HYDROGEOLOGIC INFLUENCES ON THE PRESERVATION OF ORESTIAS-ASCOTANENSIS(TELEOSTEI, CYPRINODONTIDAE), IN SALAR DE ASCOTAN, NORTHERN CHILE

Orestias ascotanensis Parenti 1984, is a small native fish found in is olated freshwater pools at Salar de Ascotan. Other Orestias are found in freshwater lakes in the Altiplano to the north, separated by hundre ds of kilometers of desert. The distribution of fish in the Salar is l imited by freshwater availability and thus the populations are located within very short extension (less than 1 000 m) on each spring and po ol. The fish apparently arrived at Ascotan during a high stand at the last glacial maximum (LGM, similar to 17 ka) of Lake Minchin, which fi lled the internal drainage of the Altiplano. During Holocene time, wit h drier climate, the Ascotan pools have been maintained by groundwater flow which includes recharge from the Ascotan topographic basin and f rom recharge in Pastes Grandes Caldera, a Miocene-Pliocene ignimbrite center at higher elevation to the east. Such hydrogeologic features cr eate a permanent water supply allowing the preservation of a unique la ndscape and biota including the small and very isolated populations of Orestias.