LAUSR

Fish trophic niches reflect important ecological interactions and provide insight into the structure of mangrove food webs. Few studies have been conducted in mangrove fish predators to investigate interpopulation trophic niches and ontogenetic shifts. Using stable isotope analysis and two complementary approaches, we investigated trophic niche patterns within and between two ontogenetic groups (juveniles and subadults) of a generalist predator (Acentrogobius viridipunctatus) in four mangroves with heterogeneous environmental conditions (e.g., tidal regimes, salinity fluctuations and mangrove tree community). We hypothesized that the trophic niche between populations would vary regionally and trophic position would increase consistently from juvenile to subadult stages. Our results revealed that both δ13 C and δ15 N values varied greatly across populations and between ontogenetic groups, and complex spatio-ontogenetic variations were expressed by Layman's metrics. We also found some niche separation in space, which is most likely related to resource availability in spatially diverse ecosystems. Additionally, trophic niche position increased consistently from juveniles to subadults, indicating ontogenetic feeding shifts. The isotopic plasticity index and Fulton's condition index also showed significant spatial-ontogenetic variation, which is consistent with optimal foraging theory. Our findings highlight that trophic plasticity has a high adaptive value for mangrove fish predators in dynamic ecosystems. This article is protected by copyright. All rights reserved.