Resource availability determines food chain length in Chinese subtropical rivers

Three prevailing hypotheses, namely resource availability, ecosystem size, and disturbance, are often used to explain variations in food chain length (FCL). Rivers vary widely in size, resources, and disturbance dimensions, even within the same catchment, providing an ideal platform to test ecological drivers of FCL in aquatic systems. In this study, we tested how resource availability (indicated by macroinvertebrate biomass), ecosystem size (indicated by basin area), and disturbance (indicated by daily water-level coefficients of variation) affected stable isotope-based estimates of FCL in subtropical rivers in the Province Jiangxi, China. The FCL varied widely among the studied rivers with a mean of 3.09 (range 2.00–3.99). Model-selection results indicated that resource availability could explain 60 % of the observed variation in FCL. The FCL of the studied rivers was positively correlated with fish richness and the total area of fish community δ13C–δ15N bi-plot space, thereby indicating that an increase in fish diversity could influence the trophic structure within the food web and lead to a longer FCL. Taken together, our results suggest that resource availability could predict FCL in subtropical rivers and plays a significant role in maintaining longer FCLs by providing more energy to support upper trophic-level fishes.