Page 86 - Science Course 3 (Book 1)

Mo2-L6a:How Living Organisms Interact?

Symbiotic Relationship Sometimes the size of a population changes
because the ecosystem changes.
a relationship in which two different species live
together and interact closely over a long period of Population density describes the number of
time organisms in the population relative to the
amount of space available.

If a population is very dense, organisms might have
a hard time finding enough resources to survive.

Let’s Begin

Populations
The area in which a population lives can be very The size of a population can change in different ways.
large, such as the population of all the fish in the
ocean, or very small, like fish in a lake.

If either biotic or abiotic factors that affect an
organism change, that organism’s population can The population increases
also change. as more fish hatch.

Some fish caught or
eaten reducing the
population

The area a population lives
in can be large or small.
As fish die, the
population gets
smaller

Some fish might leave the
population by moving to
another location.

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