• Investigating (a)symmetry in a small mammal's response to warming and cooling events across western North America over the late Quaternary

      Balk, Meghan A.; Betancourt, Julio L.; Smith, Felisa A.; Univ Arizona, Bio5 Inst (CAMBRIDGE UNIV PRESS, 2019-09)
      Many mammalian populations conform spatially and temporally to Bergmann's rule. This ecogeographic pattern is driven by selection for larger body masses by cooler temperatures and smaller ones by warming temperatures. However, it is unclear whether the response to warming or cooling temperatures is (a)symmetrical. Studies of the evolutionary record suggest that mammals evolve smaller body sizes more rapidly than larger ones, suggesting that it may be "easier" to adapt to warming climates than cooling ones. Here, we examine the potential asymmetrical response of mammals to past temperature fluctuations. We use the fossil midden record of the bushy-tailed woodrat, Neotoma cinerea, a well-studied animal that generally conforms to Bergmann's rule, to test the ability of populations to respond to warming versus cooling climate throughout its modern range in western North America over the late Quaternary. We quantified the response to temperature change, as characterized by the Greenland Ice Sheet Project 2 temperature record, using N. cinerea presence/absence and "darwins." Our results show that populations within the modern range of N. cinerea show little difference between warming and cooling events. However, northern, peripheral populations are absent during older, cooler periods, possibly due to climate or taphonomy. Our study suggests adaptation in situ may be an underestimated response to future climate change.
    • Processes of Paleoindian site and desert pavement formation in the Atacama Desert, Chile

      Ugalde, Paula C.; Quade, Jay; Santoro, Calogero M.; Holliday, Vance T.; Univ Arizona, Sch Anthropol; Univ Arizona, Dept Geosci (CAMBRIDGE UNIV PRESS, 2020-06-19)
      A distinct feature of many of the earliest archaeological sites (13,000-11,200 cal yr BP) at the core of the Atacama Desert is that they lie at or just below the surface, often encased in desert pavements. In this study, we compare these sites and undisturbed desert pavements to understand archaeological site formation and pavement development and recovery. Our results indicate these pavements and their soils are poorly developed regardless of their age. We propose that this is because of sustained lack of rain and extreme physical breakdown of clasts by salt expansion. Thus, the core of the Atacama provides an example of the lower limits of rainfall (<50 mm/yr) needed to form desert pavements. At site Quebrada Mani 12 (QM12), humans destroyed the pavement. After abandonment, human-made depressions were filled with eolian sands, incorporating artifacts in shallow deposits. Small and medium-sized artifacts preferentially migrated upwards, perhaps due to earthquakes and the action of salts. These artifacts, which now form palimpsests at the surface, helped - along with older clasts - to restore surface clast cover. Larger archaeological features remained undisturbed on top of a deeper Byzm horizon. The vesicular A horizons (Av horizons) have not regenerated on the archaeological sites due to extreme scarcity of rainfall during the Holocene.