Data from: A framework for elucidating the temperature dependence of fitness

Climate warming is predicted to cause large-scale extinctions of
ectothermic species. A striking difference between tropical and temperate
ectotherms is that tropical species exhibit an upper temperature limit for
survival (T_max) that is closer to the temperature at which fitness is
maximized (T_opt). Thus, even a small increase in environmental
temperature could put tropical ectotherms at high risk of extinction,
whereas temperate ectotherms have a wider temperature cushion. Although
this pattern is widely observed, the mechanisms that produce it are not
well-understood. We develop a mathematical framework to partition the
temperature response of fitness into its components (fecundity, mortality
and development) and test model predictions with data for insects. We find
that fitness declines at high temperatures because the temperature
responses of fecundity and mortality act in opposite ways: fecundity
decreases with temperature once temperatures exceed the optimal range,
whereas mortality continues to increase. The proximity of T_opt to T_max
depends on how the temperature response of development mediates the
interaction between fecundity and mortality. When development is highly
temperature-sensitive, mortality exceeds reproduction only after fecundity
has started to decline with temperature, which causes fitness to decline
rapidly to zero once temperatures exceed T_opt. The model correctly
predicts empirically observed fitness-temperature relationships in insects
from different latitudes. It potentially explains the widely-reported
phenological shifts and latitudinal differences in fitness responses.