Species extinctions strengthen the relationship between biodiversity and resource use efficiency

Dissolved organic carbon and microplastics decrease the biodiversity effect on resource use efficiency of crustacean zooplankton

The relationship between biodiversity and ecosystem functioning has always been the focus of attention in ecology. Although many studies have indicated positive effects of species and functional diversity on ecosystem functioning, our understanding of how the relationships are altered in the face of environmental changes remains limited. In recent years, human activities such as urbanization have led to a significant influx of dissolved organic carbon (DOC) and microplastics into lake ecosystems, which altered the lake's water quality and ecosystem services. Here, by conducting a two-month mesocosm experiment, we found that increasing DOC concentration generally increased the crustacean zooplankton taxonomic species richness, functional richness, resource use efficiency (RUE) and body size. In addition, we found that species richness, functional richness and body size have a positive relationship with zooplankton RUE, indicating higher biodiversity and larger body size are essential for maintaining high ecosystem functions. More importantly, we found that increasing the pressure of DOC and microplastic reduced the biodiversity effect on trophic transfer efficiency, especially for the relationship between functional richness and zooplankton RUE. Our results suggested that biodiversity effects on ecosystem functioning could be probably reduced in the current global environment change context, indicating that we may underestimate the negative impact of diversity loss on ecosystem functions and services. Therefore, more efforts are needed to conserve biodiversity and to maintain the valuable services that the ecosystem provides.

Water regulation weakens the relationship between biodiversity and ecosystem multifunctionality: Insights from a highly managed Chinese lake

Water diversions can mitigate water scarcities by strategically reallocating water resources. Despite their benefits, these interventions may profoundly affect biodiversity and multiple ecological functions ("multifunctionality") within highly managed lake systems. However, the specific impact of such interventions on the relationship between biodiversity and multifunctionality remains elusive, which limits our grasp of how water regulation shapes the dynamics of managed lake ecosystems. In this study, we investigated the differences in biodiversity and ecological functions between periods with and without water regulation in a highly managed lake, and extended this analysis by calculating diversity and multi-diversity indices and assessing the ecosystem's multifunctionality, with the goal of improving our understanding of how water regulation affects the ecological integrity of such lakes. We found that the diversity and multi-diversity indices both decreased markedly during the regulation period, indicating a negative impact on biodiversity. Conversely, multifunctionality remained stable. To clarify these responses, we developed linear mixed-effects models that incorporated multi-diversity indices and multifunctionality. Our analysis uncovered a robust positive correlation between multi-richness and multifunctionality. However, this relationship weakened during the periods with water regulation. Finally, we established structural equation models based on trophic cascade theory to pinpoint the key biological groups that sustained multifunctionality. We found that plants and omnivorous fish were instrumental in supporting multifunctionality during the non-regulation period, whereas planktivorous fish played a crucial role during the regulation period. These findings significantly enhance our understanding of how water regulation influences both biodiversity and multifunctionality, and provide insights for future management of regulated lakes.

Geology Can Drive the Diversity-Ecosystem Functioning Relationship in River Benthic Diatoms by Selecting for Species Functional Traits

The biodiversity-ecosystem functioning (BEF) relationship has been studied extensively for the past 30 years, mainly in terrestrial plant ecosystems using experimental approaches. Field studies in aquatic systems are scarce, and considering primary producers, they mainly focus on phytoplankton assemblages, whereas benthic diatoms in rivers are considerably understudied in this regard. We performed a field study across nine rivers in Greece, and we coupled the observed field results with model simulations. We tested the hypothesis that the diversity-biomass (as a surrogate of ecosystem functioning) relationship in benthic diatoms would be affected by abiotic factors and would be time-dependent due to the highly dynamic nature of rivers. Indeed, geology played an important role in the form of the BEF relationship that was positive in siliceous and absent in calcareous substrates. Geology was responsible for nutrient concentrations, which, in turn, were responsible for the dominance of specific functional traits. Furthermore, model simulations showed the time dependence of the BEF form, as less mature assemblages tend to present a positive BEF. This was the first large-scale field study on the BEF relationship of benthic diatom assemblages, offering useful insights into the function and diversity of these overlooked ecosystems and assemblages.