Long-term changes in multi-trophic diversity alter the functioning of river food webs

Increasing human pressures threaten fish diversity, with potentially severe but unknown consequences to the functioning of riverine food webs. Using a 17-years dataset from multi-trophic fish communities, we investigated the long-term effects of human pressure (represented by human footprint) on the species richness and energy flux across fish food webs, a measure of ecosystem functioning. Combining metabolic scaling theory and ecological network principles, we calculate the annual energy flux through varying trophic compartments (i.e., top-carnivore, mesocarnivore, detritivore, and omnivore). Species richness across all trophic compartments was positively associated with energy flux. However, species richness decreased over time, alongside with the energy flux at the whole-network level, which reduced by 75%. Human pressure negatively affected both species richness and energy flux, and the negative impacts of human pressure have intensified over time. These results illustrate how human pressure can reduce diversity and erode the energy flux through food webs, with long-term negative implications for the functioning of natural ecosystems