Size-abundance rules? Evolution changes scaling relationships between size, metabolism and demography

Area of Science:

• Evolutionary biology
• Physiological ecology
• Microbiology

Background:

• Body size is known to correlate with demographic rates across species.
• Metabolism is often proposed as the underlying mechanism linking size and demography.
• Empirical evidence for these causal links within a single species is scarce.

Discussion:

• Artificial selection on the microalga Dunaliella tertiolecta created substantial body size variation over 400 generations.
• Energy flux measurements showed size-dependent scaling, but metabolic theory failed to predict observed demographic rates.
• Demographic rates fluctuated unpredictably in strength and sign, diverging from theoretical predictions.

Key Insights:

• Metabolism and body size appear to independently influence demographic processes within a species.
• The scaling of energy fluxes with size does not reliably predict demographic outcomes.
• Observed within-species dynamics challenge established theories based on cross-species correlations.

Outlook:

• Further research is needed to elucidate the independent mechanisms driving size and metabolism effects on demography.
• Investigating diverse species and evolutionary contexts will clarify the generalizability of these findings.
• Revising metabolic theories may be necessary to incorporate independent size and metabolic influences on population dynamics.