Desert regions have no continuous supply of water. Irregular rain may be heavy, causing floods, but is followed by long dry periods. Surface water fills clay pans or follows wide flood plains usually ending in salt lakes.
Salt in desert environments is plentiful.
Animals and plants have developed strategies to cope with high temperatures and long hours of sunlight, long periods without rain and water and the large amounts of salt present.
| Vegetation
Plants in this region are generally woody, smaller and spaced further apart than those in wetter regions or are ephemerals, escaping the harsh conditions as seeds. Typical water saving features include small, light coloured leathery leaves sometimes covered with reflective hairs, scales or resins. Ephemeral plants survive without these features by having a fast growing short life cycle triggered only after heavy rains revive dormant seeds. |
Whistling spider
Selenocosmia stirlingi
The whistling spider ambushes large insects, small mammals, reptiles, frogs, and even small birds near its burrow entrance at night. This "primitive" spider with a leg span of about 140 mm does not make a web to catch prey. It is venomous but not dangerous to humans.
At the end of the one metre long burrow the soil is moist and cool. During the day the open entrance is covered by a silk film to keep the burrow humid. A low silk-covered mound around the entrance traps dew or raindrops for drinking and helps prevent flooding in heavy rain. If the burrow does flood air is trapped around the spider’s hairy body until the water soaks away. When a spider starts to dehydrate its legs lose their rigidity. The spider cannot keep its legs straight and with further water loss the spider will die.
The mature male moves around at night during or after rains in humid weather (often during autumn) to avoid dehydration. It searches for the burrow of a female. The females can whistle and produce a scent to attract a male. After mating the sperm from the male is stored inside the female until she is ready to breed, usually in late summer. The female suspends the large (30 x 10 mm) eggsac near the cool moist bottom of the burrow. As many as 12 months may pass after mating before the eggs are laid and the young spiders emerges. The young disperse during or after rains to begin digging their own burrow in the damp soil which makes digging easier and helps prevent dehydration.
Burrows are permanent homes. Land cultivation destroys the burrow and grazing stock destroy the moisture-trapping silk and trample soil so the risk of flooding is increased. These activities also reduce availability of food although in some relatively undisturbed areas the introduced mouse may be an important food source.
References
Kotzman, M. 1990. Annual activity patterns of the Australian tarantula Selenocosmia stirlingi (Araneae: Theraphosiade) in an arid area. Journal of Arachnology, 18, 123-130.
Sand grasshopper
Urnisa guttulosa
Desert grasshoppers such as the sand grasshopper can only feed and reproduce following rains that lead to the germination of green plants.
The rest of the time, and during the heat of the day, the sand grasshopper must shelter. Some desert grasshoppers shelter on trees and shrubs, but the sand grasshopper covers itself with sand. The sand grasshopper has special long middle legs to scoop out sand and eyes located at the very top of its head so it can sit buried with just its eyes and antennae exposed.
Desert grasshoppers do not breed regularly. Whenever it rains they feed, reproduce and lay eggs in the soil. Eggs can remain dormant for years if necessary, until the next heavy rain.
The sand grasshopper and many others such as the gibber grasshopper use the "stay-put" strategy of desert survival, and never reach plague numbers or damage crops like some locusts.
Eyrean grasswren
Amytornis goyderi
The Eyrean grasswren eats seeds and small invertebrates. These provide all the water requirements for this bird which has very efficient kidneys and produces very dry concentrated excreta.
The birds are mostly found on sand dunes in clumps of sandhill cane grass Zygochloa paradoxa. Here they shelter from the heat of the midday sun and predators. The streaked upper parts of the similar looking male and female camouflage them perfectly in the densely tangled bushes.
The nest, built among the stems of the bush, is a deep cup of grass stems with the rim sloping at 45¼ and facing the leeward side of the dune to reduce exposure to the wind and sun. Two eggs are laid.
This species was described by Gould in 1875 but was not seen again reliably until 1961 (by the Macumba river) and in 1976 (in the Simpson Desert). What was thought to be a possibly extinct species is now known to be very common through the vast sandhill cane grass areas in north-east South Australia, south-east Northern Territory and south-west Queensland. Its highly elusive nature and remote habitat kept it hidden from Europeans until persistent fieldwork solved the mystery of how to find it.
This region is unsuitable for grazing cattle, so there has been little disturbance of this species by humans.
References
Parker, S A, May, I A and Head, W. 1978. Some observations on the Eyrean grasswren Amytornis goyderi (Gould, 1875). Records of the South Australian Museum, 17(24), 361–371.
Reader’s Digest complete book of Australian birds. 1990. Reader’s Digest, Sydney.
| Vegetation
Cane grass zygon (Greek) = pair chloe (Greek)
= grass - referring to the separate male and female
parts Cane grass has few and reduced leaves to minimise water loss. For photosynthesis it depends mainly on its green moisture retaining stems which also collect and channel water to the roots. Cane grass flowers quickly after rain and can root from basal stems, enabling it to slowly move with drifting sand. Grass wrens too, reproduce more successfully when moisture becomes readily available in their environment, although both cope well with the long dry periods. The Eyrean grasswren reduces its exposure to the sun and predators by living amongst the cane grass. The dense growth of cane grass provides a more protected favourable living site for both the wren and the plant itself. |
Shield shrimp
Triops australiensis
The shield shrimp relies on temporary ponds filled by heavy downpours of rain. Here it lives under submerged plants protected from the sun and eats decaying organic material (detritus).
Eggs hatch as soon as rain creates a suitable habitat and the microscopic larvae develop into adults within a few weeks. As the ponds dry out the adults die and are eaten by birds. Eggs are remarkably resistant to dry conditions and remain viable for several years. They may be blown by the wind to reach unusual locations like the top of Uluru.
Human activity, such as constructing dams, provides the shield shrimp with extra habitat.
| Vegetation
Desert nardoo Marsilea = named after an Italian naturalist Marsigli, drummondii = named after the collector Drummond who was the first Western Australian government botanist, nardoo = an Aboriginal name for paste or porridge The desert nardoo has tough, woody sporocarps (capsules) containing spores that can remain dormant for many years. After rain, the sporocarps burst and the spores begin to grow, and nardoo spreads rapidly across moist ground or along the edges of flooded claypans and watercourses. Insulating hairs help minimise water loss by increasing the humidity around the frond. When an area dries out, nardoo dies, leaving its sporocarps to wait for the next rain just like shrimp eggs. Aboriginal people grind the sporocarps into flour for cooking. |
Spinifex hopping-mouse
Notomys alexis
The spinifex hopping-mouse can survive without drinking water. During drought its water requirements are met from moisture in food—seeds, insects, plant roots—and from metabolic water made from carbohydrates in the seeds that it eats. To reduce water loss the hopping-mouse has no sweat glands, excretes almost dry faeces, and has one of the most concentrated urines of all mammals.
The hopping-mouse digs a deep sloping tunnel 1–2 m down to where the desert sand is damp. There it digs several vertical entry tunnels and for protection fills in the first long burrow. Burrows are scattered and not easily detected. The humidity in the burrow is increased by communal living. The hopping mouse is active on the surface at night, when it is cooler, looking for food
At any time of the year, even in drought conditions, the hopping mouse can breed but most often does so in spring and summer and in good seasons. To conserve water the mother produces concentrated milk and drinks the urine of her 3–4 infants.
| Vegetation
Spiny fan flower Scaevola = left-handed, referring to the lobes of petals all on one side, spinescens = spiny Spiny fan flower is a long lived woody shrub that can survive for long periods without rain. It may drop its leaves in times of drought to conserve water. Spines which extend beyond the leaves, help protect the plant from leaf eating animals. A layer of star-shaped hairs covering the leaves, buds and stems form a protective insulating microclimate and reduce water loss. Many desert plants avoid high water loss during the hottest part of the day by closing their pores (stomata), just as the hopping-mouse avoids the drying heat by resting in its burrow. Strong smelling flowers attract insects during the night when many of these pollinators are most active. Moist, attractive fruits extend beyond the spines putting them within easy reach of birds who readily eat the fruit and help spread the seed. Spiny fan flower has deep roots to search out moisture underground and help maintain water levels just as the increased humidity underground can help the hopping-mouse to retain its moisture. |
Water-holding frog
Cyclorana platycephalus
The water-holding frog lives underground and takes the opportunity of occasional desert rainstorms to feed and breed on the surface. Without rain it remains trapped underground unable to escape until water softens the ground above. Survival is a gamble!
As the rainwater evaporates the water-holding frog burrows down into soft soil using "spade" shaped projections on its heels. The frog sheds a layer of skin which forms a cocoon. All the frog’s body processes slow down during this underground stay. Water is stored in its bladder and it can remain underground for several years. Once it has rained, the ground softens and the frog eats the cocoon and works its way through the softened earth to the surface.
The frog breeds in temporary rain-filled claypans. The tadpoles grow large (about 70 mm long) in about four weeks but must change into frogs and dig their burrow before the claypan dries out again.
Local Aborigines hunt this and other frogs as a source of food and water. Knowing where to find these animals can be crucial to human survival in the desert.
| Vegetation
Paper daisy leucas = white, chrysum = yellow, the flower’s colour, fitzgibbonii = named after Fitzgibbon. "Paper" describes the papery flower. Paper daisy is an annual plant with a small, shallow root system and a covering of resinous hairs to help conserve water in the leaves and stems. This plant grows rapidly, flowers and sets seed quickly after rain and dies when the earth dries. The seeds are dispersed by wind and can remain dormant for many years until the next substantial rain. Dormancy until water comes is a survival feature of both the water-holding frog and seeds of the paper daisy. |
Sand-sliding skinks Lerista species
The genus Lerista includes about 60 species of small skinks specialised for "sliding" through sand and loose soil. A common name for these lizards is "sliders’. Legs are unnecessary for this sort of locomotion (and may even get in the way) and all species have reduced legs mostly with fewer than five toes. Some species have lost the forelimbs altogether.
Most of their food of termites and cockroaches is found below the surface of sand, and they are active on the surface only at night. Although they can tolerate a body temperature of 46–48¼C they prefer about 30¼C (40–41¼C is lethal to most reptiles). Desert species of Lerista do not drink and their kidneys produce insoluble uric acid. They do not excrete water from their bodies.
Sand-sliding skinks have shovel-shaped heads, little eyes and their under-jaw is "countersunk" to help them "slide" through the dry sand.
These skinks lay 2–6 eggs in a shallow burrow. The insulation of air between dry sand grains keeps temperatures lower. A sand-sliding skink may live for up to 10 years.
References
Greer, A E 1989. The biology and evolution of Australian lizards. Surrey Beatty, Chipping Norton.
Glasby, C J (ed), 1993. Fauna of Australia, Vol 2A : Amphibia and reptilia. Australian Government Publishing Service, Canberra.