Animals living in polar regions or at high altitude have anatomical, physiological and behavioural adaptations that reduce heat loss.Anatomical
• Small surface area to volume ratio. Large, compact bodies with small extremities (short legs, small ears and tails) lose less heat relative to the heat they produce. For example, the Arctic fox has much smaller ears than the fennec fox of the desert.
• Thick insulation. Dense fur or feathers trap a layer of still air. Marine mammals such as seals and whales have a thick layer of blubber (fat) under the skin, which insulates even in water, where fur is less effective.Physiological
• Countercurrent heat exchange. In the legs of penguins and the flippers of seals, arteries carrying warm blood to the extremity lie right next to veins carrying cold blood back. Heat passes from the arterial blood to the venous blood along the whole length, so the extremity stays cool, little heat is lost from it, and blood returning to the core is rewarmed.
• Brown fat for rapid heat production.
• Hibernation in some mammals: body temperature and metabolic rate are lowered for the winter, saving energy stores.
Worked example (SA:V). A cube-shaped animal of side 1 cm has SA:V = 6:1. One of side 4 cm has SA = 96 cm2 and V = 64 cm3, so SA:V = 1.5:1. The larger animal loses heat far more slowly relative to its volume.Behavioural adaptations, such as huddling, are covered in a later lesson.
• Small surface area to volume ratio. Large, compact bodies with small extremities (short legs, small ears and tails) lose less heat relative to the heat they produce. For example, the Arctic fox has much smaller ears than the fennec fox of the desert.
• Thick insulation. Dense fur or feathers trap a layer of still air. Marine mammals such as seals and whales have a thick layer of blubber (fat) under the skin, which insulates even in water, where fur is less effective.Physiological
• Countercurrent heat exchange. In the legs of penguins and the flippers of seals, arteries carrying warm blood to the extremity lie right next to veins carrying cold blood back. Heat passes from the arterial blood to the venous blood along the whole length, so the extremity stays cool, little heat is lost from it, and blood returning to the core is rewarmed.
• Brown fat for rapid heat production.
• Hibernation in some mammals: body temperature and metabolic rate are lowered for the winter, saving energy stores.
Worked example (SA:V). A cube-shaped animal of side 1 cm has SA:V = 6:1. One of side 4 cm has SA = 96 cm2 and V = 64 cm3, so SA:V = 1.5:1. The larger animal loses heat far more slowly relative to its volume.Behavioural adaptations, such as huddling, are covered in a later lesson.