What are the types of thermoregulation? Heat needed for thermoregulation can either come from internal metabolism or the external environment. Animals that use metabolic processes to generate their own heat to maintain their internal temperature within the tolerance range are called endotherms, while organisms who rely on the external environment for temperature regulation are called ectotherms. What are endotherms? Endotherms are animals that retain heat generated via metabolic activity within their body. They are also usually described as being homeothermic, aka, they maintain a relatively constant temperature. Endotherms have a range of adaptations that serve as mechanisms for controlling heat gain or heat loss. Animals such as birds and mammals can generally maintain a stable internal environment, independent of external temperature fluctuations. In a cold environment, an endotherm generates enough heat to keep its body within its tolerance range and at temperatures which are significantly higher than its surroundings. In a hot environment, such as the Australian desert during the day, endothermic vertebrates use special mechanisms to keep cool and maintain their temperature in their tolerance range.

What are ectotherms? Ectotherms are animals that absorb their heat from the external environment; they don't use their body to generate heat. They are usually also described as being poikilothermic, meaning that they cannot control their internal temperature which fluctuates with its surroundings. Animals such as amphibians, some reptiles and fish (alongside most invertebrate organisms) cannot maintain a stable internal environment. In order to gain heat, ectotherms may obtain heat from the sun or from objects in their surroundings, this meaning that their body temperature fluctuates with the external environment. Ectotherms have adaptations that help in controlling heat gain or heat loss to regulate temperature, but these are behavioural and structural, not physiological.