8.6 Australasian realm

The Australasian realm is a unique biogeographic region encompassing Australia, New Zealand, and numerous Pacific islands. Its isolation has led to the evolution of distinctive flora and fauna, including marsupials, monotremes, and endemic plant families.

Australasia's biodiversity is shaped by its Gondwanan origins, tectonic movements, and varied climates. The region faces conservation challenges from habitat loss, invasive species, and climate change, making it a priority for biodiversity research and protection efforts.

Geographic extent of Australasia

• Encompasses a vast region in the South Pacific, including Australia, New Zealand, New Guinea, and numerous smaller islands
• Represents a unique biogeographic realm with high levels of endemism and biodiversity
• Plays a crucial role in understanding global patterns of species distribution and evolution

Boundaries and major regions

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• Australia forms the largest landmass, covering approximately 7.7 million square kilometers
• New Guinea serves as a biogeographic bridge between Australasia and Southeast Asia
• New Zealand comprises two main islands (North and South) and numerous smaller offshore islands
• Includes diverse archipelagos such as the Solomon Islands, Vanuatu, and Fiji
• Extends eastward to include Polynesia and Micronesia

Isolated island groups

• Comprise remote volcanic and coral islands scattered across the Pacific Ocean
• New Caledonia hosts unique flora and fauna, including the flightless kagu bird
• Hawaii represents the most isolated archipelago with extreme levels of endemism
• Lord Howe Island and Norfolk Island feature distinctive ecosystems despite their small size
• Chatham Islands off New Zealand harbor endemic species like the black robin

Geological history

• Australasia's formation spans millions of years, shaped by tectonic forces and volcanic activity
• Understanding its geological past provides insights into current biodiversity patterns
• Plays a crucial role in explaining the distribution of flora and fauna across the region

Gondwanan origins

• Australasia originated as part of the supercontinent Gondwana approximately 180 million years ago
• Began separating from other landmasses during the breakup of Gondwana in the Jurassic period
• Carried ancient lineages of plants and animals, explaining the presence of relict species
• Isolation led to the evolution of unique flora and fauna, including marsupials and monotremes
• Gondwanan elements persist in modern Australasian ecosystems (Nothofagus trees, ratite birds)

Tectonic plate movements

• Australia's northward drift began around 85 million years ago, separating it from Antarctica
• New Zealand split from Australia approximately 80 million years ago, leading to its distinct biota
• Collision of the Australian and Pacific plates formed New Guinea and the Solomon Islands
• Tectonic activity created the deep trenches and island arcs of the western Pacific
• Ongoing plate movements continue to shape the region's geography and biodiversity

Volcanic activity

• Played a significant role in forming many islands and archipelagos throughout Australasia
• Created the Hawaiian Islands through hotspot volcanism over millions of years
• Formed the North Island of New Zealand, including active volcanoes like Mount Ruapehu
• Contributed to the formation of mineral-rich soils supporting diverse plant communities
• Ongoing volcanic activity in places like Vanuatu and Tonga creates new habitats for colonization

Climate and ecosystems

• Australasia encompasses a wide range of climatic zones, from tropical to temperate
• Climate diversity has led to the evolution of varied ecosystems and adaptations
• Understanding climate patterns helps explain species distributions and ecological processes

Tropical vs temperate zones

• Tropical regions include northern Australia, New Guinea, and many Pacific islands
• Support diverse rainforests, mangroves, and coral reef ecosystems
• Temperate zones found in southern Australia, Tasmania, and New Zealand
• Feature eucalyptus forests, grasslands, and alpine environments
• Transitional areas between zones harbor unique ecotones with high biodiversity

Arid interior regions

• Central Australia contains vast deserts (Great Sandy Desert, Gibson Desert)
• Characterized by low rainfall, extreme temperatures, and specialized adaptations
• Support unique flora like spinifex grasses and mulga shrubs
• Home to desert-adapted fauna (thorny devil, bilby, red kangaroo)
• Ephemeral water sources create temporary oases of biodiversity

Unique island habitats

• Isolated islands have developed distinctive ecosystems through long-term evolution
• New Caledonia's ultramafic soils support specialized plant communities
• New Zealand's absence of terrestrial mammals led to unique avian adaptations
• Hawaiian Islands showcase extreme adaptive radiation in various plant and animal groups
• Galapagos-like speciation observed in snails and insects across Pacific islands

Flora of Australasia

• Australasian flora exhibits high levels of endemism and unique evolutionary adaptations
• Plant diversity reflects the region's geological history, climate variations, and isolation
• Understanding Australasian flora provides insights into global plant evolution and biogeography

Endemic plant families

• Proteaceae family includes iconic genera like Banksia and Grevillea
• Myrtaceae family features eucalyptus, tea trees, and bottlebrushes
• Casuarinaceae family comprises she-oaks adapted to nutrient-poor soils
• Goodeniaceae family includes fan-flowers and scaevolas
• New Caledonia hosts the endemic family Amborellaceae, considered the most basal angiosperm

Adaptive strategies

• Sclerophyllous leaves help plants conserve water in arid environments
• Fire-adapted species like eucalyptus use lignotubers for post-fire regeneration
• Carnivorous plants (sundews, pitcher plants) thrive in nutrient-poor habitats
• Parasitic plants (mistletoes, Nuytsia) evolved to exploit other plants for resources
• Mycorrhizal associations allow plants to survive in nutrient-deficient soils

Megadiverse hotspots

• Southwest Australia recognized as a global biodiversity hotspot
• Wet Tropics of Queensland harbor ancient rainforest lineages
• New Caledonia's ultramafic flora represents a unique evolutionary experiment
• New Zealand's alpine plants show high levels of endemism and adaptation
• Papua New Guinea's forests contain an estimated 15,000-20,000 plant species

Fauna of Australasia

• Australasian fauna is characterized by high endemism and unique evolutionary lineages
• Isolation has led to the development of distinctive animal groups not found elsewhere
• Understanding Australasian fauna provides insights into evolutionary processes and biogeography

Marsupial dominance

• Marsupials diversified into various ecological niches in Australia and New Guinea
• Include iconic species like kangaroos, koalas, and wombats
• Tasmanian devil represents the largest extant carnivorous marsupial
• Possums and gliders adapted to arboreal lifestyles
• Marsupial moles evolved convergently with placental moles

Monotreme uniqueness

• Monotremes (egg-laying mammals) found only in Australasia
• Platypus adapted to semi-aquatic lifestyle with unique bill and venomous spurs
• Echidnas evolved long, sticky tongues for feeding on ants and termites
• Represent an ancient mammalian lineage with both reptilian and mammalian features
• Provide insights into early mammalian evolution and reproductive strategies

Avian diversity

• Birds of paradise showcase extreme sexual selection and plumage diversity in New Guinea
• Kiwis in New Zealand evolved flightlessness and nocturnal behavior
• Honeyeaters diversified to fill various nectar-feeding niches across Australasia
• Cockatoos and parrots show high species diversity and endemism
• Megapodes (mound-builders) use environmental heat to incubate their eggs

Biogeographic barriers

• Biogeographic barriers play a crucial role in shaping species distributions in Australasia
• Understanding these barriers helps explain patterns of endemism and biodiversity
• Provides insights into the historical and ongoing processes of species dispersal and isolation

Wallace Line significance

• Marks the boundary between Asian and Australian faunal regions
• Runs between Bali and Lombok, and between Borneo and Sulawesi
• Reflects the deep water channel that persisted during Pleistocene sea level changes
• Explains the distinct faunal compositions of Borneo (Asian) and Sulawesi (transitional)
• Named after Alfred Russel Wallace, who first recognized this biogeographic boundary

Lydekker Line importance

• Defines the eastern edge of the Sahul Shelf, including Australia and New Guinea
• Separates the Australian region from the transitional Wallacea region
• Marks the limit of marsupial distribution in the east
• Reflects the maximum extent of land connections during Pleistocene low sea levels
• Named after Richard Lydekker, who refined Wallace's biogeographic concepts

Weber Line implications

• Represents a transitional zone between the Wallace and Lydekker Lines
• Marks the western limit of many Australasian faunal elements
• Highlights the complex nature of species distributions in Wallacea
• Demonstrates the gradual transition between Asian and Australian biotas
• Named after Max Weber, who studied the biogeography of the Malay Archipelago

Island biogeography

• Island biogeography theory explains patterns of species richness and composition on islands
• Applies to both true islands and habitat islands within continents
• Provides a framework for understanding biodiversity patterns in Australasia's many islands

Species-area relationship

• Larger islands generally support more species than smaller islands
• Relationship typically follows a power law function: $S = cA^z$
• S represents species number, A is island area, c and z are constants
• Explains why Australia harbors more species than smaller islands like Tasmania
• Deviations from the relationship can indicate unique ecological or evolutionary factors

Endemism patterns

• Isolated islands often have high proportions of endemic species
• New Caledonia boasts over 80% endemism in its native flora
• Hawaii's native birds show nearly 100% endemism due to extreme isolation
• Endemism rates generally increase with island age and isolation
• Provides insights into evolutionary processes and conservation priorities

Colonization vs extinction

• Island species richness results from a balance between colonization and extinction rates
• Closer islands experience higher colonization rates from mainland source populations
• Larger islands have lower extinction rates due to larger population sizes
• Equilibrium theory predicts a dynamic balance between species gains and losses
• Explains why remote islands like Hawaii have fewer native species but high endemism

Human impact

• Human activities have significantly altered Australasian ecosystems over thousands of years
• Understanding human impacts is crucial for conservation and management efforts
• Provides insights into the resilience and vulnerability of Australasian biodiversity

Indigenous peoples' influence

• Aboriginal Australians used fire-stick farming to modify landscapes for over 50,000 years
• Maori arrival in New Zealand led to the extinction of moa and other large bird species
• Pacific Islanders introduced crops and animals, altering island ecosystems
• Traditional ecological knowledge contributes to modern conservation efforts
• Indigenous land management practices often promoted biodiversity in certain habitats

European colonization effects

• Introduced numerous invasive species (rabbits, foxes, cats) with devastating impacts
• Led to widespread habitat destruction through agriculture and urbanization
• Caused extinctions of many native species (thylacine, passenger pigeon)
• Altered fire regimes, leading to changes in vegetation structure and composition
• Introduced diseases that affected both wildlife and indigenous human populations

Modern conservation challenges

• Climate change threatens unique ecosystems like the Great Barrier Reef
• Habitat fragmentation isolates populations and reduces genetic diversity
• Invasive species continue to pose major threats to native flora and fauna
• Overexploitation of resources impacts marine and terrestrial ecosystems
• Balancing economic development with biodiversity conservation remains an ongoing challenge

Evolutionary processes

• Australasia's isolation has led to unique evolutionary processes and outcomes
• Understanding these processes helps explain the region's high biodiversity and endemism
• Provides insights into broader evolutionary theories and mechanisms

Adaptive radiation examples

• Hawaiian honeycreepers diversified into over 50 species from a single ancestral population
• Eucalyptus in Australia adapted to various climatic conditions across the continent
• New Zealand's moa evolved into nine species filling different ecological niches
• Drosophila flies in Hawaii show extreme morphological and ecological diversity
• Acacia species radiated to occupy diverse habitats throughout Australia

Convergent evolution cases

• Tasmanian wolf evolved dog-like features despite its marsupial lineage
• New Zealand's weta insects fill roles similar to small mammals in other ecosystems
• Succulent plants in Australia converged with those in Africa and the Americas
• Flightless birds evolved independently in New Zealand (kiwi) and Australia (emu)
• Burrowing frogs in Australia converged with similar species in other arid regions

Relict species preservation

• Tuatara in New Zealand represents the last surviving member of the order Rhynchocephalia
• Wollemi pine discovered in Australia is a "living fossil" dating back to the Jurassic period
• Platypus and echidnas retain primitive mammalian features from early evolutionary stages
• Ginkgo biloba, while not native, thrives in Australasia as a relict species
• Coelacanth populations in the Indian Ocean represent ancient fish lineages

Biogeographic regions

• Australasia comprises several distinct biogeographic regions with unique characteristics
• Understanding these regions helps explain patterns of species distribution and endemism
• Provides a framework for conservation planning and biodiversity research

Australian vs Oceanian subregions

• Australian subregion includes mainland Australia, Tasmania, and nearby islands
• Characterized by high marsupial diversity and eucalyptus-dominated landscapes
• Oceanian subregion encompasses Pacific islands east of the Lydekker Line
• Features high levels of avian endemism and unique island adaptations
• Transitional zones between subregions harbor mixed faunal and floral elements

New Guinea's transitional role

• Serves as a biogeographic bridge between Southeast Asia and Australia
• Harbors a mix of Asian and Australian faunal elements
• Supports high biodiversity due to varied topography and climate
• Home to unique species like tree kangaroos and birds of paradise
• Represents a center of plant diversity with an estimated 15,000-20,000 species

New Zealand's distinctive biota

• Isolated for over 80 million years, leading to highly endemic flora and fauna
• Lacks native terrestrial mammals (except bats) due to long-term isolation
• Developed unique avifauna including flightless birds (kiwi, takahe)
• Hosts ancient plant lineages like the kauri and southern beech forests
• Marine environments support diverse cetacean populations and unique fish species

Conservation priorities

• Australasia faces numerous conservation challenges due to its unique and vulnerable ecosystems
• Prioritizing conservation efforts is crucial for preserving the region's biodiversity
• Understanding conservation needs helps inform policy decisions and research directions

Threatened species hotspots

• Great Barrier Reef faces threats from climate change and ocean acidification
• Southwest Australia's plant diversity is at risk from habitat loss and fragmentation
• New Zealand's endemic birds are vulnerable to introduced predators
• Papua New Guinea's rainforests are threatened by logging and palm oil expansion
• Christmas Island's endemic species face multiple threats including invasive species

Habitat fragmentation issues

• Fragmentation of Australian eucalyptus forests impacts koala populations
• New Zealand's wetlands have been reduced to a fraction of their original extent
• Pacific island forests face fragmentation due to agriculture and development
• Fragmentation of mangrove ecosystems affects both terrestrial and marine species
• Habitat corridors are being established to reconnect fragmented landscapes

Invasive species management

• Cane toads in Australia continue to spread, impacting native predator populations
• Rats and cats on Pacific islands threaten ground-nesting birds and reptiles
• Invasive plants like lantana and mimosa disrupt native ecosystems
• Feral pigs cause significant damage to native vegetation and wildlife
• Biological control methods are being developed for some invasive species (rabbit calicivirus)