41-1 copyright 2005 mcgraw-hill australia pty ltd ppts t/a biology: an australian focus 3e by knox,...

41-1Copyright 2005 McGraw-Hill Australia Pty Ltd PPTs t/a Biology: An Australian focus 3e by Knox, Ladiges, Evans and Saint

Part 6: Ecology

Chapter 41: Australian biota


Southern connections

• 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


Fig. 41.4: Sea-floor spreading


Ancient forests: Permian times

• 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)


Ancient forests: the Triassic, Jurassic and Cretaceous

• 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


Forests at the end of the CretaceousClimate 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


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


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


Fig. 41.6: Laterite

Copyright © Professor Pauline Ladiges, University of Melbourne


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


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


Arrival of humans—when?

• 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


Fig. 41.10: Vegetation changes associated with increased burning


Modern Australian environments—terrestrial

• Continent spans latitude10–40°S, so wide range of climate

– 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)


Fig. 41.12: Australian climatic regions


Modern Australian environments—marine• 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


Marine biodiversity—flora

• Rhodophyta (red algae) – includes many endemic species– growing for pharmaceutical and economic use

• 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)


Marine biodiversity—fauna

• Fish: 3 500 species in Australia- high species diversity but low endemism in north- lower diversity but higher endemism (85 per cent) in

south

• 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


Australian terrestrial flora• 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


Myrtaceae: the eucalypt family

• 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


Proteaceae: the banksia family

• 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 2- celled ovary

• Flowers attract bird-pollinators


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


Fig. 41.25a: Phyllodinous acacia


Fig. 41.25b: Acacia longifolia


Fig. 41.25c: Acacia mearnsii


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


Biogeographic patterns—frogs

• 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


Australian reptiles

• 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


Adaptive radiation in mammals

• 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


The Prototheria: platypus and echidna

• Endemic to the Australian plate• Fossil representatives known from South America• Display many primitive features

– egg-laying– secrete milk from glands with no nipples– cloaca– reptilian features

• But also display specialisations– sense weak electric fields to locate prey


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


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

41-1 copyright 2005 mcgraw-hill australia pty ltd ppts t/a biology: an australian focus 3e by knox,...

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