Science Assessment ~ Topics ~ Interdependence in Ecosystems ~ Item IE019014 ~ Student Performance

The diagram below shows the feeding relationships between populations of plants and animals in and around a pond. The arrows point from the organisms being eaten to the organisms that eat them.

More people than usual go fishing at the pond this year and take a lot of the large fish out of the pond. Using only the relationships between the plants and animals shown in the diagram, which of the following is likely to happen and why?

The number of insects is likely to decrease because with fewer large fish to eat the tadpoles, there would be more tadpoles eating more water plants and fewer water plants available for the insects.
The number of small fish is likely to decrease because with fewer large fish for the large birds to eat, the large birds would have to eat more small fish.
The number of large birds is likely to stay the same because large fish and large birds are not connected by an arrow in the diagram.
The number of large fish is all that is likely to change because only large fish were taken out of the pond.

Distribution of responses
Answer Choice		Overall	Grades		Gender		Primary Language
		n = 1368	6–8 n = 758	9–12 n = 607	Male n = 683	Female n = 660	English n = 1275	Other n = 68
A.	The number of insects is likely to decrease because with fewer large fish to eat the tadpoles, there would be more tadpoles eating more water plants and fewer water plants available for the insects.	41%	37%	46%	39%	43%	41%	29%
B.	The number of small fish is likely to decrease because with fewer large fish for the large birds to eat, the large birds would have to eat more small fish.	19%	21%	16%	17%	21%	18%	29%
C.	The number of large birds is likely to stay the same because large fish and large birds are not connected by an arrow in the diagram.	24%	24%	24%	26%	22%	24%	22%
D.	The number of large fish is all that is likely to change because only large fish were taken out of the pond.	16%	18%	14%	18%	14%	16%	19%

Science Assessment

Item IE019014: Changes in a population may affect populations that are not directly connected by a feeding relationship even if they are several steps away in a food web (pond ecosystem).