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.

Verified step by step guidance

1. Identify the trade-offs related to gigantism: Consider how increased body size could impact various aspects of the tortoises' biology and ecology, such as metabolism, thermoregulation, and vulnerability to predators.
2. Analyze option a: Larger animals have more thermal mass, which generally means they retain heat longer, not cool down rapidly. Thus, option a is unlikely to be a correct trade-off of gigantism.
3. Analyze option b: Larger animals typically have lower mass-specific metabolic rates, meaning they require less energy per unit of body mass compared to smaller animals. Therefore, sustaining their metabolism on a plant-based diet might not be as difficult as suggested in option b.
4. Analyze option c: Larger size could make it more challenging for the tortoises to find shelter or move to different microclimates quickly, making it harder to avoid extreme temperatures. This option seems plausible as a trade-off of gigantism.
5. Analyze option d: Larger size would make it more difficult, not easier, for tortoises to hide from predators, especially nonnative ones that might not have co-evolved with such large prey. Thus, option d is not a likely trade-off of gigantism.

Key Concepts

Island Gigantism

Island gigantism is a biological phenomenon where species on islands evolve to larger sizes compared to their mainland relatives. This adaptation is often attributed to the absence of large predators and reduced competition for resources, allowing these species to grow larger as they exploit available niches. Examples include giant tortoises and large birds found on isolated islands.

Metabolic Rates

Metabolic rate refers to the rate at which an organism converts food into energy. Larger animals typically have lower mass-specific metabolic rates, meaning they require less energy per unit of body mass compared to smaller animals. This can pose challenges for giant island tortoises, as sustaining their energy needs solely on a plant-based diet may be difficult due to their size.

Thermoregulation

Thermoregulation is the process by which organisms maintain their internal body temperature within certain limits, despite external temperature variations. Larger animals, like giant tortoises, may struggle with thermoregulation, as their increased body mass can lead to difficulties in dissipating heat, making them more susceptible to overheating in warm environments or cooling too quickly in cold conditions.