Field metabolic rate and body size

Area of Science:

• Zoology
• Physiology
• Ecology

Background:

• Field metabolic rates (FMRs) represent daily energy expenditure in free-living animals.
• Understanding FMR variation is crucial for ecological and evolutionary studies.

Purpose of the Study:

• To evaluate the range and determinants of FMR variation across 229 terrestrial vertebrate species.
• To investigate the influence of body size, thermal physiology, taxonomy, and habitat on FMR.

Main Methods:

• Utilized data from 229 species measured using the doubly labeled water method.
• Employed nonlinear regression and Independent Contrasts Analysis to account for phylogenetic biases.
• Analyzed the impact of body mass, taxonomic class, habitat, and diet on FMR.

Main Results:

• FMRs spanned nearly six orders of magnitude, from 0.23 kJ/day (gecko) to 52,500 kJ/day (seal).
• Body size accounted for over 70% of the variation in log-transformed FMR.
• Endothermic mammals and birds had 12x and 20x higher FMRs, respectively, than ectothermic reptiles of equivalent size.
• Residual variation in mass-adjusted FMR was influenced by taxonomic level, habitat, diet, and foraging strategy.

Conclusions:

• Body size and thermal physiology are the primary drivers of FMR variation in terrestrial vertebrates.
• Significant residual variation exists within taxonomic classes, highlighting the importance of other ecological factors.
• Phylogenetic biases were addressed, confirming the robustness of the findings on FMR scaling and determinants.