Heat islands, landscaping, and the thermal ecology of urban lizards

Background/Question/Methods: Climate change is predicted to drive 40% of lizard populations extinct by 2080. This assertion that large-scale shifts in climate are relevant to small ectotherms which experience temperature on a near instantaneous sub-meter scale assumes that species will not adapt by dispersal or shifting their activity patterns. However, local adaptations may already be observable in Phoenix, AZ, where a heterogeneous urban heat island (UHI) averages +3 ^oC and can locally exceed +10 ^oC at night. Interestingly, Phoenix also has an urban oasis effect, where heavily irrigated mesic landscaping can be cooler than the native desert during the day. This potential UHI mitigation strategy was evaluated from the perspective of lizards using the CAP-LTER North Desert Village experiment. Thermally realistic lizard models with temperature data loggers were placed in a bare lot (control), and several treatments that represent the dominant landscaping styles in Phoenix.

Results/Conclusions: In midsummer, potential lizard activity time was found to be almost non-existent in native and xeric plots, while the mesic plot allowed for continual activity during even the hottest days. Interestingly, underground temperatures in the mesic plot were actually too cold for proper egg development. A preliminary inspection of microhabitat characteristics revealed that shade explained the vast majority of variation in model temperatures. Distance to vegetation and relative humidity did not appear to influence model temperature, suggesting that artificial shade structures may also extend potential lizard activity time in summer.