Where does population collide?

In statistics the population is the entire collection of units about which one wants to draw a conclusion: the sample is drawn from it, and inference runs from the observed sample back to the unobserved population. Fisher's 1922 On the mathematical foundations of theoretical statistics framed the task of statistics as the study of a hypothetical infinite population, of which the data in hand are a random sample, and cast estimation as the recovery of that population's parameters. The referent is an abstract set fixed by the question asked, real or hypothetical and often never observed in full, and it is not a group of living organisms, a nation's inhabitants, or a breeding pool of genes.[1]

Unit

The full set of units a sample is drawn from and generalised to

Recovery means

Not applicable

Measured by

Not counted directly; its parameters are estimated from a sample, with the error of that estimate quantified

In ecology a population is a group of individuals of one species that live in the same area and can interbreed, treated as a unit whose numbers rise and fall through birth, death, immigration, and emigration. Berryman's 2002 Population: a central concept for ecology? argued that the population, a group of interacting organisms of a single kind, is the basic object whose dynamics ecology sets out to explain. The referent is a real assemblage of living organisms in a place, counted as a density that changes over time, and it is not an abstract set sampled by a statistician, a nation's people, or a pool of alleles.[2]

Unit

A local group of one species, as a density that changes over time

Recovery means

Numbers depleted by a bad season can be rebuilt by later births and immigration, up toward the habitat's carrying capacity

Measured by

Estimated by counts, mark-recapture, or density sampling, and tracked as birth, death, and growth rates

In demography the population is the set of people in a defined territory at a given time, described by its size, its structure by age and sex, and the way both change through births, deaths, and migration. Preston, Heuveline, and Guillot's 2001 Demography: Measuring and modeling population processes set out how a human population's number and composition are measured and projected, with change governed by the balance of entries and exits. The referent is a concrete human aggregate, enumerated by census and vital registration, and it is not a statistician's sampling frame, an ecologist's field group, or a geneticist's breeding pool, even though all four share the word.[3]

Unit

The people in a territory, by size, age-sex structure, and rate of change

Recovery means

Not applicable

Measured by

Enumerated by census and estimated from vital registration and surveys, then projected forward

In population genetics a population is a Mendelian population: a community of interbreeding, sexually reproducing individuals that share a common pool of genes, and it is this pool, not any one organism, whose allele frequencies shift from generation to generation as evolution proceeds. Wright's 1931 Evolution in Mendelian populations analysed how those frequencies change under selection, mutation, migration, and the drift of finite numbers, making the breeding population the unit in which evolution is measured. The referent is a shared gene pool tracked by its allele frequencies, and it is not a sampled set, a counted field group, or a censused nation, though a breeding population may coincide with an ecological one.[4]

Unit

A shared gene pool, tracked by its allele frequencies across generations

Recovery means

Not applicable

Measured by

Characterised by allele and genotype frequencies estimated from genetic sampling, and by their change between generations