Body-Size Change in a Rodent Is Affected by Environmental Warming and Population-Specific Thermoneutral Zone

Area of Science:

• Zoology
• Ecology
• Physiology

Background:

• Rodent body size displays varied temperature-size patterns, potentially linked to thermoneutral zones (TNZs) and warming.
• Understanding these patterns is crucial for predicting species' responses to climate change.

Purpose of the Study:

• To investigate how differential thermoneutral zones and habitat warming influence body size variation in *Apodemus agrarius* populations.
• To assess the impact of spatial and temporal temperature changes on rodent body size.

Main Methods:

• Analyzed body size and annual mean minimum temperature data across nine sites spanning 1150 m elevation.
• Measured resting metabolic rate via indirect calorimetry to infer population-specific TNZs.
• Examined body-size changes over eight years (2013-2020) in southern and northern populations.

Main Results:

• Body size increased with rising temperatures across space, and the TNZ narrowed.
• Body size increased in a cold-site population experiencing warming, while remaining stable in a warm-site population.
• The rate of body size change per degree Celsius was greater along the temporal than spatial temperature gradient.

Conclusions:

• Differential habitat warming and population-specific TNZs drive variations in rodent body size.
• Narrow TNZs can limit a population's ability to adjust body size in response to warming.
• Findings support the hypothesis that site-specific warming and TNZs explain rodent temperature-size patterns.