Getting around
Many factors affect the distribution and evolutionary history of spiders. These involve geological, environmental, genetic, ecological and behavioural processes.
An austrochiloid spider, Progradungula carraiensis.
Photo: M Gray © Australian Museum.
Continental drifters
The world' s continents, with the plants and animals on them, have drifted together and broken apart over many millions of years.
Some 150 million years ago, Australia was part of the southern supercontinent of Gondwana.
When Gondwana broke up, spiders were isolated on separate continents, where they evolved independently into new (but related) spider groups. The recognition of related plant and animal taxa on widely separated continents like Australia.
150 million years ago Australia was part of the southern supercontinent of Gondwana. Map showing Gondwanan with probable distribution of austrochiloid spiders.
The distribution of austrochiloid spiders after the breakup of Gondwana. When Gondwana broke up, spiders were isolated on separate continents, where they evolved independently into new (but related) spider groups.
Ballooning around
Spider species that are found in many places are often good travellers. Many of these spiders get around by behaviour called ballooning. Young spiders, and even small adults of some species, put out silk threads which are caught by the wind, carrying them up and away. Many land close by, sometimes swathing the landscape in gossamer silk; but others may travel long distances across land or sea. Ballooning helps maintain and extend the distributions of these spiders. Spiders as different as orb weavers and wolf spiders disperse by ballooning.
Massed Nephila plumipes webs at Homebush Bay, New South Wales. Photo: © B Chudleigh.
Map of Australia, New Zealand, Papua New Guinea and neighbouring islands showing the distribution of Golden Orb Web Spiders, Nephila edulis.
A blind cave spider (Tartarus nurinensis) in its web.
Photo: © N Poulter.
Staying at home
Many events, like climate change or rising sea levels, can result in animals like spiders becoming isolated in 'refuge' habitats, like caves, mountain tops and islands, where they are unable to survive in the 'hostile' areas surrounding their refuge. These isolated populations are often small and can be subject to considerable random genetic variation - a 'bottleneck' effect. Such spiders may not only evolve into new species but may also become specifically adapted to living in specialised habitats like caves. These highly adapted species cannot survive outside the cave refuge even after surface climatic conditions have improved. It is logical that such species are poor dispersers that need to spread only over relatively short distances by walking.
Refuge habitats are important for conservation because many of the animals and plants that live in them are not found anywhere else. Their presence gives us valuable information about evolutionary processes and environmental history.
Nullarbor cave entrance.
Photo: M Gray © Australian Museum.
Map of Australia showing position of Nurina Cave; Murdoch Cave; Mullamullang Cave and Thampanna Cave. These caves on the Nullarbor Plain have their own species of blind cave spiders.
