Predicting the Effects of Changes in Ecosystems Caused by Living Organisms

A foreign insect is introduced into the Texas. It eats a lot of leaves, and trees start to become leafless. Many different animals feed on the new insect, but even they cannot control its numbers. Eventually, trees begin to die. Why would a rapid increase of the new insect population cause certain species of herbivores to vanish or be fewer in number?

• They would not have enough to eat. 
• They would not have enough space to live.
• They would not have tree bark to eat.

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A manatee is a water-dwelling herbivore on the list of endangered species. If manatees were to become extinct, what would be the most likely result in areas where they had lived?

• Certain producer organisms would become more abundant in the area.
• Other manatees would move into the area and restore balance.
• Predators in the area would have more food to eat.
• The area would not be affected.

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How would beavers building a dam cause an increase in the fish population? The dam

• blocks a river and creates a lake.
• causes predators to hunt more fish.
• forces many birds to leave the ecosystem.
• removes trees from around the river.

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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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The Coqui frog is native to Puerto Rico. These frogs were accidentally introduced in Hawaii. Coqui frogs are extremely noisy; since they are nocturnal they make loud noises at night. Although these frogs are small, they eat a lot! They eat insects and spiders that are also eaten by birds in Hawaii. Besides being noisy, how do these frogs most likely harm other animals? 

• By causing other animals to reproduce more.
• By competing with other animals for food.
• By eating foods that no other animals eat.
• By moving slower than most other animals.

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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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Highways allow people to travel between towns and cities, but it also divides ecosystems into smaller pieces. Animals can become separated from lakes they use for food and shelter. For example, tiger salamanders use lakes for these reasons. How could the building of highways affect animals such as the tiger salamander?

• Tiger salamanders could improve lake ecosystems.
• Tiger salamanders may be cut off from important resources.
• Tiger salamander habitats may have less pollution.
• Tiger salamander habitats within ecosystems would become larger.

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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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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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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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