Bumble bee nest density is lower in drought years.

Area of Science:

• Ecology
• Environmental Science
• Entomology

Background:

• Climate change is increasing drought frequency and intensity globally.
• Drought impacts on animal populations, especially invertebrates like bumble bees, are not well understood.
• Bumble bees are crucial pollinators, making their population dynamics important for ecosystem health.

Purpose of the Study:

• To assess the demographic effects of drought on bumble bee nest abundance and apparent survival.
• To investigate species-specific responses of bumble bees to drought conditions.
• To understand the long-term implications of intermittent environmental disturbances on bumble bee populations.

Main Methods:

• Conducted 7 years of bumble bee nest surveys.
• Analyzed nest abundance and apparent survival data across drought and non-drought years.
• Compared responses of common (Bombus impatiens, Bombus griseocollis) and rarer bumble bee species.

Main Results:

• Nest abundance significantly declined during drought years (19.3 vs. 11.3 nests).
• Common species' relative abundances did not change, but Bombus impatiens shifted to forest habitats during droughts.
• Rarer species disappeared after the first drought, while common species recovered post-drought.

Conclusions:

• Droughts negatively impact bumble bee populations, likely through reduced floral resources.
• Common bumble bee species exhibit some resilience and habitat plasticity during droughts.
• Long-term monitoring is essential for understanding and mitigating the effects of climate change-induced disturbances on invertebrate populations.