Adaptations of endotherms living in cold environments

Question 1

Good insulation:

Answer 1

fur/feathers/fat/blubber

Question 2

Blubber (fat):

Answer 2

: Low thermal conductivity (good insulator); metabolically inactive so needs
little blood supply (which would lead to heat loss). Level of blood flow through blubber can
be regulated which gives it an advantage over fur or feathers as insulation. Blood flow
through blubber is increased to dissipate heat e.g. when the animal is very active in warmer
waters.

Question 3

Fur and feathers can be fluffed to reduce heat loss, but cannot be modified to allow
increased heat loss on short-term basis

Answer 3

Areas of the body with less insulation (face, feet) are
needed to dissipate heat, especially during intense exercise. Postural changes and regulation
of blood flow modulates the amount of heat lost from these poorly insulated areas. In the
longer term, the level of insulation is modified by seasonal changes in fur thickness- thick in
winter, thinner in summer to avoid heat stress.

Question 4

Large size:

Answer 4

• smaller surface area to volume ratio reduces rate of heat loss
• can carry thicker insulation layer

Question 5

Countercurrent heat exchange

Answer 5

Found in flipper of porpoise, legs of birds and arctic land mammals.
Limbs have less insulation (blubber or fur would hinder locomotion) and are a potential
location for substantial heat loss. Countercurrent exchangers reduce this.

Question 6

The blood vessels are so arranged that

Answer 6

warm arterial blood flowing into the limb gives up
heat to venous blood returning from the limbs where it has cooled.
By the time it reaches the periphery, arterial blood is precooled to within a few degrees of
ambient and so, little heat is lost at the surface. As the venous blood returning to the core is
warmed by the arterial blood it does not contribute much to cooling the core.

Question 7

These heat exchangers can be very efficient

Answer 7

a gull with its feet in iced water for 2 hrs lost
only 1.5% of metabolic heat production through its feet. However, at temperatures below
zero there is a danger of the feet freezing if the blood were at ambient; with increasing cold,
intermittent pulses of blood flow to the feet delivers more heat; more heat is lost from the
feet, and this is made up for by an increase in metabolic rate.
If the animal needs to dissipate heat the countercurrent system can be bypassed.

Question 8

Other adaptations of endotherms to cold environments-Huddling

Answer 8

g reduces exposed surface and hence heat loss and energy expenditure. Emperor
penguin males incubate eggs for 2 months at ambient of –30 to –40oC; use half as much
energy in huddle as when alone.

Question 9

Avoidance:

Answer 9

• live in burrows;
• torpor including hibernation (see later),
• migration.