A giant's appetite: how body size drives the diet and trophic position of the Japanese giant salamander

In predators, growth often drives ontogenetic dietary shifts (ODSs), leading to increasing trophic position (TP) with body size as growing individuals gradually incorporate larger prey in their diet. In species exhibiting extreme size variation, particularly those with gigantism, TP may increase markedly with body size, as large individuals might gain access to prey considerably higher in the food chain and inaccessible to smaller conspecifics. This can ultimately lead to apex predator status in the largest individuals. In this study, we investigated for the first time ODSs in one of the world's largest amphibians, the Japanese giant salamander Andrias japonicus . We combined stomach content and stable isotope analysis (δ 15 N, δ 13 C) from 160 individuals across a broad size range to quantify dietary patterns and TP changes. We found a non‐linear increase in TP with body size, from approximately 3.0–5.1, with a marked inflection point at a snout–vent length of 39 cm. This threshold corresponded to a clear dietary transition: from primarily consuming aquatic insects, to feeding predominantly on fish, anurans, and freshwater crabs. This transition likely reflects morphological and physiological adaptations associated with gigantism, enabling the exploitation of large prey. Our findings suggest that gigantism may be adaptive in predators such as giant salamanders by promoting ecological opportunities, allowing individuals to access high trophic levels through extensive growth and ultimately function as apex predators. These results contribute to a broader understanding of the ecological consequences of body size evolution in predatory vertebrates, highlighting how extreme growth can reshape species' ecological roles.