Meeting Abstract
Climate variability has long been implicated in shaping the thermal breadths of organisms. In 1967, Daniel Janzen extended the climate variability hypothesis to include elevation gradients and suggested that increased temperature overlap across elevation on seasonally variable temperate mountains favors organisms with wider thermal breadths compared to organisms on thermally stable tropical mountains. Few studies have tested this hypothesis using standardized methods, and to our knowledge no studies have examined thermal tolerance patterns in aquatic systems, where fluctuations in temperature are reduced relative to air. To investigate how climate variability at a given site determines thermal tolerance, we first confirmed that stream temperatures at our temperate locality (Colorado Rocky mountains) have greater annual variation than streams at our tropical locality (Ecuadorian Andes mountains). We then measured thermal breadth in over 20 species of temperate and tropical aquatic insects by calculating the difference between the natural, un-manipulated critical thermal maximum and minimum limits. We found that temperate aquatic insects from the Rockies typically have wider thermal breadths (i.e. higher CTmax and lower CTmin values) compared to their tropical Andean relatives. Across elevation we detected a trend of narrower thermal breadths for temperate high elevation insects but wider thermal breadths for tropical high elevation insects. Our results indicate that climate variability may play an important role in shaping the thermal breadth of aquatic insects and may give insight into their vulnerability to climate warming.
