Population Facts For Kids

Population means a group of living things of the same kind that live in the same place at the same time. For example, all the frogs in a pond or all the oak trees in a park can be one population. Scientists describe a population by asking who is in it (the species), how many individuals there are (size), where they live (area), and when we look (time).

Different scientists sometimes use the word in slightly different ways, which can be confusing. Still, the easiest idea to remember is a population is a set of the same species that share a space and time.

The English word "population" comes from older languages. Long ago people used the Late Latin word populatio, which meant a group of people or a crowd. That word came from the Latin word populus, which meant the people of a place.

Over time the word moved into other languages and began to mean groups of living things as well as people. Today we use it for animals, plants, and people, but scientists often use it in a special, careful way.

People do not always agree on one exact definition of population. Biologists may focus on different things, so they use the word in different ways. A group can be split from others by space (where they live), by demography (ages and how many are born or die), or by genes (how they are related).

Long ago, the word could mean all kinds of species in a region. Now scientists usually mean members of a single species. When many species are together, ecologists often call that a community. A special phrase, polyspecific population, sometimes names a mixed group, but community is more common.

Scientists study populations in two main ways. The ecological view looks at where the group lives and how its members interact with each other and their home. The genetic or evolutionary view looks at how genes move and change as animals or plants reproduce. A population has its own gene pool, which is the collection of genes in its members, and that pool can slowly change over time.

To follow these changes, scientists use population dynamics, which means using math to model how size and ages in a population go up or down. These ideas also help study diseases (called epidemiology) and even how animals make choices, using ideas from evolutionary game theory—a way to compare behavior like players in a game.

In a living group, gamodeme is a useful word scientists use for a breeding group — a set of plants or animals that belong to the same species and can mate with each other. If a gamodeme is very large and everyone mixes freely, it is called “panmictic,” which means gene versions (alleles) spread evenly through the group. When mating is random like that, scientists can predict how common different gene combinations will be.

But in nature, breeding groups are often partly separated. When groups stay apart, their genes can change in different ways and more individuals may end up with two copies of the same gene. This rise in sameness can make some traits weaker, a thing called inbreeding depression. Farmers and plant breeders use this idea on purpose with methods like line breeding, pure-line breeding, and backcrossing to keep good traits or make plants and animals better over time. These methods work whether a species mainly self-fertilizes or mainly mates with others.