Abstract

In this study, we evaluated the isotopic niche dynamics in resident and migratory populations of facultative amphidromous fish Galaxias maculatus (Jenyns, 1842). We hypothesised that the isotopic niche space occupied by its populations differs between resident and migratory populations and among river ecosystems. To evaluate these hypotheses, we compared the isotopic niches of G. maculatus populations along the longitudinal gradient in five river systems in the central–southern Chile. Our results revealed differences among the isotopic niches of migratory and resident populations with greater diversity of carbon sources (wider isotopic niches) in amphidromous populations and narrower isotopic niche spaces in resident populations. Galaxias maculatus is a species with complex ecological characteristics that is frequently abundant in temperate river ecosystems of the Southern Hemisphere. The dynamics of its isotopic niches and carbon sources seems to strongly relate to life-history strategy employed by specific populations and mediates trophic structure and energy flow in river ecosystems where they are abundant. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.