Thermal biology and growth of bison (Bison bison) along the Great Plains: examining four theories of endotherm body size

Abstract

Abstract Body size of bison (Bison bison) declines with rising global temperature across the fossil record and rising annual temperatures across the Great Plains, but what are the underlying drivers? Body size depends on growth, which depends on maximizing net energy and nutrient flows for the production of tissues at seasonal scales across the range of the species. We measured thermoregulation costs of body surface temperature (°C) and heat exchanges (W and W/m2) of 350 adult and 345 adolescent Bison from 19 herds in summer and winter along the Great Plains from Saskatchewan (52° N) to Texas (30° N). At the smallest scale, daily body surface temperature increased with solar radiation and decreased with relative humidity and wind speed, which is consistent with Kooijman’s dynamic energy budget theory. Total surface heat transfer (W) increased with body mass (kg) at an exponent of 0.63 ± 0.03, which is consistent with Schmidt‐Nielsen’s principle of surface‐area‐to‐volume ratios (b = 0.67). On an annual scale, growth (kg/yr) of adolescent Bison decreased with increasing total surface heat transfer (W) during summer, which supports Speakman and Król’s heat dissipation limit theory. On the largest scale, heat flux was weakly related to latitude in summer and winter for adolescent Bison, which provides support for Bergmann’s rule and suggests a role for local primary production along the Great Plains. Cooler summers are more optimal for Bison growth because of reduced heat loads during the growing season. Rising temperatures are likely to constrain body size and productivity of Bison and other large endotherms in North America.

Keywords

• allometry
• Bergmann’s rule
• body size
• climate change
• dynamic energy budget
• Great Plains