ECOLOGICAL PLASTICITY OF MORPHOLOGICAL DESIGN - AN EXPERIMENTAL-ANALYSIS WITH TIT SPECIES

To determine whether behavioural plasticity in foraging modes is conti ngent upon the morphology of the species, we analyzed the variability in frequency of use of foraging postures (standing versus hanging) und er the selection pressure of predation risk. We studied the leg morpho logy of two contrasting tit species (flue Tit, Parus caeruleus, and Cr ested Tit, P. cristatus). Results demonstrated that the leg morphology of the Blue Tit provides it with greater ecological plasticity in ter ms of foraging posture than that of the Crested Tit. Observed interspe cific differences in ecological plasticity are not attributable to int erspecific differences in morphological variability (between individua ls within species). The morphofunctional bases of ecological plasticit y in foraging posture are discussed. Morphological design may be consi dered an important factor in explaining niche width and potential for niche shifts, as morphology might determine the range of ecological '' space'' within which a species is allowed to move. The same niche shif t in different species could represent different costs when morphologi cal constraints are considered in relation to behavioural performance.