Table 1.

Proposed evolutionary processes linking body size evolution to environmental variables variation in amphibians. Multiple processes can also interact, thus leading to complex and nonlinear relationships. See also Ficetola et al. (2010) for additional details.

Hypotheses	Proposed process	Implicated bioclimatic variable(s) considered in this study
Heat balance	Large body size advantageous for thermoregulation in cold environments because increases thermal inertia (Olalla-Tárraga & Rodríguez, 2007)	Mean temperature
Endurance	Large body size favoured in areas with high thermal excursion, because it is associated to more fat reserves (Ashton, 2002)	Thermal excursion
Seasonality	Large body size favoured in areas with long growing season (Mousseau, 1997, Schutze & Clarke, 2008)	Temperature, thermal excursion, precipitation seasonality*
Starvation resistance	Large individuals have more reserves and can better survive during periods of food shortage, thus large body size is favoured in seasonal/cold environments where animals are inactive for long periods (Arnett & Gotelli, 2003, Ashton & Feldmann, 2003)	Temperature, thermal excursion, precipitation seasonality*
Water availability	Large body size is favoured in dry climates because it reduces desiccation tolerance (Ashton, 2002)	Precipitation, aridity
Primary productivity	Evolution of large body size favoured in more productive environments, where food supply is higher (Olalla-Tárraga & Rodríguez, 2007, Ficetola et al., 2010)	Normalized Difference Vegetation Index (NDVI)

*amphibian activity depends on both temperature and water availability