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Scientists have been studying the size of three populations in a region. In this ecosystem, lions eat wild pigs, and wild pigs eat frogs. The data showed that all three populations were stable. Then the frog population decreased suddenly. What will likely happen to the size of the wild pig population as a result?

The size of the wild pig population will . . .

• increase. The smaller frog population will need fewer energy storage molecules so there will be more energy storage molecules available to the wild pig population. This will lead to more births.

• decrease. The smaller frog population will provide fewer energy storage molecules for the wild pig population, so the wild pig population will reproduce less. This will lead to fewer births than deaths.

• decrease. A decrease in any population causes a decrease in the sizes of all other populations in an ecosystem.

• stay the same. The size of their consumer population did not change, so the number of deaths in the wild pig population did not change. There will be the same number of births and deaths

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?

The size of the shark population will . . .

• decrease. The larger crab population will leave fewer energy storage molecules available in the ecosystem for the shark population, so there would be fewer births.

• 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

• stay the same. Sharks do not eat crabs, so the number of births and deaths in the shark population will stay the same.

A large population of ducks lives in an area with a lake. In the last 40 years, the size of the duck population has stayed the same. What must be true about the duck population during the last 40 years?

• The number of ducks that were born was the same as the number of ducks that died.

• No ducks were born and no ducks died.

• Humans started protecting the duck population so they stopped dying.

• The ducks did not have any baby ducks during these years.

zScientists have been studying the size of three populations in a swampland. In this ecosystem, herons (a type of bird) eat frogs, and frogs eat dragonflies. The data showed that all three populations were stable. Then the dragonfly population increased suddenly. What will likely happen to the frog population as a result?

The size of the frog population will . .

• increase. An increase in any population within an ecosystem causes an increase in the sizes of all other populations in an ecosystem.

• increase. The larger dragonfly population will provide more energy storage molecules for the frog population, so they will reproduce more. This will lead to more births than deaths

• stay the same. The size of its consumer population did not change, so the number of deaths in the frog population did not change. There will be the same number of births and deaths

• decrease. The larger dragonfly population will take more energy storage molecules from the ecosystem, leaving fewer available for the frog population. This will lead to fewer births

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?

• stay the same. Eagles and bears do not eat each other, so the number of births and deaths in the bear population will stay the same.

• 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

• 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

• decrease. A decrease in the size of one population leads to a decrease in the sizes of all other populations in an ecosystem.

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?

The size of the cod population will . . .

• decrease. A decrease in the size of one population leads to a decrease in the sizes of all other populations in an ecosystem.

• 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

• stay the same. Polar bears do not eat cod, so the number of births and deaths in the cod population will stay the same.

• 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