Climate-Driven Body Size Changes in Birds and Mammals Reveal Environmental Tolerance Limits

Area of Science:

• Ecology
• Climate Change Biology
• Zoology

Background:

• Climate change is causing widespread shifts in animal body size, impacting ecological dynamics.
• The variability in these body size responses remains unclear, with smaller sizes potentially aiding thermoregulation but increasing dehydration risk.

Purpose of the Study:

• To investigate the associations between body size (mass and length) in birds and mammals and climatic conditions (thermal and aridity limits).
• To assess the influence of human land use on these body size responses to climate change.

Main Methods:

• Analyzed extensive datasets of bird and mammal body mass and length records.
• Correlated body size data with species' thermal and aridity tolerance limits derived from geographic ranges.
• Evaluated the impact of agricultural land use extent and its interaction with thermal environments.

Main Results:

• Smaller body mass in birds and mammals correlates with proximity to upper thermal (hot) and lower aridity (dry) tolerance limits.
• Agricultural land use shows a positive association with increased body mass for both taxa.
• Shorter body lengths are observed closer to species' upper thermal limits, with combined hot and dry conditions intensifying negative associations with body mass.

Conclusions:

• Body size shifts in birds and mammals are driven by thermoregulatory and osmotic balance pressures responding to climate change.
• These body size changes represent a significant, under-recognized biotic response to anthropogenic climate change with broad ecological and evolutionary implications.