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2 EVOLUTION AND ECOLOGY
EXTENDED LECTURE OUTLINE
Evolution (p. 22)
2.1
2.2
2.3
Darwin’s Voyage on H.M.S. Beagle (p. 22; 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. 24; 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.
The Theory of Natural Selection (p. 25; 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.
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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. 27)
2.4
2.5
The Beaks of Darwin’s Finches (p. 27; 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. Darwin Was Right After All
1. Natural selection does seem to be operating to adjust the beak to its food supply.
How Natural Selection Produces Diversity (p. 30; 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. 31)
2.6
2.7
What Is Ecology? (p. 31; 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
1. 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. 32; Fig. 2.14)
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.
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2.8
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.
How Species Evolve to Occupy Different Niches Within an Ecosystem (p.33; Fig2.15, 2.16)
A. Resource Partitioning
1. Species that live in the same geographical area avoid competition by exploiting
different resources.
2. Character displacements reduce niche overlap as seen among Darwin’s finches.
Populations and How They Grow (p. 34)
2.9
2.10
Patterns of Population Growth (p. 34; Figs. 2.17, 2.18, 2.19, 2.20)
A. The rate at which a population will increase when there are no limits on its growth is called
the biotic potential.
B. Population ecologists usually calculate r as the realized rate of population increase, which is
the number added to the population (birth + immigration) minus the number lost from it
(death + emigration).
C. Exponential Growth
1.
A population’s innate capacity for growth is largely dependent on its physiology.
2.
When population growth rate = rN, where N = population size, then growth is
exponential.
D. Carrying Capacity
1. A population usually stabilizes at its carrying capacity.
2. The logistic growth equation, which describes sigmoid growth, is as follows:
population growth rate = rN (K-N)/K where K is the number of individuals that can be
supported at one place indefinitely.
E. Life History Strategies
1.
Most populations exhibit characteristics between traits that favor exponential growth (rselected life history strategy) and those that favor slower growth and are good
competitors for limited resources (K-selected life history strategy).
2.
Organisms in transient environments are often adapted to reproduce rapidly, while
those in stable environments tend to reproduce more slowly.
Human Populations (p. 36; Figs. 2.21, 2.22, 2.23, 2.24; Table 2.1)
A. Humans exhibit many K-selected life history traits that evolved during the early history of
hominids.
B. Throughout human history, populations have been regulated by food availability, disease,
and predators.
C. The Advent of Exponential Growth
1.
Starting in the 1700s, technology led to the development of superior weapons, cures for
many diseases, and improvements in shelter and food storage.
2.
These changes led to an explosive population growth over the last 300 years.
3.
Both the current human population level and the projected growth rate have potentially
grave consequences for our future.
D. Population Pyramids
1. Population growth is not uniform over the planet, and some countries experience much
more rapid growth than do others.
2.
Populations whose “pyramids” are rectangular are neither growing nor shrinking.
3.
A triangular pyramid is characteristic of a country that will exhibit rapid future growth.
4.
Inverted triangles are characteristic of populations that are shrinking.
E. The Level of Consumption in the developed world is also a problem.
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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.”
Differentiate between exponential and logistic population growth and the conditions under which each
occurs.
State why the human population has been growing rapidly for the past 300 years.
KEY TERMS
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evolution (p. 22)
natural selection (p. 22)
On the Origin of Species (p. 22) 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. 23)
adaptive radiation (p. 30) 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. 31) The study of ecology is not synonymous with the study of environmental concerns.
population (p. 31)
ecosystem (p. 31)
resource partitioning (p.33)
biotic potential (p. 34) This only occurs under ideal conditions, which are rarely met for long, and is
opposed by environmental resistance (factors that could result in early death).
exponential growth (p. 34) A good analogy for exponential growth is that it occurs in a way similar to
compound interest.
carrying capacity (p. 35) Discuss whether the carrying capacity for the human population has been
reached.
life history strategy (p. 35) Make a table on the chalkboard comparing life history traits of r and K
strategists and discuss which traits are more suitable to transient and to stable habitats.
Ecological footprint (p. 38)
LECTURE SUGGESTIONS AND ENRICHMENT TIPS
1.
2.
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.
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3.
Consider China’s example of one child per family as a means of population control. Ask your students
whether they would be willing to restrict the size of their families to one child. Are there any drawbacks
to this approach?
CHANGES TO THE NEW EDITION
Refer to the Johnson instructor web site at http://www.mhhe.com/biosci/genbio/tlw4 for a complete list of
changes to this edition.
CRITICAL THINKING QUESTIONS
1.
2.
3.
4.
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.
Comment on Malthus’ ideas about population growth and food supply as they relate to projected future
population growth in developing countries.
FILMS/MEDIA SUGGESTIONS
(Telephone and fax numbers and/or web sites for the sources of the following materials are listed in the
Appendix.)
Charles Darwin Explains the Diversity of Life. This video explains the work of Charles Darwin and how
the theory of evolution laid the foundation for all modern biological thought. 1994. 21 minutes.
Hawkhill Video, #192
Evolution. This two-part video teaches the basics of modern evolutionary theory. Part I explains how the
theories of evolution were developed. Part II shows evolution by natural selection. 1994. 38 minutes.
Hawkhill Video, #108
The Evidence for Evolution. The nature of the evidence in support of the theory of evolution is explained
here. 30 minutes.
CLEARVUE/eav WWW5VH 1192
Organic Evolution. This video compares biblical accounts of creation with scientific evidence for
evolution. Other topics included are Darwin's contributions, Hardy-Weinberg law, genetic drift, and the
upward progression of species. Six-part series, each 10 minutes.
Ward's Biology, 193 W 0313 VHS
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