Effects of Population Size

An experiment was conducted on the population growth of worms. Worms were added to two identical bins. The bins were both kept at 20°C, except for the month of January when bin 2 was kept at 30°C. Each week, 2.5 kg of food was added to bin 1. In bin 2, 2.5 kg of food was added each week in all months except April. In April, 3.5 kg of food was added per week. The results of the experiment are shown.

Which of the following probably accounted for the large drop in population in bin 2 from January to February?

• lack of food

• overpopulation

• lack of water

• overheating

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Lake trout are found in the Great Lakes because they can only live in cold environments.

This example shows how the number of populations an ecosystem can support is limited by _______.

• temperature

• water

• air

• food

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A commercial fishing company moves into the ecosystem shown in the food web below and begins to use nets to catch crustaceans. The crustaceans are taken out of the water and sold as food.

How will this most likely affect the species in this ecosystem?

• There will be an increase in the number of crustaceans which will cause a decrease in the shark population.

• There will be an increase in the number of crustaceans which will cause a decrease in the algae population.

• There will be a decrease in the number of crustaceans which will cause an increase in the dolphin population.

• There will be a decrease in the number of crustaceans which will cause a decrease in the fish population.

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One year, heavy rain makes Lake Raymond very deep. The next year, however, rain is very light, and not much water is left in Lake Raymond.

How will this most likely affect animal life in Lake Raymond?

• There will be an increase in bacterial life the second year.

• There will be more animal life the second year.

• There will be several new species of fish the second year.

• There will be less animal life the second year.

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It was hypothesized that there is a maximum number of worms that can survive under the conditions of bin 1.

Is this hypothesis supported by the results of the experiment?

• No, because the number of worms in bin 2 decreased between May and June.

• Yes, because the number of worms in bin 2 steadily increased between February and May.

• Yes, because the number of worms in bin 1 remained fairly constant between January and June.

• No, because the number of worms in bin 1 decreased from January until June.

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A population of black bears depends on salmon from a stream for food.

If a drought causes the stream to run dry one year, how will this likely impact the black bear population?

• The population's size will decrease.

• The population's size will increase.

• The population will be unaffected.

• The population will thrive on new species of fish.

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Many people want to live in urban areas. One of the main factors that limits the number of people that can live in an area is

• the amount of public transportation that is available.

• the amount of space that is available to build shelter.

• the number of people who don't want to live in an area.

• the location of schools, churches, and libraries.

A new predator is introduced into the ecosystem shown in the food web. This predator feeds on bees and mice.

How will this most likely affect the species in this ecosystem?

• There will be a decrease in bees and mice which will cause an increase the black bear population and a decrease in the fox population.

• There will be a decrease in bees and mice which will cause a decrease in the populations of both black bears and foxes.

• There will be an increase in bees and mice which will cause an increase in the populations of both black bears and foxes.

• There will be an increase in bees and mice which will cause a decrease in the black bear population and an increase in the fox population.

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A food web is shown.

A drought in this ecosystem makes the ground become very dry. Which of the following would most likely result from this change?

• The grass will shrivel and die, which will cause a decrease in the impala population.

• The grass will grow more rapidly, which will cause a decrease in the cheetah population.

• The grass will shrivel and die, which will cause an increase in the cheetah population.

• The grass will grow more rapidly, which will cause a decrease in the impala population.

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Beavers, like the one shown below, prefer to live near rivers and streams, where they can easily find food and building materials for their homes and where they can better protect themselves from predators.

Although beavers are social creatures in the sense that they tend to mate for life and live with their families, they are also very territorial. In fact, in order to prevent other beavers from intruding, they create scent mounds around the perimeter of their territories. Because of this behavior pattern,

• there can be an unlimited number of beavers living in an ecosystem, as long as intruders can become part of a family.

• intruders are forced to adapt and create nests in trees, like birds, rather than live on the water.

• food and other resources are often shared between different families living in an ecosystem.

• the number of beaver populations that an ecosystem can support is limited by the amount of space available to make habitats.

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