Comparison of Open and Closed Models for Cotton Rat Population Estimates

摘要: Population estimates of hispid cotton rats (Sigmodon hispidus) in 2 southern Florida sugarcane fields were obtained from capture-recapture data. A model for population estimation that assumes an open individuals with equal probabilities capture (Jolly-Seber) and a sequence models (program CAPTURE) closed varying yielded similar estimates, despite considerable heterogeneity over 8-day trapping periods. The trends the indices, minimum number known to be alive captures per 100 trap-nights, similar: size both was reduced following harvest, remained low during spring early summer, increased late summer throughout fall. Minimum appeared more sensitive index fluctuation than trap-nights. J. WILDL. MANAGE. 46(1):156-163 Despite literature on statistical methods based data, many researchers prefer use indices abundance or simple estimators such as Lincoln Index. Indices animals alive, trapped, 100-trap nights are commonly used. gap exists between practical various estimation, each their restrictive assumptions, understanding how data given species meet fail models' assumptions. Otis et al. (1978), drawing recent work by Pollock (1974) Burnham Overton developed allow unequal studies, formulated computer program CAPTURE test fit these select most appropriate set, compute estimate under model. Such approach gives biologist objective means learning which assumption(s) violate seriously when using specific model(s), if any, al.'s (1978) assume population, is, recruitment, immigration, emigration, mortality not allowed, this may limit usefulness studies. However, periods short relation opportunity occurrence factors, area trapped is sufficiently large, assumption can approximately met. Smallmammal studies conducted fairly w ll-defined period week, example, often closure criterion adequately. In contrast above models, Jolly-Seber (J-S) (Jolly 1965; Seber 1965, 1973) so-called model, allowing period. assumes, however, vary only occasion, thus individual among behavioral response permitted. Both J-S "geographic" 156 Wildl. Manage. 46(1):1982 This content downloaded 207.46.13.103 Thu, 20 Oct 2016 04:32:10 UTC All subject http://about.jstor.org/terms ESTIMATING SIZE OF COTTON RAT POPULATIONS* Lefebvre 157 closure; concept occupying defined geographical made up absolute individuals, implicit types models. Our study investigates rat compares (MNA) D. Decker, U.S. Fish Wildlife Service, much handling assisted preparation. C. Ingram developing design, N. Shafer obtaining W. Braley, T. O'Brien, Buecker, P. Gall, Maddox, M. Sandsberry, K. Simpson, Steffen, S. Williams setting traps recording. Anderson reviewed earlier version several helpful suggestions.