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Animal Body Types - Basics

Endotherms are animals that primarily produces its own heat.
Ectotherms are animals that primarily gains heat through the environment.

Homeotherms are animals that have a constant body temperature.
Poikilotherms are animals whose body temperature adjusts depending on the environment.



Animal Body Types - Further Reading

The two extremes in the animal kingdom are endothermic homeotherms and ectothermic poikilotherms. Most mammals, including humans, as well as most birds are endothermic homeotherms, while most fish, invertibrates, reptiles, and amphibians are ectothermic poikilotherms.

Some animals fit into the endothermic poikilotherm profile as well as the ectothermic homeotherm profile. Mammals that engage in hibernation, or a long torpor, are considered endothermic poikilotherms, as they can produce their own heat but allow their temperature to vary depending on the environment. The desert pupfish constrasts hibernating mammals, in that it does not produce its own heat, but does maintain a constant body temperature by moving to environments with different temperatures. [1]

Animals that are endothermic have adapted to the environment differently than ectothermic animals. Endothermic animals may stay active in cold weather, which may result in a greater ability to survive. However, endothermic animals require more energy to heat their bodies and therefore require more food. Ectothermic do not require energy to heat themselves, and can spend their energy on reproduction, which in some environments is more valuable than staying active in cold weather. [17]