lesson
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If you spot a single clownfish darting into an anemone, you are looking at one living thing — but that fish cannot survive in isolation.
To make sense of how life is structured in nature, biologists organize living systems into specific nested levels.
How do we draw the line between a single fish, a whole group of them, and everything else living on the reef?
The Three Biological Levels
An organism is a single, individual living entity, such as one clownfish or one oak tree. A habitat is the specific physical place where that organism lives.
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What happens when multiple organisms of that exact same type live and breed together in one place?
Populations: Counting One Species
A species is a group of organisms that can breed together to produce fertile offspring. A population is all the individuals of that single species living in the same geographic area at the same time.
For instance, one red fox in a forest is an individual organism, whereas all 42 red foxes living across that entire forest make up the red fox population.
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In nature, no population lives in an empty vacuum. What do we call all the different living populations sharing that same forest?