Island eradications: Approaches and assessment of success
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Transcript of Island eradications: Approaches and assessment of success
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Island eradications: Approaches and assessment of success
Biodiversity Bonanza
Dean AndersonLandcare 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
0Search effort
Probability of detection
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Probability of detection and success
1
0Search effort
Probability of detection
Probability of eradication success
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Probability of detection and success
1
0Search effort
Probability of detection
Probability of eradication success
Threshold
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Probability of detection and success
1
0Search effort
Probability of detection
Probability of eradication success
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How do we get this “key” relationship?
1
0Search 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, NZDOC
Goats on Guadalupe Island, Mexico- Luciana Luna, Conservacion de
Islas
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Catch – effort model:(knock-down phase)
0 200 400 600 800 1000 1200
200
400
600
800
1000
1200
Cumulative Observer Hours
Goa
ts D
ispa
tche
d
Helicopter
Helicopter
Helicopter
Ground
Goa
ts d
ispa
tche
d
Hunting hours
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Probability of detection and success
1
0Search 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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Isabel82 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
Isabel Island, 1 pregnant female
*
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Wax-tag survey year 2
Isabel Island, N rats = 10
*
Spatial-detection Model• Home range size• Detection probability
of tags• Population growth
rate• Dispersal kernel
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Wax-tag survey year 3Isabel Island, N rats = 106
*
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Repeat 1000 times
Isabel Island, 1 pregnant female
*
Isabel Island, 1 pregnant female
*Isabel Island, 1 pregnant female
*
Each female takes on slightly different parameter values
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Results
Median Low 2.5% CI High 97.5 CIProb. Success 2009 0.74 0.62 0.83Prob. Success 2010 0.96 0.76 0.99Prob. Success 2011 0.99 0.99 1.00
* Confidence intervals reflect the uncertainty in input parameters
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Results
Median Low 2.5% CI High 97.5 CIProb. Success 2009 0.74 0.62 0.83Prob. Success 2010 0.96 0.76 0.99Prob. Success 2011 0.99 0.99 1.00
* Confidence intervals reflect the uncertainty in input parameters
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One – survey approach
50 100 150 200
0.6
0.7
0.8
0.9
1.0
Device Spacing (m)
Pro
babi
lity
of S
ucce
ss
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One – survey approachIsabel Island
*50-m spacing
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Summary
• Why quantify probability of success?– Management– Funders– Identify failure early
Isabel Island, N rats = 106
*
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Summary
Carcasses counted1) Catch – effort model
• Collect data during “knock-down” phase• Establish relationship between detection & effort
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SummaryCarcasses not available
2) Spatial – detection model• Estimate parameters with experiments or literature
– Homerange size– Detection probability of device– Reproductive rates– Dispersal kernels
• Incorporate uncertainty
Isabel Island, 1 pregnant female
*
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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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