On the relation between basal and maximum metabolic rate in mammals

Area of Science:

• Physiology
• Zoology
• Ecology

Background:

• Metabolic rate is a key physiological parameter influencing an organism's energy budget and ecological niche.
• Understanding the scaling of metabolic rate with body mass is crucial for explaining physiological diversity and evolutionary adaptations.
• The 'aerobic capacity' model proposes a link between basal and maximum metabolic rates in the evolution of endothermy.

Purpose of the Study:

• To investigate the allometric relationships between basal metabolic rate (BMR) and maximum metabolic rate (MMR) in wild mammals.
• To determine if mass-independent metabolic rates correlate, as predicted by the 'aerobic capacity' model.
• To assess the validity of the 'aerobic capacity' model for explaining the origin of endothermy.

Main Methods:

• Compiled literature data on basal and maximum metabolic rates for 18 wild mammal species.
• Analyzed oxygen consumption data to determine allometric regression equations for BMR and MMR.
• Performed statistical analysis to compare mass exponents and assess correlations between mass-independent metabolic rates.

Main Results:

• The mass exponent for maximum metabolic rate (0.841) was significantly higher than for basal metabolic rate (0.745) in the studied mammals (P < 0.05).
• No significant correlation was found between mass-independent basal and maximum metabolic rates.
• The observed scaling patterns do not align with the predictions of the 'aerobic capacity' model.

Conclusions:

• Mammalian metabolic rate scaling differs between basal and maximum levels, with MMR scaling more steeply with body mass.
• The lack of correlation between mass-independent metabolic rates refutes a key tenet of the 'aerobic capacity' model.
• Alternative hypotheses are needed to explain the evolutionary origins of endothermy in mammals.