Key Idea: All organisms, both land-based and aquatic, are connected to other organisms by their need for food. This results in a global network of interconnections, which is referred to as a food web.

Students are expected to know that:

  1. When organisms eat or are eaten by other organisms, there is an effect on the two organisms involved and on the populations to which they belong.
  2. When organisms eat or are eaten by other organisms, there may be an effect on other populations that are not eating or being eaten by those organisms. This is because once an individual organism (or part of an organism) is eaten, it is no longer available as food for other populations of organisms and/or will no longer eat other organisms from other populations.
  3. Changes in the size of a population may result from changes in the size of the populations of organisms that it consumes, that consume it, or both.  Specifically, if the size of a population increases  (or is introduced), the size of a population of organisms that consumes it may increase because there will be more food available to that population, and if the size of a population increases (or is introduced), the size of a population of organisms that it consumes may decrease because more of them may be consumed. If the size of a population decreases (or the population disappears), the size of a population of organisms that consume it may decrease because less food is available to that population, and if the size of a population decreases (or the population disappears), the size of a population of organisms that it consumes may increase because there are fewer organisms to consume them.
  4. Changes to the size of populations of organisms due to changes in the size of populations it consumes or that consume it take time, and the relative sizes of the starting populations involved may affect the outcome.
  5. The network of populations of organisms being eaten by other populations can be thought of as a single global food web encompassing all populations, but food webs can also be described for populations in particular environments.
  6. Feeding interactions among selected populations of organisms in food webs can be represented by diagrams with arrows from populations being eaten to populations doing the eating. If an arrow is not present in a diagram, there is no feeding interaction between two populations, and if an arrow is present, there is a significant feeding interaction between the two populations.

Boundaries:

  1. Students are not expected to know that microorganisms are part of food webs. This is addressed in a later idea.
  2. Students are not expected to know the terms producer, consumer, or trophic level.
  3. Students are not expected to know what any particular organism eats apart from what can be determined from food web diagrams they are given.
  4. Students are not expected to know that although a population may be connected by arrows to more than one population, organisms may rely on some organisms more than others for food.
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number
Knowledge Being Assessed Grades
6–8
Grades
9–12
Select This Item for My Item Bank

ID029006

Changes in a population of organisms in a food web (worms) can affect the population of its predator (robins).

84%

80%

ID032005

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.

73%

79%

ID031007

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.

70%

81%

ID027005

Changes in a population in a food web (grasshoppers) can affect the populations of both its predator (frogs) and its prey (grass).

66%

78%

ID026005

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 (no specific organisms indicated).

72%

74%

ID026004

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 (ocean ecosystem).

69%

77%

ID014004

Changes in a population in a food web (robins) can affect the population of its prey (caterpillars).

66%

74%

ID029005

Changes in a population in a food web can affect the population of its predator (no specific organisms identified).

63%

74%

ID031006

Changes in a population in a food web can affect other populations of organisms even if they are not directly connected in a feeding relationship (no specific organisms identified).

63%

72%

ID019016

Changes in a population in a food web (large fish) can affect the population of its prey (tadpoles).

61%

69%

ID073004

Changes in a population in a food web can affect the population of its prey (no specific organisms identified).

59%

68%

ID032004

Changes in a population in a food web can affect populations of other organisms even if they are not directly connected in a feeding relationship (no specific organisms identified).

56%

68%

ID027004

Changes in a population in a food web can affect the populations of both its predator and its prey (no specific organisms identified).

55%

66%

ID012012

Changes in a population in a food web (wolves) can affect populations of other organisms (grass) even if they are not directly connected in a feeding relationship (text only, no diagram).

55%

58%

ID034005

Changes in a population (rabbits) may affect populations that are not directly connected by a feeding relationship (crickets) even if they are several steps away and not within the same chain in a food web.

51%

62%

ID012011

Changes in a population in a food web (wolves) can affect populations of other organisms (grass) even if they are not directly connected in a feeding relationship.

53%

57%

ID020004

Changes in a population (fish in a pond) may affect populations that are not directly connected in a feeding relationship (large birds).

52%

57%

ID025005

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 (no specific organisms identified).

50%

53%

ID025004

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 (woodland ecosystem).

44%

53%

ID028006

Changes in a population (frogs) may affect populations that are not directly connected by a feeding relationship (mice) even if they are several steps away and not within the same chain in a food web.

34%

45%

ID019014

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).

37%

46%

ID028005

Changes in a population may affect populations that are not directly connected by a feeding relationship even if they are several steps away and not within the same chain in a food web (no specific organisms identified).

35%

42%

ID019015

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

35%

40%

ID017005

Changes in a population (introduction of a new organism) may affect populations that are not directly connected by a feeding relationship even if they are several steps away in a food web (woodland ecosystem).

29%

38%

ID017006

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 (woodland ecosystem).

20%

28%

ID016008

Changes in a population (introduction of a new species) may affect populations that are not directly connected by a feeding relationship (caterpillars) even if they are several steps away in a food web.

20%

27%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

IEM022

If a population in a food web is disturbed, there will be little or no effect on populations that are not within the linear sequence in the food web (Webb & Boltt, 1990).

31%

30%

IEM065

Varying the size of a population of organisms will affect only those populations of organisms that are directly connected to it in a feeding relationship, not organisms that are one or more steps removed/away from it (Griffiths & Grant, 1985; Webb & Boltt, 1990).

20%

19%

IEM021

If a population in a food web is disturbed, there will be little or no effect on populations below it in the food web (e.g. if a predator is removed, no effect on prey: Webb & Boltt, 1990; Leach, 1996).

18%

15%

IEM006

Organisms higher in a food web eat everything that is lower in the food web (Griffiths & Grant 1985).

15%

12%

IEM030

If the size of one population in a food web is altered, all other populations in the web will be altered in the same way (Griffiths & Grant, 1985).

12%

8%

IEM029

A change in the size of a prey population has no effect on its predator population (Griffiths & Grant, 1985).

10%

8%

IEM061

Changes in a population in a food web do not affect the populations of any other organism in the food web (AAAS Project 2061, n.d.).

10%

8%

IEM047

The top predator in a food web will never be significantly affected by changes in the populations of organisms below it in the food web (AAAS Project 2061, n.d.).

9%

7%

Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.