Changes to Ecosystems

Scientists are concerned about overfishing of shark populations. Sharks feed on rays and rays feed on scallops. Without sharks, rays consume all the scallop beds. This situation demonstrates that: 

• humans can improve an ecosystem by removing predators.
• humans can upset an ecosystem by removing species.
• reducing the shark population increases the quantity of scallops that can be taken.
• sharks are not important for the stability of the ecosystem.

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Raccoons eat aquatic animals. If chemicals entered the lake with rain water and destroyed the plants, how would this impact the raccoon population?

• Raccoons would have more aquatic animals to eat.
• Raccoons would begin eating land plants.
• Raccoons would have less aquatic animals to eat.
• Raccoons would only drink water.

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A park is home to a large number of robins, squirrels and rabbits. The robins and squirrels live in the park’s trees. The robins feed on earthworms and insects that live on the ground. The squirrels eat the acorns produced by the park’s oak trees. The rabbits hide in the bushes and feed on the grass. Which factor would negatively impact the number of rabbits living in the park?

• Collecting acorns off the ground.
• Planting more trees.
• Removing park bushes.
• Removing the squirrels.

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If humans cleared a forest to build homes, we would expect _____________.

• fewer tree-dwelling animals
• increased insect populations
• more development of soil
• more frequent thunderstorms

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People who own cows and other animals that eat grasses create plans to move these animals over time. They move the animals from one area to another so they can eat grasses in different places. This allows grasses to continue to grow. Why is it important to have a plan for grazing animals that allows grasses to grow in a healthy way?

• It causes soil erosion and allows for planting of new species.
• It prevents the dispersal of seeds and the overgrowth of plants.
• It protects the predators in an area by providing plants to eat.
• It protects the soil so plants will continue to grow; food will be available for herbivores.

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