Biology subjects

Schaefer, R. B.

Publications and source records attributed to Schaefer, R. B..

4 recordsLinked to original sources

bioRxiv2024

Multiple stressors in river networks: local and downstream effects on freshwater macroinvertebrates

River networks are complex ecosystems characterized by a continuous exchange of material and energy through longitudinal gradients. These ecosystems are threatened by various human-induced stressors, which frequently co-occur and may interact in complex ways, potentially triggering cascading effects in the river network. Aiming at assessing single and combined effects of flow intermittency and light pollution on macroinvertebrate communities, we performed a multiple stressors experiment in 18 flow-through mesocosms. Each mesocosm was designed to mimic a simplified river network, with two upstream tributaries merging downstream, to assess both local and cascading effects. The experiment was performed in Summer 2021 for seven weeks (26 days of colonization, 23 days of treatment), applying the stressors either separately or combined in the upstream sections, in a randomized block design. Flow intermittency was simulated as the ponded phase of the drying process, whereas light pollution was applied with LED strips (set at 10 lux) that automatically turned on at sunset and off at sunrise. Drifting macroinvertebrates were sampled weekly during the treatment phase, and benthic macroinvertebrates at the end of the treatment phase. Both stressors individually applied had negative effects on the benthos, whereas drift decreased with flow intermittency and increased with light pollution. When combined upstream, stressors showed dominant effects of flow intermittency on the benthos and interactive effects on the drift. The effects of the single stressors and their interactions propagated along the river network, with stronger downstream effects when stressors co-occurred upstream. These findings showed that the spatial distribution of multiple stressors along the river network can affect their resultant downstream effects, highlighting the importance of framing multiple stressors research in a spatial context. Considering the pressing needs of the growing human population, our results represent a step forward in anticipating cumulative stressors effects, informing efficient conservation strategies for protecting freshwater ecosystems.

ecology↗

bioRxiv2024

Global-scale quantification of responses to anthropogenic stressors in six riverine organism groups

Rivers globally are impacted by numerous anthropogenic stressors, including water pollution, habitat degradation, and climate change, which collectively stress biodiversity and ecosystem functioning. This study systematically reviews and analyses published and unpublished data to understand how five aquatic organism groups (bacteria, algae, macrophytes, invertebrates, fish) respond to seven common stressors (salinization, oxygen depletion, fine sediment enrichment, temperature increase, flow modifications and nitrogen or phosphorus enrichment). Using an analytical framework that includes Generalized Linear Models (GLMs) and Robust Bayesian Meta Analysis (RoBMA), we extracted data from 143 relevant datasets out of 29,749 screened articles. Our results reveal a negative relationship between invertebrates and salinity, fine sediment enrichment, and temperature increase, while fish respond positively to increased oxygen levels and temperature. Bacteria and algae show variable responses, with algae positively associated with nitrogen. The findings highlight strong variability in stressor-response relations across organism groups and stressor types, and emphasize the need for more targeted studies on underrepresented groups like macrophytes and microorganisms. This analysis enhances the predictive understanding of stressor impacts on riverine biodiversity, informing future river ecosystem management and restoration efforts.

ecology↗

bioRxiv2024

Putting the Asymmetric Response Concept to the test: modeling multiple stressor exposure and release in a stream food web

Communities in stream ecosystems often respond asymmetrically to increase and release of stressors, as indicated by slow and incomplete recovery. The Asymmetric Response Concept (ARC) posits that this is due to a shift in the relative importance of three mechanisms: tolerance, dispersal, and biotic interactions. In complex natural communities, these mechanisms may produce alternative outcomes through poorly understood indirect effects. To understand how the three mechanisms respond to different temporal stressor scenarios, we studied multiple scenarios using a stream food web model. We asked the following questions: Do groups of species decline as expected on the basis of individual tolerance rankings derived from laboratory experiments when they are embedded in a complex dynamic food web? Does the response of ecosystem function match that of communities? To address these questions, we aggregated data on individual tolerances at the level of functional groups and studied how single and multiple stressors affect food web dynamics and nutrient cycling. Multiple stressor scenarios involved different intensities of salt and temperature increase. Functional groups exhibited a different relative tolerance ranking between the laboratory and dynamic food web contexts. Salt as a single stressor had only minor and transient effects at low level but led to the loss of one or more functional groups at high level. In contrast, high temperature, alone or in combination with salt, caused the loss of functional groups at all tested levels. Patterns often differed between the response of communities and ecosystem function. We discuss our findings with respect to the ARC. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=106 SRC="FIGDIR/small/601677v1_ufig1.gif" ALT="Figure 1"> View larger version (23K): org.highwire.dtl.DTLVardef@2924f0org.highwire.dtl.DTLVardef@138400aorg.highwire.dtl.DTLVardef@1f45126org.highwire.dtl.DTLVardef@fba006_HPS_FORMAT_FIGEXP M_FIG C_FIG

ecology↗

bioRxiv2023

Meta-analysis on the effects of chemical stressors on five ecosystem functions: are there generalizable relationships?

Despite considerable progress in our predictive capacity for the response of different trophic levels to chemical stressors, generalizable relations between chemical stressors and ecosystem functions are lacking. We addressed this knowledge gap by conducting a meta-analysis (153 studies; 350 observations) on the responses of freshwater ecosystem functions (community respiration, organic matter decomposition, nutrient cycling, photosynthesis, and primary production) under controlled conditions (laboratory or outdoor mesocosms) to pesticides, pharmaceuticals, and metals. We identified monotonic dose-response relationships between standardized chemical concentrations, in terms of toxic units, for selected chemical use groups and organic matter decomposition by decomposer-detritivore-systems as well as photosynthesis by algae and macrophytes. By contrast, consistent relationships were not found for other ecosystem functions, such as organic matter decomposition by microbial decomposers alone and primary production under the conditions studied. Importantly, the shape and direction of the relationships identified here match those reported in field-based studies, indicating a decrease in functioning as chemical stress increases, strengthening the ecological relevance of our findings. Finally, we found a disconnect between regulatory ecological quality targets and ecological outcomes, highlighting a need to re-evaluate risk assessment approaches if they are supposed to be ecologically meaningful and protective of ecosystem functions.

ecology↗