PIKAS AND PERMAFROST - POST-WISCONSIN HISTORICAL ZOOGEOGRAPHY OF OCHOTONA IN THE SOUTHERN ROCKY-MOUNTAINS, USA

Occurrence of pikas (Ochotona princeps) in the southern Rocky Mountains is closely tied to past and present distribution of alpine permafrost conditions, which produce anti maintain appropriate talus-slope habitat. Estimates of full-Wisconsin elevational depression of alpine permafrost and vegetation zones support the existence of glacial-maximum dispersal corridors between currently isolated populations of O. princeps. Altithermal warming accounts for 66.7% of apparent post-Wisconsin extinctions of insular populations of pikas in the region. Populations at sites with altithermal refugia > 100 km(2) enjoyed high survivorship (93.8%) compared to smaller refugia (6.1-15.2%). Extant populations are located within 5 km of current alpine permafrost and within 20 km of the estimated altithermal occurrence of permafrost, indicating minor subsequent dispersal from a more restricted distribution of 6000 yr ago. Recolonization of sites within 20 km has been rare (less than or equal to 7.8%). Depending on the time scale considered, pikas are either expanding their range in response to regional cooling (100,000-yr and 1000-yr scale) or retreating in the face of regional warming (10,000-yr and 100-yr scale), which in mesic habitat results in filling of taluses by vegetation encroachment and soil formation.