4th Grade Science - Chapter 4 Changes In Ecosystems

Book: Science By Scott Foresman
Changes In Ecosystems
Vocabulary And Test Review
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What are 3 key things about Ecosystems?
They are healthy when their parts are in balance.

All living things are interrelated - what happens to one population affects the entire community.

Balanced ecosystems are constantly changing.

for example: when water evaporates from a pond, rain replaces the water.
This keeps the ecosystem in balance
What happens when the number of organisims in a population increases?
All of the other living things population in the ecosystem will increase.
What are two things that might prevent a plant population from growing in size?
There are too many plant eating animals in the ecosystem.

There hasn't been enough rain to help the grass grow.

Other animals may have eaten many more of the grass eating animals.
When two or more species must use the same limited resources.
What are two behaviors that help animals avoid or reduce competition?
Living in groups

Hunting in the morning or evening.

Two different organisms live together to assist each other.
The organism in a relationship that is helped by the other.
The organism in a relationship that is harmed by the other.
What might happen to a parasite if its host were to die?
The parasite may die because it does not have any food from the host.
Gradual Change from one community of organisms to another.
Give an example of succession.

Usually occurs in stages.

Example: Bare land becomes grassland, grassland becomes shrubs, shrub land becomes forest land.
When a species dies out and is gone forever.
What are 3 reasons that an animal may become extinct?
Changes in the earth's environment:
Climate changes
habitat destruction

Endangered Species
Populations of a species that have been reduced so much that they are in danger of becoming extinct.
Can endangered and threatened species sometimes lave an area to search for a more suitable environment?

What are some examples where rapid change can help an ecosystem?
A forest fire - clears away dead plant matter and assists trees to creat a new forest by forcing sealed cones to release seeds.

Volcanic Ash - enriches the soil.

Floods - create more area for fish population to increase.

Name two processes that change an environment over a very long period of time.
Forest regrowth
canyons being created
lakes being created

Name two processes that change an environment rapidly.
Forest Fires
Volcanic Eruptions
What are some of the examples of ways that people disturb the balance in the ecosystem?
Cutting down trees to make houses and paper.
Clearing prairies to plant crops or build roads.
Polluting the air and water.
What are some examples of air pollution?
Automobile fumes
Large factories that produce smoke
Chemicals that farmers spray on their fields.
What are some examples of water pollution?
Chemicals that get into the rivers, lakes and oceans.
Oil Spills
Hazardous Waste
Substances that are harmful to humans and other organisms.

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