Metabolic theory predicts animal self-thinning

Area of Science:

• Ecology
• Ecological Physiology
• Population Dynamics

Background:

• The metabolic theory of ecology (MTE) links individual metabolic rates to ecological patterns, but lacks empirical support for population-level predictions.
• Self-thinning, a density-dependent mortality phenomenon, is well-documented in plants but less understood in animals, with no consensus on universal thinning slopes.

Purpose of the Study:

• To test MTE's population-level predictions using animal self-thinning.
• To determine if self-thinning can be induced in house cricket (Acheta domesticus) populations.
• To assess if self-thinning trajectories align with predictions derived from MTE and species-specific metabolic rates.

Main Methods:

• A laboratory experiment tracking the growth of Acheta domesticus cohorts across five different starting densities.
• Analysis of self-thinning slopes using cross-sectional and longitudinal statistical methods (OLS, linear mixed effects models).
• Investigation of temperature effects on thinning intercepts to estimate activation energy.

Main Results:

• Self-thinning was observed in 96% of cohorts at higher densities, with estimated thinning slopes closely matching MTE predictions (-1.11 OLS, -1.13 mean OLS, -1.09 LMM).
• Sensitivity analyses confirmed the robustness of these findings.
• Temperature negatively impacted thinning intercepts, yielding an activation energy estimate consistent with MTE.

Conclusions:

• This study provides strong empirical support for MTE by demonstrating a direct link between individual metabolic rates and population-level processes (self-thinning).
• Findings support integrating body mass, metabolism, and competition into ecological models of populations and communities.
• Animal self-thinning can serve as a valuable tool for testing MTE's quantitative predictions at the population level.