Data from: Elevational and microclimatic drivers of thermal tolerance in Andean Pristimantis frogs

Aim: We analysed elevational and microclimatic drivers of thermal
tolerance diversity in a tropical mountain frog clade to test three
macrophysiological predictions: less spatial variation in upper than lower
thermal limits (Bretts’ heat invariant hypothesis); narrower thermal
tolerance ranges in habitats with less variation in temperature (Janzen´s
climatic variability hypothesis); and higher level of heat impacts at
lower altitudes. Location: Forest and open habitats through a 4230 m
elevational gradient across the tropical Andes of Ecuador. Method: We
examined variability in critical thermal limits (CTmax, and CTmin), and
thermal breadth (CTmax-CTmin) in 21 species of Pristimantis frogs.
Additionally, we monitored maximum and minimum temperatures at the
local-scale (tmax, tmin), and estimated vulnerability to acute thermal
stress from heat (CTmax-tmax) and cold (tmin – CTmin), by partitioning
thermal diversity into elevational and microclimatic variation. Results:
Our results were consistent with Brett’s hypothesis: altitude promotes
more variation in CTmin and tmin than in CTmax and tmax. Frogs inhabiting
thermally variable open habitats have higher CTmax and tmax and greater
thermal breadths than species restricted to forest habitats, which show
less climatic overlap across the elevational gradient (Janzen´s
hypothesis). Vulnerability to heat stress was higher in open than forest
habitats and did not vary with altitude. Main conclusions: We suggest a
mechanistic explanation of thermal tolerance diversity in elevational
gradients by including microclimatic thermal variation. We propose that
the unfeasibility to buffer minimum temperatures locally may explain the
rapid increase in cold tolerance (lower CTmin) with elevation. In
contrast, the relative invariability in heat tolerance (CTmax) with
elevation may revolve around the organisms’ habitat selection of open and
canopy buffered habitats. Secondly, on the basis of microclimatic
estimates, lowland and upland species may be equally vulnerable to
temperature increase, which is contrary to the pattern inferred from
regional interpolated climate estimators.