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 o C. Above ground range of 16 – 44 o C. This means they can be active during day – escape to burrow to dissipate heat. Many have high T b (40 – 44 o C)

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 T a exceeds 50 o C. 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 T a is 32 o C they can shed 100% of excess heat through the ears.

Endureres Thermal Inertia (adaptive hyperthermia) T b allowed to fluctuate. Heat stored during day and dissipated at night ~ peaks at or just after sunset. Camels 34 – 41 o C (occasionally 45 o C). 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 o C. 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.

Source: Schmidt-Nielson et al 1957; Hudson 1962; Gaughan et al 2004 Lower values set by physiology Upper limits by behaviour

Camel T b increases during the day – max about 2000 h. Controlled increase – dissipate heat at night. T b 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 H 2 O 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 T b increases during the day – max about 2000 h Un-controlled increase – dissipate heat at night. T b 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. T b increases and decrease during the day - constant at night. Forages 100 m from burrow. Very active + SR + radiant heat from ground = increased T b. 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.