Extreme Habitats - 1
What is extreme?
• Hot ~ thermal and water balance problems
(deserts). Differences between hot &
humid; hot & dry.
• Cold – towards the poles, and high altitude.
Water loss not a major problem.
• Regions – hot and cold (e.g. regions of Nth
America and Europe).
• Animals acquire specialist adaptation
mechanisms to the extremes.
Animal Size
• (see previous lecture)
• In general animals are larger towards the poles.
• For example, penguins in Australia are
considerably smaller than those in Antarctica.
• However, many small birds and rodents can be
found in the northern polar regions.
• The best strategy in extreme habitats appears to
be - be very large or very small
Large v Small
• Large animals (>50 kg)
lower water loss (as % of size);
high thermal inertia – stay warmer in cold,
and cooler in heat.
• Small animals (<15 kg; most less than 5)
exploit microhabitats e.g. burrow
Were are the medium sized
animals?
• Dogs, sheep, goats – do well on the
fringes of deserts:
• Do moderately well in cold climates (dogs
esp.)
• Animals can be divided into two broad
categories which are related to size:
• Small ‘evaders’ e.g. rodents
• Large ‘endurers’ e.g. camels
• A third group (rare) middle sized
‘evaporators’ e.g. dogs.
Evaders
• Small mammals – greater surface area/wt
– gain more heat from environment – need
a lot of water – or do something else.
• Active at night – usually burrow.
• Partially active during the day rest in
shade or burrows during the hottest part of
the day.
Why Burrow?
• Small rodents burrow 1 m underground –
almost constant 26 oC.
• Above ground range of 16 – 44 oC.
• This means they can be active during day
– escape to burrow to dissipate heat.
• Many have high Tb (40 – 44 oC)
Why Burrow?
• High humidity – aids osmotic regulation
strategies.
• Remember the mole rat – uses the high
humidity to minimise evaporation.
• Escape from predators.
• Food storage.
Evaporators
• Birds, dogs, cats, small antelope, goats &
sheep.
• Need water – therefore not common in
deserts.
• Do better in rocky deserts cv to sand
deserts. Why?
Evaporators
• How are they adapted to hot, dry and hot
humid conditions? See previous lectures.
• However, many are nomadic - migratory
Endurers
• Camels, desert gazelle (Oryx) – both desert
specialists:
• Elephants, eland, African rhinos, Bos indicus
cattle – ok but not specialists
• Camels – live in areas where Ta exceeds 50 oC.
• Oryx: exceptional ability to survive in extremely
arid zones.
Endureres
• Large animals – difficulty in losing heat to their
surface.
• Lack thick fur and insulation.
• Long legs, ears, long horns, tails and necks.
• EG elephant ears - when Ta is 32 oC they can
shed 100% of excess heat through the ears.
Endureres
• Thermal Inertia (adaptive hyperthermia)
• Tb allowed to fluctuate.
• Heat stored during day and dissipated at
night ~ peaks at or just after sunset.
• Camels 34 – 41 oC (occasionally 45 oC).
• Storing heat reduces water loss.
• Light coat colour & curly coat dorsally.
• Dark strip on flanks.
• White under bellies and rump.
Fur/hair
• Non-living – undamaged by high
temperatures.
• Dorsal surface – heavy and thick.
• Surface temp. can exceed 70 oC.
• Extreme temperature gradient exists
between skin and surface of fur.
• Stops SR and reflected environment
radiation reaching the skin.
Fur/hair
• Hair thickness reduces as body size
increases (opposite to cold climates).
• Lack of hair in groin area, scrotum and
mammary glands.
• Allow heat loss via vasodilation.
• Scrotum & udders contain temperature
sensors ~ early warning for pending heat
stress.
Back to Coat Colour
• What is the advantage of black hair in the desert?
• High temp on tips enhances convective & radiant heat
loss.
• Radiant heat from the ground ~ absorption not colour
dependant.
• In winter with cold nights black hair maybe
advantageous.
• Black goats have 25% lower metabolic rate than white
goats – can absorb more heat from sun & shiver less
Behaviour
• Lie on ground to minimise area exposed to
radiation.
• Inactive during heat of day.
• Orientates head-on towards sun.
• Stand on mounds or small hills to catch air
movement.
• Seek shade.
Lower values set by physiology
Camel
Antelope Ground Squirrel
44
Upper limits by behaviour
Steer
40
38
36
2300
2200
2100
2000
1900
1800
1700
1600
1500
1400
1300
1200
1100
1000
900
800
700
600
500
400
300
200
100
34
2400
Body Temperature
42
Hours
Source: Schmidt-Nielson et al 1957; Hudson 1962; Gaughan et al 2004
Camel
• Tb increases during the day – max about 2000 h.
• Controlled increase – dissipate heat at night.
• Tb returns to normal.
• Can keep this up indefinitely.
Camel
• Can endure 30% water loss (see previous lecture).
• Can drink 200 L (1/3 of BWt) in 3 min.
• Can store large amounts of H2O in gut for about
24 h – does not lead to osmotic shock.
• Dehydrates without affecting blood viscosity and
composition.
• Robust RBC – withstand osmotic shock
(kangaroos are similar)
Camel
• What about the hump?
•
•
•
•
Does not store water.
Does store fat – as an energy source.
This is a great piece of adaptation.
Rather than store fat over the whole body
it is localised – reduces the insulation
effect.
Steer
• Tb increases during the day – max about 2000 h
• Un-controlled increase – dissipate heat at night.
• Tb does not return to normal.
• Can keep this up indefinitely – provided access to water
and nights cool down.
• Can keep this up for 3 – 4 days if water limited or no
night-time relief.
Antelope Ground Squirrel
• Burrows.
• Active during the day.
• Tb increases and decrease during the day
- constant at night.
• Forages 100 m from burrow.
• Very active + SR + radiant heat from
ground = increased Tb.
• Goes to burrow to cool off.
Study Questions
• What are the advantages and disadvantages of
large size in hot arid habitats?
• Describe the coping methods animals cn use
when they are exposed to hot arid habitats.
• Define, evaders and endurers and give an
animal example for each.
• What are the advantages of burrowing in terms
of body heat regulation?
• Why is the ability to concentrate urine imprtant in
desert animals.