Populations and Resources Critical Juncture

A population of tigers lives in Bangladesh. Over 50 years, the size of the tiger population increased. What best explains the increase in the size of the tiger population?

• A lot of tigers were born and none of them died.

• The tiger population is always increasing because no animal eats tigers.

• Fewer tigers were born than died.

• More tigers were born than died.

Scientists have been studying the size of three populations in a grassland. In this ecosystem, lizards eat fireflies, and fireflies eat gnats (a type of insect). The data showed that all three populations were stable. Then the lizard population decreased suddenly. What will most likely happen to the size of the firefly population as a result? The firefly population will . . .

• increase. The smaller lizard population will need fewer energy storage molecules so they will eat fewer fireflies. This will lead to fewer deaths than births in the firefly population.

• increase. The smaller lizard population will leave more energy storage molecules available for the firefly population to reproduce more. This will lead to more births in the firefly population.

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

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

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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? The size of the fox population will . .

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

• stay the same. Opossums and foxes do not eat each other, so the number of births and deaths in the fox population will stay the same.

• 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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A population of bluefish lives in the Gulf of Mexico. Over the last 50 years, the size of the bluefish population has decreased. What best explains the decrease in the size of the bluefish population?

• A lot of bluefish died and no new bluefish were born.

• More bluefish were born than died.

• Fewer bluefish were born than died.

• The bluefish population is always decreasing because bluefish are always being eaten.

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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 in the wild pig population.

• 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 in the wild pig population.

• 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 wild pig population.

  stay the same.

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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 in 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.

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

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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.

Scientists 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 in the frog population.

• 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 in the frog population.

• 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 the frog 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 . . .

• 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 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.

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

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A population of mice lives in the northeastern United States. Over the last 50 years, the size of the mouse population decreased. What best explains the decrease in the size of the mouse population?

• 
  Fewer mice were born than died.

• A lot of mice died and no new mice were born.

• More mice were born than died.

• The mouse population is always decreasing because mice are always being eaten.

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