Ch. 39 - Animal Form and Function

Freeman - Biological Science 7th Edition

Freeman7th EditionBiological ScienceISBN: 9783584863285Not the one you use?Change textbook

Freeman 7th Edition

Ch. 39 - Animal Form and Function

Problem 12

Chapter 39, Problem 12

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 allow species to exploit more resources and free 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?

Verified step by step guidance

Understand the concept of island gigantism: Island gigantism is a biological phenomenon where species on islands grow larger than their mainland relatives due to factors like reduced competition and predation.

Consider the energy requirements of larger animals: Larger animals generally have lower metabolic rates per gram of body mass compared to smaller animals, meaning they require less food per gram of body mass.

Analyze the environmental factors: On islands, the scarcity of predators and competitors allows animals to grow larger, potentially reducing their need for frequent feeding compared to smaller mainland species.

Compare the tortoises: Island tortoises, being larger due to island gigantism, likely have lower metabolic rates per gram of body mass than mainland tortoises, which are smaller and may need more food per gram of body mass.

Conclude based on metabolic rates: Mainland tortoises, being smaller, need to eat more food per gram of their body mass compared to island tortoises, which are larger and have lower metabolic rates per gram.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Island Gigantism

Island gigantism refers to the evolutionary phenomenon where species on islands grow larger than their mainland counterparts. This occurs due to reduced competition and predation, allowing species to exploit available resources more freely. The lack of predators and competitors means that animals can grow larger without the need to hide or escape quickly.

Metabolic Rate

Metabolic rate is the rate at which organisms convert food into energy. Larger animals typically have a lower metabolic rate per gram of body mass compared to smaller animals, meaning they require less food relative to their size. This concept is crucial in understanding why island tortoises might need less food per gram of body mass compared to mainland tortoises.

Resource Availability

Resource availability on islands can differ significantly from the mainland due to isolation and limited biodiversity. The abundance or scarcity of food resources influences the size and metabolic needs of island species. In the context of island gigantism, the availability of resources without competition allows species to grow larger, impacting their dietary requirements.

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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 lived—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 allow species to exploit more resources and free 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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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 allow species to exploit more resources and free 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.

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Textbook Question

True or false: The body temperatures of island tortoises always closely match the temperatures in their environments.

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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 allow species to exploit more resources and free them from the need to hide in small refuges. Suppose that a small mainland tortoise and a large island tortoise are placed in the same pen at a zoo.

Which tortoise will be more poikilothermic, the small or large tortoise? Why?

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