Figure 1.

Diagram of the multi-level evolutionary character concept applied to avian agonistic behaviour. The behavioural character ‘aggressiveness’ is represented as a latent variable affecting the expression of observed behaviours (calls, approach distance, occurrence of attack and songs). The hypothesized expression of the latent variable is plastic within the same individual, as it varies as a function of environmental conditions (top-left), but also differs between individuals owing to genetic and environmental effects specific to the individual (lower-left). Consequently, expressed behaviours are correlated in a similar fashion between versus within individuals.