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
• Inertial homeothermy/endothermy

  • These animals have no specific strategies for raised MR and are essentially ectothermic and bradymetabolic - can end up with a rather high and constant Tb if they are large bodied due to SA relatively too small to dissipate the slowly generated internal metabolic heat from their enormous volumes
• 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

  • Temperature control in animals is largely concerned with manipulating the various avenues of heat exchange with that environment in the animal's favour, depending on its immediate needs and circumstances
• Conduction

  Transfer of heat (kinetic energy) between two materials (solid or fluid) in contact, i.e., heat flows from the warmer to the cooler material, by a direct transfer of the kinetic energy as molecules collide
• Convection

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

  Takes places in the absence of direct contact, travels with the speed of light and is emitted by all bodies whose temperature is > absolute zero (-273 ºC), 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 MR of the endotherm is at a minimum known as the Basal Metabolic Rate (BMR), the only energy required is that to maintain the body's activities, O2 consumption (respiration) is at its lowest
• Endotherms tend to be very well insulated (with thick fur or fat) and are often large (with a small surface area: volume), so they do not lose or gain body heat easily
• 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)
• 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.
• Evaporative cooling

  One way for an animal to get rid of extra heat is by sweating
• Water

  Water is scarce in arid environments. Animals need to ensure they do not dehydrate i.e. that water loss = water gain.
• Water conservation

  1. Concentrating urine

  2. Producing very dry faeces

  3. 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.
• Adaptations to Heat

  • Water loss
  • Breathing
• There is no single set of adaptations for mammals surviving in hot environments. Despite different adaptations, all may be equally successful for survival.
• Small mammals

  • Have a large surface area: volume. This means that they gain and lose heat rapidly. They survive in hot environments by behaviour which helps them to avoid heat gain: they find refuge in burrows; and are often nocturnal which allows them to avoid the heat of the day.