KISS Notes Evolution of Australian Biota

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Preliminary Biology Topic 4 “Evolution Aust.Biota”copyright © 2005-22008 keep it simple sciencewww.keepitsimplescience.com.au

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What is this topic about?To keep it as simple as possible, (K.I.S.S.) this topic involves the study of:1. PLATE TECTONICS & THE FORMATION OF AUSTRALIA

2. EVOLUTION IN AUSTRALIA3. ADAPTATIONS FOR REPRODUCTION

4. MAINTAINING BIODIVERSITY

but first, an introduction...Plate Tectonics &

Moving ContinentsYou may already be aware that a map of the world would notalways have looked as it does today.

The science of Plate Tectonics has revealed that theEarth’s crust is made up of a number of separate“plates” which slowly move the continents about,splitting up and colliding over millions of years.

In this topic you will consider some of the evidence forthe moving continents, and learn how Australia cameto be the “island continent”.

More on Evolution...In the previous topic you learned some of the“Facts of Evolution”... the evidence that life onEarth has changed over millions of years.

In this topic you will learn about the process of“Natural Selection” which is believed to be thedriving force that causes evolution to happen

Preliminary Biology Topic 4

EVOLUTION OF AUSTRALIAN BIOTA

... and the losers!

Australia’s Unique Biota“Biota” means all the plants (“Flora”) and animals

(“Fauna”) of a particular region.

You already know that Australia’s native plantsand animals are sometimes cute, sometimes

deadly dangerous and always interesting for theirunique appearance and habits.

In this topic you will find out a little about some ofthe earlier inhabitants of Australia, and what

happened to them.

You will also study some of the ways that ourbiota is superbly adapted to Australia’s harsh and

unpredictable climate.

?

Naturechooses

thesurvivors




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Structureof the Earth

ChangingIdeas aboutAustralianAnimals

The Evidencefor Climate

Change

Evolution ofAust. Plants

Value ofBiodiversity

HowPalaeontology

Can Help

Case Study:Extinction ofthe Thylacine

When AsexualReproduction

is Useful

ReproductiveAdaptations

ofAustralian

Plants

ReproductiveAdaptations

ofAustralianAnimals

Asexual v Sexual

Mitosis v Meiosis

External v Internal Fertilization

NaturalSelection,Variation

and Evolution

Megafauna&

ExtinctionEVOLUTION

ofAUSTRALIAN BIOTA

Plate Tectonics& the

Formation of Australia

Evolutionin Australia

Adaptationsfor

ReproductionMMaaiinnttaaiinniinngg BBiiooddiivveerrssiittyy

Evidencefor

PlateTectonics

CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorising the OUTLINE of a topic helps them learn and remember

the concepts and important facts. As you proceed through the topic, come back to this page regularly to see how each bit fits the whole.

At the end of the notes you will find a blank version of this “Mind Map” to practise on.




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1. PLATE TECTONICS & THE FORMATION OF AUSTRALIA

MMooddeerrnn ccooaassttlliinneess

EEddggee ooffccoonnttiinneennttaall

sshheellff

THE ANCIENT SOUTHERN CONTINENTGONDWANA

AAffrriiccaa

SSoouutthh AAmmeerriiccaa

IInnddiiaa

Aussttrraa

lliiaaAAnnttaarrccttiiccaa

The Evidence for Plate Tectonics

The Structure of the EarthSeismology is the study of earthquakes and the behaviour of the shock waves they produce.

During the 20th century, seismology revealed that the Earth is not a solid ball of rock, but made up of a number of layers.

CROSS-SSECTION of the EARTH

CRUSTooff lloowweerr

ddeennssiittyy rroocckkss

MANTLE ooff hhiigghheerr

ddeennssiittyy rroocckk

OUTERCORE

LLiiqquuiidd iirroonn&& nniicckkeell

INNERCORE

SSoolliidd iirroonn&& nniicckkeell

Furthermore, we have come to realize that thecrust is not a single solid “skin” on the outsideof the Earth. Rather, it has fractured into about adozen “plates” which slide around as the mantlecurrents push from below. Since they are alltouching on the surface of a sphere, as the platesmove they must:

• move apart from each other or, • slide sideways past each otheror, • collide with each other.

As the plates move, they carry the continents,and the crust under the oceans, with them.

Australia wasn’t always the island continent of today.

We now know that the outer layer, the“crust” is not tightly attached to the“mantle” below it. Also, the mantle is notrigid and solid, but “plastic”, and canslowly flow in huge convection currentsthat are bringing heat energy outwardfrom the Earth’s core. These convectioncurrents push against the crust.

SEA-FFLOOR SPREADING

OOcceeaann

AAss ppllaatteess mmoovvee aappaarrtt,, nneewwrroocckk ffiillllss tthhee ggaapp,, ccrreeaattiinngg aa

““mmiidd-oocceeaann rriiddggee””

CCoonnttiinneenntt

Convection Currents inMantle

ppuusshh ccrruusstt ppllaatteess aappaarrtt

CContineent

The Shape of the Continents

The continents of the Earth are like jig-saw puzzle pieces... they fit togetherquite well, especially along the lines ofthe “continental shelf” rather than theactual coastline.

The continental shelf is the true edgeof each continent. In most cases it isunder water today.

The evidence suggests that about 130million years ago all the southerncontinents (plus India, New Zealandand New Guinea) were joined togetherin a single super-continent called“Gondwana”. Forces under the crust,however, caused Gondwana to begin tobreak apart.

Moving at a rate of a few cm per year,Gondwana broke apart and thefragments moved gradually to theirmodern-day positions.



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East Africa issplitting awayfrom the rest

of thecontinent

Great RiftValley

In a few places on Earth, spreadingzones are visible on dry land too. The“Great African Rift Valley” is aspreading zone which will one day makemost of east Africa into an island.

The Rift Valley contains many deeplakes between parallel escarpments.There are several active volcanoes, andthe area is an active earthquake zone.

The Mid-Ocean RidgesIt’s not just the shapes of the continents that convince scientists of “Continental

Drift”. On the ocean floors, under several kilometers of water, the mid-ocean ridgesshow strong evidence of sea-floor spreading where plates are moving apart.

The rocks of the parallel ridges areyoungest in the middle and getprogressively older as you moveoutward.

The “residual magnetism” in the rocks(which was aligned as the rockhardened from molten lava) shows asymmetry on either side of the centralridge. Each matching band ofmagnetism represents a line of new rockformed as the crust plates moved apart.Later, these bands were separated byeven newer rock injected from below asthe crust plates continued to move.

MantleConvectionCurrents

push plates apart

CCeennttrraall RRiifftt

SSyymmmmeettrriiccaall ppaatttteerrnnss ooffmmaaggnneettiissmm oonn eeiitthheerr

ssiiddee ooff cceennttrraall rriiffttPPaarraalllleell uunnddeerrsseeaa

rriiddggeess

NNeeww mmoolltteennrroocckk ffiillllss tthhee

rriifftt

YYoouunnggeessttrroocckkss

OOllddeerrrroocckkss

OOllddeerrrroocckkss

Fossil Evidence for Moving ContinentsThe distribution of certain fossils gives us more evidence of the moving continents.

One particular fossil is a plant calledGlossopteris. It has been discovered in rocks inmany parts of the southern hemisphere,including Antarctica.

A number of animal fossils, dating from 100-200million years ago, have been found only inS.America & Africa, or in Africa, India &Australia. The crocodile-like Mesosaurus isknown from fossils in Africa & South America.

These places are now widely separated, and it isvery unlikely that these plants or animals couldcross an ocean. The explanation is that theseorganisms lived in a united Gondwana, and theirfossils have been separated by later continentalmovement.

AAffrriiccaa

SSoouutthhAAmmeerriiccaa

IInnddiiaa

OOzz

GONDWANA

Mesosaurus

Glossopteris



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India split off early, and bulldozed its waytowards Asia. That collision produced the

Himalayas, with some seafloor sediments now 9km above sea level! Africa also moved north and

is still colliding with Europe.

South America separated about 50mya. Itwent west, and north, and rotated. About 20

mya, it made contact with North America.

Australia and Antarctica (still joined) initially movedeast. Then Antarctica separated and went seriously

south. By 40mya, Australia was isolated from other landmasses, but connected to India by the

oceanic crust of the Indian Ocean.

Since then, Australia has been moving north. Our plateis colliding with Asia, and the Pacific Plate.

Is Australia Still Moving?Apparently so! The ocean floors have now beenwell mapped so we know where the mid-oceanridges are. The positions of frequentearthquakes and active volcanoes identify theplate boundaries.

The volcanic islands to our north indicate thatthis is a “collision zone” between the Indo-Australian plate and the Asian plate.

How fast is the movement?It averages between 2-5 cm per year. This

means about 50km per million years. Asvolcanoes add to the islands, and the plate

slides north, it is likely you will be able to walkto China in 5-10 million years... but you’ll haveto climb over some serious mountains!

GONDWANAFragments

AAffrriiccaa


IInnddiiaa

AAuussttrraalliiaa

AAnnttaarrccttiiccaa

Future Map of East Asia?

Japan joinedto Asianmainland

NZ islandsfurther apartand larger

Indonesianislands becomemountainousland bridgeconnecting

Australia to Asia

The Break-up of Gondwana

There are some living species whichshow the same pattern of distribution asthe fossils such as Glossopteris.

The explanation is that these groupsevolved in Gondwana, and then werecarried to their current locations by thedrifting continents.

Evidence from Distribution of Modern Species

Marsupial mammals which are foundonly in Australia, New Guinea &America. (Fossils are found in Africa)

Antarctic Beech trees found only inAustralia & South America (& fossils inAntarctica).

Large flightless birds; emu, ostrich,rhea & the recently extinct moa (NewZealand) & elephant bird (Madagascar).

Freshwater lungfish in Australia, Africa& S.America.

LungfishMarsupials Flightless birds Antarctic beech



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It was eventually accepted as real, butwhen it became known that itreproduced by laying eggs, it and theechidna were classified into a separatesub-class of mammals... the“Monotremes”.

For more thana century, themonotremeswereconsidered as“living fossils”and thought tobe extremely“primitive” andtherefore,somehowinferior tomainstreamplacental mammals.

The marsupials were thought to be onlyslightly more advanced, and theconsensus was that Australian fauna,like the nation itself, was a bit“backward”.

It was thought that the only reason such“primitives” had survived into themodern era, was because Australia hadbeen isolated so that they faced nocompetition from superior, moreadvanced mammals.


Changing Ideas About Australian AnimalsWhen the first specimen of a platypus was sent back to England after the

European settlement of Australia, it was thought to be a hoax. The platypus seemed an impossible animal, with a duck-like bill, fur like an otter,

webbed feet and a sharp, poisonous spur on its leg.

That perception is changing. Fossildiscoveries in South America ofplatypus-like animals prove thatmonotremes did not just evolve inAustralia, but in wider Gondwana.

They had already faced

competition from“advanced”

placentalmammals before

Australia becameisolated... and

they won!

Furthermore, themore research is

done on the platypus andother native Australians animals, the

more scientists realize that these are not“primitive” creatures. Yes, they have anancient lineage, but they are highlyadapted to the unpredictable Australianclimate, and have thrived throughmillions of years of ecological changesin one of the harshest environments onEarth.

Australian native plants and animals arenow being seen as ancient, but highlysophisticated life forms.

Poisonousspur

Lays eggs, yetproduces milk tofeed its babies

Duck-bill

Webbed feetwith claws




7

Fill in the blank spaces

The study of earthquakes is calleda).................................. This science hasrevealed that the Earth has a number oflayers. On the outside is a thinb)....................... and under it is the thickc)........................ The crust is fracturedinto a number of d)...................... whichcan slide around, driven bye).................... currents in the mantle.This whole concept is referred to as“Plate f)...............................”

The continents fit together like jig-sawpieces, especially if you fit them alongtheir g)........................... shelf rather thancoastline. The continents of Australia,Africa, h)....................., ..........................and .................................... were onceconnected forming the super-continenti)...............................

From about 75 MYA i).............................began to break up forming the separatecontinents of today. Australia separatedfrom j).......................... about 40 MYA andspent k)................ million years totallyisolated. It was in this time that many ofAustralia’s plants and animals evolvedfrom Gondwanan ancestors.

Evidence for “Continental Drift”includes the l)..................................ridges, found along the ocean floors allaround the Earth. These are zoneswhere crustal plates arem).................................. The ocean-floorcrust shows a series of ridges which areyoungest n)........................... and getolder as you go further in eachdirection. The rocks show matchingpatterns of o).......................... on eitherside of the central rift. As the platesmove apart, new crust is formed fromp)............................... coming up fromthe q).............................

More evidence for plate movementcomes from fossils such as the plantr).............................. Its fossils are foundon all southern continents and India.The explanation is that it lived in areasright across s).....................................,and the fossils have been separated byplate movement.

The distribution of some modernspecies can also be explained bycontinental drift. Marsupials are foundin Australia and t).................................Lungfish are in Australia,u)........................ and ................................Other examples are thev)................................ (e.g. emu, ostrich)and the w)..................... ................... tree.

The ancestors of each of these groupsare thought to have lived throughoutGondwana, and the various populationswere separated when the plates moved.

Australia is currently being carriedx)........................ (direction) on they)................................................. plate at aspeed of about z)................ cm per year.

Australian native animals are mainlyaa).................................. (pouched) plusthe platypus and ab)...............................which are egg-laying ac)..........................

They were considered ad)........................and inferior to placentals, but are nowbeing seen as ancient, but highlyae)..................................

WHEN COMPLETED, WORKSHEETS BECOME SECTION SUMMARIES

Worksheet 1 Plate Tectonics & Australia’s Formation



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Multiple Choice1. The movement of the “Tectonic Plates” isdriven by:A. the plates pushing on each other.B. movements of the liquid core.C. thrusting of earthquakes at plate

boundaries.D. convection currents in the mantle.

2. Which present-day landmass was NOT part ofGondwana?A. IndiaB. EuropeC. New ZealandD. Africa

3. Of the following, the youngest rocks would befound:A. near the centre of a mid-ocean ridge.B. at the continental shelf.C. on the ocean floor, well away from the

mid-ocean ridge.D. under folded continental mountains.

4. The distribution of fossils of the plantGlossopteris provide evidence that:A. plant seeds can drift across an ocean

and survive.B. the southern continents were once all

joined together.C. dinosaurs were widespread in Gondwana.D. modern Australian plants evolved from

Glossopteris.

Longer Response QuestionsMark values given are suggestions only, and areto give you an idea of how detailed an answer isappropriate. Answer in the spaces provided.

5. (4 marks) Indentify and describe TWO pieces of evidencethat support the assertion that Australia wasonce part of a larger landmass calledGondwana.

6. (3 marks) Outline how the ideas of scientists aboutAustralian species, such as the platypus, havechanged over the past 200 years.

7. (3 marks) The “ratites” are a family of flightless birds suchas the emu, ostrich and kiwi. None of this groupare native to the northern hemisphere, but arefound throughout the south. Being flightless,and poor swimmers, it is impossible that theyspread by crossing the oceans. Account for their presence on all the majorlandmasses of the southern hemisphere.

Worksheet 2 Practice Questions section 1




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Natural Selection & Evolution

The fact that life on Earth hasundergone a sequence of changes wasdealt with in the previous topic.

The scientific theory to explain how andwhy evolution occurs all hinges on theconcept of “Natural Selection”, and thekey to this is the “variation” within eachspecies... the simple fact thatindividuals are not the same as eachother.

“Natural Selection” refers to the waythat the conditions of nature constantlyselect who survives and who dies. Ifsurvival depends on speed to run from apredator, then the faster individualssurvive and the slower ones get eaten.In a drought those plants with slightlythicker cuticle on their leaves conservewater and survive, while others die.

The Importance of VariationIt is vital for the on-going survival of aspecies that it has variation among theindividuals of the population.

When changes occur in theenvironment, a species with a lot ofvariation has more chance to survive,because out of all the different “types”there is a good chance that at leastsome will survive to breed and continuethe species.

A species with little variation within it,might have no survivors from anenvironmental change, and becomeextinct.

What constitutes an environmentalchange? It could be...• a change of climate.• a new disease, predator or competitor

in the ecosystem.• a change in availability of a food

resource, or any other factor.

It may seem as if Evolution is anintelligent force which directsorganisms in an appropriate direction.In our fictitious population of animals,the climate became colder and it wouldseem that some evolutionary forcecaused an appropriate change in thepopulation... they became squat & hairyto conserve body heat better.

But of course “squat” and “hairy” werealready in the population. They simplybecame more common, and finallypredominant, because these typessurvived in greater numbers andreproduced to pass on theircharacteristics to their offspring.

Evolution is not intelligent. Natureselects the survivors from the different“types” available. Survivors breed... ifyou’re dead, you can’t reproduce!

2. EVOLUTION IN AUSTRALIAHow Natural Selection Works

A population of a species with a lot of “variations”

hairy long long light big squatneck legs colour ears body

Then, the climate changes... winters get colder

hairy survives Squat survives

Survivors breedover many generations

Many die in the harsh winters

The survivors pass on their characteristics.Soon most of the population are squat and hairy.No single animal changed, but the population has

changed because of which animals survived and reproduced.



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The Evidence for Climate Change

Fossils dated between 50-100 millionyears old show that most of centralAustralia was once covered by lushforests. Some of the common plantsincluded the seed-fern Glossopteris andthe rainforest species “AntarcticBeech”.

This proves that at that time much ofAustralia (and much of Gondwana) hada much wetter climate than today. Whensea-levels rose about 40 million yearsago, parts of central Australia werecovered by an inland sea.

Animal fossils include those ofcrocodiles, flamingos and tortoiseswhich indicate extensive waterenvironments.

As Gondwana split up, and Australiamoved north, the climate graduallybecame drier. The evidence is theappearance in the fossil record, at about25 million years ago, of sclerophyllplants beoming very common.

The Sclerophyll Plants

Scleropylls are those plants which areadapted to dry climates. They arecharacterized by thin, small leaves witha very thick waxy cuticle and are veryresistant to drying out. In drought, whenother leaves would wilt and wither,scleropyll leaves maintain their shape,and when water is available again theyquickly regain their normal functioning.

Australian flora today is dominated bythree main sclerophyll types:• Eucalypt (Gum trees)• Banksia (Bottle brush and Grevillia)• Acacia (Wattle & mulga)

Fossils of leaves and pollen in NewZealand and South America show thatthe Eucalypts and Banksias werealready Gondwana inhabitants before 50million years ago, but must have beenrelatively rare and unimportant duringthe time of the great rainforests inAustralia.

However, as the climate dried therainforest plants (like Antarctic Beech)struggled and the sclerophylls thrived.About 25 million years ago sclerophyllpollens suddenly become very commonin the fossil record.


... so there has been a lot ofenvironmental change,

... and a lot of evolution!

Evolution of Australian Biota

TypicalGum Forest

GONDWANAFragments

AAffrriiccaa


IInnddiiaa

AAuussttrraalliiaa

AAnnttaarrccttiiccaa

Over the past 100 million yearsAustralia has gone from being

part of Gondwana to a separate island continent...



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From 2 MYA to Today

By about 2 million years ago, therainforests had lost the battle west ofthe Great Dividing Range. CentralAustralia was partly desertenvironment, with open grasslands andsclerophyll forests surrounding thedeserts. The rainforests still dominatedthe mountains and many valleys alongthe east coast.

The sclerophyll forests containedeucalypts, banksia and acacia and anumber of other types such asCasuarinas.

Then about 100,000 years ago anotherenvironmental factor changed... firebecame more common. We find layersof charcoal and ash in the sedimentsfrom these times. Presumably, the fireswere initially caused by lightning strikesin the dry bushland, but after about40,000 years ago the evidence for firebecomes even more noticeable.

We think the Aboriginal people hadarrived by then, and part of their culturewas to deliberately set fires. They knewthat fire encouraged the growth of moreopen grassland, which attracted moregrazing animals (e.g. large kangaroos)and this meant better hunting for thepeople.

Fire also altered the composition of thesclerophyll woodlands. Some of thesclerophyll plants (especially Banksia)can survive and regenerate quickly afterfire. They became more common.Others, such as Casuarina do notsurvive fire as well, and became lesscommon. Today, the Casuarinas (“she-oaks”) are common in swampy areas,and along creek margins where fireshave less impact, but they are no longera dominant type in the bush as theyonce were.

Adaptations of Banksias to Fire

The Banksia plants of Western Australiaare more “primitive” and resemble thefossils and their modern day Gondwanarelatives in South Africa and NewZealand.

In Eastern Australia the Banksias aremore distantly related and there aremany different species, with manydifferent ways of dealing with fire intheir environment. This seems to be theresult of natural selection acting on thevariations that were present in ancestralBanksia populations.

Some adaptations to cope with fire are:

• Thick, corky bark with epicormic budsunderneath.The buds are stimulated by fire, and sothe blackened trunk soon sprouts newshoots after a fire.

• Lignotubers - thickened roots, fromwhich new shoots sprout after firedestroys everything above ground.

• Hard, woody seed pods (“Banksiamen”) which split open after beingscorched by fire, dropping seeds intothe fertile ashes and germinate rapidlyafter any slight rain.


Banksia showing a seed pod




When Australia became isolated from otherGondwana fragments about 40 million years agoits fauna was dominated by the marsupials(pouched mammals) and reptiles.

As happened in many parts of the world in thepast 20-30 million years, some animals evolvedto be very, very large... the “megafauna”. In theNorthern Hemisphere it was species likemammoth, sabre-tooth cats and hugerhinoceros species. In Australia, the megafaunaincluded:

• Diprotodon - a 2 tonne wombat relative.• Procoptodon - a 3 metre tall kangaroo.• Megalania - a 7 metre, 1,000 kg goanna.

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Climate Change Extinction?Perhaps the megafauna just could not cope withthe climate changes, including the severecooling and drying during the last ice-age?

But then, these animals, and their forebears hadsurvived many previous ice-ages over 25 millionyears. The most recent ice-age was not assevere as some previous.

We await more evidence to settle this debate!

EXAMPLES OF AUSTRALIA’S EXTINCT MEGAFAUNA

Meanwhile, the Animals...There were also many other species of hugekangaroos, wombats, snakes and crocodiles,but it seems that Australia’s megafauna werenot as big as in other parts of the world, possiblybecause the developing sclerophyll flora, andthe ancient, poor soils could not support asmuch biomass as (say) Europe.

It is also notable that the top predators seemedto be reptiles rather than mammals. Oneplausible theory is that reptiles, which do notneed to constantly “burn” food to maintain bodytemperature, need less food and can eat lessoften. Reptiles can survive as top predators infood pyramids that contain less total biomass. Amammal predator needs to eat more often andneeds a food pyramid containing more biomass.

PROCOPTODON

DIPROTODON

Humanfiguregivesscale

What Happened to the Megafauna?In Europe, Asia and North & South America there is convincing evidence that

humans contributed to the extinction of the large mammals. Climate change at theend of the last “Ice-Age” probably helped too, but there is no doubt that early

humans hunted large mammals, like the mammoth, in large numbers.Human-Caused Extinction?

In Australia, most of the megafauna speciesdisappeared between 35,000 and 10,000years ago. Aborigines were well establishedby those times and undoubtably lived at thesame time as these mega-species. However,there is no evidence of them hunting thesespecies... no animal bones in human campsites, no tool cuts on the animal bones.



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A Timeline of Australian Evolutionary Historykeep it simple science

®

00

1100

2200

3300

4400

5500

6600

7700

8800

9900

110000

111100

Sclerophylldominancecomplete

2 MYASclerophyll pollens becomevery common in fossil record.

Australia separates from Antarcticaand begins 25 million years

of complete isolation.South Americaseparates.

MMiilllliioonn

ss ooff YY

eeaarrss

AAggoo

Australia part of Gondwana super-ccontinent.Glossopteris plants common.

Dinosaurs are the dominant animals. Mammals exist, but are minor players.

Gondwana begins breaking up.Africa & India separate.Australia still joined toAntarctica & S.America

Major ExtinctionEvent.

Dinosaurs extinct.Mammals begin evolvingto fill ecological niches

left vacant. Australian Flora dominatedby rainforest species

e.g. Antarctic Beech.Fauna dominated by mammals

and birds.

Australian climate begins to getdrier... rainforests come under

pressure... sclerophylls become more common.

Marsupial & Reptile Megafaunadominate the continent.

Australia “makescontact” with Asia. Bats& various birds come

in by “island hopping”.Acacia plants arrive,

and being sclerophylls,they thrive.

Mega fauna extinct35,000 - 10,000

years ago

Aboriginal people arrive from S.E. Asia, approx 40,000 years ago.Introduce the dingo, and use fire topromote grasslands. Fire alters thebalance of sclerophyll plant types.



14


The Huxley - Wilberforce Debate of 1860

Darwin published his evidence andideas on evolution in 1859, but it tooksome time for people to become awareof them. On first reading, Darwin’s ideasare not easy to absorb and fullyunderstand, so it took time for thetheory to “sink-in”. To this day, itremains one of the least understood ofall the major theories of Science.

One of the events that focused attentionon this new theory was a famous debateat Oxford University in 1860.

The main speakers were ThomasHuxley, who argued the case forDarwin’s theory, and ArchbishopSamuel Willberforce who wasvehemently opposed to it, on bothscientific and religious grounds.

It has generally been considered thatHuxley got the better of the debate andthis event helped establish the Theoryof Evolution as a credible scientific idea.

Probably what was more important wasthat the debate sparked interest inevolution among scientists and led tomuch more study, experiment anddebate over the following years. 150years later we are still researching andlearning about the evolution of life onEarth.

Charles Darwin and Evolutionary TheoryIn the 1830’s a young English naturalist, Charles Darwin, sailedaround the world on board the navy survey ship HMS Beagle.

He studied the plants and animals, and rocks and fossils in many places, especially in South America.

He became convinced that life on Earth had changed, and was capable of evolving by Natural Selection.

He devoted his life to developing his theory, and collecting more evidence to support his ideas. He knew that his

theory would not be readily accepted by the conservative society of the time.

Darwin in AustraliaOn its journey around the world, theBeagle called into Sydney, and Darwinspent time ashore, travelling overland toBathurst and collecting and studyingAustralia’s flora and fauna.

He noted how well suited the plants wereto the dry Australian climate. He was laterto link this to his idea of Natural Selection,explaining the sclerophyll characteristicsas adaptations to the climate.

He also noticed similarities betweensome Australian plants and species hehad seen in S.America and in Africa. Hecould not explain this except by seedsdrifting across oceans, and he carriedout many experiments immersing plantseeds in sea-water to test if it waspossible. (He had no knowledge of “Continental Drift”.)

He was fascinated by the marsupialfauna, but considered them as “inferior”to the placental mammals of othercontinents, and believed they had onlysurvived because of lack of competitionfrom “real” mammals.

In terms of evolution he believed themarsupials were bound to lose the“Survival of the Fittest” competition andwould eventually become extinct.

The city of Darwin, Northern Territory,was named in his his honour.




15

Fill in the blanks spaces.

When the natural environment“chooses” which organisms survive toreproduce, and which do not, we saythat a)................................................ is atwork. The more b)...................................among the members of a species, thebetter chance the species has to survivewhen c)......................................... .............

We know that Australia was largelycovered by rainforest between 50-100MYA, because of fossils ofd)....................................... (seed fern) ande)...................................... Beech. At onetime central Australia was covered by aninland f)...................... Animal fossils,including g)........................................indicate many water environments.

Australia separated fromh)................................... about i)................MYA, and became totally isolated. As itdrifted north the climate graduallybecame j).................................... By aboutk).................. MYA the fossil pollen froml)....................................... plants becomescommon.

Sclerophylls are characterized bym)............................ leaves with a thickn)............................ which resists waterloss. The main three types areo)............................, ............................ and.................................. Two of these typesevolved in Gondwana, but thep)........................ probably came fromAsia.

By 2 MYA, most of Australia wasdominated by q)........................................forest with rainforest only remainingalong the mountains and ther)........................ coast.

About 100,000 years ago a newenvironmental factor became important...s).................... At first it was probablystarted by t)........................... but later theAboriginal people set it deliberately inorder to u)....................................................which improved hunting. Regular firesaltered the balance of the different planttypes: the v)................................. becameless common, while fire resistant typesbecame predominant.

Some of the adaptations shown byBanksias to cope with fire includew).............................. which are thickenedroots which sprout new shoots after fire,and x)............................. seed pods whichrelease seeds only after fire.

The animal life, or y)......................, wasdominated by reptiles andz).................................. (type of mammal).Some very large animals, collectivelyknown as aa)................................ evolved.The largest was a 2-tonne relative of thewombat called ab)......................................All the megafauna became extinctbetween 35,000-10,000 years ago. It maybe their extinction was caused byac)........................ .............................. orsimply that they could not cope withad)..............................................................

Charles Darwin studied the Australianbiota during his voyage on HMSae)........................... in the 1830’s. Henoted how well adapted to the climatethe af)................................. were andlinked that to his theory of evolution byag)........................... ............................However, he thought the animals wereah).................................... and believedthey would soon becomeai)....................................... in competitionwith aj)....................................... mammals.


Worksheet 3 Evolution in Australia



16


Longer Response QuestionsAnswer on back, if insufficient space.

9. (2 marks) Identify the relationship between variationswithin a species and the chances of survival ofthe species, when the environment changes.

10. (5 marks) Discuss the changes that occurred to theAustralian climate, and to the flora over thepast 50 million years. In your answer, describe the evidence for thechanges you describe.

11. (5 marks) a) How would you identify a plant as a“sclerophyll”?

b) Identify two common types of sclerophylls inthe modern Australian flora.

12. (4 marks)a) Identify a member of Australia’s extinct“megafauna” known from its fossils.

b) List similarities and differences between thenamed example in (a) and any related livingspecies.

13. (4 marks) Discuss Charles Darwin’s observations ofAustralian biota and relate these to his theoryof evolution.

Multiple Choice1. “Natural Selection” is the process when:A. living things change to suit their

environment.B. the organisms with “better”

characteristics live longer.C. the conditions of the environment

determine which “variations” survive.D. the surviving individuals are the ones

which breeed.

2. For long-term survival of a species, it is anadvantage to have:A. a lot of genetic variations in the population.B. a lot of individuals who are very similar.C. a lot of very large and strong individualsD. a fast-changing environment.

3. The fossil evidence shows that 50-100 MYAmost of Australia was covered by:A. desertB. oceanC. rainforestD. sclerophyll forests

4.Which of the following would NOT beconsidered a sclerophyll plant?A. Red gumB. Golden wattleC. Bottle-brushD. Morton Bay fig

5. According to the fossil evidence, thesclerophyll plants became significant membersof Australian flora about:A. 2 MYA B. 25 MYAC. 40 MYA D. 100 MYA

6. A significant factor in the Australianenvironment for the past 100,000 years has been:A. widespread rainforest.B. fire.C. an inland sea.D. heavy rain and flooding.

7. A “lignotuber” is an adaptation of the Banksiaplants to help them:A. reproduce asexuallyB. attract pollinating animalsC. survive a bushfireD. achieve internal fertilization.

8. Australia’s “megafauna” were not as large asthe megafauna that evolved in other parts of theworld. One possible explanation for this is:A. humans hunted and killed the largest ones.B. the larger animals could not outrun fires.C. being marsupials, they grew more slowly.D. the soils and plant life could not support

so much biomass.

Worksheet 4 Practice Questions section 2




17

3. ADAPTATIONS FOR REPRODUCTION

Asexual Reproduction

Sexual ReproductionSexual reproduction always involves 2 parents who combine part of their genetic

information to produce offspring which are different to both parents.

Asexual Reproduction in Multicellular Life

Many multi-cellular organisms are able toreproduce asexually.

Fungi, such asmushrooms, reproduce byreleasing “spores”. Eachspore is a single cell whichcan grow into a new fungus.The spore cells areproduced by mitosis, andreleased from a single “parent”.

Many Plants can reproduce asexually bysending out “runners”.

These same plants can also reproduce sexually with their flowers.

Unicellular ReproductionSingle-celledorganismssuch asbacteriareproduce bysimplydividing intwo bymitosis. The offspring cells are geneticallyidentical to each other, and to the “parent cell”.

ParentPlant

The runner is anoutgrowth stemwhich grows into

a new plant.

offspringplant

Regardless of the details, asexual reproduction always:

• requires only one parent.• involves mitosis cell division.• produces offspring which are genetically

identical to the parent and to each other.

MaleParent

Grows by mitosis

Sperm cell Egg cell

Zygote(first cell of

the offspring)

Embryo(developingoffspring)

FemaleParent

Fertilisation

meiosismeiosis

The key to sexual reproduction is theproduction of the “reproductivve cells”

((egg and sperm).This invvolvves a special cell divvision

called mmeeiioossiiss.

Advantage Asexual reproduction can produce largenumbers of offspring quickly, to take advantageof a sudden or temporary increase in someenvironmental resource such as food.

DisadvantageBy producing genetically identical offspring, thereis less variation in the population. If anenvironmental change occurs, a low-variationspecies is at risk of extinction.

AdvantageSexual reproduction produces more variation ina population, by mixing genes in newcombinations. This helps a species survivewhen environments change.

DisadvantageSexual reproduction is more complex, and oftentakes more time and energy to achieve.



18


External FertilisationFor organisms that live in water, fertilisation isgenerally achieved by both parents simplyreleasing eggs and sperm into the waterenvironment. Since fertilisation occurs outsidethe organisms’ bodies, this is externalfertilisation.

Each species may have some strategy to ensurethat male and female parents release theirgametes at the same time and in the same place:

Most fish species have “mating rituals” andvisual signals which stimulate a mating pair torelease gametes together.

External and Internal FertilisationSexual reproduction always involves the process of fertilisation...

when egg and sperm fuse together forming one new cell (the “zygote”) which contains genetic information from both parents.

For fertilisation to occur, the sperm cells must swim to the egg.Organismssuch as coralsand spongesreleasegametes whena certain“environmentaltrigger” occurs,such as a fullMoon, or anespecially high tide.

Either way, external fertilisation is to someextent a “hit-and-miss” strategy, often involvingmillions of gametes, many of which are wasted.

Terrestrial Plants• produce their male gametes wrapped in a

protective capsule to prevent drying... a pollen grain.

• use either the wind, or animal pollinators (e.g. bees) to carry the pollen to a flower.

• the pollen grain then releases its sperm cellinto a fluid-filled tube (the pollen tube). The sperm can swim down to reach the egg,inside the ovary of the flower.

Internal FertilisationFor organisms which live on land, an unprotected egg or sperm cell would rapidly dry out and die.

Also, the sperm cells cannot “swim” through the air, or across the ground surface... they needwater to swim through. To solve these problems, terrestrial organisms use internal fertilisation.

Many speciesuse brightly

coloured petals toattract animal

pollinators

Internal Fertilization in a Flowering Plant

Pollen grain onstigma of flower

Pollen releasessperm cell whichswims through

pollen tube tofertilize an egg

Eggs, insideovary

Terrestrial AnimalsThe male uses his penis (or similar structure) todeposit sperm inside the female’s reproductivetract. The sperm cells are never exposed to thedrying outside environment.

The female system is lined with tissue with afilm of moisture always present, so the spermcells can swim to find and fertilise the egg(s)inside the female’s body.

There are a number of strategies fordevelopment of the zygote after fertilisation:

Birds & Most ReptilesThe female lays eggs and the embryos developoutside her body and hatch from the eggs.

Some ReptilesThe female keeps the fertilized eggs within herbody. When they hatch, the babies emerge fromher body vent as if being born.

Marsupial MammalsAfter a very short gestation, the foetus is bornand crawls into a pouch. It feeds on milk, whiledeveloping fully in the pouch.

Placental MammalsThe foetus develops for a relatively long time insidethe female’s body, nourished via the placenta.When fully developed, the baby is “born”.



19

Internal & External Fertilisation SimilaritiesBoth involve sperm fertilising the egg in sexualreproduction. The sperm must swim to the eggin both cases.

DifferencesExternal InternalSperm & eggs Sperm released inside both released into female body.outside environment.

Sperm swim in the Sperm swim in fluidwater of the in female reproductiveenvironment. tract.

Usually many eggs Usually fewer eggs produced to improve because fertilisation chance of fertilisation. is more likely.


Comparison of Mitosis and MeiosisMITOSIS MEIOSISSingle cell-division, Double division, producesproduces 2 “daughter 4 egg or sperm cellscells

Chromosomes line up Chromosomes line up in singly during division pairs during division

Daughter cells identical Gamete cells are all to parent cell, and to different to each othereach other

Number of Number of chromosomeschromosomes halved (so that chromos.is maintained number is restored at

fertilisation)

Occurs in asexual Occurs only to makereproduction and in gametes for sexualgrowth and repair reproduction

Internal fertilisation is an adaptation to the terrestrial environment

As part of your studies in this section,the syllabus requires you to comparethe 2 cell divisions, Mitosis & Meiosis.

The syllabus also requires you to“compare & contrast” internal andexternal fertilisation. This means to findsimilarities and differences.

How Fertilisation Method Relates to HabitatThe great success of sexual reproduction is that it greatly increases the amount of

variation in a species. This gives Natural Selection more opportunity when theenvironment changes, and more chance for species survival and evolution.

The big problem with sexual reproduction is achieving fertilisation.

The Evolution of SexIn the previous topic it was shown that sexualreproduction was “invented” by living thingsabout 1 billion years ago, in the aquaticenvironment. The process evolved in a wateryenvironment where the cells could not dry out,and where one gamete cell, if equipped with aflagellum tail, could actively swim to seek outthe other gamete. The result is that externalfertilisation is totally suited to the aquaticenvironment where it first evolved.

The first land plants to evolve were mosses andlater ferns. To this day, both these types rely onvery moist conditions for the sexual stage oftheir complicated reproductive cycles. Bothtypes are confined to relatively wet habitats, orto places where there is a “wet season” duringwhich their male gametes can swim to find theeggs.

The first land vertebrates were the amphibians.They never reallymastered the terrestrialenvironment and 300million years later, theirdescendants still returnto water to breed sothat their externalfertilisation will work.

The true colonisation ofthe terrestrialenvironment came only when internalfertilisation was first invented:

• in plants by the cone-bearing “conifers”

• in animals by the reptiles, and later birds and mammals.



20

Adaptations for PollinationSome Australian plants, such as the Acacia(wattles) rely on the wind to achieve pollination.

They produce large amounts of fine, light pollenwhich blows easily on the breeze.

Their flowers have protruding stigmas, whichcatch any incoming, wind-blown pollen.

Many other plants rely on animals to carrypollen from plant to plant. Unlike the northernhemisphere, where the honey bee is the majorpollinator, many Australian plants rely onvertebrate animals such as birds, bats andpossums.

The Callistemons (Bottle brushes) andGrevillias mainly depend on the many “honey-eaters” and parrots which feed on nectar.

They produce flowers which lack petals, buthave masses of stamens to produce pollen, andstigmas to receive pollen from another flower.

They have brightly coloured flowers, producinghuge quantities of sugary nectar, to attract birds.

Their pollen grains are sticky, or covered withtiny hooks, so they cling to bird feathers.

As the birds move from plant to plant feeding,they accidentally pick up masses of pollengrains and later deposit some on receptiveflowers of the same species.

Many of the Melaleucas(paperbarks) rely on “flying-foxes”for pollination. Since these fruitbats are nocturnal, and relativelyheavy animals, the paperbarkflowers:

• are carried on strong branches,to support feeding bats.

• grow in large clusters, so at least some will survive beingeaten by the bats.

• are white or pale yellow to be seen better in moonlight.

Adaptations for Seed DispersalOnce again, some Australian plants haveadapted to use the wind, while others enlist thehelp of animals to disperse their seeds.

Some of the desert grasses, such as featherspear grass, produce tiny seeds which have finehairs attached. Being so light and “fluffy” theycan be picked up on the slightest breeze. Instronger winds they can be transportedhundreds of kilometres.

The familiar bindii plant relies on animals. Itsseeds have a sharp point which penetrates anyfoot that steps on them, (or shoe or bicycle tyre)so they are carried some distance away beforefalling out or being picked out. The dispersedseed lies dormant in the soil until it germinatesin the following season.

In the “burr” plants, such as sheep’s burr, theseed is covered in small spikes and hooks.These will stick to the fur of any passing animaland be carried off to a new location. Eventuallythe animal will groom itself or shed its fur, thusdepositing the seed possibly many kilometresfrom the parent plant.

Many of Australia’s rainforest plants, such asnative rasberry, produce their seeds inside afleshy fruit which is highly attractive as food forthe fruit bats and various birds. The seeds areeaten too, but are not digested and pass throughthe digestive system intact. Eventually theseeds are deposited in a new location, and withthe added bonus of a rich manure fertilizer.

Some plantshave a tough

seed coatwhich only

allowsgermination

after beingsoftened byan animal’s

digestivesystem.


“Flying Fox” batsare important

pollinators and seed dispersers

in Australianrainforests

Reproductive Adaptations of Australian FloraFor a terrestrial plant the first step toward achieving fertilisation is to successfullytransfer pollen from one plant to the flowers of another. After fertilisation, the big

problem is to disperse the seeds so they can germinate and grow.



21

Australia is the only continent where themammal fauna is almost exclusivelymarsupials... the pouched mammals. For over acentury the opinion of most biologists was thatmarsupials were “primitive”.

However, we now realize that the marsupialsdominate the Australian scene because they aresuperbly adapted to survive in the harsh andunpredictable climate. One of the major aspectsof their adaptation to the environment is theirmethod of reproduction.

Short GestationMarsupials have a very short gestation period andthe baby is born in a very undeveloped state. Thiscan be an advantage under conditions of droughtand severe food shortage. If the baby dies, then at

least the mother hasnot “wasted” a lot of

her own bodyresources as a

placental mammalwould in a much

longer gestation. Thisgives the adult a

greater chance tosurvive until

conditions improve,and breeding can

recommence.

High Birth RateUnder good conditions, when there is plenty offood, a marsupial can breed rapidly andincrease the population more quickly. Forexample, the red kangaroo can have an olderjoey at foot, but still feeding from the milkglands in the pouch, while having a younger onein the pouch, and another embryo in the wombawaiting its turn.

Suspended DevelopmentThe development of a marsupial embryo canalso be suspended (“embryonic diapause”) iftimes are tough. When conditions improve, theembryo continues its development and is bornwhen conditions are better for its survival.

Under extreme conditions, it has been knownfor the lone female survivor from a kangaroomob to raise her male joey, who was in“suspended animation” for 2 years, then matewith him and re-establish the population.

No placental mammal could ever do that.

Adaptations to Ensure FertilisationLike mammals in many other parts of the world,in many Australian species the males competewith each other for the right to mate with thefemales.

All the largerkangaroo and wallabyspecies compete with

“boxing” matchesamong the males.This competition

ensures that only thestrongest and

healthiest males getto father the babies.

This behaviour helpsto ensure successful

fertilisation andhealthy, robust offspring.

Among native rodents, such as the spinifexhopping mouse, a male secretes a “plug” ofmucous into the female’s vagina after his spermhas been deposited. This helps ensurefertilisation of the eggs, and prevents othermales mating with the female.

In many parts of the world, where the seasonsare highly predictable, many species have a“breeding season” so that the young will beborn in spring when food is plentiful. InAustralia this technique is used (e.g. the many“Christmas beetles”) but many amphibians,reptiles and mammals breed not by the seasons,but by the rains.

They might not breed for several years duringdrought, but when rain falls in the desert there isa sudden burst of plant growth and animalmatings. Females ovulate and become receptiveand the males become sexually active and seekout their mates.

This instinctive behaviour helps to ensuresuccessful fertilisation, and that the offspringwill be born while there is ample food. Anexample is the “water-holding” desert frog,which lies dormant for years, buried deep insandy soil, surounded by a waterproof layer ofmucous. Within hours of heavy rain, thousandsof frogs emerge to mate and lay eggs in theshort-lived desert pools.


Reproductive Adaptations of Australian Fauna



22

Sexual reproduction has the advantage ofproducing genetic variation in the population.The disadvantage is that it costs more, in energyand time, to make all that pollen, or the nectar toattract pollinators, or for animals to find theirmates, compete with others or defend aterritory.

Sometimes it is an advantage to be able toreproduce asexually. Many Australian plants areable to reproduce by both methods.

Sturt’s Desert PeaThis plant grows in aridareas of central Australia.It reproduces sexually,producing seeds whichcan lie dormant in thesoil for many yearswaiting for suitableconditions to germinate.

It can also reproduceasexually by sending out“runners”. In theoccasional periods ofgood rain in the desert, a single plant can sendout many runners and rapidly produce dozensof offspring, which cover large areas ofground.

By using both methods, the desert pea gains theadvantages of both... the ability to reproducecheaply and rapidly to take advantage of goodconditions, and achieve the genetic variationswhich help a species survive when theenvironment changes.

Asexual Animals

A few simple animals can do somethingsimilar. Among the insects, the aphidscan reproduce asexually to produceenormous numbers of offspring in ashort time, to take advantage of a short-term abundance of food. The femaleaphids are able to produce hundreds ofunfertilised eggs which develop into aclone of identical female offspring.

At other times, the females matesexually with males to produceoffspring with greater genetic variety.


Many of the examples already given notonly help ensure successfulfertilisation, but also that the offspringwill have a better chance of survival.

For example:

• males competing to mate ensures that offspring get genes from strong and healthy fathers.

• timing reproduction to the conditionsensures that babies are born at times of good food supply.

Adaptations to Ensure Offspring SurvivalAnother adaptation that helps ensuresurvival of offspring is the territorial andfamily behaviours in many Australianspecies such as kookaburras andmagpies.

By living in family groups which holdand defend a territory against others ofthe same species, they ensure that theoffspring can be well fed from theresources within the territory, as well asbeing protected and nurtured by asupportive family group.

When Asexual Reproduction is Useful

Magnified view of ofaphids on a plant leaf.The smaller ones areasexual offspring of

the larger ones.




23

Fill in the blank spaces.

Asexual reproduction involves a)................parent(s). The offspring are geneticallyb)....................... to their c).......................... and toeach other. They are a d)........................... Theadvantage of asexual reproduction is that itallows e)..................................................................to take advantage of good conditions. Thedisadvantage is lack of f).................................,which helps a species survive wheng)...........................................................................

All forms of asexual reproduction involve thecell division called h).......................................

Sexual reproduction involves the cell divisioni)............................. to produce the reproductivecells or j)........................ Each gamete isgenetically k)........................... and the number ofl)..................................... has been halved, so thatthe correct number is restored whenm)..................................................... occurs.

AnimalsThe marsupials all give birth to babies that arevery t)............................ This is an advantage intime of drought because u)............................................................................................................Many marsupials are able to suspend thedevelopment of the embryo in the uterus, anddelay the birth until v).........................................................................

In many species the males w)......................... forthe right to x)..................... with the females. Thishelps ensure that the healthiest, strongest malespass on y)........................ to the next generation.Rather than having a regular “breeding season”,many Australian animals are stimulated to breedwhen z)............................... ..................................

Many species such as aa)..................................live in family groups and hold a “territory”. Thishelps ensure that offspring ab).............................

Many plants, such as ac).........................................can reproduce both ad)................................. andsexually. When conditions are good, the plantssend out ae)............................... to rapidly buildup the population. When conditions are tough,the sexually produced seeds survive untilaf)............................ By using both reproductivestrategies, the plant gains the advantages ofboth. It can ag)........................... when conditionsare good, and has genetic ah)........................which helps a species survive whenai)............................................................................

Worksheet 5 General Adaptations for Reproduction

Worksheet 6 Australian Adaptations for ReproductionPlantsAmong Australian flora there are a variety ofadaptations to achieve pollination and seeddispersal.. Wind pollination is used by thea)............................ plant group. The pollengrains are b)................................. and the flowershave stigmas which c)..................................... soas to catch pollen better.

The bottle-brushes and Grevillias rely ond)................... to carry pollen. They producelarge amounts of e)................. to attract birds,and the pollen is f).................. so that itg)...................... to the feathers. Many of theMelaleuca plants rely on h)...................... forpollination. Their flowers are light coloured sothat i)................................. They grow in largemasses so that j)...................................... andthey grow on strong branches so k)..........................................

For seed-dispersal, the feather spear grassrelies on l).......................... Its seeds have manym)............................ attached which means it canbe n)........................ even on a light breeze. Otherplants such as o)................. and p)......................have seeds covered in spikes or hooks so theywill be q).......................... by animals. Manyrainforest plants produce fruit which are eatenby r)................ and ................ The seeds survivedigestion and are deposited elsewhere. Someseeds will only germinate after s).........................................................................

In n).......................... environments, fertilisationoften occurs outside the organisms body. This iscalled o).................................. fertilisation. Interrestrial environments, most organisms haveevolved to use p)................................ fertilisation.

Land plants have adapted to have the malegamete, called q)............................., enclosed in acapsule. This can be transported by ther)........................... or carried by various animals.Once it reaches a receptive flower, the “sperm”cell is released to swim along thes)........................ tube to the t)............................. ofthe flower where the eggs are.

In animals, the female reproductive system iskept u)......................... so that sperm can swim tothe eggs. In most cases of internal fertilisation,v)...................... (more/less) eggs are producedcompared to external fertilisation.





24

The Value of BiodiversityBiodiversity refers to the variety of differentspecies of plants and animals. In allecosystems, the greater the biodiversity, themore stable and resilient the system is... thebetter able it is to survive and adjust whenchanges occur or disasters happen.

The greatest threat to biodiversity is humanactivities. Humans:-• destroy habitats to create space for

agriculture, roads, etc.• introduce exotic species to habitats where they

have no natural predators or diseases. Theyover-populate and out-compete the natives.

• pollute environments with industrialchemicals or pesticides which kill species andupset the balance of the ecosystem.

We need to maintain biodiversity in order tohelp the natural ecosystems survive in asustainable form.

Current Efforts to Monitor BiodiversityTo have any chance of maintaining biodiversitywe first need information about things like:

• how many species live in each ecosystem.• the abundance of species, especially those

thought to be rare or endangered.• how the abundance changes over time.

This sort of information can only be gathered bypeople setting out to observe, measure andcount organisms in their natural habitats.

At any given moment there are dozens ofprojects running all over NSW. These projectsare organized and run by government agencies,NSW National Parks & Wildlife Service,Universities and “wildlife organizations”.

Many projects are not just done by professionalscientists, but rely on amateur volunteers. Acouple of interesting projects running at thetime of writing are:

• NSW Fisheries Dept. are tagging grey nursesharks, and asking for any sightings to bereported. They hope to build up information aboutshark movements and population size.

• The NSW Wader Study Group are seekingvolunteers to “adopt” an estuary and carry outregular counts of shorebirds.

How Palaeontology Can HelpPalaeontology, the study of fossils, providesinformation about plants and animals of thepast, how they evolved and in some cases howthey became extinct.

This can give us pointers about modern plantsand animals, and allow us to make predictionsabout how they may evolve in the future, andwhat factors might threaten them withextinction.

For example, recent research on the fossil teethof kangaroos gives some evidence that some ofthe modern, living species seem to havebecome smaller over the past 30,000 years orso. One explanation is that the aborigines havetended to take the larger individuals whenhunting, thereby leaving more smallerindividuals to breed the next generation.

Over thousands of years this “selective hunting”has acted just like Natural Selection, causingchanges in the populations... in this case a“shrinking” of the average size of the animals.

This helps us to predict the effects of humanactivities on species. For example, when wecatch fish we tend to keep the largest, andrelease the smaller ones. Will this cause the fishpopulations to evolve to be smaller? Fisheriesscientists are already finding evidence for thisoccurring in some fish species.

Palaeontology has revealed how the flora andfauna of Australia changed in its relativeabundance and in its distribution as the continentunderwent climate change over the past 50 millionyears. For example, we understand reasonablywell how, as the climate dried, the rainforestscontracted to the mountains and east coast andrainforest species, such as the antarctic beechdeclined from being a dominant species to nearextinction.

Meanwhile, the sclerophyll plants expandedtheir distribution to become the dominant flora.

We now face a major climate change in the formof “Global Warming”. The knowledge gainedfrom palaeontology allows scientists to makepredictions about the future changes todistribution of our modern plants and animalsas climate changes occurs.

4. MAINTAINING BIODIVERSITYC

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25

Case Study: the ThylacineEvolution, Survival & Extinction

of a SpeciesThe Thylacine or “Tasmanian Tiger” was onceone of the major marsupial carnivores inAustralia. It became extinct on the mainlandabout 3,000 years ago, but survived in Tasmaniauntil about 70 years ago. The last knownindividual died in Hobart Zoo in 1936. Therehave been a number of unconfirmed reportedsightings since then, but it is generally believedto be extinct.

Reasons for Thylacine EvolutionAccording to the fossil record (admittedly rathersparse) ancestral Thylacines evolved about 50million years ago. Related to the quolls, thesuccessful evolution of the species canprobably be attributed to:

The extinction of the dinosaurs left an“ecological vacuum” which allowed mammalsand birds to undergo a huge diversification andradiation of different types

The general success of marsupials onthe Australian continent, especially after itbecame isolated from other parts of Gondwana.

Aspects of this success have already beendiscussed, but certainly the marsupialreproductive method seems especially wellsuited to the uncertainties of an irregularclimate like Australia’s.

Reasons for Thylacine SurvivalThe Thylacine possessed a number ofadaptations which may have allowed it to thriveas top predator for tens of millions of years.

It had an enormously wide and powerful bite.The Thylacine jaw could open to almost 180o,and it possessed powerful jaw muscles. Thisallowed it to deliver skull-crushing bites to itsprey, so this relatively small animal could takerelatively large prey. It could also eat every partof its prey, including large bones. This was amajor advantage in the tough Australianconditions.

It was also a solitary animal. The Thylacinecould not afford to hunt in packs because thelow productivity of the sclerophyll forests andpoor soils could not support herds of grazingprey animals which a hunter group need.

Thylacines kept a solitary existence, comingtogether only to mate. This helped this small butdeadly predator to thrive in the low-productivityAustralian bush.

Reasons for Thylacine ExtinctionThe Thylacine died out on the Australianmainland about 3,000 years ago. This wasprobably due to the introduction of the dingofrom Asia, possibly by Malay fishermen whovisited the northern coasts by boat.

The dingo’s abundance rose as that of theThylacine declined... a classic example of whathappens when 2 species compete.

The dingo never got to Tasmania, and there theThylacline survived. However, when theEuropean settlers arrived, the Thylacinesquickly learned to hunt sheep. This promptedthe government to place a bounty on them in1888. Thousands were shot, and an epidemic ofan introduced disease killed even more.

Ironically, in the year that the last Thylacinedied, the species was given “protected” status.


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26


Multiple Choice1. Which statement about mitosis isINCORRECT?A. the chromosome number is halved.B. the daughter cells are genetically identicalC. is the basis for all asexual reproduction.D. produces 2 daughter cells from a single

division.

2. A “pollen grain” can be thought of as:A. an egg in a shell.B. a plant seed.C. a sperm cell in a waterproof capsule.D. an asexual spore

3. Internal fertilization, when compared toexternal fertilization, usually:A. involves fewer eggs being produced.B. is less likely to be successful.C. wastes a lot of gametes.D. occurs in the aquatic environment.

4. A plant which relies on the wind forpollination is likely to produce:A. large sticky pollen grains.B. small flowers with protruding stigmas.C. large, colourful flowers.D. large amounts of nectar.

5. A plant which produces masses of whiteflowers supported on strong branches may berelying on which pollinator?A. an insect B. a birdC. the wind D. a fruit bat

6. The sharp “prickles” of the “bindii” plant isan adaptation for A. pollination B. seed dispersalC. internal fertilization D. fire resistance

7. Many Australian animals improve thechances of survival of their offspring by:A. reproducing rapidly by asexual means

when conditions are tough.B. holding them in a pouch during

development.C. timing reproduction to rain and good

food suppyD. competing with each other for the

right to mate.

8. Which of the following is NOT an adaptationpossessed by the extinct Thylacine?A. Camouflage stripes and colouration.B. Extremely powerful bite.C. Solitary habits.D. Gave birth to highly developed offspring.

Longer Response QuestionsAnswer on back if insufficient space.9. (4 marks) Distinguish between the processes of Mitosisand Meiosis in terms of the daughter cellsproduced.

10. (6 marks)a) Compare and contrast internal and externalfertilization.

b) Discuss the relative success of these formsof fertilization in relation to the colonization ofthe terrestrial and aquatic environments.

11. (4 marks) Describe the conditions underwhich asexual reproduction is advantageous,with reference to a specific Australian example.

12. (5 marks) For many years Australian marsupials wereconsidered “primitive” and “inferior” toplacental mammals. Explain how the marsupialmethod of reproduction is actually anadvantage under Australian conditions.

13. (6 marks) Describe, with named examples, TWO differentmechanisms found in Australian flora forpollination.

14. (3 marks) Outline the reasons for the extinction of anamed Australian animal.

15. (4 marks) a) Explain the need to maintain Biodiversity.

b) Discuss a current effort to monitorbiodiversity.

Worksheet 7 Practice Questions sections 3 & 4




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EVOLUTIONof

AUSTRALIAN BIOTA

CONCEPT DIAGRAM (“Mind Map”) OF TOPICSome students find that memorising the OUTLINE of a topic

helps them learn and remember the concepts and important facts. Practise on this blank version.



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Answer SectionWorksheet 1a) seismology b) crustc) mantle d) platese) convection f) Tectonicsg) continentalh) South America, Antarctica & Indiai) Gondwana j) Antarcticak) 25 l) mid-oceanm) moving apart/spreading /growingn) in the middle o) (residual) magnetismp) molten rock / lava / magmaq) mantle r) Glossopteriss) Gondwana t) Americau) Africa & S.America v)flightless birds (ratites)w) antarctic beech x) northwardsy) Indo-Australian z) 2-5 cmaa) marsupials ab) echidnaac) Monotremes ad) primitiveae) adapted / sophisticated

Worksheet 21. D 2. B 3. A 4. B5.(1) The shapes of the continents are like jig-sawpieces. They fit together almost perfectly if the“continental shelf” is used as the actual edge ofeach continent. Such fitting together suggestsstrongly that Australia was once joined toAntarctica & India.

(2) Fossils & rock layers match up perfectly ondifferent continents. For example, fossils of theextinct seed fern “Glossopteris” are foundacross S.America, Africa, India, Antarctica andAustralia. The explanation is that this plant oncelived right across Gondwana, and its fossilshave been carried to their current locations bythe drifting of the continents.6.Initially specimens of the platypus were thoughtto be fakes. Later it came to be considered as“primitive” and inferior to “real” (placental)mammals. As more evidence and knowledgeaccumulates, it is now realized that theplatypus, and other Australian animals, areancient, but highly adapted to the unpredictableAust. environment.7. It is thought that the ancestors of the ratitesevolved in Gondwana when it was still onecontinent. As Gondwana split up, populations offlightless birds were carried away on eachfragment. Each population, now isolated fromothers, evolved into the modern species on theseparate continents... ostrich in Africa, emu inAustralia etc.


Worksheet 3a) Natural Selection b) variationc) the environment changesd) Glossopteris e) Antarcticf) sea g) crocodiles/flamingosh) Antarctica i) 40j) drier k) 25l) sclerophyll m) thin, smalln) cuticle (waxy covering)o) Eucalypts, Banksia, Acaciap) Acacia q) sclerophyll forestr) east s) firet) lightningu) encouraged growth of grasslands v) Casuarina w) lignotubersx) hard, woody y) faunaz) marsupials aa) megafaunaab) Diprotodon ac) hunting by humansad) climate change ae) Beagleaf) plants ag) natural selectionah) primitive ai) extinctaj) placental

Worksheet 41. C 2. A 3. C 4. D5. B 6. B 7. C 8. D

9.The greater the amount of variation in a species,the better the chance of the species survivingwhen the environment changes. If all themembers of a species are very similar (littlevariation) then there is a good chance therewould be no survivors of an environmentalchange, and the species would become extinct.

10. Between 50-100 MYA much of Australia wascovered with rainforest, wetland environments,and partly by an inland sea at one time. Theevidence is the fossil record, which shows thatrainforest species, such as Antarctic Beechwere widespread, and the animal life includedmany crocodiles, flamingos and turtles... allevidence of a wet climate.

About 25 MYA the fossils show a markedincrease in pollens from sclerophyll plants.These are adapted to survive drought, and showthat the climate must have become drier. Adecrease in pollens from rainforest speciesshows that these habitats were shrinking.

By 2 MYA, the rainforests had disappeared frommost of Australia. After about 100,000 years ago,a lot of ash and charcoal in the sedimentsindicates the increasing occurrence of fire in theenvironment, indicating that the modern, dry &drought-prone climate was in place.



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Worksheet 4 (cont)11.a) Sclerophylls are characterized by small, thinleaves with a thick, waxy cuticle. Unlike non-sclerophylls, their leaves do not wither underdry conditions. They retain their shape, andsimply resume normal operations when waterbecomes available again.b) Eucalypts (gum trees) & Acacias (wattles)

12. a) Diprotodon was a “giant wombat”, weighingabout 3 tonnes. Several fossil part-skeletonshave been discovered, allowing accuratereconstruction.b) Diprotodon was similar to living wombats.• both were/are marsupials, with same body plan.• both were herbivorous... plant eaters.D. was different to living wombats in• body size being approx 50 times bigger.• modern wombats burrow and spend a lot oftime underground. D’s size may have made thisimpossible.• D was probably a “browser” of leaves andvegetation, while modern wombats eat a lot ofplant roots and tubers.

13. Darwin noted that many Australian plantsseemed well-suited to the dry climate. He laterlinked this to his Theory of Evolution by arguingthat the ancestors of modern sclerophylls were“selected” by nature because they hadcharacteristics that helped survival in the dryclimate. By this “natural selection” the plantshad evolved to thrive in the harsh climate.

He noted that the animals too, were well suitedto the environment, but never fully understoodjust how well. He thought the marsupials andmonotremes were “primitive” and would notsurvive if faced with competition from “moreadvanced” mammals. In line with his theory,Darwin assumed that the marsupials wouldeventually become extinct, just as the dinosaurshad, as more advanced types took over.

Worksheet 5a) one b) identicalc) parent d) clonee) rapid increase in the population/ rapidreproductionf) genetic variationg) the environment changesh) mitosis i) meiosisj) gametes k) different / uniquel) chromosomes m) fertilisationn) aquatic o) externalp) internal q) pollenr) wind s) pollen tubet) ovary u) moistv) less (fewer)

Worksheet 6a) Acacia (wattle) b) fine or lightc) protrude from the flowerd) animals / birds e) nectarf) sticky / have hooks g) sticks / clingsh) bats/flying foxesi) they can be seen at night / in moonlightj) some survive being eatenk) the weight of the bat can be supportedl) wind m) fine hairsn) picked up / carried o) bindiip) burrs q) carried awayr) birds & batss) passing through an animal gutt) undeveloped/immatureu) if the baby dies, little has been “wasted”, andthe adult can survive until conditions improve.v) conditions get better / more food & water isavailablew) fight / compete x) matey) their characteristics / their genesz) rains occur / food is availableaa) kookaburra/magpie ab) well fedac) Sturt’s desert pea ad) asexuallyae) runners af) conditions improveag) increase numbers quicklyah) variationsai) the environment changes

Worksheet 71. A 2. C 3. A 4. B5. D 6. B 7. C 8. D

9.Mitosis involves a single cell division whichproduces 2 daughter cells which:• are identical to each other.• are identical to the parent cell.• have the same number of chromosomes.Meiosis is a double division which produces 4cells which:• are all different genetically to each other.• are different to the parent cell.• have only half the number of chromosomes.

10.a) External fertilization is when the egg & spermunite in the outside environment. Internalfertilization occurs inside the body of the femaleparent.b) External fertilization evolved in the aquaticenvironment and still works well there. Since theenvironment is water, the gamete cells cannotdry out, and the sperm cells can swim to find theeggs.

Internal fertilization evolved to suit theterrestrial environment where gametes couldrapidly dry out, and sperm would not be able toswim to the egg. The inside of the femalereproductive system is kept moist (simulatingthe aquatic environment) to keep sperm aliveand swimming towards the eggs.




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Worksheet 7 (cont)11. Asexual reproduction is an advantage whenconditions suit a rapid increase in numbers, totake advantage of a temporary increase in foodsupply or other resources. It allows rapidreproduction of many offspring without theexpenditure of energy and resources thatsexual reproduction requires.

An example is Sturt’s desert pea which canrapidly send out “runners” to populate an areaafter the occasional desert rain. This allows theplants to take advantage of temporary goodconditions. Under normal dry conditions itreproduces sexually, producing seeds which liedormant for years awaiting suitable conditionsfor germination.

12. Marsupials have a very brief gestation and givebirth to a partly developed embryo whichmatures inside the pouch. This can be anadvantage under extreme drought. If the babydies, which may well happen, then at least themother has not “wasted” much of her bodyresources. This gives her more chance tosurvive, and she can rapidly begin breedingagain when conditions improve.

Some marsupials, such as the red kangaroo,can even “suspend” the development of anembryo in the uterus and hold it there for manymonths until conditions improve.

13. (1) The Acacias (wattles) rely on the wind forpollination. The plants produce large quantitiesof fine, light-weight pollen which can be carriedlong distances by any breeze. The flowers havea number of stigmas which protrude from theflowers to catch any incoming pollen.(2) The “bottle brushes” and Grevillias rely on“honey-eater” birds and lorikeet parrots forpollination. The flowers lack petals, but producelarge amounts of nectar for the birds to feed on.They have many stamens producing largepollen grains which are sticky, or covered withsmall hooks, so the grains adhere to thefeathers of the feeding birds and are carried onto other receptive flowers for pollination.

14. The Thylacine, or “Tasmanian Tiger”, was oncethe top predator across much of the continent. Itbecame extinct on the mainland approximately3,000 years ago probably due to the arrival of anew competitor, the dingo. Dingos wereprobably introduced by humans, became feraland spread over most of the continent.

Dingos never reached Tasmania, so there theThylacine survived. When the European settlersarrived, the Thylacines began taking sheep, sothe government put a bounty on them, and manywere shot. Many others died from a diseaseepidemic in the 1890’s. The last nown specimendied in the Hobart Zoo in 1936.

15. a) It has been found that the greater the varietyof different species in any ecosystem, the morestable the system is, and the more able it is tocope with changes. Maintaining biodiversity isimportant in order to help natural ecosystems tosurvive in a sustainable form.

b) The NSW Wader Study Group is enlisting thesupport of interested amateurs to “adopt anestuary” and carry out regular counts of shorebird populations. The data will help monitor thebiodiversity of these ecosystems, and keeptrack of changes to various speciespopulations.


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