Final answer:
Endotherms in cold climates are often larger to minimize heat loss, as smaller endotherms lose heat more rapidly due to having a higher surface area to mass ratio. Larger endotherms have adaptations to retain heat more efficiently, such as polar bears' thick fur and fat layer.
Step-by-step explanation:
The observation that endotherms in cold regions tend to be larger in body size than those from warmer regions is related to the concept of heat retention and loss. Larger body size in colder climates helps reduce heat loss, which is essential for maintaining a stable internal temperature. The phenomenon can be explained through the principle that smaller organisms have a higher surface area relative to their mass, resulting in faster heat loss compared to larger organisms. This is why you are less likely to find small endotherms like mice in polar regions, whereas larger endotherms such as polar bears thrive.
To maintain a stable body temperature, endotherms use a variety of strategies. Polar bears, for example, utilize adaptations like thick fur and a dense layer of fat under their skin to minimize heat loss (endotherms). In contrast, smaller endotherms require more energy to sustain their internal temperature, leading to a higher basal metabolic rate (BMR) per unit of body weight than larger endotherms.