Flood disturbance, algal productivity, and interannual variation in food chain length

The length of a river food chain changed from year to pear, shifting with t he hydrologic regime. During drought years, grazers suppressed algae across a nutrient gradient, while predators were functionally unimportant. Follow ing flood disturbance, predators suppressed grazers, releasing algae. These results suggest that hydrologic regime, rather than productivity, determin es the functional length of this river food chain. Within years, algae and grazer biomass responded to an experimental productivity gradient in patter ns predicted by simple trophic models that assume efficient energy transfer . Understanding differences among species within trophic levels, however, w as crucial in delineating the controlling interactions.