Meeting Abstract
Lizard populations that live on the northern edge of their geographic range in the northern hemisphere encounter greater environmental variation relative to populations near the core of their range. For example, daily and seasonal activity lengths for northern populations are constrained by cooler environmental temperatures. It is unclear how individuals in these northern populations are able to profit energetically and persist in these cool climates. In this study, we investigated how individuals of Sceloporus occidentalis living in a cool, maritime climate in Washington state could profit energetically enough to permit persistence of the population. We also compared the energetics of these lizards to individuals from a warmer southern-and-inland population east of the Cascade mountains. During summer, we found no difference in total daily activity time or daily energy expenditure (DEE) between these populations. We also found no difference in field-active body temperatures (Tb) (t1, 54 = 0.735, p = 0.466) or preferred Tb in the lab (t1,43 = 0.548, p = 0.587). Prey availability, however, was 82% higher for the northern population. Northern lizards also consumed more food energy (t1, 40 = 3.667, p<0.001). Northern lizards were 15% heavier relative to body length than lizards from the warm inland habitat (F1, 110 = 11.8, p<0.001). We infer that despite a shorter activity season for the coastal population and similar etho-physiotypes (preferred Tb and DEE) between populations, the higher food availability and sufficient sunny weather during the summer on the coast permits enough individual activity and production to allow the persistence of the northern coastal population.
