Page 47 - Science Course 3 (Book 1)

Mo2-L1a: How Population Mo2-L1a: How Population Changes Affect an Ecosystem?
Changes Affect an Ecosystem?

Key Concept All the populations living in an area at the same time
form a community.
How Population Changes Affect an Ecosystem?

How can you describe an Ecosystem?

Population Changes
Populations increase when offspring are produced or
when new individuals move into a community.

Populations decrease when individuals die or move
away.

Changes in the abiotic factors of an ecosystem
affect population size.

If a drought reduces plant growth, less food is avail-
able for plant eaters, which can lead to a decrease in
plant eater populations.

Increase Population Decrease Population

natality = birth rate mortality = death rate

Habitats Population emigration
immigration individuals have
A habitat is the area within an ecosystem that individuals have Size moved out of the
provides the biotic and abiotic factors an organism moved into the area area to somewhere
needs to survive and reproduce. from somewhere else
else.

Interactions between organisms also affect population
size.

For example, the wolf population can keep increasing
until there are no longer enough moose to support it.

60 2000
1800
50
Moose 1600
40 1400
Populations and Communities 1200
30 1000
A population is the number
of individual organisms of 20 800
the same species that live 60
in an ecosystem at the 10 Wolf 40
same time. 0 20
1955 1960 1965 1970 1975 1980 1985 1990 1995
Year
39