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

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

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Answer is important: 1)Influence management practice 2)Funders want to know outcome 3)If fail, want to know sooner rather than later.

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

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Key relationship 1 0 Search effort Probability of detection

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

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

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

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

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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

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

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

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No carcasses: Rat Eradication with single toxin drop

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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

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Isabel 82 ha Mexico Pacific Ocean Gulf of Mexico Araceli Samaniego Conservacion de Islas

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

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

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

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Wax-tag survey year 3

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Repeat 1000 times Each female takes on slightly different parameter values

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

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

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One – survey approach

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50-m spacing

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

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

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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

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

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Acknowledgements John Parkes Araceli Samaniego Luciana Luna Conservacion de Islas, Mexico Department of Conservation, NZ

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