Ecological plasticity of morphological design: An experimental analysis with tit species

To determine whether behavioural plasticity in foraging modes is contingent upon the morphology of the species, we analyzed the variability in frequency of use of foraging postures (standing versus hanging) under the selection pressure of predation risk. We studied the leg morphology of two contrasting tit species (flue Tit, Parus caeruleus, and Crested Tit, P. cristatus). Results demonstrated that the leg morphology of the Blue Tit provides it with greater ecological plasticity in terms of foraging posture than that of the Crested Tit. Observed interspecific differences in ecological plasticity are not attributable to interspecific differences in morphological variability (between individuals within species). The morphofunctional bases of ecological plasticity in foraging posture are discussed. Morphological design may be considered 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 shift in different species could represent different costs when morphological constraints are considered in relation to behavioural performance.