Abstract
Floods and droughts are a fundamental driver of riverine ecosystems. The occurrence timings of such hydrologic events are associated with organismal phenology and can affect riverine biodiversity. We aimed to evaluate a relationship between basin-scale fish species richness and the occurrence timing of high/low flow pulses at 59 rivers worldwide using circular statistics. As a result, the periodicity of large and medium floods had second-order polynomial relationship with native species richness per area, which supported the intermediate disturbance hypothesis. The periodicity of small floods was negatively correlated to native species richness per area. We conclude that the high periodicity in the occurrence of small high flow pulses may increase competition within a fish community for benefitting from floodplain at a restricted timing, while the high stochasticity in those occurrence can alleviate the competition by offering more opportunities for the benefit across a wider variety of timing.
