Human land use and non-native fish species erode ecosystem services by changing community size structure.

Organism body size influences ecosystem services, and human pressures alter the size structure of ecological communities. However, our understanding of how different human-induced pressures (such as land use and biotic invasion) interact to drive community size structure and ecosystem services remains limited. Combining 21 years of fish size spectrum data and fishery potential (fishery monetary value in the Upper Paraná River Floodplain, Brazil), we demonstrate that the size spectrum exponent of native species has become more negative over time, indicating a relative decrease in the biomass of large versus small individuals. Conversely, the size spectrum exponent of non-native species has become less negative over time owing to the increased abundance of large species. Overall, fishery potential declined by more than 50% over time. Human land use replaced the coverage of natural environments, indirectly reducing native richness. This scenario decreased the exponent of the native size spectrum, indirectly reducing fishery potential. Our study illustrates how intensification of human land use alters the size structure of communities, favouring non-native individuals and suppressing ecosystem services.