Partitioning within-species variance in behaviour to within- and between-population components for understanding evolution.

Phenotypes vary at multiple hierarchical levels, of which the interspecific variance is the primary focus of phylogenetic comparative studies. However, the evolutionary role of particular within-species variance components (between-population, between- or within-individual variances) remains neglected. Here, we partition the variance in an anti-predator behaviour, flight initiation distance (FID), and assess how its within- and between-population variance are related to life history, distribution, dispersal and habitat ecology. Although the composition of within-species variance in FID depended on the phylogeny, most variance occurred within populations. When accounting for allometry, density-dependence, uncertainty in the phylogenetic hypothesis and heterogeneity in data quality, within-population variance was significantly associated with habitat diversity and population size. Between-population variance was a significant predictor of natal dispersal, senescence and habitat diversity. Accordingly, not only species-specific mean values of a behavioural trait, but also its variance within and among populations can shape the evolutionary ecology of species.