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Assessing Eradication Success: Methods and Key Relationships

Learn about approaches and success assessment in island eradication efforts, key relationships, the importance of detection probability, and methods to determine success. Discover how to establish relationships between detection and effort, actively search for survivors, and collect data for a thorough assessment. Explore models, surveys, and the significance of quantifying success probability for effective management and early identification of failures.

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Assessing Eradication Success: Methods and Key Relationships

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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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