Thermal biology is the study of the physiological, biochemical and behavioural strategies that animals have developed to deal with maintaining body temperature homeostasis. It is important for animals to keep their body temperature within an appropriate temperature range because this influences biochemical reactions and other biological functions.
Different ecosystems present a range of thermal challenges, whether it being very hot or very cold temperatures. For example, a hot desert presents the challenge of daily variation with temperatures being very hot and humid during the day, but much cooler at night. On the other hand, an alpine environment presents more stable conditions because the temperature is generally extremely cold all-year-round.
Animals have developed two different thermal strategies which differ in terms of their advantages and disadvantages. The first strategy is tolerance, this means that as the ambient temperature changes (outside temperature), the body temperature can change as well. The other strategy is regulation, which means that even if the outside temperature changes, the internal temperature of the animal cannot.
For example, ectotherms are species in which the ambient temperature of their environment determines their body temperature. Conversely, endotherms are species which maintain a body temperature homeostasis. Endotherms are capable of generating internal heat. The terms ectotherms and endotherms describe the source of thermal energy controlling body temperature. Birds are examples of endotherms, whereas amphibians are ectotherms.
Poikilotherm and homeotherm are two other important concepts which are related to body temperature stability. Poikilotherms are capable of having a variable body temperature, whereas homeotherms maintain stable body temperatures. For example, reptiles are ectotherms, but also poikilotherms because their temperature is controlled by their environment and they can survive variable temperatures. Conversely, tropical fish are also ectotherms, but are homeotherms because they can only survive warmer temperatures.
Thermal biology is a rather large topic with includes many other concepts such as body size (surface area to volume ratio), heat exchange and insulation. Even behavioural activities such as posture and huddling employed by animals are important for maintaining appropriate body temperatures. Thus, thermal biology is an integral concept in animal biology.