Climatic rainfall regime shapes energy flow, trophic structure, and secondary production in streams.

Changes in precipitation patterns linked to climate change have profound implications for the structuring and functioning of riverine ecosystems. This study investigates how rainfall influences secondary production by examining nine rivers across a sharp natural rainfall gradient over 3 years. Utilizing a groundbreaking dataset, we assess community production of both invertebrates and vertebrates, providing one of the most comprehensive multisite and multiyear evaluations of secondary production to date. Our findings reveal that annual rainfall drives significant shifts in productivity and biomass turnover rates. Specifically, we observe a transition from inverted biomass pyramids supported by detritivorous invertebrates in more mesic streams to simplified food webs dominated by vertebrate herbivores in arid environments, where these streams exhibit twice the secondary production and biomass turnover rates. This research underscores the critical role of rainfall as a master variable shaping food web structure and ecosystem productivity. With broad implications for other precipitation-dependent ecosystems, our study offers valuable insights into the future of lotic systems within the context of climate change. Furthermore, our work lays a solid foundation for future investigations into the complex interactions among climate, hydrology, and ecosystem functioning.