Australian Flora

Question 1

What are the 5 mechanisms that shaped the evolution of the Australian flora?

Answer 1

1. Biogeographic processes that influence evolution 🌏 (vicariance = continental drift resulting in a geographic barrier at the end of the Eocene.
   Dispersal = immigration through colonisation, transoceanic dispersal, land bridges)
2. Fire 🔥 (which creates open communities and led to the dominance of eucalypts aka Myrtaceae)
3. Climate Change 🌡️❄️🌡️❄️ (three global cooling events during the Cenozoic, the last 65mio years caused floristic turnover as the wet biome contracted and the dry biomes expanded)
4. The processes of Geomorphology (includes a range of factors: Topography of the landscape can lead to isolation: plateaus and mountain ranges, variability in soil fertility which can facilitate speciation, many niches)
   Australia favours dominance of sclerophylly and specialised adaptations for extracting nutrients from deficient soil.
5. Ecological opportunities
   - formation of new habitats
   - evolution of new mutualisms
   - key innovations/adaptations
   - release from antagonists likely resulted in adaptive radiations

Question 2

Gondwanan Vs dispersal - plants of Australia

Answer 2

45 % known to originate in Gondwana

48 % likely arrived via dispersal

7 % of unknown origin

Question 3

Australian flora during the Cretaceous 146-65 mio years ago (where it was still attached to Gondwana)

Answer 3

Dark, wet forest of conifers, ferns gingko and Angiosperms of the families casuarinaceae, proteaceae, and nothofagus

Question 4

Australian flora during the Eocene 55-38 mio years ago (Gondwana split, But Australia stil attached to Antarctica and South America)

Global climate is wet and warm, south pole free from ice

Answer 4

Broad leaved rainforests and nothofagus replace conifer forest

Question 5

When did the fire-adapted communities start occurring in Australia?

Answer 5

From the Cretaceous onward, however fire did not become frequent in Oz until the Oligocene (33mya)

Australia is a fire-prone continent because much of the area is occupied by flammable vegetation and it experiences fire promoting weather (lightning strikes)

Fire regimes vary:
Monsoonal savannahs burn every 2-5 years

Temperate, wet eucalypt forests experience infrequent large, hot fires (decade to century scale)

Question 6

How does fire control ecosystems?

Answer 6

Controls boundaries between rainforest and sclerophyll forest or savannah.

Soil depth is associated with extent of rainforest. It has to be deep enough to hold the moisture needed for the rainforest to survive dry seasons.
That means: the rainforest ecosystem will grow to the boundary of the deep soil layer and it will be pushed back once in awhile by fires in the eucalypts.

Question 7

Xeromorphic plants

Answer 7

Have a great capacity to store water

Question 8

Establishment of the circumpolar current

Answer 8

At the end of the Eocene, separation of Australia and South America from Antarctica opened the southern ocean and changed the climate of the world.

The current steepened the temperature gradient from the Equator to the south pole –> Antarctica glaciated, cooler more seasonal climates worldwide.

Australia’s climate was influenced by its northwards drift, making it warm in the north despite the cooling in the south

Question 9

Cooling events

Answer 9

Four really important cooling and drying events

1. Eocene-Oligocene boundary. 33 Mya
2. Mid-Miocene 14mya (initiated aridification)
3. Late Pliocene 4-2 Mya (lead to formation of the central Australian desert)
4. Pleistocene, all throughout (20 glacial periods, 8 of which where in the last 750,000 years, rainfall halved across the whole planet, temperatures much cooler than now. Led to loss of rainforest along the east coast of Oz)

Question 10

What does it mean that the processes of Geomorphology affects biodiversity

Answer 10

Oz is flat, dry and geologically old. The soil is nutrient poor. These bad conditions have favoured dominance of plants with specialised adaptations for Extracting nutrients from deficient soils

Types of specialisation:
Sclerophyll leaves - hard, often waxy coating, smaller and resistant to drought, stomata sunken into pits or grooves.

Long-lived leaves with capacity to withdraw nutrients prior to senescence.

Proteaceous roots - masses that form when P availability is low. They solubilise P from soil and mineralise it in the rhizosphere.

ALSO:
Weathered landscapes and deficient soil contribute to evolution via 1) Allopatric speciation by splitting populations 2) sympatric speciation by creating soil mosaics.

Question 11

Ecological opportunity and plant evolution

Answer 11

Adaptive radiation: A response to

1) new habitats
2) key innovations
3) release from antagonists