Changing Population Trends

A team of scientists visits an island in the Caribbean Sea. They find a diverse community of turtles, lizards, birds, and a variety of trees, shrubs, and grasses. No humans live on the island. Several years later, the scientists return to the island. They find a much smaller community, with reduced populations of all of the species they had identified earlier. Some of the animals now appear to be absent from the island. Which is the most likely explanation for the changes that the scientists observed?

• Competition for resources caused all of the island populations to decrease at the same time.

• A disease or parasite affected all of the island populations.

• A natural disaster, such as a hurricane, struck the island.

• Stress from overcrowding affected all of the island populations.

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Gibbons are small apes that live in the trees of southeast Asia. A scientist predicts that at the current rate of deforestation in southeast Asia, the region's carrying capacity for gibbons will decrease by 10 percent every year. The scientist's prediction provides the strongest support for which of these conclusions?

• The gibbon population will decrease by 5 percent every year until reaching a certain minimum size, which it will maintain.

• The gibbon population will decrease by 10 percent every year until reaching a certain minimum size, which it will maintain.

• Gibbons will maintain their current population size as they adapt to new environments.

• Gibbons will eventually become extinct in the wild.

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What is the main reason for the change in the shark population's behavior?

• Change in geographic range

• Change in population density

• Change in population distribution

• Change in carrying capacity

What is the primary factor that limits the populations of wolves and moose on Isle Royale?

• Abiotic factors

• Density-dependent predation

• Density-independent predation

• Density-dependent predator-prey relationships

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What is the carrying capacity for this sheep population?

• 9 million

• 0.9 million

• 1.6 million

• 1.0 million

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When a population grows past the ecosystem's carrying capacity, what happens to the population?

• Continues to grow

• The population starts to die off to return to carrying capcity

• The population will go extinct due to lack of resources

• The population grows then finds a new carrying capacity

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If a population grows larger than the carrying capacity of its environment, the

• death rate may rise

• birth rate may rise

• death rate must fall

• birth rate must fall

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The population of adult frogs in a wetlands ecosystem has increased to 1000 individuals, which is its carrying capacity. The frogs eat flies and other small animals, and they are prey for raccoons, snakes, and a variety of large birds. Which most likely would happen if an additional 200 adult frogs immigrated to the ecosystem?

• The carrying capacity for frogs in the ecosystem would increase by 200 frogs.

• The carrying capacity for frog predators in the ecosystem would increase by 200 individuals.

• The frog population would experience a pattern of exponential growth.

• About 200 adult frogs would die because of lack of resources, or by predation or disease.

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On Isle Royale, wolves are the main predators of moose. The graph shows the changing wolf and moose populations on the island over a 50-year time span. Which statement provides the strongest explanation for the trends in the two populations?

• The populations of predators and prey are limited by abiotic factors only.

• Predation acts a density-dependent limiting factor on prey, but not on predators.

• Predation acts as a density-independent limiting factor on predators, but not on prey.

• Predator-prey relationships act as density-dependent limiting factors on both predators and prey.

Answer explanation

The correct choice is that predator-prey relationships act as density-dependent limiting factors on both predators and prey.

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On Isle Royale, wolves are the main predators of moose. The graph shows the changing wolf and moose populations on the island over a 50-year time span. What could be a cause of the sudden drop in wolves around 1979-1980?

• Wolves became the prey of Grizzly Bears

• A disease came through the wolf population.

• The roles of Moose and Wolves switched and Moose now eat Wolves.

• Hunting was allowed and the wolves were targeted by humans.

Answer explanation

A disease came through the wolf population, causing the sudden drop in wolves around 1979-1980.

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