2. Organisms and Their Ecosystems  Have you ever heard of the zebra mussel?  It was accidentally brought to the Great Lakes from Europe, probably on the bottom of a boat.  It eats up so many tiny organisms that native fish and organisms die.

3. Ecosystems are such complicated and carefully balanced places that changing one thing can have a domino effect and change many others.

4. Are you predator or prey?  Predation: One organism feeds on another. If an organism is a predator, it must have characteristics that make it a good hunter. Hawks have excellent eyesight and strong wings.

5. Wolves, foxes, and other wild predators have sharp teeth and fast leg muscles.

6. If you are a prey, fast leg muscles are useful to help you escape from your predator. A rabbits good hearing helps to warn it. An arctic hare has white fur in winter, in the snow, but brown in the summer, like dirt.

7. Mice, Snakes, and Hawks Imagine an ecosystem with mice, snakes and hawks. If a disease kills most of the mice in this ecosystem, the snakes will have less to eat. When they die, there are less snakes reproduced. Then the hawks will have to look elsewhere for food or die, too.

8. So changing the population of one organism can change the populations of other organisms. Mice >>Snakes>>Hawks

9. Limiting Factors  Environmental factors that cause the populations in ecosystems to change are called limiting factors. Water food, space, weather, and pollution are all examples of limiting factors.  EXAMPLES: Drought, construction, polluted soil and water.  Some organisms will die, and their populations will go down.

10. Droughts and Pollution

11. Fit to Survive  Fish don’t live in the desert because they need water.  Frogs need moist, warm environments and water to lay eggs.  Reptiles can handle limiting factors of dry, hot habitat

12. Reptiles  Reptiles can handle the limiting factors of a dry, hot habitat because they have scales that allow them to keep water inside them. Their eggs are leathery and don’t have to be laid in water. But the are cold-blooded and can’t survive in cold habitats. They would freeze to death.

13. Mammals  Mammals have fur, which gives them an advantage in colder environments. Large, heavy, thick-furred mammals might have trouble living in hot areas because they would have a tendency to overheat.

14. Survival  It is important to remember that the living things in an ecosystem are there because their characteristics and needs match what that ecosystem has to offer. If something in that ecosystem changes, then those living things will have to hope that they are able to handle the change. If not, they won’t be found in that ecosystem much longer.

15. Predicting Population Changes in Ecosystems

16. Graph  The lynx is a predator to the snowshoe hare. This graph shows the relationship between the lynx and the snowshoe hare populations over many years. In 1855, the number of snowshoe hares started to go up. Maybe something in the ecosystem changed to make it easier for snowshoe hares to find food or reproduce.

17. Lynx…  What happened to the population of lynx at this same time? It went up, too. Why? Most likely it was because there were more snowshoe hares around and the lynx had more food and could survive better. The reverse happened in 1885. The number of hares started going down for some reason. Maybe hunters killed them, or humans built homes in their habitat. With less food around, the lynx population went down too.