<b>Behavior Outpaces Form When Linking Traits to Ecological Responses Within Populations: A Meta-Analysis</b>

Intraspecific variability is fundamental to ecology, yet we still know remarkably little about what governs the strength of the links between traits expressed by individuals of a similar size and ecological dynamics. To guide through this overlooked aspect of diversity, we asked whether the strength of correlations between traits and a large spectrum of ecological responses could differ (<i>i</i>) between intraspecific levels (among <i>vs</i>.within populations), (<i>ii</i>) among ecological responses across levels of biological organization (from ecological performances to ecosystem functioning), and (<i>iii</i>) among trait types (morphology, physiology and behavior). We performed a meta-analysis synthesizing a thousand effect sizes from nearly two-hundred studies, on a hundred of animal species and a broad range of traits and ecological responses. The average effect size was |<i>r</i>| = 0.25 [0.21 – 0.29] (95% confidence intervals). At the individual level, effect sizes were larger for ecological performance (foraging, diet) than for fitness (reproduction), and tended to be larger again for community responses. Physiology and behavior showed larger effect sizes than morphology. Our meta-analysis not only confirms intraspecific variability as a central driver of ecological dynamics, it highlights physiology and behavior as key to better understand the ecological consequences of individual diversity.