico Gulf of Mexico Isabel 82 ha PacificOcean AraceliSamaniegoConservacion de Islas

  16. Isabel Island, Mexico • 1 toxin drop • 3 annual wax-tag surveys • No rats detected

  17. Eradication success??? Spatial-detection Model • Home range size • Detection probability of tags

  18. Wax-tag survey year 2 Spatial-detection Model • Home range size • Detection probability of tags • Population growth rate • Dispersal kernel

  19. Wax-tag survey year 3

  20. Repeat 1000 times Each female takes on slightly different parameter values

  21. Results * Confidence intervals reflect the uncertainty in input parameters

  22. Results * Confidence intervals reflect the uncertainty in input parameters

  23. One – survey approach

  24. One – survey approach 50-m spacing

  25. Summary • Why quantify probability of success? • Management • Funders • Identify failure early

  26. Summary Carcasses counted • Catch – effort model • Collect data during “knock-down” phase • Establish relationship between detection & effort

  27. Summary Carcasses not available • Spatial – detection model • Estimate parameters with experiments or literature • Homerange size • Detection probability of device • Reproductive rates • Dispersal kernels • Incorporate uncertainty

  28. Summary • Requires biological understanding and statistics • Arguably better than “wait-and-see”

  29. Acknowledgements • John Parkes • AraceliSamaniego • Luciana Luna • Conservacion de Islas, Mexico • Department of Conservation, NZ

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