Size-related predation reduces intramorph competition in paedomorphic Alpine newts

Evolutionary theory assumes that facultative paedomorphosis in newts and sa lamanders is adaptive in allowing either a younger age at maturity or resou rce partitioning between the heterochronic morphs. In newt populations that only take the metamorphic ontogenetic pathway, juveniles are terrestrial a nd avoid food competition with larvae and breeding adults. In contrast, in populations where paedomorphosis occurs, branchiate newts of all sizes coex ist in the aquatic habitats, posing the question of whether intramorph comp etition exists and its relationship with the evolution of paedomorphosis. W e studied size-related predation in such a size-structured community of bra nchiate Alpine newts (Triturus alpestris) inhabiting a deep alpine lake. Al though gape limitation may explain such size-related predation, individuals also exhibited selectivity according to prey size. Amongst small prey that were within the capture range of all newt size classes, smaller newts prey ed on smaller items than did larger ones. We assume that such decisions fav our the coexistence of different-sized individuals. It is suspected that su ch size-selective predation on items which are avoided by water-living meta morphs allows the maintenance of facultative paedomorphosis, in favouring r esource partitioning between morphs.