Temperature and its effects

• Warm blooded vs cold blooded

  Warm or cool to the touch
• Problems with warm blooded vs cold blooded classification, e.g. Reptiles basking or hibernating mammal with Tb as low as 5ºC
• Poikilothermic vs homeothermic

  Referring to constancy of Tb rather than its actual setting
• Poikilotherms

  Have a variable Tb
• Homeotherms

  Have a rather constant Tb
• Problems with poikilothermic vs homeothermic classification, e.g. a fish or worm living in cold, deep waters at 5ºC is every bit as homeothermic as a hamster or human; a hibernating mammal or a small tropical hummingbird with nightly torpor may have a Tb almost as variable as that of a reptile living in similar conditions

  
• Ectothermic vs endothermic

  Emphasises the heat sources used, rather than the settings or constancies of achieved Tb
• Regional endothermy

  • Localized areas of musculature routinely operate at a much higher temperature than the rest of the body, allowing for more sustained locomotory activity, or maintained sensory abilities, in cold environments
• Regional heterothermy

  • The extremities are much cooler than the core due to cardiovascular adjustments serving to reduce heat loss
• Inertial homeothermy/endothermy

  • These animals have no specific strategies for raised metabolic rate and are essentially ectothermic and bradymetabolic, can end up with a rather high and constant Tb if they are large bodied due to small surface area to volume ratio
• The biochemical reactions of metabolism go faster at higher temperatures
• Q10

  The rate that a reaction increases for every 10-degree rise in the temperature
• Log Q10 = (log R2 - log R1) X 10/(T2 - T1)
• Heat transfer

  • Heat will be transferred whenever there is a difference between Tb & Ta
  • Heat will be transferred along a thermal gradient from hot to cold
  • The steeper the gradient between Tb & Ta the faster the transfer of heat
  • Heat is transferred by conduction, convection, radiation and evaporation
• Conduction

  Transfer of heat (kinetic energy) between two materials (solid or fluid) in contact, from warmer to cooler material
• Convection

  Flow of heat between two bodies by the mass movement of an intervening fluid (gas or liquid), much faster than conduction
• Radiation

  Takes place in the absence of direct contact, emission of electromagnetic 'heat' waves

  
• Evaporation

  Water molecules absorb thermal energy, evaporative loss of water is an excellent way of dissipating heat
• Metabolic rate

  Increases above and below the thermoneutral zone
• Thermoneutral zone (TNZ)


  The range of environmental temperatures where the metabolic rate is at its lowest

  
• In the TNZ, no extra energy is expended on temperature regulation, the metabolic rate is at the Basal Metabolic Rate (BMR), and O2 consumption is at its lowest
• Endotherms tend to be well insulated and large, so they do not lose or gain body heat easily
• Figure 7. Metabolic rates of various species in relation to ambient temperature
• Extremely cold environments may be cold throughout the year, or just seasonally cold. Even deserts often experience extreme cold at night.
• Animals living in extreme cold have adaptations which reduce heat loss to the environment.
• Adaptations to reduce heat loss in extreme cold

  • Reduce surface area
  • Rounder body shapes
  • Shorter appendages
• Animals with adaptations to reduce heat loss

  • African bat-eared fox
  • European fox
  • Arctic fox
• Tb = 37ºC, Ta = 25ºC (African bat-eared fox)
• Tb = 37ºC, Ta = 12ºC (European fox)
• Tb = 37ºC, Ta = 0ºC (Arctic fox)

  
• Figure 8. Differences in ear length of three fox species living at different temperatures
• Figure 9. Variable pelage thickness of Lama guanico
• Figure 10. Temperature variation in a husky dog.
• Figure 11. A squirrel uses hibernation to reduce metabolic rate and allows Tb to fall
• Animals living in extremely hot environments

  • Have adaptations which maximize the transfer of heat to the environment
• Hot environments are also very dry and so animals have several problems to overcome
• Heat


  • When it is hot, Ta is greater than Tb. So they gain heat from the environment
  • They also produce heat of their own by their normal metabolic processes
  • If this heat had to accumulate, proteins would begin to denature, and death would follow
• Sweating

  Evaporative cooling
• Water

  • Water is scarce in arid environments
  • Animals need to ensure they do not dehydrate i.e. that water loss = water gain
  • They conserve water by concentrating urine; producing very dry faeces and by using water produced by metabolic activities
  • Water is also a by-product of respiration
• Food

  • Food is scarce and so they need to reduce their energy demands
  • They cannot afford to use lots of energy to lose heat
  • Cooling mechanisms that use energy have to be short-term solutions