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.

Verified step by step guidance

1. Understand the concept of island gigantism: Island gigantism is a biological phenomenon where the size of animals on islands is larger compared to their mainland relatives. This is often due to reduced competition and predation, allowing species to grow larger as they exploit available resources.
2. Consider the potential trade-offs of being larger: While being larger can have advantages, such as increased access to resources and reduced predation, it can also come with disadvantages or trade-offs.
3. Analyze the options provided: a. Cooling rapidly during cold weather, b. Difficulty sustaining high mass-specific metabolic rates on a plant diet, c. Difficulty avoiding thermally unfavorable conditions, d. Easier hiding from predators.
4. Evaluate each option in the context of gigantism: Larger animals generally have lower surface area to volume ratios, which affects their heat retention and metabolic needs. Consider how these factors relate to the options.
5. Identify the most likely trade-off: Larger size could lead to challenges in thermoregulation and metabolic demands, making options b and c more plausible trade-offs. Consider which of these aligns best with the known challenges of large size in animals.

Key Concepts

Island Gigantism

Island gigantism refers to the phenomenon where animal species on islands evolve to be larger than their mainland relatives. This is often due to reduced competition and predation, allowing species to exploit available resources more freely. The lack of predators and competitors can lead to evolutionary changes that favor larger body sizes, which can be advantageous in resource-rich environments.

Metabolic Rate

Metabolic rate is the rate at which organisms convert 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. However, sustaining a high metabolic rate on a plant-based diet can be challenging, as plants generally provide less energy compared to animal-based foods, potentially leading to nutritional limitations for large herbivores.

Thermal Regulation

Thermal regulation is the process by which animals maintain their body temperature within certain limits, despite external temperature changes. Larger animals, like giant tortoises, may face challenges in avoiding thermally unfavorable conditions due to their size, which can make it difficult to find shelter or move quickly to different microclimates. This can be a trade-off of gigantism, as larger body sizes may limit mobility and adaptability to temperature fluctuations.