Skip to main content
Dryad

Data and code from: When giant amphibians rule the river: Community trophic structure of Japanese giant salamander ecosystems

Duret, Clément1; Lejeune, Benjamin1; Lepoint, Gilles1; Bartet, Tiphanie1; Okada, Sumio2; Fukushima, Keitaro3; Kishida, Osamu4; Denoël, Mathieu1

Published Jun 02, 2026 on Dryad. https://doi.org/10.5061/dryad.fn2z34v89

Data files

Jun 02, 2026 version files 97.93 KB

Click names to download individual files

Abstract

Trophic interactions among species determine the structure and functioning of food webs and ultimately govern ecosystem organization. Top predators, at the highest trophic levels, play a pivotal role in shaping food webs. Yet, the ecological consequences of body-size–related trophic shifts in large predators are poorly explored in freshwater ecosystems, despite being well documented in marine and terrestrial systems. This gap is particularly evident in river ecosystems dominated by giant salamanders. We investigated the trophic ecology of a freshwater community dominated by the Japanese giant salamander (Andrias japonicus) to assess how extreme ontogenetic body-size variation modifies intra- and interspecific interactions and contributes to overall community structure. We also aimed to identify the dominant carbon sources fueling the community by estimating the relative contributions of terrestrial versus aquatic energy pathways. Using stable isotope analysis, we quantified trophic positions and isotopic niche metrics for all major consumer species. Our results reveal clear trophic shifts in A. japonicus: smaller individuals overlapped with mesopredators (teleost fish, prawns, turtles), suggesting potential competition, while trophic position increased progressively with size, placing large individuals at the top of the food chain. At the community level, the presence of large salamanders broadened the δ¹⁵N range, increased trophic evenness, and expanded isotopic space, enhancing vertical complexity. Basal source tracing indicated complementary reliance on aquatic and terrestrial carbon across taxa, revealing multiple energy pathways sustaining the food web. These findings show that gigantism in A. japonicus reshapes trophic hierarchies by reducing redundancy and strengthening trophic stratification. More broadly, they underscore the ecological importance of ontogenetic niche shifts and body size in structuring freshwater food webs, highlighting how such shifts cascade to influence ecosystem functioning. By integrating isotopic niche metrics with basal source contributions, our study provides a generalizable framework for linking predator ontogeny, energy pathways, and food web structure, with direct relevance for conserving vulnerable freshwater ecosystems. Moreover, it highlights that endangered top predators such as A. japonicus may contribute to food web resilience and ecological integrity in vulnerable freshwater ecosystems.