Riverine ecosystems are governed by patterns of temporal variation in river flows. This dynamism is threatened by climate change and the near-ubiquitous human control of river flows globally, which may have severe effects on species distributions and interactions. There is therefore a fundamental need to forecast riverine ecosystem responses to changing river flooding and drought conditions over long timescales. We employed a modeling framework based on stochastic, coupled structured population models. The model uses fundamental vital rates to explore ecological futures across a spectrum of possible flow regimes for a typical snowmelt-driven river in the American Southwest. By simulating ecosystems under a diverse range of flow modification scenarios from natural to extreme flooding, drought and flow homogenization, we identify alternative potential futures where climate- and human-induced changes lead to significant shifts in the structure of ecological communities. We used network theory as a way to visualize and quantify these consequences, as it provides opportunities to understand how organisms interact with each other under different environmental contexts and allows the exploration of how effects propagate throughout complex systems.
Here we show that even slight modifications to the natural flow regime can have severe consequences for the structure of riparian plant networks. Networks of emergent interactions were most dense at the natural flow regime and became simplified as a function of flow alteration. The most influential component of flow alteration was flood reduction, with drought and flow homogenization both having greater negative community-wide consequences than increased flooding. While much focus has been on drought, flow homogenization (due to damming) may be equally detrimental to riparian communities. Therefore, managers should strive to preserve or restore natural flow dynamics, particularly floods, as a vital driver of the ecology of rivers. Maintaining floods under future climates will be needed to overcome the negative long-term consequences of flow modification on riverine ecosystems.