Chapter 4 Animal Adaptations: Thermoregulation

Chapter Outline

Introduction
   Ectothermy and Endothermy
Thermal Energy Budgets
   Metabolic heat
   Radiation
   Conduction and convection
   Evaporative cooling
   Microclimates
Morphological, Behavioral, and Physiological Adaptations
   Animal coloration
   Burrowing
   Other behaviors that reduce heat gain or enhance heat loss
   Appendages as radiators
   Surface area-to-mass ratios
   Plumage and pelage
   Physiological mechanisms
      Blood circulation
      Evaporative cooling
   Tolerable thermal regimes
      Ectotherms
      Endotherms
      Torpor
   High-temperature mortality

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Study Questions

1. Describe the thermal energy budget of an animal. Do not just list fluxes, describe how each results in heat gain or loss.

2. Black body temperature more accurately characterizes an animal's thermal environment than does air temperature. a) Explain this statement. b) What elements of an animal's thermal environment are not measured by black body temperature?

3. Black coloration of desert animals may seem thermally maladaptive, yet many desert organisms are dark. Explain how dark color may be beneficial to a darkling beetle and a phainopepla. Is there any evidence to support your explanations?

4. Many animals go below ground during the heat of a summer day. Describe the benefits of such retreats.

5. Bergman's rule states that animals of warmer regions tend to have smaller body sizes. Describe the thermoregulatory and energetic explanations for this trend.

6. Consider a large lizard. a) Describe how vasoconstriction and dilatation can enhance both heat gain and heat loss. Include hypothetical situations to help illustrate how controlling skin blood flow can be beneficial. b) As a reptile basks in the sun the head can warm faster than deeper body tissues. Describe how shunting blood flow can relieve brain hyperthermia.

7. Some mammals have a carotid rete. a) Describe how this structure can cool the brain. b) Is there a correlation between the mammals that have this structure and their natural history? Explain.

8. Evaporative cooling can be an important means of heat loss for vertebrates. Describe how desert vertebrates evaporatively cool themselves. Include energy-conserving mechanisms.

9. Plot a curve that shows the effect of body temperature (x axis) on activity (y axis) of desert ectotherms. Consider a beetle shuttling between sun and shade to maintain optimal body temperature. Why might it be said that it is living on the thermal edge? Explain.

10. Many desert birds and mammals are able to tolerate mild to extreme fluctuations in body temperature. Consider instances of both hypothermia and hyperthermia. What are the adaptive advantages in each case? Use specific observations to justify your answers where possible.