Climate tolerance and interspecific variation in geographic range size

Area of Science:

• Ecology and Biogeography
• Climate Change Biology
• Plant Ecology

Background:

• Species distributions are influenced by climate, a fundamental ecological principle.
• Significant variation exists in species' geographic range sizes, with most species occupying small areas.
• The extent to which climate explains this range size variation is not fully understood.

Purpose of the Study:

• To test three climate-based hypotheses explaining variation in species range size.
• To investigate the role of climate extremes, seasonality, and climate optima.
• To identify the primary climatic factor driving continental-scale species distributions.

Main Methods:

• Utilized a large dataset of North American tree and shrub species.
• Tested the 'climate extremes hypothesis' using the lowest January average daily minimum temperature (T(MIN)).
• Compared support for climate extremes against hypotheses based on seasonality and climate optima.

Main Results:

• The lowest January minimum temperature (T(MIN)) explained nearly 80% of the variation in species range size.
• The relationship between range size and T(MIN) was consistent across latitudes, tree/shrub types, and growth forms.
• Freezing resistance was strongly correlated with both T(MIN) and range size in analyzed species.

Conclusions:

• Climate extremes, particularly minimum winter temperatures, are the dominant factor determining species' continental-scale range sizes.
• Interspecific variation in range size is likely driven by differential freezing resistance.
• The findings underscore the importance of cold tolerance in shaping plant biogeography.