02.2 - Limits to Growth (10 pts.)

Which of the following statements describes density-independent limiting factors?

• Competition is an example.

• Parasitism and disease are examples.

• Environmental extremes, such as a hurricane or drought, are examples.

• Their effects increase as the population increases in an area.

Answer explanation

Density-independent limiting factors, such as environmental extremes like hurricanes or droughts, are not influenced by population size and can affect a population regardless of its density.

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A scientist is developing a computer model to determine the maximum population size, or ​ ​ (a)   , of eagles and other birds of prey in a forest ecosystem. The model should represent all of the ​ (b)   that affect the populations.

• limiting factors

• limiting population

• immigration factors

• carrying capacity

Answer explanation

The correct choices are carrying capacity and limiting factors because they are key components in determining the maximum population size of eagles and other birds of prey in a forest ecosystem.

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A population of mountain lions lives in an alpine forest. As the population increases, which of these events becomes more likely to occur?

• Female mountain lions raise an increasing number of pups per litter, and a greater percentage of pups survive to adulthood.

• Competition for territory and other resources acts to slow the growth rate of the population.

• A wildfire, drought, or other natural disaster acts to decrease the mountain lion population by at least 50 percent.

• A decrease in competition acts to increase the growth rate of the population.

Answer explanation

Competition for territory and other resources acts to slow the growth rate of the population.

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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.

• 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.

Answer explanation

A natural disaster, such as a hurricane, is the most likely cause for the reduced populations of all species on the island.

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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.

Which of these conclusions is supported by the by the scientists' prediction?

• 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.

Answer explanation

The correct choice is that Gibbons will eventually become extinct in the wild as the scientist predicts a 10% decrease in carrying capacity every year due to deforestation.

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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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