Evolution of
Australian
Environments
due to..
Biological Isolation
Geological stability
Climatic variations
Facts about Australia’s uniqueness
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High fire rates
Highly erratic climate
Susceptible to extended periods of drought
Highly isolated (We’re on an island!)
Large amount of uniquely native species (compared to the rest of
the world)
Unique flora and fauna adapted to landscape
Relatively flat continent
Unique flora and fauna adapted to climatic conditions
Low soil quality (low in phosphorus which allows for extensive
plant growth)
Why?
Biological Isolation Geological stability Climatic variations
Facts about Australia’s uniqueness
•
•
•
•
•
•
•
•
•
High fire rates
Highly erratic climate
Susceptible to extended periods of drought
Highly isolated (We’re on an island!)
Large amount of uniquely native species (compared to the rest of
the world)
Unique flora and fauna adapted to landscape
Relatively flat continent
Unique flora and fauna adapted to climatic conditions
Low soil quality (low in phosphorus which allows for extensive
plant growth)
Why?
Biological Isolation Geological stability Climatic variations
Biological
Isolation
What is it??
Biological Isolation refers to when a collection of species do
not have contact with another species that they are able to
breed or mate with. This process can be man made or
natural.
Examples:
Man made = scientist in a laboratory segregating species,
Natural = natural disasters such as floods.
Looking at the Natural History of Australia before humans,
we will be focusing on the effects of Natural biological
Isolation. Natural Isolation occurred when Australia split
from Gondwanaland to form it own land form in isolation.
Biological isolation
This can occur when organisms travel to islands and then
can no longer breed with organisms from the main land.
Natural disasters such as earthquakes, volcano eruptions
and mud slides can force populations into separate areas.
This means that these organisms will either die out or
evolve separately.
(Wilderness bohanson, 2008).
Natural Selection
• Geographical Isolation contributed to Charles Darwin’s
theory of evolution by natural selection. This theory
evolved from the evidence and movement that scientists
had found about how Australia formed before humans.
• In short, Charles Darwin’s theory was that species change
over time, or evolve in response to the environment. This
is basically what biological isolation is; the change of
species over time by being isolated from one another.
Biologically isolated flora
The flora in Australia has strong affinities with the flora of Gondwana, and
below the family level has a highly endemic flora whose diversity was shaped
by the effects of continental drift and climate change since the Cretaceous
period.
• Prominent features of the Australian flora are adaptations to aridity (low
amounts of water) and fire which include scleromorphy and serenity.
• Sclerophyll is a type of vegetation that has hard leaves and short internodes
(the distance between leaves along the stem). The word comes from the
Greek sclero (hard) and phyllon (leaf).
• These adaptations are common in species from the large and well-known
families Proteaceae (Banksia), Myrtaceae (Eucalyptus - gum trees), and
Fabaceae (Acacia - wattle).
Animals and plants evolve to life without specific predators or threats and
ecosystems evolve to find an equilibrium where no one predator wipes out
everything.
In Australia this has lead to the evolution of flora and fauna that can survive in
the harsh conditions they live in
• This unfortunately increases the impact of introduced fauna
species such as the rabbit, cane toad and even flora such as
Patterson’s curse.
Animal example
An example of Biological Isolation and the evolution can
specifically be seen when looking at the platypus. Large
water rats were around in the Gondwana period. When
Australia split from the larger sections of Gondwana, water
rats in Australia where left without diversity in their
breeding partners. As suggested by Charles Darwin,
biological isolation resulted in the water rats in Australia
forming into their own species, as we know as the platypus.
Geological
Stability
What is it?
Australia has been without volcanic activity or movement
for many years due to being located relatively in the center
of a tectonic plate (Australasian).
The last volcanoes on the continent of Australia were active
many years ago compared with other continents.
This, combined with very little geological activity, has led to
Australia having soil poor in nutrients. The state of the soils
has had an influence on the Australian flora and fauna as
those who were unable to adapt were also unable to
survive.
Geological stability
Australia has low tectonic, volcanic and glacial activity.
There are few mountain ranges and the landscape is
generally flat, making it prone to floods and erosion, and
therefore affecting the survival of flora and fauna.
• What animal has adapted to Australia’s flat landscape?
• What adaptions would plants need to make to deal with
poor soil quality?
Climatic
Variations
What is it?
Australia experiences a relatively
erratic climate in comparison to
other continents of the world. There
seems to be two main extremes,
long, lean droughts in El Niño years
and flooding rains in La Nina years
(See wiki for further information).
These periods can last anywhere
from 1 – 10 years, this low level of
predictability has had an impact on
the adaptability and diversity of
flora and fauna. The Australian
climate varies on longer timescales, over decades and centuries.
These variations are more subtle than yearly changes but
can still have significant impacts on human life. Australians
are well accustomed to short-term variations in climate,
such as a particularly hot summer or low annual rainfall.
However, it is important to recognise that the climate also
varies over longer time-scales.
For example, farming in some parts of Australia expanded
into marginal agricultural areas during decades of good
rainfall. However, many of these areas turned to dust bowls
during the poor growing seasons associated with a
downturn in the long-term rainfall cycle.
Climate patterns
Climate patterns on time-scales longer than decades also
influence life in Australia. Short term climate variations are
superimposed on long-term trends. It is these extremes in
climate that have the greatest impacts on human activities.
The landmass of Australia has been exposed to many extreme
climate changes all of which have had an effect on the current
landscape, flora and fauna. Some plants have developed deep
root systems to access water in times of drought and some
animals such as the Koala, has evolved with a relatively small
brain to conserve energy.
Adaptions to Australia’s erratic
climate
Plants
 Hard, glossy leaves resist
water loss through
transpiration
 Evergreens reduce energy
usage
 Long, narrow leaves that hang
vertically presenting small
surface area to sun
 Small leaves, or none
 Dormancy
Animals
 Water storage
 Metabolic adaptations to
minimise water loss
 Energy efficient movement –
eg. hopping
 Energy saving adaptations –
eg. Koala’s brain
Serotiny
Serotiny is an ecological adaptation exhibited by some seed plants, in which
seed release occurs in response to an environmental trigger, rather than
spontaneously at seed maturation. The most common and best studied
trigger is fire, and the term serotiny is often used to refer to this specific case.
Possible triggers include:
• Death of the parent plant or branch (this form of serotiny has been
technically termed necriscence)
• Wetting (hygriscence)
• Warming by the sun (soliscence)
• Drying atmospheric conditions (xeriscence)
• Fire (pyriscence)
• Fire followed by wetting (pyrohydriscence)
Some plants may respond to more than one of these triggers. For example
Pinus halepensis exhibits primarily fire-mediated serotiny, but responds
weakly to drying atmospheric conditions. Similarly, some Banksia species are
strongly serotinous with respect to fire, but also release some seed in
response to plant or branch death.
Flora releasing seeds after a fire
Banksia (pictured) is a common species to have developed this trait
along with the Australian Mountain Ash
These have evolved uniquely due to poor Australian soils. Fire
indicates the release of nutrients from burnt materials which is ideal
conditions for the growth of new seedlings. Basically reducing wasted
seeds due to being released onto soils with minimal nutrients.