INVERTEBRATE COMMUNITIES OF RELICT STREAMS IN THE ARID ZONE - THE GEORGE GILL RANGE, CENTRAL AUSTRALIA

The George Gill Range (24-degrees-S, 132-degrees-E) 220 km south west of Alice Springs in the Northern Territory, lies within one of the dri est regions of Australia. Diel and seasonal temperature differences ar e extreme and the average rainfall is 250 mm per annum. The streams of the Range are the largest group within the Central Ranges and are rel atively pristine. Their flow regimes are episodic but deep rock pools appear to act as reservoirs of surface runoff and may also receive gro undwater from the Mereenie aquifer. The waterbodies of the Range and s ome nearby areas were sampled in July and December 1986 to determine t he composition of the macroinvertebrate communities and biogeographica l relationships with the fauna of lotic systems elsewhere in Australia . Macroinvertebrate species richness at the Range was comparable with that of other Australian streams but no Plecoptera, Isopoda or Amphipo da were collected. The almost complete absence of shredders may reflec t low allochthonous inputs, because riparian vegetation in the arid zo ne is generally sparse. A small proportion of the fauna of the Range a ppears to be a relictual stream fauna. Species of low vagility such as the waterpenny, Sclerocyphon fuscus, would not be capable of dispersa l across the large tracts of arid land that now separate the Range fro m southern Australia, where it is also found. The occurrence of new sp ecies at the Range suggests that it is also a site of allopatric speci ation within some groups. The conservation values of the streams of th e George Gill Range and other sites, such as Giles Springs in the Chew ings Range, are extremely high. They represent unique aquatic communit ies of both ecological and evolutionary importance in the arid zone.