Paleoecology of late Pleistocene arctic ground squirrel middens and glacial environments of west-central Yukon Territory

Fossil arctic ground squirrel (Spermophilus parryii) middens (nests and caches) recovered from ice-rich loess sediments in west-central Yukon Territory are new paleoecological archives for Eastern Beringia. Middens reveal glacial steppe-tundra ecosystems during the Marine Isotope Stage (MIS) 3/2 transition (ca. 24,000 - 29,500 14C yr BP) and early MIS 4 (ca. 82 kyr) intervals. Middens contain a diversity of graminoids ( Poa, Elymus Carex spp., and Kobresia myosuroides), steppe and tundra forbs (Draba spp., Erysimum cf. cheiranthoides, Plantago cf. canescens, Phlox hoodii, Bistorta vivipara, Ranunculats spp., Potentilla), dwarf shrubs (Salix cf. arctica, S. cf. polaris), sage (Artemisia frigida) and rare conifers (Picea). Beetles and weevils are dominated by Lepidophorcis lineaticollis and Connatichela artemisiae and suggest predominantly, dry/cold glacial conditions. Some middens indicate that glacial steppe-tundra was established by ca. 29,450 14C yr BP, during the MIS 3 interstadial. Midden plant assemblages constrast with a 25,300 14C yr buried in situ mesic riparian meadow consisting of grasses (Deschampsia caespitosa, Alopecurtcs sp.), sedges (Carex), horsetail (Equisetum cf. palustre), and bryophytes. The steppe-tundra ecosystem at ca. 25,000 14C yr BP included Picea mariana and P. glauca trees. Modern arctic ground squirrel forage studies indicate cache preference are habitat specific and can favor a variety, of different plants in boreal and tundra environments. Selection factors may include perishability, proximity of vegetation to burrows and abundance of fruits and seeds per plant. Although multivariate comparison (MRPP, NMS and Indicator Species Analysis) of the MIS 3/2 and MIS 4 plant assemblages reveal significant differences, these are likely the result of selection bias based on local-scale habitat variability, rather than differences in zonal vegetation. Glacial conditions characterized by open, steppe-tundra vegetation and well-drained loessal substrates enabled arctic ground squirrels to establish widespread populations in regions such as the Klondike where they are rare or absent today. Arctic ground squirrels endured numerous Quaternary glacial-interglacial oscillations because their generalist foraging adaptations and ability to track environmental changes enabled them to persist in "interglacial refugia" that retained some environmental characteristics of the glacial "mammoth-steppe".;Keywords. paleoecology, Beringia, Pleistocene, arctic ground squirrels, plant macrofossils, Yukon, steppetundra, middens.