Definition 1 (Complete AZ Biology Handbook (3rd edition), Indge, 2003):
A group of individuals belonging to one species. In ecological terms, this usually refers to the area being studied, so it is possible to consider the population of frogs in a pond or of aphids on a sycamore tree. In evolutionary terms, however, it is usually necessary to add that members of a population are able to breed with each other.
Definition 2 (Longman Biology Handbook (3rd edition), Curtis, 1985):
A group of organisms of the same species which occupies a particular space over a given period of time. The actual numbers of individuals within a population may rise and fall as a result in changes of the birth and death rate and such factors as climate, food supply, and disease.
Definition 3 (A Dictionary of Biology (6th edition), 2008):
- A group of individuals of the same species within a community. The nature of a population is determine by such factors as density, sex ratio, birth and death rates, emigration, and immigration.
- The total number of individuals of a given species or other class of organisms in a defined area, e.g. the population of rodents in Britain.