A population is a group of individuals of the same species that live in the same area at the same time and interact with one another.
To explore this definition further, what exactly do we mean by “interact”? In species that reproduce sexually, a population might be defined as the group of individuals that interact by interbreeding.
In species that reproduce asexually, however, such as dandelions or the fish Poecilia formosa, a population must be defined by other kinds of interactions, such as competition for common sources of food. Our definition of a population also incorporates the area over which members of a species interact. If that area is known, as in a population of lizards that live on and move throughout a small island, we can report population abundance either as population size (the number of individuals in the population) or as population density (the number of individuals per unit of area). For example, if there were 2,500 lizards on an island of 20 hectares (ha), or roughly 50 acres, the population size would be 2,500 lizards, and the population density would be 125 lizards per hectare.In some cases, the total area occupied by a population is not known. For example, when little is known about how far a sexually reproducing species or its gametes (e.g., plant pollen) can travel, it is difficult to estimate the area over which individuals interbreed frequently and hence represent a single population. For asexual species, similar problems are encountered when we try to estimate the area over which interactions other than interbreeding occur. When the area occupied by a population is not fully known, ecologists use the best available information about the biology of the species to delimit an area within which the size and density of the population can be estimated.
More on the topic A population is a group of individuals of the same species that live in the same area at the same time and interact with one another.:
- CONCEPT 9.1 Populations are groups of individuals of the same species that vary in size over space and time.
- Species richness increases with area and decreases with distance
- Individuals within species differ in their life histories
- Local and regional processes interact to determine local species diversity
- Some species exhibit population cycles
- CONCEPT 18.3 Regional differences in species diversity are influenced by area and distance, which determine the balance between immigration and extinction rates.
- Latin America, defined here as the nineteen American republics that once constituted almost all of the overseasterritories of the monarchies of Spain and Portugal, now accounts for 8 per cent of the world's population and 13 per cent of its land area.
- CONCEPT 18.2 Global patterns of species diversity and composition are influenced by geographic area and isolation, evolutionary history, and global climate.
- CONCEPT 6.2 Natural selection, genetic drift, and gene flow can cause allele frequencies in a population to change over time.
- CONCEPT 16.1 Communities are groups of interacting species that occur together at the same place and time.