Endothermy: Regulation and Adaptations

• Endothermy is the production of heat to maintain a constant, normal body temperature.
• Air temperature is usually lower than body temperature.
• Body temperature can be increased by metabolism, thermogenesis, and insulation.
• Body temperature can be decreased by sweating or panting.
• The lower critical temperature (LCT) is the point where an animal must increase metabolic heat production to balance heat loss.
• Endotherms can maintain stable body temperatures over a range of environmental temperatures.

Benefits of Endothermy

• The ability to maintain a high body temperature when solar radiation is unavailable or insufficient, such as at night or in winter.
• Endothermy allows for living in cold-weather climates due to thermoregulatory capacity.

Costs of Endothermy

• Endothermy is energetically expensive.
• Endothermy requires a higher metabolic rate.
• Gram-for-gram endotherms need more food than ectotherms.

Adaptations to the Cold

• Insulation greatly decreases LCT.
• Most mammals and birds shed or molt their insulation in the autumn and spring because winter insulation is denser than summer coverings.
• Animals avoid going outside as often and create nests to share body heat.

Facultative Hypothermia

• Facultative hypothermia is the intentional lowering of body temperature.
• It is common in small mammals and birds.
• There is a large surface/volume ratio, meaning that heat loss is high.
• There are also large food requirements because the energy consumed per gram of body weight is higher than in larger species.
• Layers of insulation are thinner than those of larger animals.

Seasonal Hypothermia

• Seasonal hypothermia reduces body temperature up to 5°C in the winter.
• Time outside of nests is limited.

Rest-Phase Hypothermia

• Rest-phase hypothermia decreases of body temperature from 5-10°C during normal times of inactivity.
• An example of this is migratory stopovers.

Hibernation

• Hibernation generally occurs only in small mammals where they essentially become comatose.
• Body temperature can be at or below freezing.
• Respiration is slow.
• Heart rate is reduced.
• Blood stays in the core.
• Some animals use communal hibernation.
• Bears do not hibernate, instead enter winter dormancy, which only decreases body temperature about 5°C and metabolism decreases by about 50%.

Adaptations for Heat

• Avoidance: Shelter during the heat of the day, climbing away from the ground, and flying above the heat.
• Relaxation of Homeostasis: Small mammals limit their exposure and can cool down quickly.
• Large mammals use more of their thermal inertia.
• Camels lay on the cool ground in the morning in groups and conserve water by not using evaporative heat loss.

Countercurrent Exchange in the Head

• The blood being carried to the brain passes by the blood coming back from the nasal passages.
• The blood coming back from the nasal passages is cooler because of evaporative heat loss in the nose.
• This cools the blood coming from the heart before it reaches the brain.

Explore endothermy, the process of maintaining a stable body temperature through heat production. Learn about the benefits and energetic costs and how adaptations allow animals to thrive in cold climates. Understand metabolic rates and lower critical temperatures.