Behavior and Physiology Outpace Form When Linking Traits to Ecological Responses Within Populations: A Meta-Analysis

Intraspecific variability is fundamental to ecology, yet we still know remarkably little about what governs the strength of the associations between traits expressed by individuals and ecological dynamics. To explore this overlooked aspect of diversity, we asked whether the strength of correlations between traits and a wide spectrum of ecological responses could differ (i) between intraspecific levels (among vs. within populations), (ii) among ecological responses across levels of biological organization (from ecological performance to ecosystem functioning), and (iii) among trait types (morphology, physiology, and behavior). We performed a meta-analysis synthesizing over a thousand effect sizes from nearly two hundred studies spanning approximately a hundred animal species across a broad range of traits and ecological responses. The average effect size was |r| = 0.26 (95% confidence interval: 0.21 – 0.30). At the individual level, effect sizes were larger for ecological performance (foraging, diet) than for fitness (reproduction), and tended to be larger for community responses (e.g., community composition of surrounding organisms). Physiology and behavior showed larger effect sizes than morphology. Our meta-analysis not only confirms that intraspecific trait variability is central to ecological dynamics, but also highlights physiology and behavior as key traits for unraveling the ecological consequences of individual variability.