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: 1)Influence management practice 2)Funders want to know outcome 3)If fail, want to know sooner rather than later.
Assessing success Establish relationship between search effort and probability of detection. Actively search for survivors Collect spatial and temporal data on search effort
Key relationship 1 0 Search effort Probability of detection
Probability of detection and success 1 0 Search effort Probability of detection Probability of eradication success
Probability of detection and success 1 0 Search effort Probability of detection Probability of eradication success Threshold
Probability of detection and success 1 0 Search effort Probability of detection Probability of eradication success
How do we get this “key” relationship? 1 0 Search effort Probability of detection Depends on eradication method
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
Catch – effort model: (knock-down phase) Helicopter Ground Goats dispatched Hunting hours
Probability of detection and success 1 0 Search effort Probability of detection Probability of eradication success
No carcasses: Rat Eradication with single toxin drop
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
Isabel 82 ha Mexico Pacific Ocean Gulf of Mexico Araceli Samaniego Conservacion de Islas
Isabel Island, Mexico 1 toxin drop 3 annual wax-tag surveys No rats detected
Eradication success??? Spatial-detection Model Home range size Detection probability of tags
Wax-tag survey year 2 Spatial-detection Model Home range size Detection probability of tags Population growth rate Dispersal kernel
Wax-tag survey year 3
Repeat 1000 times Each female takes on slightly different parameter values
Results MedianLow 2.5% CIHigh 97.5 CI Prob. Success Prob. Success Prob. Success * Confidence intervals reflect the uncertainty in input parameters
Results MedianLow 2.5% CIHigh 97.5 CI Prob. Success Prob. Success Prob. Success * Confidence intervals reflect the uncertainty in input parameters
One – survey approach
50-m spacing
Summary Why quantify probability of success? –Management –Funders –Identify failure early
Summary Carcasses counted 1)Catch – effort model Collect data during “knock-down” phase Establish relationship between detection & effort
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
Summary Requires biological understanding and statistics Arguably better than “wait-and-see”
Acknowledgements John Parkes Araceli Samaniego Luciana Luna Conservacion de Islas, Mexico Department of Conservation, NZ