Abundance estimates from CJS

questions concerning analysis/theory using program MARK

Re: Abundance estimates from CJS

Postby cooch » Thu Nov 09, 2017 8:12 pm

jlaake wrote:Both are possible problems. The first for animals that capture themselves and the second is correctable with a good design. However if you are going to make a general statement it would be that robust designs with closure is preferable and not that all cjs/js abundance estimates are not useful. But closure can often be suspect as well.


Agreed about RD (like most things, good design compensates for many problems). And, of course, closed sample estimation is based on a 'design choice' (sample when population is ~closed). Optimal, but not always practical.
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Re: Abundance estimates from CJS

Postby SoConfused » Sun Nov 12, 2017 2:14 pm

Thank you all so much for your comments. The sampling is fully random (one blessing), but that doesn't mean closure during sampling - some seasonal differences in recapture have been noticeable. Robust design models are on my list to try out next.
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Re: Abundance estimates from CJS

Postby Bryan Hamilton » Fri Dec 29, 2017 2:09 pm

I've been working through some of the issues discussed on this thread and have a couple follow up questions.

1. With a "largish" p, abundance estimates from open population, JS models are more robust What constitutes a largish p?

2. Heterogeneity in capture probability between uncaptured and recaptured individuals is likely, violating the assumption of equal capture probability. Does anyone know of a reference for this? I feel like I've come across something but can't recapture it.
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Re: Abundance estimates from CJS

Postby cooch » Fri Dec 29, 2017 9:39 pm

Bryan Hamilton wrote:I've been working through some of the issues discussed on this thread and have a couple follow up questions.

1. With a "largish" p, abundance estimates from open population, JS models are more robust What constitutes a largish p?


Everything is better with high p. The answer to the question of 'how high is high enough for CJS abundance estimates to be useful' will depend on many things (including how you define useful). Simulation is your friend, here...

2. Heterogeneity in capture probability between uncaptured and recaptured individuals is likely, violating the assumption of equal capture probability. Does anyone know of a reference for this? I feel like I've come across something but can't recapture it.


Burnham, K. P., and W. S. Overton. 1978. Estimation of the size of a closed population when capture probabilities vary among animals. Biometrika 65:625–633.

Burnham, K. P., and W. S. Overton. 1979. Robust estimation of population size when capture probabilities vary among animals. Ecology 60:927–936.

Rosenberg, D. K., W. S. Overton, and R. G. Anthony. 1995. Estimation of animal abundance when capture probabilities are low and heterogeneous. Journal of Wildlife Management 59:252–261.

and, probably the most referenced cite:

Seber, G. A. F. 1982. The estimation of animal abundance and related parameters. Second edition. Arnold, London, United Kingdom.

For a nice review of such things,

Chao, A. 2001. An overview of closed capture-recapture models. Journal of Agricultural, Biological and Environmental Statistics 6:158–178.
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Re: Abundance estimates from CJS

Postby Fish_Boy » Tue Jan 09, 2018 5:17 pm

Also a good read on closure...

Kendall, W.L. 1999. Robustness of closed capture-recapture methods to violations of the closure assumption. Ecology 80: 2517-2525.

We do a lot of lake sturgeon studies and find that a "largish p" is >0.20. The main thing we have learned is that consistency, in timing and effort, produce repeatable results. In addition, the type of river can have a dramatic effect on results. For example, estimates of survival from JS models are much lower in prairie rivers (high mobility) compared with boreal shield rivers (low mobility). This is especially apparent when capture-recapture studies are supplemented with telemetry i.e., you know survival is much higher than estimated. I suspect this same phenomenon would occur with other species, as it is a function of the spatial scale at which species use different types of rivers.
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