Chapter 7. Chapter 7: Population Ecology

What is carrying capacity...?

Why You Should Care

Carrying capacities are the theoretical maximum sustainable population sizes predicted by the amount of resources available. If you think back to past chapters, it should be easy to see why carrying capacities are important. Organizations like the United Nations are working hard to predict whether humans are overshooting their carrying capacity and how long it will take the global population to stabilize and to prepare for the possibility of a population crash. What does overshooting the carrying capacity look like for humans? There is a real possibility that we soon may not have enough water, farmland, or energy resources on a global scale for the human population. History tells us that, when resources are scarce on a local scale, large-scale social upheavals will ensue. Studying populations of other species will give us insight into our own.

Examine the idealized population growth curve below and answer the questions that follow:

2.

Are the factors that cause the crash after overshooting the carrying capacity more likely to be density independent or density dependent? --------Density independentDensity dependent

999

Try again.

Correct. Since the crash appears to be the result of an increase in population size, it is logical to conclude that density-dependent factors such as resource competition or predation are at play.

Incorrect. Since the crash appears to be the result of an increase in population size, it is logical to conclude that density-dependent factors such as resource competition or predation are at play.

3.

Thought Questions: Explain two reasons that a crash could occur in a population of:

A) a primary consumer—in other words, a prey animal.

B) a secondary consumer—that is, a predator.

A) Example of two plausible reasons: When populations of the prey species overshoot their carrying capacities, the population could decline because of competition with other members of the population for food or because dense populations are more easily hunted by predators.

B) Example of two plausible reasons: Predator populations will also suffer from having too much competition for food resources. They are also more susceptible to infectious disease.

4.

Examine the population data for wolves and moose on Isle Royale and answer the questions that follow:

Which of the following statements is FALSE?

A.

An increase in moose numbers is usually followed by an increase in wolf numbers.

B.

The moose population does not remain at its carrying capacity.

C.

Both density-dependent and density-independent factors have affected the moose population.

D.

Just before the 1980 parvovirus, the wolf population was at its highest recorded point, which was very close to the highest point for moose around 1995.

999

Try again.

Correct. Close inspection of the graph will show you that the wolf and moose populations are actually represented at two different scales. There are actually always far fewer wolves than moose.

Incorrect. Close inspection of the graph will show you that the wolf and moose populations are actually represented at two different scales. There are actually always far fewer wolves than moose.

5.

Thought Question: Do you think that density-dependent or density-independent factors are more important influences on wolf and moose populations at Isle Royale?

The fact that the two populations fluctuate in response to each other suggests that density-dependent factors are the most important. In other words, density-dependent competition for resources causes both species' populations to crash. Disease is also a liability of high population densities. Density-independent factors like harsh winters will impact populations but aren’t predictable enough to cause the cycles seen in wolf and moose populations.

Activity results are being submitted...