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?

Verified step by step guidance

1. Understand the concept of poikilothermy: Poikilothermic animals, also known as ectotherms, have body temperatures that vary with the environment. They rely on external sources of heat to regulate their body temperature.
2. Consider the size of the tortoises: Larger animals generally have a lower surface area-to-volume ratio compared to smaller animals. This means they lose heat more slowly and can maintain a more stable internal temperature.
3. Analyze the environmental conditions: In the zoo pen, both tortoises are exposed to the same environmental conditions. However, the larger tortoise, due to its size, may be able to retain heat better than the smaller tortoise.
4. Evaluate the implications of island gigantism: Island gigantism may result in larger body sizes that are advantageous for thermoregulation, allowing the tortoise to be less affected by external temperature fluctuations.
5. Conclude which tortoise is more poikilothermic: Based on the understanding of poikilothermy and the effects of body size on heat retention, the smaller tortoise is likely to be more poikilothermic, as it would be more susceptible to changes in environmental temperature.

Key Concepts

Island Gigantism

Island gigantism refers to the phenomenon where species on islands evolve to be larger than their mainland counterparts. 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.

Poikilothermy

Poikilothermy is a biological term describing organisms whose internal temperature varies considerably. Unlike homeotherms, poikilotherms do not maintain a constant body temperature and are influenced by external environmental conditions. This trait is common in reptiles, where body temperature can fluctuate based on ambient temperature, affecting metabolic rates and activity levels.

Thermal Regulation in Tortoises

Thermal regulation in tortoises involves balancing body temperature with environmental conditions. Larger tortoises, due to their size, have a greater thermal inertia, meaning they change temperature more slowly than smaller tortoises. This can make larger tortoises less poikilothermic, as their size helps buffer against rapid temperature changes, allowing them to maintain a more stable internal temperature.