14.5.2 Population Ecology: The Reality of Limited Resources

Question 1

Population Ecology: The Reality of Limited Resources

Answer 1

• The exponential growth model charts a population undergoing unlimited size increase.
• Under real conditions resources limit the growth of populations.
• The logistic growth model charts a population undergoing limited size increase. Logistic growth is characterized by an initial increase in the rate of growth. After the point of inflection, this rate of increase decreases until it reaches zero at the population’s carrying capacity.
• Carrying capacity is the maximum size of a population that can be maintained by the resources of the area it occupies.

Question 2

exponential growth model

Answer 2

• In 1937, a small group of ring-necked pheasants was
  introduced to Protection Island, off of the coast of Washington state. By 1940, the population had exploded to 1,000 birds.
• The first graph compares growth of the pheasant population (the jagged pink line) to an exponential growth model (the smooth blue line). In 1941 and 1942, the population continued to grow, but at a slower rate. The second graph illustrates the slower rate of growth that occurred after 1940.
• At first, the population seemed to be experiencing exponential growth. Eventually, however, limited resources (such as food or nesting sites) limited the population’s growth.

Question 3

logistic growth model

Answer 3

• The graph on the left illustrates the logistic growth model. The first part of the curve shows the population experiencing increasing growth rates over time. After the point of inflection, the population is still increasing in size but the rate of increase in growth is decreasing. When the population reaches carrying capacity (represented by the horizontal broken line), the change in the population equals zero, and there is no further increase in the population.

Question 4

Carrying capacity is expressed in units of

Answer 4

• numbers of individuals

Question 5

True or false?

The model for logistic growth includes a portion in which the population is decreasing.

Answer 5

• false

Question 6

In the first phase of logistic growth, the rate of change of the population _____________, in the second phase the rate of change of the population ___________________.

Answer 6

• is increasing; is decreasing

Question 7

In 1937 8 ring-necked pheasants were introduced on Protection Island. By 1940, their numbers had increased to about 1000. However after 1940, the numbers stopped increasing and remained around 1000. Which statement best describes what happened?

Answer 7

• The pheasants followed a logistic growth curve.

Question 8

Which of the following is not a limitation of the logistic growth model?

Answer 8

• It assumes that resources are unlimited.

Question 9

What is the rate of change of a population when it has reached its carrying capacity?

Answer 9

• 0