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. 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 term 'poikilothermic': Poikilothermic, or ectothermic, refers to organisms that cannot regulate their body temperature internally and rely on external sources of heat. This is common in reptiles, including tortoises.
2. Consider the size of the tortoises: Larger animals generally have a lower surface area to volume ratio compared to smaller animals. This means that larger animals lose heat more slowly and have more thermal inertia.
3. Apply the concept to the tortoises: Given that the island tortoise is larger, it will have a lower surface area to volume ratio compared to the smaller mainland tortoise. This suggests that the island tortoise will be less affected by external temperature changes.
4. Conclude which tortoise is more poikilothermic: The smaller mainland tortoise, with a higher surface area to volume ratio, will be more poikilothermic. It will be more susceptible to external temperature changes and less able to retain its body heat compared to the larger island tortoise.
5. Summarize the comparison: Therefore, the small mainland tortoise will be more poikilothermic than the large island tortoise because it is more influenced by the external temperature due to its higher surface area to volume ratio.