Chapter 10 Outline
Temperature and Heat
- BOX 10.1 Global Warming
Heat Transfer between Animals and Their Environments
- Conduction and convection: Convection is intrinsically faster
- Evaporation: The change of water from liquid to gas carries much heat away
- Thermal radiation permits widely spaced objects to exchange heat at the speed of light
Poikilothermy (Ectothermy)
- Poikilotherms often exert behavioral control over their body temperatures
- Poikilotherms must be able to function over a range of body temperatures
- Poikilotherms respond physiologically to their environments in all three major time frames
- Acute responses: Metabolic rate is an approximately exponential function of body temperature
- Chronic responses: Acclimation often blunts metabolic responses to temperature
- The rate–temperature relations and thermal limits of individuals: Ecological decline occurs at milder temperatures than the temperatures that are lethal
- Evolutionary changes: Species are often specialized to live at their respective body temperatures
- Temperature and heat matter because they affect the functional states of molecules, as well as the rates of processes
- Poikilotherms threatened with freezing: They may survive by preventing freezing or by tolerating it
- BOX 10.2 Evolutionary Genomics: The Genes for Antifreeze Proteins Are Descended from Genes for Other Functional Proteins
Homeothermy in Mammals and Birds
- BOX 10.3 Thermoregulatory Control, Fever, and Behavioral Fever
- Metabolic rate rises in cold and hot environments because of the costs of homeothermy
- The shape of the metabolism–temperature curve depends on fundamental heat-exchange principles
- Homeothermy is metabolically expensive
- Insulation is modulated by adjustments of the pelage or plumage, blood flow, and posture
- Heat production is increased below thermoneutrality by shivering and nonshivering thermogenesis
- Regional heterothermy: In cold environments, allowing some tissues to cool can have advantages
- Countercurrent heat exchange permits selective restriction of heat flow to appendages
- Mammals and birds in hot environments: Their first lines of defense are often not evaporative
- Active evaporative cooling is the ultimate line of defense against overheating
- Mammals and birds acclimatize to winter and summer
- Evolutionary changes: Species are often specialized to live in their respective climates
- Mammals and birds sometimes escape the demands of homeothermy by hibernation, torpor, or related processes
- Human thermoregulation
Warm-Bodied Fish
Endothermy and Homeothermy in Insects
- The insects that thermoregulate during flight require certain flight-muscle temperatures to fly
- Solitary insects employ diverse mechanisms of thermoregulation
- Colonies of social bees and wasps often display sophisticated thermoregulation
Coda
- BOX 10.4 Warm Flowers