Mark-recapture is a classic biodiversity monitoring method: camera traps "mark" (identify) animals in a first survey session, then a second session counts how many of the previously marked animals reappear. The Lincoln-Petersen estimator turns that overlap into a population estimate — without ever counting every individual directly.
N̂ = (M · C) / R
M = marked in session 1
C = total detected in session 2
R = of C, how many were already marked
- True population (hidden) — the real number of animals in the study area; the survey never sees this directly.
- Camera traps deployed — more traps sample more of the area per session, improving detection.
- Detection radius — how close an animal must pass to a trap to be recorded.
- Animal movement speed — faster mixing between sessions makes the second sample more representative of the whole population.
Real-world application: field ecologists use camera-trap or tag-based mark-recapture exactly like this to estimate populations of elusive species (tigers, bears, sea turtles) that can't be counted by direct observation.