Practice question

The Lincoln–Petersen estimate requires three counts: M, the number initially marked and released; C, the total number captured on the second occasion; and R, the marked individuals found within that second capture. The number unmarked in the second sample is C − R, so it is not mathematically independent but can help determine C when only marked and unmarked counts are recorded. Population sex ratio is unnecessary for the basic estimator because the marked proportion, not sex composition, drives N ≈ MC/R. Sex ratio becomes relevant only if capture probabilities differ by sex, sampling targets one sex, or separate demographic estimates are desired. More generally, all animals should have comparable chances of capture, marks should persist, and the population should remain effectively closed between samples. If one sex is disproportionately trappable, ignoring that heterogeneity can bias the estimate, but measuring sex ratio is still not a required parameter in the formula. The distinction is between data needed algebraically and biological covariates that may be useful for diagnosing violations of model assumptions.