Amplify Populations and Resources at a Critical Juncture

In the Arctic Ocean, sharks eat whales, and whales eat crabs. In the last 10 years, the sizes of the populations have been stable, but recently the size of the crab population increased. What will likely happen to the shark population?

• increase. An increase in the size of any population leads to an increase in the sizes of all other populations in an ecosystem.

• increase. More energy storage molecules will be available to the shark population from the larger whale population, so the shark population will reproduce more. This will lead to more births than deaths in the shark population.

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Scientists have been studying the size of three populations in Peru. In this ecosystem, pumas (large wild cats) eat deer, and deer eat grass. The data showed that all three populations were stable. Then the puma population increased suddenly. What will most likely happen to the size of the deer population as a result?

• stay the same. The size of their resource population did not change, so the amount of energy storage molecules available for the deer did not change. There will be the same number of births and deaths in the deer population.

• decrease. The larger puma population will need more energy storage molecules, so they will eat more deer. This will lead to more deaths than births in the deer population.

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In the Arctic region, polar bears eat seals, and seals eat cod (a type of fish). In the last 7 years, the sizes of all the populations stayed stable, but recently the size of the polar bear population decreased. What will likely happen to the cod population?

• decrease. The smaller polar bear population will lead to more seals. The larger seal population will need more energy storage molecules to reproduce, so they will eat more cod. This will lead to more deaths than births in the cod population.

• increase. The smaller polar bear population will leave more energy storage molecules available in the ecosystem for the cod population, so there will be more births in the cod population.

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In Australia, both opossums and foxes eat rats. The sizes of the populations have been stable for the last 12 years, but recently the size of the opossum population increased. What will likely happen to the fox population?

• decrease. The larger opossum population will leave fewer energy storage molecules for all other populations in the ecosystem, so the fox population will reproduce less. This will lead to fewer births than deaths in the fox population.

• decrease. Fewer energy storage molecules will be available to the fox population from the smaller rat population, so the fox population will reproduce less. This will lead to fewer births than deaths in the fox population.

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In North America, both bears and eagles eat trout. The sizes of the populations have been stable for the last 9 years, but recently the size of the eagle population decreased. What will likely happen to the bear population?

• increase. The smaller eagle population will leave more energy storage molecules for all other populations in the ecosystem, so all populations will reproduce more. This will lead to more births in the bear population.

• increase. More energy storage molecules will be available to the bear population from the larger trout population, so the bear population will reproduce more. This will lead to more births than deaths in the bear population.

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In North America, both bears and eagles eat trout. The sizes of the populations have been stable for the last 9 years, but recently the size of the eagle population decreased. What will likely happen to the bear population?

The size of the bear population will . . .

• increase

• decrease

• stay the same

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What is the primary factor that can lead to an increase in a population's size at a critical juncture?

• Increased birth rate

• Decreased death rate

• Increased immigration

• All of the above

Which of the following resources is most likely to become a limiting factor for a population at a critical juncture?

• Water

• Sunlight

• Carbon dioxide

• Nitrogen

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In an experiment to study population growth, which variable would be most critical to control?

• Temperature

• Light intensity

• Food availability

• Predator presence

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How does the concept of carrying capacity relate to population amplification at a critical juncture?

• It determines the maximum population size that can be supported.

• It is irrelevant to population growth.

• It decreases as population size increases.

• It increases indefinitely with population growth.

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