Population ecology
Density-dependent effects strengthen with crowding, such as competition or transmission of some diseases. Density-independent events can act without a consistent relationship to crowding, though their consequences may still vary. Age structure helps estimate future reproductive potential, and survivorship curves describe how survival changes with age. Mark–recapture estimates assume representative capture, mark retention, mixing, and an approximately closed population over the sampling period. Violations can bias estimates.
If 40 individuals are marked and released, then 10 of 50 recaptured individuals are marked, the simple estimate is N≈(40×50)/10=200. It works only if the marked fraction represents the whole population.
A large population is not necessarily a dense one: density depends on the area or volume occupied.