2.1.5—Population definition

A population is made up of organisms from one species living in a defined area at a defined time. This definition makes a population count meaningful: we know exactly what has been counted.

A population has three boundaries:

• One species — the organisms can potentially interbreed.
• One area — the counting boundary is stated.
• One time — the survey refers to a defined moment or period.

If one boundary changes, you may be describing a different population.

A Tuesday survey finds 18 mallards and 6 Canada geese in one pond. The place and date are the same, but the species are different. Therefore, this describes two populations, not one population of 24 birds.

The same rule explains why “20 frogs were counted this month” is incomplete. The report must also state the frog species, exact area and survey window before the number can be compared with another count.

Key idea: same species + defined area + defined time.

Sharing a place does not make organisms one population. The species, area and time boundaries all matter.