Population Density

Population density expresses the size of a population relative to a defined unit of space and time — in effect, how many individuals of a species are packed into their natural habitat. It can be measured in several complementary ways: as abundance, the absolute headcount of the whole population; as numerical density, the number of individuals per unit area or volume, used when individuals in the population are of fairly uniform size; as biomass density, the total biomass (rather than head count) per unit area or volume; or as ecological density, density expressed specifically relative to the actual habitat area available to the species, as distinct from the total physical space of the study region. These related but distinct indices — summarised alongside crude density and relative abundance — let ecologists choose the measure of p …