Predicted asymmetrical effects of warming on nocturnal and diurnal soil-dwelling ectotherms

Climate 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 (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 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. In particular,
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.