Field thermal ecology of the eastern short-horned lizard (Phrynosoma douglassi brevirostre) in southern Alberta

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Abstract
Phrynosoma douglassi brevirostre has a median body temperature (Tb) of 32.9 °C in southeastern Alberta, with a sharply peaked and negatively skewed Tb frequency. The range of the Tb frequency distribution in daylight hours during the active season (activity temperature range) is wide (20.0 °C). The realized thermal niche is approximately 7 °C wide, centred loosely on the median Tb. The populations examined are active over a wide range of ambient temperatures. With regard to substrate temperature and air temperature at 10 cm, the populations examined are intermediate between thermoconformity and thermal independence, but with regard to air temperature at 1 m they display more thermal independence. Habitat use is most varied on sunny days. Tb is not significantly different between situations, indicating that shuttling is an important thermoregulatory strategy. There is a significant difference in median Tb between small lizards and large lizards, but not between either of these size groups and medium-sized lizards. Small lizards utilize significantly warmer substrates than the other two size groups. Large lizards are more closely coupled to substrate temperature, and less closely coupled to air temperature, than small lizards. Medium-sized lizards have a wider realized thermal niche than the other two size groups and are intermediate in their thermal relations relative to the other two size groups.