Should congruence between intra- and interspecific ecomorphological relationships be expected? A case study with the great tit, Parus major

We studied the relationship between leg morphology and posture while feeding in a population of great tits (Parus major) under controlled conditions to investigate to what extent morphology and ecology are linked at the individual level. From predictions generated at the interspecific level within the genus Parus (Moreno & Carrascal 1993), we tested whether intraand interspecific ecomorphological relationships are consistent. Within our population, neither leg bone lengths nor leg muscle morphology were related to the feeding posture of individuals. However, differences in body weight were correlated with interindividual differences in time spent hanging. These results demonstrate that the association between intraand interspecific ecomorphological relationships is not uniform. We argue that, at the intraspecific level, body weight overrides the significance of other traits that have a functional meaning at the interspecific level (i.e. leg segment lengths, muscular morphology), due to isometric variation of morphological traits (muscular and skeletal) with body mass. Thus, the discrepancy between the ecomorphological associations at intraand interspecific levels is the result of a problem of scale (morphological changes in evolutionary time and isometric variation of morphological traits with body mass in ecological time).