SUMMARY

CONCEPT 14.1 Competition can be direct or indirect, vary in its intensity, and occur between similar or dissimilar species.

14.1.1 Define the difference between exploitation competition and interference competition.

The most common form of competition is exploitation competition, which occurs when species compete indirectly as they share the use of a limiting resource.

Another form of competition, called interference competition, occurs when species compete directly for access to resources.

14.1.2 Analyze how and why competition can vary in its intensity.

If resource levels become sufficiently low, the intensity of competition can increase.

Competition is often asymmetrical, affecting one competitor more strongly than the other.

Competition can occur between closely or distantly related species.

14.1.3 Describe the importance of competition within communities.

Competition for resources is common—though not ubiquitous—in natural communities.

CONCEPT 14.2 Competing species are more likely to coexist when they use resources in different ways.

14.2.1 Define the competitive exclusion principle and explain how it differs from competitive coexistence.

The competitive exclusion principle states that if competing species use the same limiting resource in the same way, they cannot coexist.

In reality, most species show competitive coexistence, or the ability to coexist with one another despite sharing limiting resources.

14.2.2 Define and give examples of resource partitioning (or niche partitioning).

Field studies have revealed many examples of resource partitioning, in which competing species use one or more shared resources in different ways.

14.2.3 Describe how competition can lead to character displacement and resource partitioning.

In character displacement, competition causes the phenotypes of competing species to evolve to become different from each other over time, thereby reducing the intensity of competition and allowing resource partitioning.

CONCEPT 14.3 Competitive interactions can be modeled using the logistic equation.

14.3.1 Formulate the components of the Lotka-Volterra competition model, including the competition coefficient.

Lotka and Volterra modeled the effects of interspecific competition by modifying the logistic equation.

The Lotka-Volterra competition model includes a competition coefficient, which is a constant used to indicate how strong the competitive effect of one species is on another.

14.3.2 Diagram and interpret the four competitive outcomes of the Lotka-Volterra competition model.

Graphical analysis of the Lotka-Volterra competition model allows four predictions for the outcome of competition—three lead to competitive exclusion, and one leads to competitive coexistence.

CONCEPT 14.4 The outcome of competition can be altered by predation, the physical environment, and disturbance.

14.4.1 Describe how herbivores or predators can change or reverse the outcome of competition.

Herbivores or predators can change or reverse the outcome of a competitive interaction if they prefer to feed on the superior competitor.

14.4.2 Explain how the physical environment can affect the outcome of competition and distribution of species.

The physical environment can affect the outcome of competition and ultimately the distribution of species.

14.4.3 Explain how disturbances can allow coexistence in highly asymmetrical competitive interactions.

Periodic disturbances that remove a superior competitor can allow an inferior competitor to persist.

REVIEW QUESTIONS

1. Plant species require nitrogen to grow and reproduce. Assume that a single application of high-nitrogen fertilizer is added to a low-nitrogen, sandy soil in which two plant species are found. Predict how the intensity of competition for soil nitrogen will change over time, and explain your prediction.

2. List four general features of competition described in Concept 14.1, and provide an example of each.

3. Suppose that each of 20 meadows contains a population of plant species 1, a population of plant species 2, or populations of both plant species. Species 1 and 2 are known to compete with each other. Each meadow is separated from the others by areas in which neither species 1 nor species 2 can grow or survive.

a. List three possible reasons why the meadows contain different combinations of the two plant species.

b. Describe an experiment that would help to evaluate one or more of the reasons you have listed.

HONE YOUR PROBLEM-SOLVING SKILLS

As described in Concepts 14.2 and 14.3, laboratory experiments, field observations, and mathematical models have been used to explain why competing species coexist in some situations but not others.

1. From each of these three approaches, describe a result that helps to explain when competing species are likely to coexist. Taken together, do these three approaches to studying competition yield similar or different explanations for why coexistence occurs in some situations but not others?

2. If α = 0.8, β = 1.6, N₁ = 140, and N₂ = 230, are individuals of species 1 or species 2 having a greater effect on the growth rate of species 2?

3. Based on graphical analyses of the Lotka-Volterra competition model, evaluate the following statement: if α < β, species 1 will always drive species 2 to extinction. Explain your answer.

LIST OF KEY TERMS

allelopathy amensalism character displacement competition competition coefficient competitive coexistence competitive exclusion competitive exclusion principle exploitation competition fugitive species fundamental niche interference competition interspecific competition intraspecific competition isocline

Lotka-Volterra competition model niche partitioning realized niche

resource partitioning

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