Preliminary Biology: Topic Summary

Australian Biota Matt Elrick

1. Evidence for the rearrangement of crustal plates and continental drift indicates that

Australia was once part of an ancient super continent

1.1 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 Gangamopteris

flora , and marsupials

- similarities between present-day organisms on Gondwanan continents

Matching continental margins:

- The continents fit together like a jig-saw puzzle. Rocks on the opposing edges are exactly

the same.

Mid-ocean ridges and spreading zones:

- Mid-ocean ridges form the boundaries of Earths crustal plates where plates move apart.

- The plates move because lava is added to these ridges.

- New rock is found in the ridge – the further away from the ridge, the older the rock

Fossils in common on Gondwana continents: - Fossils of Glossopteris and Gangamopteris plants have been found on all Gondwana

continents, nowhere else. - Also, marsupials provide evidence for plate tectonics and the past existence of

Gondwana. When Australia became isolated from the rest of the world, the marsupials’ evolved and diverse species flourished. Some species of quoll and marsupial mice have several features in common with South American marsupials.

Similarities between organisms on Gondwana continents:

- Flora of southern continents – South America, South Africa, Australia and New Zealand has many features in common.

- Flightless birds have been examined, these include the Rhea (S. America), Emu and Cassowary (Australia), Ostrich (Africa) and Kiwi (New Zealand). The distribution of these flightless birds on these different continents is due to the super continent, Gondwana.

- Various plant species which are closely related are found in Gondwana continents - Southern beach tree is only found in temperate lands of southern hemisphere - Snake fossils recovered from South America are similar to those discovered in Australia - Tree fossils in Antarctica match those found in other Gondwana continents

1.2 Discuss current research into the evolutionary relationships between extinct species,

including megafauna and extant Australian species

Present day organisms have evolved from different organisms in the distant past. Megafauna are not

believed to bet the direct ancestors of the present marsupials or reptiles. They are related and have

evolved from a common ancestor in the distant past

There are two theories as to why megafauna became extinct; climate change and arrival of humans.

Climate Change: the drying out of the continent may have disrupted their breeding cycles, due to

the drying out there may not have been enough resources to cope with the demand of the

megafauna. Fire would have become more common – destroyed food resources.

Human Arrival: Aboriginals were very successful hunters – used fire to burn off bush in order to

attract animals to new growth after fire. Megafauna are believed to have been slow – easier to hunt.

2. The changes in Australian flora and fauna over millions of years have happened through

evolution

2.1 Discuss examples of variations between members of a species

There may be variation between the two sexes of a particular species. Members of the same species

may show variation which is related to the environment in which they live:

- Animals living in cooler climates are usually larger than members of the same species in

warmer climates

- Many birds of the same species show variation between different geographical areas,

such as size, beak length and colour

- Variation in colour occurs in some Kangaroo species; populations in forests are dark with

thick fur compared to populations in open habitats with lighter, thinner fur.

- Some species of tree have gradual changes with elevation such as; height, leaf length,

bark colour.

2.2 Identify the relationship between variation within a species and the chances of survival of

species when environmental change occurs

According to the theory of natural selection, there will always be variations within species. When

environmental change occurs, the individuals that have a variation that better adapts them to their

new environment will survive, while those without the variation will die out. The greater the

variation within a species, the greater the chance that it will be able to survive in a situation of

environmental change.

2.3 Identify and describe evidence of changing environments in Australia over millions of years

- 65mya - Australia and Antarctica were joined, climate cool and wet, covered in

temperate rainforests

- 45mya – Australia separate from Antarctica and began drifting north, wind patterns then

changed, warm air from tropics was block as air and ocean currents began circling

Antarctica

- Antarctica became cooler, icecap formed and sea levels dropped

- Australia was now cooler and drier, but began warming as it drifted northwards,

rainforest shrank, other vegetation grew, climate in northern Australia became tropical

- There have been many climatic fluctuations since late Neocene period, reflecting global

cycles, overall Australia has become warmer and drier

2.4 Identify areas within Australia that experience significant variations in temperature and

water availability

Arid habitats are the most extensive habitats in Australia. In central Australia, water is scarce, rainfall

is unpredictable and temperatures are extreme. In the desert temperatures can be above 40

degrees during the day and quickly drop to near zero at night.

2.5 Identify changes in the distribution of Australian species, as rainforests contracted and

sclerophyll communities and grasslands spread, as indicated by fossil evidence

Fossils found in sedimentary rocks on the surface indicate vast changes in the distribution and

abundance of species. Some examples are:

- Areas containing limestone were once covered by warm, shallow oceans containing

many molluscs, corals and fish.

- Species once found in rainforests which covered the continent are now reduced to a

much smaller area.

- Fossils of the Thylacine show it lived in Kimberley region 80 years ago, 3000 years ago in

southern mainland and 10000 years ago in New Guinea

- As Australia became warmer and drier, rainforests declined and grasslands and

sclerophyll communities increased, organisms well suited to these conditions undertook

‘adaptive radiation’, i.e. the change in a species from its original form to a different form

adapted to different environments or ways of life.

2.6 Discuss current theories that provide a model to account for these changes

- The theory of continental drift provides one model to explain the changes in climate.

Climate change has changed the environment and therefore the distribution and

abundance of species.

- The theory of natural selection explains how some species survive and adapt to changes

in the environment.

- The theory of adaptive radiation helps explain how species can spread out and occupy

different habitats.

2.7 Discuss Darwin’s observations of Australian flora and fauna and relate these to his theory of

evolution

Darwin observed the similarities between flora and fauna in Australia with flora and fauna in other

parts of the world.

He observed the similarities between marsupials (isolated in Aust) with placentals that live in similar

environments elsewhere in the world, which have similar niches and resemble each other

structurally and physiologically.

Some examples are deer and kangaroo have similar niches and digestive systems. Flying squirrels

have adapted the same loose membrane for flying as the Australian sugar glider.

3. Continuation of species has resulted, in part, from the reproductive adaptations that have

evolved in Australian plants and animals

3.1 Distinguish between the processes of meiosis and mitosis in terms of the daughter cells

produced

Mitosis Meiosis

Daughter Cells

Produces two daughter cells identical to parent cell, with same number of chromosomes

Produces four daughter cells with half number of chromosomes as parent cell

Where? Occurs in body cells Occurs in Gametes

Why? Cell division for growth, repair, replacement of dead cells.

Reproduction

3.2 Compare and contrast external and internal fertilisation

External Fertilisation Internal Fertilisation

External fertilisation takes place outside the body, characteristic of most aquatic organisms.

Internal fertilisation occurs in most multicellular land organisms

Many aquatic organisms release gametes simultaneously into the surrounding water, in hope that they can meet and be fertilised (spawning). In External fertilisation millions of small gametes are released and the chances of fertilisation are low.

Gametes are directly transferred to the female ovum to increase chance of successful fertilisation

High risk of gametes not surviving/being eaten in water

Occurs in most land mammals as external fertilisation will result in gametes drying out due to harsh environment

3.3 Discuss the relative success of these forms of fertilisation in relation to the colonisation of

terrestrial and aquatic environments

External fertilisation is successful in water, as the gametes can spread very far and wide in the water,

increasing the chances meeting other gametes from the opposite gender, encouraging fertilisation.

Also, zygotes are able to spread to large areas, enabling successful colonisation of large areas of

water.

External fertilisation would not succeed on land. Internal fertilisation enabled the colonisation of

land, as the watery environment needed for the gametes is provided by the female’s physiology.

Without the need for external water for fertilisation, even the driest environments could be

colonised

3.4 Describe some mechanisms found in Australian flora for:

- pollination

- seed dispersal

- asexual reproduction with references to local examples

Pollination:

Pollination is the transfer of pollen from the male part of the flower (anther) to the female part

(stigma). Some flowers can self-pollinate, however most have mechanisms to ensure cross-

pollination within the species. Cross-pollination requires an external vector to transfer the pollen,

such as insects and birds or wind.

Each flower is adapted to the particular pollinating vector which they rely on, for example some

flowers which rely on birds for pollination have the seeds situated so that when the bird pokes its

beak in to get nectar, the seeds rub onto the birds head and are then transferred to another plant.

Grasses which rely on the wind for pollination have the anthers and stigma in a very exposed place

to maximise the likely hood that the wind will carry the seeds away.

Seed Dispersal:

Seed dispersal increases the survival chances of seeds and help to reach an environment which they

can survive in. There are several ways in which seeds are dispersed:

- some seeds have hooks or are sticky which enable them to hitch a ride on animals

- some fruits are eaten by animals and the seed passes through the digestive tract and is

deposited with faeces

- wind

Asexual Reproduction:

Since no gametes are produced and therefore no fertilisation takes place, clones of the parent plant

are produced.

An advantage is: A parent plant well suited to its environment can clone many copies of itself and

rapidly spread into a favourable area.

A disadvantage is: the lack of variation may mean that few will survive if there was a sudden change

in the environment.

Some plants produce extensions which are capable of taking root and starting a new plant.

3.5 Describe some mechanisms found in Australian fauna to ensure:

- fertilisation

- survival of the embryo and of the young after birth

Fertilisation:

Fertilisation will only occur if there are mechanisms to ensure that mature sperm reach ripe eggs,

most marsupials ensure this by having fixed breeding seasons where the females are sexually active.

Mating is timed so that the young emerge from the pouch in spring. Species with long gestation

periods breed in summer while species with quick gestation periods breed in winter. The red

kangaroo, which lives in areas where rainfall and food are unpredictable, breed at all times of the

year.

Survival of embryo and young:

To ensure survival of the embryo, many Australian marsupials have diapauses of the embryo. After

fertilisation, a viable embryo is held in the uterus for long periods, until the previous young leave the

pouch.

To ensure survival of the young after birth Australian marsupial have developed pouches. The young

marsupials are born prematurely and then climb into the pouch where they attach to a nipple and

complete development.

3.6 Explain how the evolution of these reproductive adaptations has increased the chances of

continuity of the species in the Australian environment

These adaptations are the result of natural selection and therefore the organisms most suited to the

environment have the best chances of survival and then pass on their characteristics to their

offspring.

Because marsupials do not expend much energy during birth, if the offspring dies there is not much energy loss. It is highly adapted to manage its reproduction to cope with the unpredictable environment of Australia.

3.7 Describe the conditions under which asexual reproduction is advantageous, with reference to

specific Australian examples

Asexual reproduction is advantageous because:

- It allows large numbers of offspring to be produced rapidly.

- Only one parent plant is needed, no fertilisation is required and therefore no mate is

needed.

- It is an advantage in an unchanging environment. Clones of the parent plant are

produced, so if the parent has characteristics that help it survive in the particular

environment then the offspring will rapidly spread.

- It is an advantage when rapid recovery is needed or when large numbers are required

(eg after bushfire)

Australian species where asexual reproduction is advantageous include:

- Colony Wattles can send up shoots from outer roots, these grow into separate plants if

parent dies or is burnt, regrowth can occur quickly.

- Corals reproduce asexually when conditions are good – large coral reefs like Great

Barrier Reef are formed this way.

4. A study of palaeontology and past environments increases our understanding of the

possible future range of plants and animals

4.1 Explain the importance of the study of past environments in predicting the impact of human

activity in present environments

Many things that happen today have happened in the past. Continental drift and increasing aridity

has shaped much of Australia’s biota. Australia continues to move north and climatic changes

continue to occur.

Knowledge gained from the study of past environments can help us to predict and determine the

future for Australia’s biota.

4.2 Identify the ways in which palaeontology assists understanding of the factors that may

determine distribution of flora and fauna in present and future environments

Using what we know about past climates and the effect that the climates had on flora and fauna we

can predict what will happen in the future. Fossils show us what happened to Australia’s plants and

animals as the continent became hotter and drier.

As the greenhouse effect raises temperatures on Earth and as the ozone layer is depleted more and

more, the Earth’s climate and environments will change and therefore the distribution and

abundance of species will also change.

4.3 Explain the need to maintain biodiversity

Biodiversity is essential for maintaining the natural functions of the Earth, such as providing clean

water, air, productive soil, and recycling matter. The general health of the planet depends on

biodiversity. Many human activities rely on biodiversity: agriculture, forestry, fisheries etc. Variation

within a species is also important to maintain a healthy ecosystem.

The loss of biodiversity can make the ecosystem less stable and less able to survive natural cycles

which the flora and fauna have adapted to.