Differences in body size between both species and sex were observed to be close to Hutchinsonian ratios in an assemblage of three species of newts (Triturus italicus, T alpestris and T carnifex) in southern Italy According to feeding, differences in body size were not related with a strict food niche segregation The diet of larger newt included indeed all the prey eaten by smaller newts but showed new prey types Differences between species were more marked than between sexes of the same species, despite a strong sexual dimorphism in body size Larger newts foraged in a wider range of microhabitats and exhibited a greater diversity of foraging tactics Triturus italicus fed essentially on plankton and chironomids in shallow water at the banks of the pond Triturus alpestris foraged also in deeper water, particularly on lsopods in vegetation Prey fallen on the water surface constituted the main part of T carnifex diet According to recent data on newt evolution, speciation consisted in the reduction of body size Our data show that this process has been related with a specialization of the diet and of habitat use