Download 2 EVOLUTION AND ECOLOGY

2 EVOLUTION AND ECOLOGY
CHAPTER OUTLINE
LEARNING OBJECTIVES
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Describe the events that led to Darwin’s conclusion that evolution occurred through natural
selection.
List the examples from Darwin’s travels that convinced him evolution had taken place.
Explain Malthus’ idea on the tendency for a population to increase geometrically, outpacing its
food supply.
Discuss the process of natural selection, and the consequences of the survival of the most fit.
Describe the example of Darwin’s finches and how adaptive radiation occurs.
Give an example of how geographic isolation promotes species formation.
Define “ecology,” “population,” and “ecosystem.”
Define the term “community” and describe how a community is identified.
Define the terms “niche” and “habitat” and differentiate between the two.
Describe how resource partitioning can lead to character displacement and thereby decrease
competition.
Define the term “predation,” distinguish between the predator and prey species, and discuss how
cycling between them occurs.
Define the terms “symbiosis,” “commensalism,” “mutualism,” and “parasitism,” and give
examples of each.
Evolution (p. 24)
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Darwin’s Voyage on H.M.S. Beagle (p. 24; Figs. 2.1, 2.2, 2.3)
A. English naturalist, Charles Darwin (1809–1882) was the first to propose natural selection as a
mechanism of evolution in On the Origin of Species by Means of Natural Selection.
B. In Darwin’s time, most people believed that species were created supernaturally once and
remained unchanged through time.
1. The views of Darwin put him at odds with most people of his time.
C. One of the most influential events in Darwin’s life was his five-year journey as ship’s
naturalist aboard the H.M.S. Beagle.
1. During this voyage around the coasts of South America, Darwin observed tropical
forests, fossils of extinct mammals in Patagonia, and related but distinct species on the
Galapagos Islands.
Darwin’s Evidence (p. 26; Figs. 2.4, 2.5)
A. The fossils and patterns of life that Darwin observed on his voyage led to his conclusion that
evolution had occurred.
B. The writings of geologist Charles Lyell (1797–1875) were highly influential to Darwin during
his voyage.
1. Lyell believed, unlike most people of his day, that the earth was extremely old.
C. What Darwin Saw
1. Fossils of extinct armadillos were similar in form to living species.
2. On the Galapagos Islands, several species of giant tortoises were observed on different
islands.
3. Darwin saw that plants and animals on these islands resembled those on the mainland, but
were distinctly different.
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The Theory of Natural Selection (p. 27; Figs. 2.6, 2.7, 2.8)
A. Darwin and Malthus
1. Mathematician Thomas Malthus (1798) wrote Essay on the Principle of Population in
which he pointed out that human populations tend to increase geometrically while food
supplies increase arithmetically.
2. However, populations remain fairly constant year after year because death limits
population size.
3. Malthus’s ideas provided the key that was needed for Darwin to develop his hypothesis
that evolution occurs by natural selection.
B. Natural Selection
1. Darwin now saw that each population could produce enough offspring to outstrip its
food supply, but only a limited number survived to reproduce.
2. This led Darwin to the idea of “survival of the fittest” in which only those organisms that
were well-adapted survived long enough to reproduce.
3. The traits of organisms that survive to produce more offspring will be more common in
future generations.
4. Darwin’s theory provides a simple and direct explanation for biological diversity.
C. Darwin Drafts His Argument
1. Darwin wrote a draft of his ideas in 1842, then turned to other research for sixteen years.
D. Wallace Has the Same Idea
1. English naturalist Alfred Russell Wallace (1823–1913) wrote an essay about his own
ideas on evolution by natural selection from his observations in Malaysia.
2. Darwin and Wallace gave a joint presentation, then expanded his 1842 manuscript.
E. Publication of Darwin’s Theory
1. Darwin’s book appeared in 1859 and began a controversy about the origin of humans.
2. After 1860, Darwin’s ideas were widely accepted in the intellectual community of Great
Britain.
Darwin’s Finches: Evolution in Action (p. 29)
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The Beaks of Darwin’s Finches (p. 29; Figs. 2.9, 2.10, 2.11)
A. Darwin’s finches from the Galapagos Islands are a classic example of evolution by natural
selection.
B. The Importance of the Beak
1. Beak shape of this group of 13 species of finches indicated a correspondence between
shape and food source.
C. Was Darwin Wrong?
1. David Lack set out to test Darwin’s hypothesis in 1938 and observed many different
species of finches eating the same seeds.
D. A Closer Look
1. In 1973, the Grants of Princeton University discovered a relationship between beak
shape, seed size, and climatic conditions which indicated that beak size was passed on
from one generation to the next, and survival rate was adjusted to the food supply.
E. Support for Darwin
1. Natural selection does seem to be operating to adjust the beak to its food supply.
How Natural Selection Produces Diversity (p. 32; Fig. 2.12)
A. Darwin’s finches, all derived from one similar mainland species, exhibit adaptive radiation of
the Galapagos Islands in the absence of competition.
B. Four groups of finches have been recognized from these islands: ground finches, tree finches,
a warbler finch, and a vegetarian finch.
Ecology (p. 33)
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What Is Ecology? (p. 33; Fig. 2.13)
A. Ecology is the study of how organisms that live in a place interact with each other and their
physical habitat.
B. Levels of Ecological Organization
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Populations are members of the same species that live together and potentially breed
with one another.
2. Communities are made up of populations of different species that utilize different
resources within the habitat that they share.
3. Ecosystems are the communities interacting with their nonliving habitats; ecosystems
regulate the flow of energy and cycling of nutrients.
4. Biomes are major terrestrial assemblages of plants, animals, and microorganisms that
occur over wide geographic areas as predicted by climate.
5. Population ecologists study the dynamics of a species; community ecologists study how
species interact with each other; systems ecologists are interested in how biological
communities interact with their physical habitats.
A Closer Look at Ecosystems (p. 34; Figs. 2.14, 2.15)
A. Ecosystems are the fundamental units of ecology.
B. Energy Flows Through Ecosystems
1. All of the energy that passes through a community comes ultimately from the sun.
2. Energy flows through the ecosystem from plant to herbivore to carnivore.
C. Materials Cycle Within Ecosystems
1. As organisms decompose after death, the materials of their bodies pass back into the
ecosystem.
2. Materials cycle between organisms and their physical environment.
D. Major Ecosystems
1. The two most important factors determining the nature of an ecosystem in an area are
rainfall and temperature.
2. On land, similarly adapted plants and animals make up major ecosystem types, called
biomes.
Communities (p. 35; Fig 2.16)
A. A community is all of the living organisms, both plant and animal, that live together in a
specific area.
B. A community is defined by the dominant species present, although many other different
types of organisms are also characteristic.
C. A community exists in a specific area because the ranges of its species overlap there.
The Niche and Competition (p. 36; Figs. 2.17–2.19)
A. The Niche Concept
1. An organism’s niche is the role it plays within the community, including how it exploits
all of the resources (space, food, etc.) of its environment.
2. When there are two organisms attempt to make use of a limited resource, competition
results.
B. Interspecific Competition
1. This type of competition occurs when two organisms of different species attempt to use
the same resources.
2. Interspecific competition is greatest between organisms that obtain food in similar
ways.
C. Intraspecific Competition
1. This form of competition occurs between two members of the same species competing
for the same resource.
How Species Evolve to Occupy Different Niches Within an Ecosystem (p. 37; Figs. 2.20,
2.21)
A. Habitat is where an organism lives.
B. Resource Partitioning
1. The principle of competitive exclusion states that no two species with the same niche
can coexist.
2. Persistent competition between species is rare because one will drive the other to
extinction or natural selection will favor changes that decrease the competition.
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Resource partitioning allows two species to live in the same habitat by exploiting
different parts of the habitat, or different food sources.
4. Character displacements are the differences that evolve between two species to
decrease competition for resources.
Predation (p. 38; Figs. 2.22–2.24)
A. Predation is the consuming of one organism by another; the organism that is eaten is the
prey and the organism that is doing the eating is the predator.
B. Predator/Prey Cycles
1. When the population numbers of prey decline, there is a resulting decline in predator
numbers.
2. This allows the prey population to recover, which in turn allows the predator
population to increase.
3. These increases and decreases in numbers result in cycles of relative abundance of
predator and prey species.
C. Defense Mechanisms
1. Animal defense mechanisms include chemical defenses, warning coloration, and
camouflage.
2. Plant defenses against herbivores include physical mechanisms (spines, thorns, and
prickles) and chemical mechanisms.
3. Chemical defenses in plants are more important, and include both foul-tasting and toxic
products.
D. Coevolution
1. The long-term reciprocal evolutionary adjustments that occur between predator and
prey species are called coevolution.
Symbiosis (p. 39; Figs. 2.25–2.27)
A. Symbiosis is a relationship in which two or more organisms interact.
B. Commensalism
1. Commensalism is a form of symbiosis in which one organism benefits and the other is
neither benefitted nor harmed.
C. Mutualism
1. Mutualism is a form of symbiosis in which both organisms benefit from the interaction.
D. Parasitism
1. Parasitism is a symbiotic relationship in which one organism is benefited and the other
is harmed.
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KEY TERMS
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evolution (p. 24)
natural selection (p. 24)
On the Origin of Species (p. 24) If possible, get a copy of this book from the school library and
show it to the students during lecture. Read a few excerpts to help your students understand the
depth of Darwin’s ideas.
Galapagos Islands (p. 25)
adaptive radiation (p. 32) Evidence from island biogeography and adaptive radiation are among
the most convincing arguments for evolution as a result of natural selection. Point out any local
examples from your own ecosystem.
ecology (p. 24) The study of ecology is not synonymous with the study of environmental concerns.
Community (p. 35)
Niche (p. 36)
Habitat (p. 37)
Interspecific competition (p. 36)
Intraspecific competition (p. 36)
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Resource partitioning (p. 37)
Character displacement (p. 37)
Predation (p. 38)
Symbiosis (p. 39)
Mutualism (p. 39)
Commensalism (p. 39)
Parasitism (p. 39)
LECTURE SUGGESTIONS AND ENRICHMENT TIPS
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Lead a discussion with your students involving their cultural or religious beliefs about the origin of life
on earth. Ask several students how they think they, as humans, got to be here. Then describe
creationism and naturalist evolution as two distant ends of the spectrum and mention that there is room
for intermediate ideas. By introducing evolution in this manner, any students who fear discussing
evolution will relax and feel more open to the subject. Be sure to mention that evolution, as a scientific
theory, is the only one of these alternatives that can be tested scientifically.
Discuss examples of artificial selection with students. If they can see how artificial selection operates,
natural selection becomes easy to understand. Darwin used artificial selection as a model to illustrate
natural selection. Describe how dog breeds, for example, are the result of thousands of years of
artificial selection, with a wolf as the original animal about 14,000 years ago. Other examples include
the variety of foods of the cabbage family (brussels sprouts, kohlrabi, Chinese cabbage) that have all
been developed from a single species of Brassica.
Discuss the composition of the community in which your school is located. Identify some of the
populations of plants and animals. Have students identify some examples of symbiotic relationships in
the community.
CRITICAL THINKING QUESTIONS
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How might it be possible to reestablish the diversity of cichlid fishes in Lake Victoria? Or, is it
possible? Discuss your ideas either way. Then, devise a plan that might help the lake to recover to its
historical condition.
Are the recent outbreaks of Ebola, AIDS, and tuberculosis that are especially prevalent in crowded,
economically poor conditions examples of how nature regulates population size? How could the idea of
“survival of the most fit” apply here?
Discuss why human populations have expanded rapidly and sometimes uncontrollably since the 1700s.
Does a well-adapted parasite always kill its host? Why might this not be a good strategy?
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