Heterothermy vs. Homeotherm — What's the Difference?

Heterothermy characterizes animals that can switch between poikilothermy and homeothermy, adapting their body temperature to varying environmental conditions. In contrast, homeotherms consistently regulate their internal temperature, keeping it relatively constant despite external temperature changes. This ability in heterotherms allows for energy conservation during adverse conditions, whereas homeotherms expend energy to maintain their temperature, ensuring optimal physiological functioning at all times.

Heterothermic animals, such as certain bats and hummingbirds, can enter states like torpor or hibernation to reduce metabolic rates and conserve energy when food is scarce or temperatures are low. Homeotherms, including most mammals and birds, cannot drastically lower their metabolic rates and are more dependent on continuous food supply and active thermoregulation mechanisms, such as sweating or shivering, to stabilize their body temperature.

In aquatic environments, heterothermy is advantageous for species like the great white shark, which can retain heat in crucial muscles to enhance performance while allowing other body parts to align with the water temperature. Homeotherms, such as dolphins, maintain a uniformly high body temperature, which supports high metabolic activities necessary for their active lifestyles and complex brain functions.

Seasonal heterothermy is observed in animals like the arctic ground squirrel, which hibernates during winter to survive the extreme cold by lowering its body temperature close to freezing. Homeotherms, such as deer, rely on behavioral adaptations like growing thicker fur and increasing fat reserves to insulate against the cold without significant changes to their core temperature.

The flexibility of heterothermy can be seen in desert environments where animals like the kangaroo rat exhibit nocturnal fluctuations in body temperature to cope with drastic day-night temperature differences. Homeotherms in similar environments would use energy-intensive processes to cool down during hot days and maintain warmth during cold nights, often requiring adaptations like burrowing or changing activity periods.