Heat waves decrease fitness and alter maternal provisioning in natural populations of Mimulus guttatus

Area of Science:

• Ecology
• Evolutionary Biology
• Climate Change Biology

Background:

• Extreme heat waves are increasing globally.
• Longitudinal studies on population demographics and fitness during heat waves are scarce.
• Understanding organismal responses to extreme events is vital for population viability.

Purpose of the Study:

• To investigate the demographic and fitness consequences of heat waves in natural populations.
• To assess how mortality, fecundity, seed provisioning, and offspring germination are affected by extreme heat events.
• To determine if the timing and severity of heat waves influence population responses and long-term viability.

Main Methods:

• Studied 12 populations of Mimulus guttatus over 5 years.
• Monitored mortality, fecundity, seed provisioning, and offspring germination.
• Analyzed data using structural equation models to link climatic factors with population responses.

Main Results:

• Two heat waves (2019 and 2021) impacted populations, causing high mortality and reduced fecundity.
• The 2021 heat dome significantly decreased seed size (34.5%) and germination (22.1%), unlike the 2019 heat wave.
• Early-season maximum temperatures and late-season precipitation were linked to reduced fecundity and slower germination.

Conclusions:

• Heat wave consequences depend on severity and timing within the growing season.
• Offspring provisioning is reduced by heat waves, potentially amplifying long-term impacts.
• Earlier growing seasons combined with delayed germination increase population extirpation risk.