Transcript Extreme Habitats - Gaughan

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
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Upper limits by behaviour
Steer
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Body Temperature
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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?
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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.