The sizes of life.

Area of Science:

• Ecology
• Biodiversity Science
• Biogeography

Background:

• Ecosystems host diverse life, but global body size-biomass distribution remains poorly understood.
• Previous research focused on specific realms or groups, lacking comprehensive global scope.

Purpose of the Study:

• To compile and analyze global body size-biomass spectra across terrestrial, marine, and subterranean realms.
• To statistically describe the distribution of biomass across organismal body sizes worldwide.

Main Methods:

• Integrated existing biomass estimates with uncatalogued body size ranges for free-living organisms.
• Propagated uncertainties in biomass and size data.
• Applied power law and bimodal Gaussian mixture models for statistical analysis.

Main Results:

• Global body size-biomass spectra show exponentially decreasing abundance (exponent -0.9) and nearly equal biomass across log size bins when analyzed with power laws.
• A bimodal Gaussian mixture model better describes biomass patterns (R2 = 0.86), indicating peaks in biomass for small (~10-15 g) and large (~107 g) organisms.
• Neither small nor large organisms exclusively dominate biomass; multiple groups share size ranges where biomass is highest.

Conclusions:

• The global body size-biomass relationship appears bimodal, with significant biomass concentrated in both small and large organisms.
• Substantial uncertainties necessitate further data to determine if universal constraints or local factors shape these global patterns.