Key Idea: Given adequate resources and an absence of disease or predators, populations of organisms in ecosystems can increase at rapid rates. Finite resources and other factors limit their growth.

Students are expected to know that:

  1. Individual organisms are added to a population by birth and removed by death so that populations increase when the number of births is greater than the number of deaths and populations decrease when the number of births is smaller than the number of deaths.
  2. Disease, predators, and availability of resources can affect how many individuals in a population die and how many offspring are produced and how the size of a population can change over time. 
  3. In the absence of factors that lead to the death of organisms in a population or a reduction in the number of offspring they produce, the size of a population will grow faster and faster (more and more between consecutive equal time points).
  4. Populations do not grow infinitely large in nature because there is always at least one factor, including disease, predators, and availability of resources, that limit the growth of a population.

Boundaries:

  1. The idea that immigration or emigration (organisms moving into or out of a population or environment) can affect the size of the population of organisms in a particular environment is not part of the scope of this idea.
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

IE077002

Populations increase when the number of births is greater than the number of deaths.

73%

81%

IE042007

The size of a population of organisms (deer) can increase when its predators are removed from an area because the deer can live longer and have more offspring that also live longer (text only, no food web diagram).

70%

80%

IE079002

Populations decrease when the number of births is less than the number of deaths.

71%

79%

IE085001

Both disease and the number of predators can limit population growth.

65%

79%

IE086001

Disease and the availability of resources can limit population growth.

62%

81%

IE042006

The size of a population of organisms can increase when its predators are removed from an area because the organisms live longer and have more offspring that also live longer (includes a food web diagram).

67%

73%

IE045003

The size of a population of organisms (deer) can increase when its predators are removed from an area because the organisms can live longer and have more offspring that also live longer (includes a food web diagram).

63%

74%

IE084001

Both the number of predators and the availability of resources can limit the growth of a population of organisms.

54%

72%

IE081002

The size of populations of squirrels can increase when there is an increase in the food available and a decrease in the number of predators.

55%

69%

IE081003

The size of populations of robins can increase when there is an increase in the food available and a decrease in the number of its predators.

57%

64%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

IEM006

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

16%

11%

IEM014

Populations exist in states of either constant growth or decline (Munson 1991).

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.