Which of the following are techniques to estimate population size? counting individuals

sampling

mark-and-recapture

population index

The Mark-Recapture technique is used to estimate the size of a population where it is impractical to count every individual. The basic idea is that you capture a small number of individuals, put a harmless mark on them, and release them back into the population.

Two important measures of a population are population size, the number of individuals, and population density, the number of individuals per unit area or volume. Ecologists often estimate the size and density of populations using quadrats and the mark-recapture method.

Wildlife managers use 4 general approaches to estimate population sizes of wildlife: total counts, incomplete counts, indirect counts, and mark-recapture methods.

The answer is counting individuals and mark-and-recapture.