The heterogeneous topography of the Great Basin province leads to one of the most climatically variable regions in the Northern Hemisphere. Along the southwestern edge lies Death Valley, an area of even more extreme climate and physiographic relief; Death Valley has the dubious distinction of being the hottest place on earth. Our research investigates the adaptive response of Neotoma (woodrats) to temperature fluctuations over the late Quaternary on the valley floor and along a nearby elevational and environmental gradient. By combining fieldwork on extant animals living on the valley floor with historical information from museum specimens and paleomiddens, we reconstruct the evolutionary histories of 2 species (N. lepida and N. cinerea) differing significantly in size and habitat preferences. Here, at the modern limit of both species' thermal and ecological thresholds, we find fluctuations in body size and range boundaries over the Holocene as climate shifted. Although N. cinerea is extirpated on the east side of the valley today, it was ubiquitous throughout the late Quaternary. Moreover, we find fundamental differences in the adaptive response of woodrats related to elevation and local microclimate. Modern work suggests the mechanism is physiological; exposure to consistently high temperatures leads to high mortality. Thus, high temperatures strongly restrict time available for the essential activities of foraging and mating. Our results illustrate the profound influence temperature has on all aspects of woodrat life history, ecology, distribution, and evolution.
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Vol. 95 • No. 6