Biologists believe that the tick-deer relationship is parasitic because the tick feeds off the deer and the deer is harmed by the tick bite. During springs with sufficient rain, forest vegetation increases, providing abundant food resources for deer to produce young.

Which of these patterns supports the idea that the tick-deer relationship is parasitic?

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What causes competition to occur in an environment?

• Members of a population have different roles.

• Good conditions make resources plentiful.

• A population falls below the environment’s carrying capacity.

• Organisms struggle for a limited resource.

Drought is a weather condition that may limit the amount of water resources available to an ecosystem. Which of the following may be one result of drought?

• Flowering plants may produce more seeds due to lack of water.

• Predator populations may increase due to increased prey populations.

• Fish populations may decline due to lower river levels.

• Birds may not build nests due to temperature change.

Which of these events would lead to an increase in the size of a population of squirrels?

• Some squirrels emigrate in search of food.

• New predators are added to the ecosystem.

• More squirrels are born than die.

• A large number of squirrels die because of a forest fire.

Which of the following is an example of an ecosystem?

• the open ocean

• fish and sharks

• an oyster

• a school of fish

In 1944, 29 reindeer were deposited on St. Matthew Island, a small island in the Arctic. The reindeer were meant to be used as an alternate food source for the soldiers stationed there. Soon after the reindeer’s arrival, World War II was drawing to an end and the soldiers left the island without hunting a single deer. The reindeer were left with an island to themselves that had an abundance of their favorite food, lichen, and a complete lack of predators. When researchers visited the island in 1957 they found the reindeer population had grown to over 1,300 deer. When they visited a second time in 1963, they found a population of at least 6,000 deer. However, the population had decreased to only 42 deer by 1966, and there were no reindeer at all on the island by the 1980s.

Which of these resources would not affect individual reindeer survival?

• access to mates

• nutrients in food

• sources of water

• adequate space

This food web shows how parts of a meadow ecosystem interact with parts of a marsh ecosystem.

Which of these is a carnivore according to the food web?

• rabbit

• grasshopper

• mouse

• small fish

Two separate food webs are pictured here.

According to the food webs, which two organisms do not exhibit a competitive relationship over resources?

• beaver and bison

• elk and beaver

• bison and elk

• eagle and black bear

Which of these is an example of a biotic factor that could limit a community in an ecosystem?

• A hurricane passes through an ecosystem.

• Living space is lost due to human activities.

• A drought occurs for several months.

• New predators move into the ecosystem.

Which of these is the most likely reason that a population in an ecosystem could have a sharp decline?

• The number of predators suddenly decreases.

• The abiotic resources in the environment suddenly drops.

• The number of prey suddenly increases.

• The competition for the same resource suddenly drops.