Visual Understanding

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Chapter 2 answers

Evolution and Ecology

Visual Understanding

Fig. 2.15

Using Darwin’s reasoning explain how these four species of lizards, all closely related, came to be separate species on a Caribbean island.
Like Darwin’s finches, perhaps only a few individual lizards originally landed on an island. Since there was no competition, the lizard population quickly grew, and different groups of lizards began to inhabit different niches, living in separate areas of the habitat and eating different food items. Over time, they became separate species.
Fig. 2.23

In the 1960s and 1970s the United States needed huge numbers of new schools, homes and then jobs for the children of the “baby boom” that occurred after World War II. Looking at where the “baby boom” bulge is by the year 2000, what goods and services are they going to need in the 2010s and 2020s? What other changes might occur?

As the “Boomers” begin to retire they will need more medical care, leisure time activities, and possibly public transportation as they continue to age and stop driving. There will probably be a huge drain on Social Security, retirement programs, and Medicare. There will be huge numbers of jobs, and possibly houses, available for a smaller number of individuals in the groups behind the Boomers – Gen X, Gen Y, and those to come. Answers may vary.
Challenge Questions


Many evolutionary pathways seem to have moved from larger to smaller organisms over time, such as the glyptodont and the armadillo, the mammoth and the elephant. Yet with other organisms, such as the tiny eohippus and the horse, they have increased in size. Explain how this can occur.
The attributes that help an organism live in its environment might be physical, physiological, or behavioral. Size is just one factor out of many. If an increase, or a decrease, in size helps an organism do better in its environment than other members of its species, then it is more likely to survive and produce offspring like itself.
Darwin’s Finches: Evolution in Action

Your friend Gustavo tells you that he has heard about the work of the famous scientist, David Lack, and that it proves Darwin was wrong about evolution and modification over time. What do you say?

The year that Dr. Lack went to the Galapagos to study Darwin’s finches happened, by chance, to have been a very rainy year, and there was a bounty of seeds. There was no competition for food that year, and all the species ate whatever seeds were available at the moment. When other researchers studied the finches for longer periods of time, during wet years and during dry years, they found that Darwin’s ideas were correct.

Chthamalus is a small barnacle that lives on rocky shores. It can survive on rocks that are underwater, or on rocks that are exposed during low tide. Balanus is a larger barnacle that can outcompete Chthamalus if they both want the same spot. Balanus can only live on rocks that are seldom exposed to air. Explain what happens when they both present.
Chthamalus has a wide niche, but is outcompeted when Balanus is present. The principle of competitive exclusion says that one of them will have to change in order to reduce the competition. Therefore you will find resource partitioning in these areas; Balanus will be low on the rocks, covered by water most of the time, and Chthamalus will be higher on the rocks, exposed during low tides.
Populations and How They Grow

People in the United States require an average of over 30 acres of land to support each individual, while in Indonesia, Nigeria and India each person needs only about 2.5 – 4 acres. The figure for the US is also about double that of some other highly industrialized countries, such as Germany. Explain the differences, and suggest ways to decrease the US figures.

People in Indonesia, Nigeria and India eat diets low in animal protein and high in vegetable carbohydrates. It takes far more acres to raise a cow to be used for hamburger, roasts, and steaks, than to raise broccoli, carrots, tomatoes, corn, wheat and rice. We also consume vast amounts of paper, cardboard, lumber, and other wood products, requiring huge areas for tree harvesting.
Increased awareness of our diet, replacing some of the meat protein we consume with vegetable proteins such as beans, nuts, and soy products is one way to decrease US figures. More recycling of organic materials is also going to help us reach a more sustainable amount of use.

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