VCE Biology Unit 2Area of Study 01

Adaptations of Organisms

Living in extreme terrestrial environments

Living in extreme terrestrial environments

Desert• Low rainfall• High level of evaporation• Hot (Australia, Sahara) or cold (Central Asia,

South America, Antarctica)Antarctica largest desert – 50 mm rain per year,

14,245,000 km2

Sahara largest ‘hot’ desert 9,000,000 km2

Living in extreme terrestrial environments

Australia has greatest percentage of continent as desert/semi-arid (44% and 37% respectively)

• High temperature• High solar radiation• Low rainfall

Living in extreme terrestrial environments

AnimalsStress– Body temperature– H2O– Salt balance

Living in extreme terrestrial environments

Survival• Regulate these factors or tolerate extreme

fluctuations

Living in extreme terrestrial environments

Temperature regulation assisted by• Behaviour that increases or decreases heat

exchange with external environment.• Circulatory adjustments alter blood flow

through skin – alters heat exchange• Increase or decrease production of metabolic

heat.• Evaporative cooling through sweating or

panting (trade off with water loss)

Living in extreme terrestrial environments

Reptiles• Behaviour changes most important to regulate

rate of heat exchange

Behavioural Thermoregulation• e.g. Australian agamid lizard, Shark Bay, WA

Living in extreme terrestrial environments

• Some iguanid lizards maintain body temperature at ~38°C for extended periods.

• Desert snakes and tortoises maintain body temperature at ~30°C adopt nocturnal behaviour during summer

Living in extreme terrestrial environments

Sleep through bad timesSome animals survive harsh conditions by going

into torpor or hibernation. Torpor (fish, frogs, lizards, birds, bats and mice) allow body temperature to decrease and become inactive or dormant.

Living in extreme terrestrial environments

Frogs burrow into sand during dry season and become dormant

Water holding frog burrows deep into sand and makes a cocoon from its cast off skin and can survive for months.

Living in extreme terrestrial environments

Escaping the cold – hibernationDo any Australian animals hibernate?Short beaked echidna goes into torpor

underground to escape winter/snow in southern mountains.

Living in extreme terrestrial environments

Hibernation• Long term torpor• Happens at onset of winter• In den/burrow• Decrease energy requirements (do not eat)• Hibernation saves 60% of an animal’s annual

energy requirement• Some evidence suggest animals may live longer.

Living in extreme terrestrial environments

Triggers for Hibernation. One of more factors• Scarcity of food• Decrease in temperature• Endocrine response to change in daily light

cycle.• Mammals and birds enter hibernation from

sleep and involve decrease of body temperature close to ambient, but never below zero

Living in extreme terrestrial environments

Triggers for Hibernation. One of more factors• Burrows/dens temperature constant• Metabolism decreased (indicated by decrease in

O2 consumption – leads to fall in body temperature

• Heart rate decreases to around 3 to 10 beats per minute

• Respiration decrease• Slow breathing with long periods of no breathing

Living in extreme terrestrial environments

Plants in arid environmentsAdaptations for reducing water loss• Xenophytes (‘lovers of dryness’)• Two types– Flesh succulent plants (e.g. cacti)– Hard-leaved plants called sclerophylls

Living in extreme terrestrial environments

Adaptations for reducing water loss• Thick waxy cuticle• Hairs covering leaves• Few stomata• Sunken or protected stomata• Reduced leaf surface area to volume• Orientation of leaves away from direct rays of

sun

Living in extreme terrestrial environments

Leaf cuticle and hairs• Xerophytes have thick waxy cuticle

impermeable to water• Hairs reduce leaf temperature and water loss

Living in extreme terrestrial environments

Distribution of Stomata• Fewer stomata. Number and size varies

between species.• Pits surrounded by hairs• Maybe closed at hottest time of day• Succulents close stomata at day and open at

night for uptake of CO2

Living in extreme terrestrial environments

Reduced surface area and leaf orientation• Surface area low to reduce water loss by

transpiration• Some species have needle like leaves (e.g. Hakea and cacti)

• Eucalypts’ leaves hang vertically. Stomata and photosynthetic cells on both sides of leaves (i.e. isobilateral).

Living in extreme terrestrial environments

Coping with salinity on land• [Salt] can be 1/10 of sea water. Combined with

high temperatures and low rain fall.• Creates osmotic stress due to lack of water

Living in extreme terrestrial environments

Halophyte adaptations• Halophytes (‘lovers of salt’) tolerant to high

levels of salt and many are succulents• Regulate water loss and salt accumulation in

leaves from transpiration of water from roots.