Download Answers to Review Questions

Answers to Review Questions
Evolution: How Populations Change Over Time (p. 68)
1. What are Darwin's four premises of evolution by natural selection?
Ans: Natural selection, as envisioned by Charles Darwin, has four premises:
1. Each species produces more offspring than will survive to maturity.
2. The individuals in a population exhibit inheritable variation in their traits.
3. Organisms compete with one another for the resources needed to survive.
4. Those individuals with the most favorable combination of traits are most likely to survive and
reproduce, passing their genetic characters on to the next generation.
Biological Communities (p. 73)
1. What is ecological succession?
Ans: Ecological succession is the orderly replacement of one community by another.
2. How do primary and secondary succession differ?
Ans: Primary succession is the change in species composition over time in a previously
uninhabited environment. Secondary succession is the change in species composition that takes
place after some disturbance destroys the existing vegetation; soil is already present.
Interaction Among Organisms (p. 79)
1. What is symbiosis? What are the three kinds of symbiosis?
Ans: Symbiosis, any intimate relationship or association between members of two or more
species, includes mutualism, commensalism, and parasitism. Mutualism is a symbiotic
relationship in which both partners benefit. Commensalism is a type of symbiosis in which one
organism benefits and the other one is neither harmed nor helped. Parasitism is a symbiotic
relationship in which one organism benefits and the other is adversely affected.
2. What is predation? Describe how evolution has affected predator-prey relationships.
Ans: Predation is the consumption of one species (the prey) by another (the predator). During
coevolution between predator and prey, the predator evolves more efficient ways to catch prey,
and the prey evolves better ways to escape the predator.
3. What is competition? What are the two main kinds of competition?
Chapter 4
Ans: Competition is the interaction among organisms that vie for the same resources (such as
food or living space) in an ecosystem. Competition occurs among individuals within a population
(intraspecific competition) or between species (interspecific competition).
The Ecological Niche (p. 82)
1. What is an ecological niche?
Ans: An organism's ecological niche is the totality of its adaptations, its use of resources, and the
lifestyle to which it is fitted.
2. What are limiting resources? How might a limiting resource affect a species' ecological niche?
Ans: A limiting resource is any environmental resource that, because it is scarce or at
unfavorable levels, restricts the ecological niche of an organism.
3. What is the principle of competitive exclusion? resource partitioning?
Ans: Many ecologists think no two species occupy the same niche in the same community for an
indefinite period. In competitive exclusion, one species excludes another as a result of
competition for limited resources. Some species reduce competition by resource partitioning, in
which they use resources differently.
Keystone Species (p. 83)
1. What is a keystone species? Why is the wolf considered a keystone species?
Ans: A keystone species is a species, often a predator, that exerts a profound influence on a
community in excess of that expected by its relative abundance. The wolf is considered a
keystone species because in areas where wolves were hunted to extinction, the populations of elk
and other herbivores increased. As these herbivores overgrazed the vegetation, many plant
species disappeared. Many smaller animals such as insects were lost because the plants they
depended on for food were now less abundant. Thus, the disappearance of the wolf resulted in an
ecosystem with considerably less biological diversity.
Species Richness (p. 86)
1. What are two determinants of species richness? Give an example of each.
Ans: Several factors appear to be significant in determining species richness, the abundance of
potential ecological niches, closeness to the margins of adjacent communities, geographic
isolation, dominance of one species over others, habitat stress, and geologic history. For
example, in a study of chaparral habitats (shrubby and woody areas) in California, those with
50
Chapter 4
structurally complex vegetation provided birds with more kinds of food and hiding places than
communities with low structural complexity.
2. What are ecosystem services? Describe some ecosystem services a forest provides.
Ans: Ecosystem services are important environmental benefits that ecosystems provide, such as
clean air to breathe, clean water to drink, and fertile soil in which to grow crops.
51