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

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Presentation on theme: "Island eradications: Approaches and assessment of success Biodiversity Bonanza Dean Anderson Landcare Research."— Presentation transcript:

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: 1)Influence management practice 2)Funders want to know outcome 3)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 0 Search effort Probability of detection

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

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

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

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

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

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

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

13 No carcasses: Rat Eradication with single toxin drop

14 2 Approaches when missing carcasses 1)Wait and see –Easy –Takes time –If fail, the problem is big 2)Actively search –Requires data and statistics –If fail, survivors may be very localised

15 Isabel 82 ha Mexico Pacific Ocean Gulf of Mexico Araceli Samaniego Conservacion 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 MedianLow 2.5% CIHigh 97.5 CI Prob. Success Prob. Success Prob. Success * Confidence intervals reflect the uncertainty in input parameters

22 Results MedianLow 2.5% CIHigh 97.5 CI Prob. Success Prob. Success Prob. Success * Confidence intervals reflect the uncertainty in input parameters

23 One – survey approach

24 50-m spacing

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

26 Summary Carcasses counted 1)Catch – effort model Collect data during “knock-down” phase Establish relationship between detection & effort

27 Summary Carcasses not available 2)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 Araceli Samaniego Luciana Luna Conservacion de Islas, Mexico Department of Conservation, NZ

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