Human land-use is changing Earth’s surface, causing a decline in biodiversity and altering ecosystem functioning. However, most of the empirical evidence of land-use impacts in the Neotropics comes from studies investigating isolated land-use types, and the pathways by which intensified land-uses affect ecosystem functioning are largely unknown. Using a database from 61 streams spanning two hyperdiverse Neotropical regions, we demonstrate that intensive human land-uses (agriculture, urbanization, pasture, and afforestation) strongly affect stream biodiversity and functioning. We showed negative associations of agriculture, pasture and urbanization with taxonomic richness, functional diversity, and diversity of trait categories (recruitment and life-history, resource and habitat-use, and body size) of fish, arthropod, and macrophyte. The impacts of intensive land-uses on standing biomass were negative and driven by direct and indirect effects mediated by declines in taxonomic and functional diversities. Our findings highlight that human land use can reshape stream biodiversity, with multiple negative consequences on ecosystem functioning.

The evaluation of extinction risk has typically focused on species, although a shift to a focus on ecosystem would appear to be an urgent priority for conservation planning. Here, we investigated how fish extinction modify the functioning of freshwater Amazonian ecosystems. We sampled the fish and environmental conditions of 63 streams in the eastern Amazon, and simulated extinction based on species vulnerability to habitat loss. The simulated extinction of vulnerable species led to a decrease in both the mean body size of the community and functional rarity, and culminated in abrupt losses of ecosystem function after 5% and 10% of extinction at local and regional scales. We provide robust predictions on the modification of the ecosystem following the extinction of fish species, which is a major step towards the development of effective conservation measures that help to prevent the loss of biodiversity and the potentially irreversible modifications of ecosystem function.

Diversity gradients are observed in various groups of organisms. For fishes in streams, the Water-Energy, Productivity and Temporal Heterogeneity hypotheses are considered the best combination to explain richness patterns. The relationship between species diversity and the variables that represent the hypotheses are generally considered linear and stationary, that is, there is equal relation of cause and effect along an entire geographical extension. The assumption of stationarity has not been tested or even observed in diversity gradients, thus producing imprecise models. Therefore, our goal is to quantify stationarity in the existing relationships between the ichthyofauna of streams and the Water-Energy, Productivity and Temporal Heterogeneity hypotheses using a Geographically Weighted Regression – GWR. In the proposed model, there is conspicuous absence of stationarity between fish species richness and the tested hypotheses. Furthermore, water-energy dynamics were observed as a possible metabolic restriction mechanism acting on the community structuring of stream fishes. This mechanism divides the fish fauna from the studied Brazilian watercourses in two regions: i) Amazonian, characterized by a stable climate and populations with little resistance to thermal variation; and ii) Central, featured by greater ranges of temperature and fish populations resistant to thermal variation.