Data from: The thermal breadth of temperate and tropical freshwater insects supports the climate variability hypothesis

Climate change involves increases in mean temperature and changes in
temperature variability at multiple temporal scales but research rarely
considers these temporal scales. The Climate Variability Hypothesis (CVH)
provides a conceptual framework for exploring the potential effects of
annual scale thermal variability across climatic zones. The CVH predicts
ectotherms in temperate regions tolerate a wider range of temperatures
than those in tropical regions in response to greater annual variability
in temperate regions. However, various other aspects of thermal regimes
(e.g., diel variability), organisms’ size, and taxonomic identity are also
hypothesised to influence thermal tolerance. Indeed, high temperatures in
the tropics have been proposed as constraining organisms’ ability to
tolerate a wide range of temperatures, implying that high annual maximum
temperatures would be associated with tolerating a narrow range of
temperatures. We measured thermal regimes and critical thermal limits
(CTmax and CTmin) of freshwater insects in the orders Ephemeroptera
(mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) along
elevation gradients in streams in temperate and tropical regions of
eastern Australia and tested the CVH by determining which variables were
most correlated with thermal breadth (Tbr = CTmax - CTmin). Consistent
with the CVH, Tbr tended to increase with increasing annual temperature
range. Tbr also increased with body size and Tbr was generally wider in
Plecoptera than in Ephemeroptera or Trichoptera. We also find some support
for a related hypothesis, the Climate Extreme Hypothesis (CEH),
particularly for predicting upper thermal limits. We found no evidence
that higher annual maximum temperature constrained individuals’ abilities
to tolerate a wide range of temperatures. The support for the CVH we
document, suggests that temperate organisms may be able to tolerate wider
ranges of temperatures than tropical organisms. There is an urgent need to
investigate other aspects of thermal regimes, such as diel temperature
cycling and minimum temperature.