7.3.3 Interactions in Ecosystems

This ecosystem reached the height of its​​ ​ (a)   for jackrabbits in about 1990. If there are no changes in biotic factors in the ecosystem, the number of jackrabbits will likely ​ (b)   over the next decade. This is because there are not enough ​ (c)   to support a larger population. There appears to be enough food, shelter, and water for about ​ (d)   jackrabbits.

• carrying capacity
• stay the same
• resources
• 350
• 300
• 600
• population
• biotic factors
• decrease
• increase

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Can a change in one population affect another population? Determine which events could occur in reaction to different changes. Match the reaction to the change that causes it by connecting a line between them. Make sure to choose the reaction that is most directly related to the change.

• All the consumers in the ecosystem suffer from a decrease in producers.

• An insect makes a home out of a certain plant type.

• A competing plant population evolves the ability to wrap around the tall plant to get to light.

• A predator population is hunted and nearly exterminated.

• It now defends the plant from would-be consumers.

• A plant evolves the ability to grow tall quickly.

• The predator population switches to a new food source.

• Algae in a coral reef die off because of warmer temperatures.

• The prey population grows and begins to overgraze.

• A prey population gains the ability to produce toxin.

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What components make up an environment?

• abiotic and biotic factors

• abiotic factors only

• biotic factors only

• communities of organisms

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Small fish are food for large fish in a marine ecosystem. If the population of small fish were to decrease, what would happen to the population of large fish?

• It would increase.

• It would decrease.

• It would remain unchanged.

• It would move to another ecosystem.

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Decomposers such as ​ (a)   , ​ (b)   , ​ (c)   , and snails obtain their energy by breaking down organic materials. Much of what decomposers break down includes dead plants and dead or living animals. As decomposers feed themselves and get energy, they release nutrients such ​ (d)   and​ (e)   back into the ecosystem, which can be used by producers such as plants.

• fungi
• bacteria
• insects
• phosphorous
• nitrogen
• algae
• oxygen

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Trophic level pyramids show the flow of energy in an ecosystem. Herbivores are important members of an ecosystem. Select the trophic level(s) where herbivores can feed.

• 1

• 2

• 3

• 4

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Which statement best summarizes what happens to energy in an ecosystem when it reaches the top of the food chain?

• The flow of energy stops when the top predator dies.

• The flow of energy stops when a secondary predator decomposes.

• The energy flows in the opposite direction, back down the food chain.

• The energy is transferred to the soil and recycled back to the producers.

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What does a food web show?

• The number of calories in different kinds of foods

• What types of foods we should eat

• The abiotic factors in an ecosystem

• The feeding relationships among organisms.

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In a forest food web, if the population size of hawks increases, what population would be expected to decrease?

• Decomposers in the area such as fungus

• Plants in the areas such as wild raspberries

• Small mammals in the area such as mice

• Large mammals in the area such as bear

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In any ecosystem, several different species of organisms might eat the same food. This will result in ______ among the species for food.

• predation

• mutualism

• competition

• commensalism