Item IE032005: Changes in the number of worms in an area can affect the number of foxes in that area even though foxes do not depend directly on worms for food.

The diagram below shows the feeding relationships between populations of organisms in an area. The arrows point from the organisms being eaten to the organisms that eat them.

Using only the relationships between the organisms shown in the diagram, which of the following statements describes what will happen to the number of foxes if most of the worms are killed and why?

  1. The number of foxes will decrease because there are more robins to eat them.
  2. The number of foxes will decrease because there will be fewer robins for them to eat.
  3. The number of foxes will not change because they are not connected to worms in the diagram.
  4. More information is needed to tell what will happen to the number of foxes.

Distribution of Responses

Chart showing distrubtion of responses for Item IE032005

Percent of students responding correctly

Overall76%
Grades 6–873%
Grades 9–1279%
Male74%
Female76%
Primary Language is English77%
Primary Language is not English59%

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