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Ch. 39 - Animal Form and Function
Chapter 38, Problem 11

Many species of animals on islands are larger than related species on the mainland. Scientists hypothesize that this phenomenon, called island gigantism, evolved in response to the scarcity of competitors and predators on islands. Reduced competition and predation allows species to exploit more resources and frees them from the need to hide in small refuges. The graph shown here compares the average carapace (shell) length of mainland and island tortoises. Summarize the results, then use the data to predict whether the surface area to volume ratio is higher in mainland or island tortoises.

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Analyze the graph to determine the average carapace length of island and mainland tortoises.
Calculate the surface area to volume ratio (SA:V) for each tortoise type using the formula: \( \text{SA:V} = \frac{\text{Surface Area}}{\text{Volume}} \).
Compare the SA:V ratios of island and mainland tortoises.
Summarize the results: Island tortoises have a larger carapace length compared to mainland tortoises.
Predict that the surface area to volume ratio is higher in mainland tortoises due to their smaller size.

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Related Practice
Open Question

a. Consider three spheres with radii of 1 cm, 5 cm, and 10 cm. Based on what you read in the chapter, predict which sphere will have the highest surface area to volume ratio, and which sphere will have the lowest.

b. Next, calculate the surface area and the volume of each sphere. (Surface area of a sphere=4πœ‹π‘Ÿ2; volume of a sphere=(4/3)πœ‹π‘Ÿ3.) Plot the results on a graph with radius on the π‘₯-axis and surface area and volume on the 𝑦-axis.

c. Which sphere has the highest surface area to volume ratio? The lowest? Explain how the graph shows the relationship between size and surface area to volume ratio.

d. Now imagine that these spheres represent a small, medium, and large endothermic animal. Which animal would lose heat most rapidly? Explain using the surface area to volume ratio.

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Textbook Question

Explain why it would be impossible for a gorilla the size of King Kong to have fur. (Your answer should explain how the surface area to volume ratio of a normal-sized gorilla would compare to Kong's; relate this to the role of surface area and volume in heat generation and heat transfer, and consider the function of fur.)

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Textbook Question

The dinosaur Apatosaurus (Brontosaurus) is one of the largest terrestrial animals that ever livedβ€”over 20 m in length and weighing over 20 metric tons. Is it more likely that Apatosaurus was homeothermic or poikilothermic? Explain.

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Textbook Question

Many species of animals on islands are larger than related species on the mainland. Scientists hypothesize that this phenomenon, called island gigantism, evolved in response to the scarcity of competitors and predators on islands. Reduced competition and predation allows species to exploit more resources and frees them from the need to hide in small refuges. Which tortoises, mainland or island, need to eat more food per gram of their body mass?

276
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Textbook Question

Many species of animals on islands are larger than related species on the mainland. Scientists hypothesize that this phenomenon, called island gigantism, evolved in response to the scarcity of competitors and predators on islands. Reduced competition and predation allows species to exploit more resources and frees them from the need to hide in small refuges. Which of the following might be a trade-off of gigantism experienced by giant island tortoises? a. They cool very rapidly during cold weather. b. It would be difficult to sustain their high mass-specific metabolic rates on a diet of plants alone. c. It could be more difficult to avoid thermally unfavorable conditions. d. They could hide from nonnative predators more easily.

292
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Textbook Question

Many species of animals on islands are larger than related species on the mainland. Scientists hypothesize that this phenomenon, called island gigantism, evolved in response to the scarcity of competitors and predators on islands. Reduced competition and predation allows species to exploit more resources and frees them from the need to hide in small refuges. True or false: The body temperatures of island tortoises always closely match the temperatures in their environments.

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