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

Intraspecific trait variability (ITV) is an important aspect of community ecology, but we still have a poor understanding of what drives the magnitude of relationships between ITV and ecological dynamics. In order to guide ecologists interested in unravelling the ecological implications of ITV, we asked whether relationships’ magnitudes differ (i) between intraspecific levels (among-vs. within- populations), (ii) among ecological responses spanning levels of biological organization (from individual performances to ecosystem functioning), and (iii) among trait categories (morphology, physiology and behavior). We performed a meta-analysis synthesizing a thousand effect sizes from nearly two-hundred studies, encompassing relationships between traits measured among individuals or populations of animals and a broad range of ecological responses. The average effect size was |r| = 0.24 [0.20 – 0.27] (95% confidence intervals). Within populations, relationships’ magnitudes were higher for ecological performance (foraging, diet), community and ecosystem responses than for fitness (reproduction). Relationships were 28% stronger for physiological and behavioral traits than for morphological traits. Our meta-analysis confirms the central aspect of ITV within populations of animals to drive ecological dynamics, and emphasizes physiological and behavioral traits to enhance the integration between the individual component of diversity and processes at community and ecosystem-levels.