Migration Bottlenecks, Climate, and the Conservation of Pleistocene Relicts in Central Asia

Abstract

Land bridges once assured transcontinental connectivity, but climate-induced habitat loss resulted in the extinc- tion of numerous North American large mammals. Using GPS technology on the formerly widespread but now endan- gered saiga in Mongolia, we identified a fine-scaled 5-km wide critical corridor, whose protection is critical for maintain- ing migration and meta-population structure. The world's great overland migrations are disappearing, truncating fundamental processes that have contributed to ecosystem functioning for millennia. With more people reli- ant on lands that were once remote, intact habitats are now replaced by livestock, fences, and people (1). Nevertheless, expansive grasslands and deserts in China, Mongolia, Ka- zakhstan, and Russia still sustain extraordinary movements between winter and summer ranges, including those of chiru (Pantholops hodgsonii), white-(Procapra gutturosa) and black-tailed (Gazella subgutturosa) gazelles, khulan (Equus hemionus), saiga (Saiga tatarica), and Bactrian camels (Camelus bactrianus) (2 - 4). The latter three species - all recognized as endangered by the IUCN - along with mam- moths, Panthera lions, and wild horses (Equus spp.) once moved between Asia and North America using the Bering Land Bridge. That conduit for inter-continental movement collapsed during the Late Pleistocene when climate changed, ocean levels rose, and the arid Mammoth Steppe of Beringea disappeared (5). Although saiga, camels, and wild horses were dependent upon these cold-adapted xeric grasslands, such remnant Pleistocene habitats and their associated fauna currently persist in situ only in Central Asia (5). While the Being Land Bridge once enabled connectivity across broad landscapes, today's conservation challenges are appropriately more linked to the maintenance of connectivity among population subunits, protecting corridors at a fine scale, and understanding the direct impacts of humans under an umbrella of climate change. Long-term conservation of fragmented populations requires maintenance of meta- population structure. With the above little-known relicts re- stricted to Central Asia, a critical challenge has been the ac- quisition of knowledge, not only about migration routes, if any, but the protection of land(s) critical to sustaining movements among disjunct population segments (6).