1. genetics a group of similar individuals sharing a common gene pool, delimited in range by environmental or endogenous factors, and considered a unit —note in crossbred organisms, the population is often defined as the interbreeding group —see character, cline, ecotype, subpopulation 2. biometrics the aggregate of all units, finite or infinite, forming the subject of study —synonym universe; kinds of population include the following:

—density the number of individuals of a species per unit area —see frequency, severity

—dynamics the aggregate of changes that occur during the life of a population, including all phases of recruitment and growth, senility, mortality, seasonal fluctuations in the biomass, and persistence of each year class and its relative dominance, plus the effects that these factors exert on the population —see epidemic

—index any indicator of the size of a population —note an index may be, e.g., animal tracks per mile, dead rabbits per mile of road, or pellet counts per unit of area —see standing crop

—persistence the capacity of a population to maintain sufficient density to persist, well distributed, over time

—pressure the combined effect of a population on the other plants and animals and the environment —note high pressure may lead to dispersal, interference with recruitment, malnutrition, overbrowsing, etc. —see concentration area, hunting pressure

—viability the probability that a population will persist for a specified period across its range despite normal fluctuations in the population and in its associated environmental conditions This definition last updated 07/30/2008