Transcript 41-3 Fig. 41.4

Part 6: Ecology
Chapter 41: Australian biota
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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Southern connections
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•
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Distributions of many plant and animal taxa are
best explained by past connections of present
southern continents
This supercontinent was called Gondwana
Australia severed its final link with Gondwana
about 30 million years ago (mya), when it split from
Antarctica (see Fig. 41.4)
Environmental changes and isolation moulded the
evolution of the modern Australian biota
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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Fig. 41.4: Sea-floor spreading
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Ancient forests: Permian times
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Fossils of seed ferns (Glossopteris) from 250 mya
occur in India, South America, South Africa and
Australia (coal formation)
Similar samples of fossils were found with the
perished remains of Capt. Scott’s fatal expedition
to Antarctica (to the South Pole)
Amphibians, insects and reptiles inhabited
Glossopteris forests
These forests dominated the Permian (246–248
mya)
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Ancient forests: the Triassic,
Jurassic and Cretaceous
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By the Triassic (230 mya) Glossopteris forests
disappeared from fossil record
Forked-frond seed ferns (Dicroidium), early
conifers and cycad fossils appear in the Triassic
From the Jurassic to early Cretaceous (213–100
mya) forests were dominated by conifers, some
genera of which survive today (e.g. Gingko)
Dinosaurs lived in Australian forests during the
Cretaceous
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Forests at the end of the
Cretaceous
Climate started to dry out…..
By 65 mya
• Dinosaurs became extinct
• Flowering plants replaced coniferous forests
– (earliest pollen is from Nothofagus and family
Proteaceae, up to 80 million years old)
•
Break-up of Gondwana was well underway
Evolution of unique Australian biota
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The Cenozoic era: climate
change
•
The circum-Antarctic current began once the
Southern Ocean was formed
• After 10 million years the sea began to freeze,
causing the south polar icecap and arid (dry)
conditions in Australia
• Gondwanan rainforests contracted to far north
Queensland
• Rainfall patterns in southern Australia changed
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The Cenozoic era: land and soil
•
Rocks were weathered and worn down to low hills
• Nutrients (e.g. phosphorus and nitrogen) were
leached out by rainfall over millions of years
• Lateritic soils formed, see Fig. 41.6
• Lakes dried out, saline mudflats remain today
(Lake Eyre)
• Inland seas retreated, leaving limestone deposits
from shelled invertebrates
• Nullarbor Plain and Murray Basin were exposed as
dry land
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Fig. 41.6: Laterite
Copyright © Professor Pauline Ladiges, University of Melbourne
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The Cenozoic era: fire
•
Preserved charcoal and pollen combinations
reveal past history
• Rarity of eucalypts and high rainfall,  fires were
not catastrophic
but
• Fire events increased as climate dried out, towards
end of Neogene
• Fire-adapted open-forest species began to replace
existing rainforest species
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The Cenozoic era: ice
•
Westerly winds first influenced Australia 2 mya
– wet winters
– hot, dry summers
Quaternary period (1.8 mya  present) is
characterised by climatic fluctuations
• Glacial periods (Pleistocene ice ages) occurred
•
– lower sea levels  land bridges (to Tasmania and New
Guinea)
– increased aridity
•
Only minor glaciation occurred in Australia, but
many dune systems formed
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Arrival of humans—when?
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Fossils e.g. Mungo Man suggest humans
colonised Australia > 40 000 years ago
Charcoal remains suggest humans had fires here
perhaps 128 000 years ago, see Fig. 41.10
Species’ extinctions 35 000–15 000 years ago
suggest effect of humans using fire, and the
associated vegetation changes
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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Fig. 41.10: Vegetation changes associated with
increased burning
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Modern Australian
environments—terrestrial
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Continent spans latitude10–40°S, so wide range of
climate
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monsoonal, tropical north has summer rainfall
subtropical
warm temperate
cool temperate southern regions have winter rainfall
Great Dividing Range separates narrow eastern, wetter
side from drier west (see Fig. 41.12)
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Fig. 41.12: Australian climatic regions
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Modern Australian
environments—marine
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Australia is an island continent surrounded by the
Pacific, Southern and Indian Oceans
Continental shelf is 15–400 km wide
Outer edge of slope is about 150 m deep
Coastlines consist of rocky shore (in South and
East), sandy shores, muddy shores with seagrass
meadows and mangroves, and coral reefs
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Marine biodiversity—flora
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Rhodophyta (red algae)
– includes many endemic species
– growing for pharmaceutical and economic use
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Phaeophyta (brown algae e.g. kelps and fucoids)
– abundant on rocky shores
– commercially harvested
•
Chlorophyta (green algae)
– also diverse, but most evident in tropical regions
•
Marine flowering plants include
– seagrasses (> 30 species)
– mangroves (about 30 species)
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Marine biodiversity—fauna
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Fish: 3 500 species in Australia
- high species diversity but low endemism in north
- lower diversity but higher endemism (85 per cent) in
south
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Molluscs and echinoderms display similar patterns
of diversity and endemism as fish
Many exotic marine species have been
accidentally introduced in ballast, on hulls etc.
These may become pests if they are successful
competitors e.g. Japanese sea star
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Australian terrestrial flora
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Major components of the flora have a Gondwanan
origin
Sclerophyll plants e.g. Eucalyptus and Acacia
species dominate the continent
Sclerophylly arose as an adaptation to low-fertility
soils, but also increased survival from drought and
fire
Succulent plants e.g. pigface and saltbush store
water to survive drought
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Myrtaceae: the eucalypt family
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Includes eucalypts, tea-trees, paperbarks and lilly
pilly
50 per cent of all genera live in Australia
Leaves: oil glands
Flowers: 4 or 5 perianth parts above the inferior
ovary
Eucalypts are fast growing: planted for timber,
paper pulp, firewood and oils
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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Proteaceae: the banksia family
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Includes Grevillea, Telopea, Macadamia, Banksia
• Proteacaea are a Gondwanan group, i.e. occur in
South Africa, India, South-East Asia, South
America, fossils in Antarctica)
• Flowers have 4-lobed perianth, 4 stamens, 1- or 2celled ovary
• Flowers attract bird-pollinators
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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Mimosaceae: the wattle family
•
Approx. 955 Australian species of wattle, all of which
are leguminous
• The family also occurs in Africa and tropical America
• Foliage: either compound bipinnate leaves or
phyllodes
• Some wattles retain mature bipinnate leaves
throughout life e.g. Acacia mearnsii
• Mature foliage of others is phyllodinous and replaces
juvenile bipinnate leaves e.g. Acacia longifolia (see
Fig. 41.25)
• Root symbionts increase nitrogen availability
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Fig. 41.25a: Phyllodinous acacia
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Fig. 41.25b: Acacia longifolia
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Fig. 41.25c: Acacia mearnsii
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A unique southern fauna
•
Characterised by many unique and endemic
groups that evolved during the break-up of
Gondwana
• Tuatara in NZ has survived 160 million years
• Australia drifted north in relative isolation
• Insect distributions show primitive Gondwanan
groups, but also some modern genera derived
from Asia
• Old connections between South America and
Australia are indicated by preferences of insects
for feeding on related plants
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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Biogeographic patterns—frogs
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Frogs (order Anura) (and mammals, class
Mammalia) have poor powers of dispersal over
seawater, so provide clear evolutionary history
The largest component of Australia’s frog fauna
are Gondwanan families that adapted to dry
environments
Adaptive radiation is best shown by the
myobatrachid frogs
Two other families of native amphibians in northern
Australia are of Asian origin
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Australian reptiles
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There are no derivative modern descendants of
the dinosaurs in Australia
The New Zealand Tuatara Sphenodon punctatus,
is a survivor from Triassic and Jurassic times
Modern reptilian fauna are probably derived from
Asian groups
Bearded dragon (family Agamidae) may have
stronger African than Asian affinities
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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Adaptive radiation in mammals
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Australia is only continent where monotremes
(Prototheria), marsupials (Metatheria) and
placental mammals (Eutheria) are represented
Terrestrial and marine mammals are very diverse
First introduced species was the dingo, 7000 years
ago
Introduced species (incl. humans) have had
profound effect on Australian ecosystems
 extinctions of native species
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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The Prototheria: platypus and
echidna
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Endemic to the Australian plate
Fossil representatives known from South America
Display many primitive features
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egg-laying
secrete milk from glands with no nipples
cloaca
reptilian features
But also display specialisations
– sense weak electric fields to locate prey
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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The Metatheria: marsupials
•
Present marsupial fauna of Australia includes 4
orders
– Dasyuromorphia and Pelamelemorphia have more than 1
pair of incisors in lower jaw. Include carnivores and
omnivores e.g. quolls, dunnarts, Antechinus, Tasmanian
devil, numbat
– Diprotodontia are herbivores with one pair of incisors in
lower jaw e.g. koalas, wombats, possums, gliders,
kangaroos, wallabies, bettongs, potoroos
– Notoryctemorphia, the marsupial moles
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PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint
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The Eutheria: bats and rats
•
Eutherians comprise a large number of endemic
fauna belonging to two orders
Chiroptera (bats)
– fruit and blossom bats and flying foxes (suborder
Megachiroptera) are large herbivores
– small predatory bats (suborder Microchiroptera) hunt
using echolocation
•
Rodentia (rats)
– >50 species of native rodents, all family Muridae
– diversified over relatively short period (last 15 million yrs)
after dispersal from the north
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