SOUTH AUSTRALIAN BUTTERFLIES
INTRODUCTION AND HABITATS
Butterflies are predominantly a tropical group of insects. It is not surprising, therefore, that the majority of the 400 odd species recorded in Australia have a distribution which includes, or is restricted to, the tropical and subtropical north and east of the continent. Seventy-eight of these species, less than one fifth of the Australian fauna, have been recorded in South Australia. This group of butterflies, though small, is rich and diverse in the southern endemic colder elements of the Australian butterfly fauna.
South Australia is a dry state. The average rainfall is 235 mm (9 "). The state can be divided into two broad vegetation areas, each largely dependent on the amount of rainfall it receives, and demarcated by the 250 mm rainfall isohyet. That area receiving the lower rainfall is the arid and semi-arid north which accounts for about 80 % of the state and is generally termed the Eyrean Zoogeographic Region. It is predominantly pastoral country. In this area, most of the meagre rainfall occurs during the hot summer monsoon months.
Nearer the coast is the area receiving rainfall greater than 250 mm which is termed the Bassian Zoographic Region. Here, the rainfall occurs mostly during the cold winter months. It is the start of the dense, temperate woodland habitat. It is also the start of intensive agriculture within the state, and consequently it has suffered the most from clearing, and it is estimated that 90 % of this region has been cleared contributing to the current dryland salinity crisis. About 60 % of the state's butterflies are largely endemic to this region. There are three subregions within this zoogeographic region. The dry woodland (mallee) habitat, the generally elevated forests and wet woodlands, and the very narrow coastal habitat.
The hot arid and semi-arid lands are located in the Far North Pastoral region and comprise 80 % of the state. It is a generally low area below 600 m and Lake Eyre itself is below sea-level. Higher rocky areas occur in the Gawler, Olary and northern Flinders Ranges (in southern areas), and the Mann, Musgrave and Tomkinson Ranges in the far north-west. Vegetation is largely controlled by rainfall and soil type. Habitats are extensive and monotonous. The vegetation is often very sparse, particularly in the Lake Eyre Basin east of the Stuart Highway, consisting of very open acacia or eucalyptus woodland, blue-bush and salt-bush shrubland, and grasslands. Sometimes the vegetation is better developed along ephemeral waterways or within the dune fields. The vegetation improves nearer the southern limits of the region where extensive, open mallee (dryland Eucalyptus) and myall (Acacia papyrocarpa) woodlands may occur.
Many of the migrant butterflies breed in this area after good rains, with five species of butterflies largely confined to the region. Some of the butterflies probably lead a nomadic existence, moving along the ephemeral waterways. Butterfly populations are believed to be mostly stable here, although the region has been poorly surveyed for butterflies. The area suffers from the effects of overgrazing from feral (camels, goats and rabbits) and domestic animals. In some areas there has been very little self generation of woody flora since the coming of European settlement (1836), due to the combined effects of periodic drought and overgrazing by the animals. Existing woody flora in such areas are as old or older than this settlement! In this area also occur the breeding grounds for the plague locust. Control of the locust by the aerial application of poisonous sprays has had a devastating effect on the local biodiversity, but hopefully new technology through the use of a Metarhizium fungus may see a lasting improvement in the environment.
The Everard, Mann, Musgrave and Tomkinson Ranges reach a maximum elevation of 1440 m. The vegetation in these ranges consists mainly of the very prickly, tussocky spinifex grass (Triodia sp), while the vegetation on the surrounding dune plains comprises mulga (Acacia aneura) woodland infested with the pale-leaf mistletoe (Amyema maidenii). Some of the valley areas contain spring water and better vegetation which support resident populations of arid-land butterflies.
This habitat dominates the southern 20 % of the state, and generally occurs in the areas receiving rainfall greater than 250 mm. This vegetation type is dominated by dryland Eucalyptus species but also contains many other smaller wood or shrub land communities dominated by either Acacia, Banksia, she-oaks (Allocasuarina), native pines (Callitris), or Melaleuca. It is interspersed with occasional broadacre native grasslands. The understorey is also complex and diverse, containing many butterfly foodplants including quandongs, Choretrum, dryland sedges, grasses, and small shrubs and herbs.
Much of this mallee vegetation is tolerant of periodic bushfires, with the Eucalyptus regenerating from lignotubers, while the Acacia and the understorey and other associated vegetation are actually dependent on the bushfires for regeneration, with the seed-base requiring the heat of the fire to weaken the hard outer seed capsule and the smoke from the fire to impart certain chemicals for germination and enhanced early growth. There is often a bushfire produced early growth cycle of certain flora immediately after the fire that includes Leguminosae and Santalaceae, to a later mature flora dominated by different plants than those present during the early part of the cycle. There are certain butterflies which have adapted to these early immature and late mature periods of the bushfire cycle.
Eucalyptus Forest and Open Wet Woodland
The forest and wet woodland habitats are confined to the higher rainfall areas of South Australia. They occur in south-east Eyre Peninsula, western Kangaroo Island, the Mt Lofty and southern Flinders Ranges, and in the Lower South-east. They often have a diverse understory of medium and small shrubs, herbs, sedges and grasses. Although small in area, this habitat is home to a large range of butterflies. Two species are uniquely confined to this habitat in the Mt Lofty Ranges.
This is a cool and wet area, with annual rainfall greater than 700 mm. The vegetation is unique, comprising forest, wet woodland and swamps with close affinities to the Grampians and Great Dividing Range in Victoria. This habitat area also contains a unique butterfly fauna with eleven of the species present not to be found anywhere else in South Australia. More unique species are likely to be found in the future, although some species are also now probably extinct as a result of the extensive clearing and swamp drainage that has occurred in the region.
Wetlands are an important habitat of low lying areas, associated with creeks, rivers, lakes and estuaries. Springs are also a very important contributor to wetlands. Sedges (Cyperaceae family), and in particular the large saw-sedge Gahnia species are an important vegetation component of wetlands. Some wetlands are dominated by sedges, and are called sedge-lands. Sedges are the dominant foodplant for the Hesperillini skippers and several brown butterflies. Due to the severe degradation of our wetlands by fragmentation and draining, nearly all of the butterflies dependent upon wetlands for habitat or foodplant are now threatened.
Native grasslands occur locally throughout the state. In the dry pastoral and mallee areas they occur as Austrostipa (spear-grass), Astrebla (mitchell grass), and Triodia (spinifex) dominated grasslands. In the wetter forest and marsh areas Poa tussock-grasses sometimes dominate the understorey. Grasslands can occur in broadacre form but more often contain isolated trees and shrubs, and occur with rushes, sedges, and small herbs. Many species of butterflies associate with grasslands, with certain skippers and brown satyrid butterflies being totally dependent on this habitat. Native grasslands have historically been severely degraded by over-grazing and stock trampling, and consequently many of the associated butterflies are threatened, including the White-veined Grass-skipper and the Cynone Grass-skipper.
This is a very narrow zone adjacent to the sea, varying from high cliffs to sand dunes and estuarine ecosystems. There is a wide range of very specific vegetation types and habitats, including estuarine mangroves, sedge wetlands and samphire marshes, shrubland and mallee in the dunes, and low coastal heaths along the cliffs. It is often a harsh habitat due to the salt laden winds, but many butterflies thrive in the environment.
The urban region is the habitat of common butterflies, and is also briefly frequented by migrating butterflies. Flowering garden plants are the resting and re-fuelling stations for butterflies as flowers contain nectar, the main food source for the adults. Buddleias, lantanas and many other plants can attract butterflies to the garden. There are about twenty species of butterflies which are commonly seen in gardens in the southern parts of the state, and include the Australian Painted Lady, the Australian Admiral, the Meadow Argus, the Monarch and various migrant butterflies such as the Caper White and the Small Grass-yellow.
Migrant and Vagrant butterflies
These species either periodically or annually migrate in numbers (migrants), or singly (vagrants) within South Australia, over short or long distances. Many butterfly species have this tendency (especially the females in the case of vagrants), and particularly during favourable seasons, as it is mostly used as a means of dispersal in Australia. This habit is particularly strong in the white, yellow and nymph butterflies. These butterflies are common near their food plants in their normal breeding habitat, which is usually either in the northern pastoral areas of the state, or interstate. Many of the species from the latter two areas are biologically unsuited to the southern parts of the state and do not establish even if the food plant is present. There are about 30 butterflies presently recorded from South Australia that have migration tendencies.
For further landcover and climatology information check the following.
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Author: R. GRUND, © copyright, 20 July 1999, all rights reserved. Updated 8 January 2007.