markrecapture

Mark-recapture is a set of methods used to estimate the size of animal populations and study their dynamics by capturing a sample, marking or tagging captured individuals, releasing them, and then recapturing another sample to see how many marked individuals are found. The approach provides a way to infer population abundance and other parameters from observed recaptures.

In closed populations (no births, deaths, or movements during the study period), the Lincoln-Petersen estimator is commonly used to estimate total population size N as N_hat = (n1 * n2) / m2, where n1 is the number of marked individuals released, n2 is the number of individuals captured in the second sample, and m2 is the number of marked individuals recaptured. For small sample sizes, Chapman’s bias-adjusted estimator is N_hat = ((n1+1)(n2+1)/(m2+1)) - 1.

Open-population models account for individuals entering and leaving the population between sampling occasions. The Jolly-Seber model estimates abundance, survival, and capture probability across multiple capture occasions, while the Cormack-Jolly-Seber model estimates survival and capture probabilities without directly estimating abundance. These models typically require more complex statistical methods and software.

Common assumptions include that tagging does not affect capture probability or survival, marks are not lost or overlooked, marked and unmarked individuals have equal capture probability or heterogeneity is modeled, marked individuals mix back into the population, and sampling is appropriately timed and spaced. Violations can bias estimates and lead to incorrect inferences about population size or dynamics.

Applications of mark-recapture include wildlife management, conservation planning, disease ecology, and ecological research on abundance and turnover. Limitations include tag loss, behavioral changes after marking, misidentification of marks, heterogeneity in capture probability, and logistical constraints.