Predicted Asymmetrical Effects of Warming on Nocturnal and Diurnal Soil-Dwelling Ectotherms

AbstractClimate is expected to have broad effects on ecological communities, but this occurs in the context of significant daily temperature variation in many localities. Because many ectotherms can restrict activity to thermally suitable places and times, daily temperature variation offers the potential to buffer impacts of warming. Using thermal activity data from a montane ground-nesting ant community, we explore how a simulated increase in temperature is expected to alter the duration of suitable activity windows. Counterintuitively, we found that simulated warming lengthens activity times for cold-active species and shortens activity times for warm-active species. We explain this result through a simulation model in which time elapsed within a range of suitable temperatures is considered as an additive resource. Fundamentally, our model results rely on the fact that the mathematical function that relates time to temperature through a day (the Parton-Logan function) is concave before and after noon and convex through the night. These properties are common across terrestrial environments with characteristic deceleration in temperature near both the daily maximum and the daily minimum. Our results suggest that the time of day during which an animal's activity temperatures occur may be an important but rarely considered feature of natural history that contributes to the predicted impact of climate change. Thermally restricted diurnal species may need to compensate for shortened daily activity windows through means such as seasonal shifts or expansions, broadened activity temperatures, or range shifts.