Conclusion

There is a paradigm shift from pattern-based hotspot management to process-based functional approach in biodiversity conservation strategy. The sustenance of goods and services provided by ecosystems requires not only the investigation of biodiversity patterns but also the identification of processes that produce and preserve regional and local biodiversity. Although community ecologists generally agree that ecological metacommunity is structured simultaneously by stochastic and deterministic rules, one assembly rule may be predominant in a given landscape. In this study, we showed that ecological stochasticity prevails in natural habitat whereas deterministic processes dominate in modified environment in a highly dynamic river-floodplain system. In addition, the patterns of community temporal dynamics are consistent with ecological stochasticity. The shift in assembly rules in modified sites are the likely outcomes of the relatively stable environment created by human interruption to hydrological connectivity. First, modification alters hydrological regime, which removes the drawdown phase variability and maintains low water levels to aid production, thereby removing the stochastic effects of periodic habitat exclusion. Second, the flattened hydrograph in the high-water phase creates dispersal barriers, reducing demographic stochasticity such as chance colonization. Third, modification reduces the topographic heterogeneity, which minimises benthic structural variability characteristic of the natural sedge habitats, leading to stronger biotic interactions.