1.5 The Evolution of Australian Flora and Fauna

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Transcript 1.5 The Evolution of Australian Flora and Fauna

Evolution of Australian Biota
Topic 5: The Evolution of Australian Flora and Fauna
Part of the Evolution of Australian Biota Module
Biology in Focus, Preliminary Course
Glenda Childrawi and Stephanie Hollis
DOT Points
 Identify and describe evidence of changing environments in Australia
over millions of years
 Identify areas within Australia that experiences significant variations in
temperature and water availability
Evidence for Changing Climate
The traditional way to infer changes of climate is from geological
structures. If rocks show evidence of ripple marks, you know
there was water. If they are covered in striations, they show
evidence of glaciers.
Evidence for Changing Climate
Another traditional way to infer climate is from fossils present in
rocks. Coral will only grow in warm, clean water so limestone is
evidence for rocks formed in low-latitude regions (near the
Evidence for Changing Climate
Plants do not move, so they provide good indicators of climate in
an area. Finding fossilised plants like conifers that grow in cooler
areas and ferns that grow in moist conditions tell us a lot about the
area. Tree rings can indicate climate on a year by year basis.
Evidence for Changing Climate
Modern technology that can measure magnetism and radioactivity
has been put to use in determining past climates. Magnetic
patterns left in rocks provide evidence for plate tectonics and these
patterns on land have allowed the movement of continents to be
Evidence for Changing Climate
The ratio isotopes of O-16/O-18 in a fossil, such as a shell, can be
used to deduce temperatures of the time. Under warm conditions
the O-16/O-18 ratio is high, and under cold conditions it is lower.
This technique has also been applied to ice cores from glaciers.
Evidence for Changing Climate
These techniques can be used to infer what the Australian climate
was like in the past and how it has changed. We can then deduce
information about flora and fauna including how and why
organisms have evolved or become extinct.
The Drying of Australia
As Australia drifted northward, it moved through different
climactic zones. Around 30 million years ago, it lay in the belt of
moisture of westerly laden winds as Tasmania and New Zealand do
today. (glue Figure 7.22 into books)
Fig 7.22 Spotlight text pg 176
The Drying of Australia
Temperate rainforests spread across the eastern and southern parts
of the continent and Central Australia was covered in grasslands.
The northern tip had started to enter the dry mid-latitudes- the
zone where deserts form.
The Drying of Australia
Around 25 million years ago the continent was a mix of temperate
rainforest and extensive grassland. Under these ideal conditions a
great diversity of marsupials developed, however, the gradual
drying of the continent as it entered the subtropical zone
contributed to the extinction of many of these marsupials,
especially the megafauna.
The Drying of Australia
Our knowledge of changes in plant and animal distribution is more
extensive for the last 20 000 years or so. This was during our last
global period and part of Australia was very cold and large sections
were desert. (Glue Figure 7.23 into your notebooks)
Diagram (a) Figure 7.23 spotlight text pg 177
The Drying of Australia
Pollen records show that Callitris, Acacia and Casuarina woodlands
occupied the Great Dividing Range, there were now forests. The
south-eastern corner was very cold, alpine vegetation or cold
grasslands spread right down the coast.
The Drying of Australia
Around 15 000 years ago the glaciation started to recede and sea
levels rose, cutting off access between the first mainland Tasmania
and then the mainland and New Guinea. A warming of the oceans
saw significant increase in rainfall and a significant change in
vegetation. A pattern almost the same as today resulted.
Diagram (b) Figure 7.23 spotlight text pg 177
The Drying of Australia
Forests reinvaded the Great Dividing Range so that Callitris, Acacia
and Casuarina woodlands are not restricted to a few remnant
pockets. When white settlers arrived 200 years ago, the Australian
flora and fauna were recovering from this very dry period.
The Drying of Australia
The Indigenous Australians
were present and used
firestick farming as part of
their survival strategy. This
use of fire has also altered
the distribution and
abundance of flora and fauna.
Australia’s Unique Flora
Modern-day flora is very
different from that on other
continents, with many species
found exclusively in Australia.
The familiar Australian native
species such as wattles,
eucalypts, banksias and sheoaks all possess adaptations
that allow them to thrive in
soils that are nutrient poor,
areas that are arid and where
fire is common.
Australia’s Unique Fauna
Australia has a wide variety of marsupial fauna today, including
bandicoots, Tasmanian devils, koalas, wallabies and kangaroos.
Most living marsupials today are found in Australia and only a few
exist in South America.
Australia’s Unique Fauna
There is ongoing debate as to what led to the changes in the
Australian flora and fauna, in particular the extinction of the
-Students to complete 1.5.1a Timeline Changes in Australia