Abstract

Over 70+ paleorecords reveal millennial-scale “pluvials” or periods of enhanced rainfall during the late Quaternary in the Altiplano and central Andes. One such period, the Central Andean Pluvial Event (CAPE) lasted from ca. 17-10 ka (or thousands of years BP). The CAPE extended throughout the central Andes and may have reached as far south as 30°S. Paleoecological evidence shows that as recurring pluvials waxed on the hyperarid western slopes of the Andes vegetation migrated downslope, only to migrate upslope during drier intervals (such as most of the current Holocene). These eastward and westward displacements predict that plant and animal populations on the Altiplano should be hybridizing during interglacials. Indeed, small mammals such as Andean degu (Octodontomys gliroides) and Andean hairy armadillo (Chaetophractus nationi) are spatially structured in response to range expansions and constrictions over the last 20 ka. The Altiplano is likely an interglacial refuge when warmer/drier climates force many of these species out of the adjacent Atacama and Monte Deserts. Desert shrub species such as Atriplex imbricata and A. deserticola and Echinopsis atacamensis cacti have all increased their local abundance in recent decades. In contrast, over the last century the local abundance of Altiplano annuals is declining as populations retract to wetter areas and woody plant species from the dry Chaco have migrated upslope. As the region continues to dry out (predicted under greenhouse gas warming scenarios) many current distributions are likely relicts of past pluvials or very recent range expansions.