Data from: Environmental degradation results in contrasting changes in the assembly processes of stream bacterial and fungal communities

Environmental degradation may have strong effects on community assembly processes. We examined the assembly of bacterial and fungal communities in anthropogenically altered and near-pristine streams. Using pyrosequencing of bacterial and fungal DNA from decomposed alder Alnus incana leaves, we specifically examined if environmental degradation deterministically decreases or increases the compositional turnover of bacterial and fungal communities. Our results showed that near-pristine streams and anthropogenically altered streams supported distinct fungal and bacterial communities. The mechanisms assembling these communities were different in near-pristine and altered environments. Environmental disturbance homogenized bacterial communities, whereas fungal communities were more dissimilar in disturbed sites than in near-pristine sites. Compositional variation of both bacteria and fungi was related to water chemistry variables in disturbed sites, further implying the influence of environmental degradation on community assembly. Bacterial and fungal communities in near-pristine streams were weakly controlled by environmental factors, suggesting that the relative importance of niche-based versus neutral processes in assembling microbial communities may strongly depend on the spatial scale and local environmental context. Our results thus suggest that environmental degradation may strongly affect the composition and β-diversity of stream microbial communities colonizing leaf litter, and that the direction of the change can be different between bacteria and fungi. A better understanding of the environmental tolerances of microbes and the mechanisms assembling microbial communities in natural environmental settings is needed to predict how environmental alteration is likely to affect microbial communities

Environmental variables and bacterial and fungal OTUs

Measured environmental variables for the study sites and occurrences of bacterial and fungal OTUs obtained using pyrosequencing. Units for environmental variables are provided in column headings. Unit for particle size is explained in a separate row below the data

Data from: Climate-driven hydrological variability determines inter-annual changes in stream invertebrate community assembly

Although flow regime is one of the major drivers of riverine communities, not much is known about how inter-annual variability and extremes of flow influence community assembly mechanisms. We used data on benthic macroinvertebrates and modelled flow regimes in 23 near-pristine boreal streams to assess how community assembly mechanisms and species occupancy varied in response to inter-annual variability in flow conditions across 11 successive years encompassing extreme (both low and high) flow events. A null model approach was used to test whether deterministic or stochastic processes dominated community assembly and how much regional (among-stream) flow variability contributed to community variability (β-diversity). Mean daily flow and the greatest rate of flow rise were the strongest flow-related descriptors of invertebrate community composition. Communities were differentially assembled depending on the direction of change in flow magnitude: in high-flow years, communities were more similar than expected by chance, while at low flows they tended to be more dissimilar than expected. Beta-diversity of macroinvertebrate communities was related to among-stream flow variability only at high flows. Common species correlated strongly with flow variability and contributed most to variation in β-diversity, suggesting that changes in assembly mechanisms are mainly driven by common species. While homogenization of communities in high-flow years reflected increased species occupancies and environmental sorting, increased turnover during low flows likely resulted from stochastic extinctions and dispersal limitation. Our findings suggest that extreme hydrological events exert a strong control over stream invertebrate community assembly, and their effect may be even more profound in the future as high and low-flow spells are expected to occur more frequently, not allowing time for communities to recover

Data_OIK05329

Bio = Invertebrate species data for each site in each year, Env = site coordinate + hydrological variables (see MS for full name of each variable

From meta-system theory to the sustainable management of rivers in the Anthropocene

Regional-scale ecological processes, such as the spatial flows of material, energy, and organisms, are fundamental for maintaining biodiversity and ecosystem functioning in river networks. Yet these processes remain largely overlooked in most river management practices and underlying policies. Here, we propose adoption of a meta-system approach, where regional processes acting at different levels of ecological organization – populations, communities, and ecosystems – are integrated into conventional river conservation, restoration, and biomonitoring. We also describe a series of measurements and indicators that could be assimilated into the implementation of relevant biodiversity and environmental policies. Finally, we highlight the need for alternative management strategies that can guide practitioners toward applying recent advances in ecology to preserve and restore river ecosystems and the ecosystem services they provide, in the context of increasing alteration of river network connectivity worldwide. In a nutshell: • Rivers are hotspots of biodiversity and provide essential ecosystem functions and services, but face numerous threats globally • Understanding of how rivers are organized across spatial scales has progressed considerably over the past several decades, proving that regional-scale processes are vital for preserving population, community, and ecosystem dynamics • However, most existing river conservation, restoration, and biomonitoring practices focus on local-scale strategies and measures • To improve the management of river networks in the Anthropocene, we suggest additional metrics and assessment approaches that incorporate regional processes more effectivel