Data from: Heatwaves decrease fitness and alter maternal provisioning in natural populations of Mimulus guttatus

Premise of study: The increasing frequency and severity of heatwaves and
droughts occurring across the globe is well known. However, there are few
longitudinal studies tracking demographic change and fitness within
natural populations, and fewer still that span multiple extreme events.
Determining how organisms tolerate, respond, and potentially adapt to
extreme events is key for assessing long-term population viability.
Methods: We examine how mortality, fecundity, seed provisioning, and
offspring germination differ across 12 populations of annual common
monkeyflower (Mimulus guttatus) over a five-year span. Key Results: Two
heatwaves occurred within the study: a 2019 heatwave occurring within the
first 10 days of the growing season, and a 2021 heat dome event occurring
nearly a month into the growing season. Mortality was high and fecundity
decreased in a population-specific manner due to both heatwaves. However,
the 2021 heat dome caused declines of 34.5% in seed size and 22.1% in the
ability to germinate, while the 2019 heatwave did not. Structural equation
models indicate that similar climatic factors including early season
maximum temperatures and late season precipitation are associated both
with declines in fecundity and slower germination. Conclusions: These
results suggest that the consequences of heatwaves will depend on the
relative severity and timing of the heatwave in the growing season, and
further suggest that this timing may have amplified longer-term impacts as
offspring have lower provisioning. Specifically, with growing seasons
shifting earlier into the spring, later or slower germination could
exacerbate population extirpation risk.