Item IE031007: Changes in a population of organisms in a food web (worms) can affect other populations of organisms (foxes) even if they are not directly connected in a feeding relationship.

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 will be fewer worms to eat the robins and so more robins to eat the foxes.
  2. The number of foxes will decrease because there will be fewer worms for the robins to eat and so fewer robins will be available for the foxes to eat.
  3. The number of foxes will not change because the worms are killed, not the foxes.
  4. The number of foxes will not change because it is not connected to worms in the diagram.
Distribution of responses
Answer Choice
Overall
Grades
Gender
Primary Language
 
n = 2804
6–8
n = 1539
9–12
n = 1257
Male
n = 1323
Female
n = 1413
English
n = 2461
Other
n = 271
A. The number of foxes will decrease because there will be fewer worms to eat the robins and so more robins to eat the foxes. 9% 10% 7% 10% 8% 8% 14%
B. The number of foxes will decrease because there will be fewer worms for the robins to eat and so fewer robins will be available for the foxes to eat. 75% 70% 81% 75% 75% 77% 62%
C. The number of foxes will not change because the worms are killed, not the foxes. 9% 11% 7% 8% 10% 9% 13%
D. The number of foxes will not change because it is not connected to worms in the diagram. 7% 9% 5% 6% 7% 6% 11%