Unit A-Chapter 4-Lesson 3 Notes

What Happens When an Ecosystem Changes?

Environmental Changes

• Change is a natural part of the history of any ecosystem.
• Changes may be long-term-for example, the result of fires, droughts, and floods- or long-term, as a result of climatic change.
• All organisms have a certain range of tolerance for conditions such as:

1. Environmental temperature
2. Amount of moisture 
3. Amount of light

• Organisms cannot usually survive in conditions that are outside their range of tolerance.
• In any ecosystem, populations change as conditions change.
• New communities of organisms, which are better adapted to new conditions in that ecosystem, may replace original communities.

Competition

   
• Organisms can live in an ecosystem only as long as it meets their needs for food, water, shelter, and other essentials. 
• Organisms that live within an ecosystem often compete for similar resources.
• This competition occurs among different kinds of organisms, as well as among members of the same species.
• Competition helps regulate population size because as competition for resources increases, population size decreases.
• When resources are limited, organisms that are well-adapted to the conditions in an ecosystem will be best able to compete for resources and survive.
• Some animals solve the problem of limited resources by migrating.
• The snowy owl, for example, inhabits the Arctic tundra, but when the population of lemming-their main food source-falls, it may migrate great distances in search for food. 
• In the winter, snowy owls are sometimes sighted as far south as Illinois.

People Affect Ecosystems

• Ecosystems change naturally, but human activities such as cutting down trees and draining wetlands can speed up the change.
• People can also change the ecosystems by introducing new species that out-compete native species.
• Conservation of resources and restoration practices can help to reduce and repair ecosystem damage.