Invetebrate communities of Relict streams in the Arid Zone: the George Gill Range, Central Australia

Abstract

The George Gill Range (24�S,132�E) 220 km south west of Alice Springs in the Northern Territory, lies within one of the driest regions of Australia. Diel and seasonal temperature differences are 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 relatively pristine. Their flow regimes are episodic but deep rock pools appear to act as reservoirs of surface runoff and may also receive groundwater from the Mereenie aquifer. The waterbodies of the Range and some nearby areas were sampled in July and December 1986 to determine the composition of the macroinvertebrate communities and biogeographical 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 Amphipoda were collected. The almost complete absence of shredders may reflect low allochthonous inputs, because riparian vegetation in the arid zone is generally sparse. A small proportion of the fauna of the Range appears to be a relictual stream fauna. Species of low vagility such as the waterpenny, Sclerocyphon fuscus, would not be capable of dispersal across the large tracts of arid land that now separate the Range from southern Australia, where it is also found. The occurrence of new species at the Range suggests that it is also a site of allopatric speciation within some groups. The conservation values of the streams of the George Gill Range and other sites, such as Giles Springs in the Chewings Range, are extremely high. They represent unique aquatic communities of both ecological and evolutionary importance in the arid zone.