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25.1 Interactions among competing species shape ecological niches.
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• Each species plays a specific role in its ecosystem; this role is called its niche.
• An organism's fundamental niche is the total niche that the organism would occupy in the absence of competition. Its realized niche is the actual niche it occupies in nature.
• Two species cannot occupy the same niche for long if resources are limiting; one will outcompete the other, driving it to extinction.
• Species can coexist by partitioning resources to minimize competition.
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1. What do you think would be the difference between interspecific competition and intraspecific competition? What is Gause's principle of competitive exclusion?
2. Is the term niche synonymous with the term habitat? Why or why not? How does an organism's fundamental niche differ from its realized niche?
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25.2 Predators and their prey coevolve.
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• Predator-prey relationships are of crucial importance in limiting population sizes in nature.
• Plants are often protected from herbivores by chemicals they manufacture.
• Warning, or aposematic, coloration is characteristic
of organisms that are poisonous, sting, or are otherwise harmful. In contrast,
cryptic coloration, or camouflage, is characteristic of nonpoisonous organisms.
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3. What morphological defenses do plants use to defend themselves against herbivores?
4. Consider aposematic coloration, cryptic coloration, and Batesian mimicry. Which would be associated with an adult viceroy butterfly? Which would be associated with a larval monarch butterfly? Which would be associated with a larval viceroy butterfly?
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25.3 Evolution sometimes fosters cooperation.
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• Coevolution occurs when different kinds of organisms evolve adjustments to one another over long periods of time.
• Many organisms have coevolved to a point of dependence.
in commensalism, only one organism benefits while the other is unharmed;
in mutualism the relationship is mutually beneficial; and in parasitism
one organism serves as a host to another to the host's disadvantage.
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5. Why is eliminating predators a bad idea for species richness?
6. How can predation and competition interact in regulating species diversity of a community?
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25.4 Ecological succession may increase species richness.
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• Primary succession takes place in barren areas, like rocks or open water. Secondary succession takes place in areas where the original communities of organisms have been disturbed.
• Succession occurs because of tolerance, facilitation, and inhibition.
• Disturbance can disrupt successional changes. In some
cases, disturbance can increase species richness of a community.
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7. Why have scientists altered the concept of a final, climax vegetation in a given ecosystem? What types of organisms are often associated with early stages of succession? What is the role of disturbance in succession?
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