L13: Energy for thermoregulation

Thermoneutral zone

environmental temperature range where endotherms do not warm/cool themselves

• means that basal metabolic heat production = heat lost to the environment

When equilibrium cannot be attained:

basal metabolic heat production ≠ heat lost to then environment so energy must be used to ↑ or ↓ body temperature

Thermoregulation

a balance between heat gained and heat lost

Heat exchange with the environment can occur through

• radiation

• convection

• conduction

• evaporation

Evaporation

Heat transfer required for a phase change to occur

• depends on a vapor pressure gradient

• latent heat flow

• energy loss occurs with a phase change

• e.g. can’t lose heat at 100% humidity (air is fully saturated)

Examples of evaporation and what animals

- sweating (equids, ungulates, primates)

- panting (canids)

- gular fluttering (birds)

- saliva spreading (rats, marsupials)

- mucus secretions (frogs)

What is common between radiation, convection and conduction

- depends on a temperature gradient

- sensible heat flow

- heat flows from warmer body → cooler body

e.g. can’t lose heat if the environment is warmer than the animal

Radiation

Heat transfer (warm → cool) via electromagnetic waves

• All animals radiate heat = infrared/longwave radiation

• Animals absorb ~95% of infrared/longwave radiation

• Black animals absorb up to 90% of solar/shortwave radiation

• *White animals only absorb up ~50% of solar/shortwave radiation

• The sun radiates heat = solar/shortwave radiation:

• infrared radiation (some)

• visible radiation

• ultraviolet radiation

*All radiation can be absorbed or reflected

Convection

heat transfer through moving air (or water)

• When air/water moves more rapidly, the rate of heat loss by convection

  increases

Conduction

heat transfer between animals and contact surfaces

Conduction on land

When on land rate of heat loss/gain comes down to surface area:

• perching

• standing

• incubating eggs

• lying down

Insulative layers include

• Boundary layer = Air

• Cover layer = Pelage/plumage (and trapped air)

• Tissue layer = muscle, fat, blood, skin

• Body core = visceral organs = metabolic heat production

Boundary layer

• still air surrounding an animal

• affected by air movement

• approximately 0.35 cm

• (still animal, no air movement)

Cover layer

- pelage or plumage

- trapped still air

Effectiveness of cover layer depends on

a) hair/feather type

b) hair density

c) cover length

d) shedding/molting

e) pilo/ptero-erection

f) wind/water

Cover layer: hair/feather type

• guard hairs (moisture protection, longer, colored) vs. underfur (insulative, shorter)

• contour feathers (moisture protection, surface layer, flight) vs. down feathers (insulative, under layer, shorter)

Cover layer: hair density

• # of hairs per cm²

• more dense = better insulation

• differs by species (horses vs cows: 1,250 vs 700 hairs/cm2)

• differs by breed

Who has the densest fur

The smallest marine mammal also has the densest fur of any species

(more than 150,000 hairs/cm²) - sea otter

Cover layer: cover length

longer cover traps more air = better insulation

Cover layer: shedding/molting

• a response to seasonal day length changes

• not a response to changes in ambient temperature

Cover layer: pilo/ptero-erection

• increases the trapped air = better insulation

• air is a poor heat conductor (so a good insulator)

Cover layer: wind/water

• wind/water will reduce the depth of pelage/plumage

• trapped air can be replaced with water

• water is a better heat conductor (so a worse insulator)

Tissue layer

• muscle, skin, fat, blood vessels

• insulation affected by blood flow; body core heat gets to skin via circulatory convection

Body core

• site of metabolic heat production

• when you’re hot = ↓ appetite

• when you’re cold = ↑ appetite