AUSTRALIAN BIOTA
The very large southern landmass, Gondwana, persisted for some time, giving rise to an array of species that spread across it. When Gondwana broke up, it did so in stages but eventually the Australian continent was isolated from Antarctica and South America.
The available evidence suggests that, as Gondwana was breaking up, a number of global climatic changes were also occurring. These changes in environmental conditions impacted on Australian ecosystems and are reflected in the fossil record. As the biotic and abiotic features of ecosystems were altered, those organisms best adapted to these changes survived and passed on their genetic information to their offspring.
The contribution of paleontology and the study of past environments are important to our understanding of how our present actions may affect our environment and the distribution of flora and fauna in the future.
Identify and describe evidence that supports the assertion that Australia was once part of a landmass called Gondwana, including:
- matching continental margins
- position of mid-ocean ridges
- spreading zones between continental plates
- fossils in common on Gondwanan continents including Glossopteris and Gangomopteris flora and marsupials
- similarities between present day organisms on Gondwanan continents
Things to consider:
- What does identify and describe mean?
- What does assertion mean?
- Underline key words
- Be succinct
There is a mountain of evidence which supports the theory that Australia was once part of a landmass called Gondwana. The following evidence shows this.
· Matching continental margins: Geologists have discovered through rock strata analysis that Southern Australia is a perfect boundary match with that of Antarctica, and between the west coast of Africa and the east coast of South America.
· Mid-ocean ridges: The study of mid ocean ridges has suggested that when plates move mantle material wells up and creates new ocean floor. Scientists have then deduced the further away from the ridge the older the rock is. This evidence suggests that Australia was once part of the landmass called Gondwana.
· Spreading zones between continental plates: These are areas of new ocean floor forming between continental plates. Analysis of the ocean floor and spreading zones has lead to the assertion that Australia was once part of the Gondwanan super continent.
· Fossils in common on Gondwanan continents including Glossopteris and Gangomopteris flora and marsupials: These plant fossils have been found in rocks of the same age in Africa, Australia, India, South America, Antarctica and New Zealand. This evidence supports the assertion that Australia was once part of the super continent known as Gondwana.
· Similarities between present day organisms on Gondwanan continents: There are many similarities between present day organisms and their Gondwanan continents. For example the Rhea, Ostrich, Emu, Cassowary and Kiwis are all examples of present day organisms which show extremely similar characteristics. These organisms also suggest by their geographical positioning that Australia was once part of the landmass called Gondwana.
Discuss current research into the evolutionary relationships between extinct species, including megafauna and extant Australian species
Things to consider:
- What does discuss mean?
- Underline key words.
- Use scientific terminology, be succinct
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Evolutionary relationship refers to how closely one organism is related to another. From this we can draw on how closely related extinct species such as megafauna are to current Australian species. Firstly megafauna as the name suggests are large animals. Current living megafauna include elephants and whales. However over the last 50000 years megafauna have becomes extinct. Extinction was more than likely due to a number of factors including climatic change and human expansion.
Evolutionary relationships can be shown between megafauna and current Australian species. For example if we compare the diprotodon and the common wombat we can identify many structural similarities. Structural similarities include skull structure, body covering, length and structure of limbs, ears and snout are all similarities between that of the wombat and the diprotodon. This example illustrates the evolutionary relationships between extinct Australian megafauna and current Australian species. (Other evolutionary relationships include; giant kangaroo vs kangaroo, giant echidna vs echidna and Genyornis vs the emu to name a few.)
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Solve problems to identify the positions of mid-ocean ridges and spreading zones that infer a moving Australian continent
Things to consider:
- What does solve mean?
- What does identify mean?
- Understand the question so that the answer is correctly and accurately represented
AIM:
To investigate and solve problems to identify the position of mid-ocean ridges and spreading zones that infers a moving Australian continent.
METHOD:
1. Using secondary sources identify the tectonic plates and the positions of mid-ocean ridges, trenches and spreading zones. You may wish to draw your answer.
DISCUSSION QUESTIONS:
1. Explain how the theory of plate tectonics has changed our ideas about the surface of the Earth.
2. Which tectonic plate is entirely oceanic?
3. It has been suggested that the Atlantic Ocean is expanding and the Pacific Ocean shrinking. What evidence supports this idea?
4. If the sea floor spreads from the mid-Atlantic ridge at the rate of 2.5cm per year, how many kilometers of new crust will be laid down over one million years?
5. The city of San Francisco has experienced Earth tremors and earthquakes over the last 100 years. What is the reason for this?
6. The Earth’s crust is recycled over time. Explain how this happens.
7. On which tectonic plate is the continent of Australia.
8. It has been said that Australia is drifting northwards at about 6cm a year. What technological advances have helped us to measure this?
9. Explain, with examples, how technological advances have increased our understanding of plate tectonics.
Identify data sources, gather, process and analyse information from secondary sources and use available evidence to illustrate the changing ideas of scientists in the last 200 years about individual species such as the platypus as new information and technologies became available
Things to consider:
- This is a secondary source question, so it’s to your discretion as to how and where you will find your information.
- What does analyse and process mean?
- Use scientific terminology
AIM:
To look at the changing ideas of scientists in the last 200 years about the platypus.
METHOD:
1. Research the platypus, identifying data sources and collecting information to write a report as outlined by the discussion questions.
DISCUSSION QUESTIONS:
For the platypus, produce an illustrated report that includes the following:
· An outline of the changes we believe have occurred over time.
· A description of the evidence for these changes (include both geological and biological evidence.)
· A discussion of the ways our ideas have changed over the past 200 years. What new information has become available? What new technologies and/or processes have allowed us to find out more?
Discuss examples of variation between members of a species
Things to consider:
- What does discuss mean?
- What examples are you going to use?
- What is variation?
Variation refers to a slight difference within a species. For example you are not identical to anyone in the classroom. This represents variation within the human species. Variation may occur for various reasons such as competition for resources or the organism’s environment.
Examples of variation between members of a species in Australia include the white – naped honeyeater (Melithreptus lunatus). This bird is distributed throughout Australia. However there is distinct variation between populations of the species. For example the eastern Australian white – naped honeyeater has a short beak and an orange patch around its eye. Compared to that of the western Australian white – naped honeyeater which has a larger beak and a white or green patch around its eye. This example shows variation within a species due largely to geographical isolation and more than likely the honeyeater’s environment.
EASTERN HONEYEATER
WESTERN HONEYEATER
NOTE THE DIFFERENCE. ORANGE VS WHITE PATCH AROUND THE EYE.
Identify the relationship between variation within a species and the chances of survival of species when environmental change occurs
Things to consider:
- What does identify mean?
- Underline key words and make sure you understand what these words mean
- Be succinct
In order for a species to survive environmental change there must be variation within that species. If there is no variation within a species that species is susceptible to many factors which in turn could eliminate that species. For example a deadly bacteria sweeps through a population if there is no variation in that species the species will die out. Therefore all species need to ensure there is variation from one generation to the next. This ensures that if there is an environmental change the species will have some chance of survival.
Identify and describe evidence of changing environments in Australia over millions of years
Things to consider:
- What does identify and describe mean?
- What type of evidence will we be looking for?
- Use scientific terminology
When Australia was still joined to Antarctica (65 million years ago) the climate was cool, wet and the land was covered by temperant rainforest. The next 20 million years saw Australia gradually breakaway from Antarctica and begin to drift northwards. While Antarctica became cooler, Australia was becoming increasingly warmer due to the northward drifting and the Australian rainforest shrank while other types of vegetation increased. As Australia continually drifted northwards, past the Tropic of Capricorn, the climate in the north of Australia became very tropical. To this day Australia continues to move north at about 6cm per year. There are many different environments including the tropical north east, the arid centre and the temperate east and western coasts. Therefore Australia’s environment has changed over millions of years.
Identify areas within Australia that experience significant variations in temperature and water availability
Things to consider:
- What does identify mean?
- How will you represent your information?
The diagram below illustrates the significant variations in temperature. Note the key.
The diagram below illustrates the significant variations in water availability. Note the key.
Identify changes in the distribution of Australian species, as rainforests contracted and sclerophyll communities and grasslands spread, as indicated by fossil evidence
Things to consider:
- What does identify mean?
- Underline key words
- Understand what the question is asking before you answer
As Australia’s environment changed so did the distribution of organisms. Organisms which could adapt to the warmer and drier conditions flourished in the new ecosystems while those organisms who struggled to adapt either became extinct or found little environmental pockets where they could survive. This is evident in such fossil sights such as Riversleigh and Naracoorte. Riversleigh fossils show that the Australian climate must have changed to warmer and drier conditions. Naracoorte fossils suggest that lakes dried up and forests became open woodland. This fossil evidence therefore suggests that the distribution of Australian species changed according to the changing environment.
The following table indicates successful species which diversified in Australia’s changing environment.
PLANTS / ANIMALS· Acacias (950 species) and Eucalypts (800 species) are highly adapted Australian vegetation.
· Acacias adapted to hot arid conditions. Found almost anywhere including; tropical rainforests, woodlands, arid areas, coastal heaths and sand dunes.
· Eucalypts adapted to Australian hot arid conditions. Found mainly in forests and woodlands. / · When Australia became a separate continent it contained three types of mammals: placentals, marsupials and monotremes.
· The most successful group were the marsupials.
· Marsupials adapted to the warmer drier conditions to occupy many ecosystems.
· Today there are 141 different species of marsupials.
Discuss current theories that provide a model to account for these changes
Things to consider:
- What does discuss mean?
- Underline key words
- Be succinct
Current theories that provide a model to account for these changes are climate change and human impact.
CLIMATE CHANGE: As Australia moved northwards the mean temperature rose and the availability of water declined. This lead to the reduction of rainforests and the beginnings of woodlands and open grass plains. Another key factor which supports this theory is the radiation of Australian marsupials and plant species such as eucalypts. These organisms also support the theory of climate change based on their distribution and abundance.
HUMAN IMPACT: Human impact is one theory behind the changes experienced on Australia. Firstly the Aborigines and their hunting practices (using fire) may have lead to the extinction of Australian megafauna.
The arrival of Europeans also changed local ecosystems due to their agricultural practices, degradation of woodlands/forests and the introduction of foreign species. These factors illustrate that human impact could be one theory that that influences Australia’s environment.
Discuss Darwin’s observations of Australian flora and fauna and relate these to his theory of evolution
Things to consider:
- What does Discuss mean?
- Who is Darwin? What is evolution?
Darwin visited Australia around 1836. He visited NSW, Tasmania and WA, in a quest to understand how and why organisms evolve. He took notes of Australia’s native flora and fauna to support his theory of natural selection. When in Australia Darwin noticed the following: crows like English Jackdaws, a rat kangaroo (potoroo) which he compared to a European rabbit both in size and behaviour and platypuses similar to that of water rats in Europe according to their behaviour. Darwin also made comparisons between the flora in Australia and Europe. These are the features (adaptations) he noticed of Australian flora: trees leaves hang vertically compared to Europe which hang mainly horizontally, leaves are light green, generally thin and have a relatively small surface area compared to that of Europe which are glossy and have a larger surface area and the bark of the trees is lighter in colour compared to that of the trees in Europe.
Darwin’s observations of Australian native flora and fauna relates to his theory of evolution because: