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Continuous-time capture-recapture population estimation when capture probabilities vary over time
Authors:Kenneth R Wilson  David R Anderson
Institution:(1) Department of Fishery and Wildlife Biology, Colorado State University, C080523 Fort Collins, USA;(2) Colorado Cooperative Fish & Wildlife Research Unit, U.S. National Biological Survey, Colorado State University, C080523 Fort Collins, USA
Abstract:Closed capture-recapture (CR) estimators have been used extensively to estimate population size. Most closed CR approaches have been developed and evaluated for discrete-time models, but there has been little effort to evaluate their continuous-time counterparts. Continuous-time estimators — developed using maximum likelihood theory by Craig (1953) and Darroch (1958), and martingale theory by Becker (1984) — that allow capture probabilities to vary over time were evaluated using Monte Carlo simulation. Overall, the ML estimators had a smaller MSE. The estimators performed well when model assumptions were upheld, and were somewhat robust to heterogeneity in capture probabilities. However, the estimators were not robust to behavioural effects in the capture probabilities. Time lag effects (periods when animals might be unavailable for immediate recapture) on continuous-time estimates were also investigated and results indicated a positive bias which was greater for smaller populations. There was no gain in performance when using a continuous-time estimator versus a discrete-time estimator on the same simulated data. Usefulness of the continuous-time approach may be limited to study designs where animals are easier to sample using continuous-time methodology.
Keywords:Abundance  mark-recapture  martingales  population size
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