Soilscapes of Mortality Risk Suggest a Goldilocks Effect for Overwintering Ectotherms

Area of Science:

• Ecology
• Climate Change Biology
• Zoology

Background:

• Changing climates are causing global animal population declines, with winter conditions often overlooked.
• Ectotherms overwintering in soil face a critical trade-off between cold damage and energy expenditure.
• Bumble bee queens, vital pollinators, are experiencing population declines linked to climate change.

Purpose of the Study:

• To investigate the trade-offs faced by overwintering bumble bee queens in soil.
• To model mortality risk across soil depths under current and future climate scenarios.
• To understand how climate change impacts overwintering survival of critical pollinators.

Main Methods:

• Developed a mechanistic model integrating freezing points and metabolic rates.
• Utilized soil temperature data across the United States for historical and climate change scenarios.
• Created landscapes of mortality risk across soil depths for bumble bee queens.

Main Results:

• Overwintering queens face a 'Goldilocks effect': shallow depths risk freezing, deep depths risk energy depletion.
• Increased mean temperatures and temperature variations exacerbate overwinter mortality risk.
• Climate change scenarios predict heightened mortality for dormant bumble bee queens.

Conclusions:

• Soil depth presents a critical survival trade-off for overwintering bumble bee queens.
• Climate change, particularly increased temperature variability, will likely increase bumble bee queen mortality.
• Further research on physiological responses to temperature during dormancy is needed for diverse taxa to improve climate change impact predictions.