title: How does spatial variation in climate cause spatiotemporal patterns in lizard energetics?
Creators: name: Powers, Sean D.
Publisher: name: Western Washington University
Year: 2010

description: <p>Sceloporus occidentalis occurs in two locales near the northern end of its geographic range that contrast markedly in climate. Both locales are in Washington state; one is cool, moist coastal temperate forest and the other is warm, dry pine-oak woodland in the state's interior. The focus of this thesis was to investigate differences in lizard production and population structure between these locales by correlating daily and seasonal patterns of temperature, precipitation, and cloud cover with the measured and estimated patterns of lizard activity, energy expenditure, feeding rates and food availability. Based on air temperature records, the estimated activity season length for Sceloporus occidentalis was greater at the inland locale, at 207 days than at the coastal locale, at 191 days. Within the activity season there were more 138 warm, sunny days available for S. occidentalis activity at the inland locale, but only there were only 79 of these days available at the coastal locale. Daily activity on these sunny days was estimated to be about 9.5 hours at both locales. The combination of equal foraging time available at both locales on warm sunny days during mid-summer and higher arthropod abundances at the coastal locale in mid-summer were correlated with higher rates of daily fecal production by the coastal lizards (0.0252 g • g-1 • d-1) than by the inland lizards (0.0221 g • g-1 • d-1). Hence, calculated food intake rates of coastal lizards (0.0360 kJ • g-1 • d-1) were greater than food intake rates of inland lizards (0.0165 kJ • g-1 • d-1). Water influx rates, as measured by the doubly-labeled water technique corroborated the fecal production analysis. Moreover, the daily field metabolism of lizards at the two locales were similar during mid-summer, corroborating the similar activity period estimates based on weather data. Despite lower rates of lizard production during mid-summer for inland S. occidentalis, the greater number of days available for activity during the activity season for the inland lizards, and the larger body sizes reached by one-year old lizards inland provides correlative evidence from which to infer that inland lizards may become reproductive at an earlier age. Relative to the coastal S. occidentalis, the inland lizards (1) hatch 2 -- 3 weeks earlier, (2) have a longer activity season into the fall, (3) followed by an earlier beginning to the activity season in the spring, and (4) presumably have adequate food availability for growth when active. Both locales are in the northern portion of the geographic range of Sceloporus occidentalis. The expectations are that climate change will result in longer activity seasons for lizards at both locales, and that heat of summer may be severe for the inland population, perhaps necessitating migration of the inland population further upslope and further west toward cooler and more mesic conditions. But if one considers the many possible anthropogenic effects on the landscape as well as the potentially rapid rate of climate change, it is unclear whether there will be available habitat to be occupied upslope and further west, thus possibly imperiling inland populations of Sceloporus occidentalis.</p>