Data from: Experimental warming in the field delays phenology and reduces body mass and survival: implications for the persistence of a pollinator under climate change

1. Climate change is rapidly altering thermal environments across the
globe. The effects of increased temperatures in already warm environments
may be particularly strong because organisms are likely to be near their
thermal safety margins, with limited tolerance to additional heat stress.
2. We conduct an in situ field experiment over two years to investigate
the direct effects of temperature on an early-season solitary bee in a
warm, arid region of the Southwestern USA. Our field experiment
manipulates the thermal environment of Osmia ribifloris (Megachilidae)
from larval development through adult emergence, simulating both previous
cooler (ca. 1950; nest boxes painted white), and future warmer (2040–2099;
nest boxes painted black) climate conditions. In each year we measure
adult emergence phenology, linear body size, body mass, fat content, and
survival. 3. Bees in the warming treatment exhibit delayed emergence and a
substantial increase in phenological variance. Increases in temperature
also lead to reductions in body mass and fat content. Whereas bees in the
cooling and control treatments experience negligible amounts of mortality,
bees in the warming treatment experience 30–75% mortality. 4. Our findings
indicate that temperature changes that have occurred since ca. 1950 have
likely had relatively weak and non-negative effects, but predicted warmer
temperatures create a high stress thermal environment for O. ribifloris.
Later and more variable emergence dates under warming likely compromise
phenological synchrony with floral resources and the ability of
individuals to find mates. The consequences of phenological asynchrony,
combined with reductions in body mass and fat content, will likely impose
fitness reductions in surviving bees. Combined with high rates of
mortality, our results suggest that O. ribifloris may face local
extirpation in the warmer parts of its range within the century. 5.
Temperature increases in already warm ecosystems can have substantial
consequences for key components of life history, physiology, and survival.
Our study suggests that the response of ectothermic insects to temperature
increases in already warm environments may be insufficient to mitigate the
negative consequences of future warming.