Interaction effects and legacy effects of multiple environmental stressors on rice growth and the rhizosphere microbiome

The effects of multiple early life stressors on adolescent alcohol consumption

While a large body of research has focused on the physiological effects of multiple environmental stressors, how behavioural and life-history plasticity mediate multiple-stressor effects remains underexplored. Behavioural plasticity can not only drive organism-level responses to stressors directly but can also mediate physiological responses. Here, we provide a conceptual framework incorporating four fundamental trade-offs that explicitly link animal behaviour to life-history-based pathways for energy allocation, shaping the impact of multiple stressors on fitness. We first address how small-scale behavioural changes can either mediate or drive conflicts between the effects of multiple stressors and alternative physiological responses. We then discuss how animal behaviour gives rise to three additional understudied and interrelated trade-offs: balancing the benefits and risks of obtaining the energy needed to cope with stressors, allocation of energy between life-history traits and stressor responses, and larger-scale escape from stressors in space or time via large-scale movement or dormancy. Finally, we outline how these trade-offs interactively affect fitness and qualitative ecological outcomes resulting from multiple stressors. Our framework suggests that explicitly considering animal behaviour should enrich our mechanistic understanding of stressor effects, help explain extensive context dependence observed in these effects, and highlight promising avenues for future empirical and theoretical research.

Understanding the consequences of the combined effects of multiple stressors—including stress from man-made chemicals—is important for conservation management, the ecological risk assessment of chemicals, and many other ecological applications. Our current ability to predict and analyse the joint effects of multiple stressors is insufficient to make the prospective risk assessment of chemicals more ecologically relevant because we lack a full understanding of how organisms respond to stress factors alone and in combination. Here, we describe a Dynamic Energy Budget (DEB) based bioenergetics model that predicts the potential effects of single or multiple natural and chemical stressors on life history traits. We demonstrate the plausibility of the model using a meta-analysis of 128 existing studies on freshwater invertebrates. We then validate our model by comparing its predictions for a combination of three stressors (i.e. chemical, temperature, and food availability) with new, independent experimental data on life history traits in the daphnid Ceriodaphnia dubia. We found that the model predictions are in agreement with observed growth curves and reproductive traits. To the best of our knowledge, this is the first time that the combined effects of three stress factors on life history traits observed in laboratory studies have been predicted successfully in invertebrates. We suggest that a re-analysis of existing studies on multiple stressors within the modelling framework outlined here will provide a robust null model for identifying stressor interactions, and expect that a better understanding of the underlying mechanisms will arise from these new analyses. Bioenergetics modelling could be applied more broadly to support environmental management decision making.

Ecosystems have multiple interacting processes that buffer against co-occurring stressors.

The move towards ecosystem-based fisheries management in coastal areas requires understanding ecosystem connections between biotic and abiotic factors and accounting for the effects of stressors on fish. The objectives of this contribution are to (1) highlight current progress in understanding how stressors affect fish and fisheries in coastal and estuarine environments, (2) reveal data gaps for current management, and (3) provide an overview of future research directions to help close these gaps. We add our perspectives and insights to the growing dialogue for coastal fisheries and ecosystem managers, emphasizing progress and gaps in field surveys incorporating habitats, laboratory experimental approaches, and ecosystem modeling. Although studies of the effects of some stressors on habitats, fish, and fisheries are available, few have effectively integrated multiple stressors. Expanding fisheries surveys both spatially and temporally to target multiple habitats and life stages can produce valuable insights into the potential effects of stressors (i.e., ocean warming, eutrophication, harmful algal blooms, hypoxia, and ocean acidification) on fisheries. In particular, the lack of surveys examining early life stages (i.e., embryos and larvae) of fish is a major concern for our understanding in the context of ecosystem-based fisheries management. Laboratory experiments have provided insights on how fish may respond to these stressors, both individually and collectively, but more research needs to be conducted, especially regarding sublethal effects. Ecosystem modeling has made great progress in simulating the effects of multiple environmental stressors on fish and fisheries, but uptake in stock assessment has been minimal. Ultimately, policymakers and ecosystem managers need to holistically integrate the effects of multiple stressors on coastal fisheries resources into management and policies.

Ecosystems worldwide are subject to the deleterious effects of multiple anthropogenic stressors. Understanding and mitigating the effects of these stressors is difficult both because stressors are confounded in space and have the potential to act both synergistically and antagonistically. Palaeoecological approaches applied to systems where stressors may be confounded in space but not in time offer a way to explore the effects of multiple stressors. This multi-proxy study of sediment records from four floodplain lakes (billabongs) on a dryland river floodplain subject to grazing, commencing in the late 1800s, and irrigated cropping, commencing in the late 1900s, tests this approach. The results suggest that the effects of both grazing and irrigation on floodplain ecosystems can be detected in the pollen and diatoms preserved in sedimentary records of billabongs. For the pollen, these changes are inconsistent, but appear to reflect local shifts in dominance among major tree taxa and among key understorey plant families. For the diatoms, the changes were also not consistent across sites, but can be generalised as reductions in epiphytic diatoms and increases in planktonic and facultative planktonic taxa that likely reflect increased fluxes of sediments and nutrients and reduced flood frequency. Overall, the effects of grazing appear to have been greater than irrigated cropping. The results also show that the relative effects of grazing and irrigated cropping on floodplain and riparian vegetation and on diatom communities vary between billabongs, with some evidence that at least some of this variation relates to the level of hydrological connection to the mainstream. Finally, the study suggests that for the most part, grazing and irrigated cropping act antagonistically in the way they impact these floodplain ecosystems, a pattern that likely reflects a release from grazing pressure associated with the increase in irrigated cropping. Future applications of the approach should increase spatial and temporal replication and develop more sophisticated frameworks that account for temporal variation in driver intensity and proxy indicators of the specific stressors that influence ecosystem structure and function.

Zooplankton communities in Boreal Shield lakes of south-central Ontario, Canada, have become increasingly exposed to the effects of multiple anthropogenic stressors, such as declines in calcium (Ca) and total phosphorus (TP) concentrations, shifts in predation regimes, and climate warming. The paleolimnological approach provides an effective means of examining cladoceran zooplankton communities prior to the onset of these major environmental stressors and assessing how the increasing impacts of these stressors have affected zooplankton community composition. We examined the chitinized remains of cladocerans from recent and pre-industrial (pre- ~1850s) sediments in 42 oligotrophic lakes from south-central Ontario and compared these assemblages using ANOSIM and SIMPER. Differences in cladoceran assemblages since pre-industrial times were related to five environmental variables that significantly influence cladoceran community composition in surface sediments. These included measured physical (depth), chemical [Ca, pH, sulphate, dissolved organic carbon (DOC)], and biological (fish community biomass) limnological variables. Two changes were recorded in the cladoceran species assemblages of the study lakes. The first was a significant increase in the ratio of pelagic species compared to littoral species over time in most lakes which we cannot attribute to any measured environmental variable with certainty but it likely represents a multiple stressor effect. The second was changes in relative abundances of daphniid cladocerans in several lakes since pre-industrial times, which we attribute to the interactive effects of several environmental stressors, including: differences in Ca availability within our lakes, resulting in decreased abundances of daphniids over time in lakes with lower Ca levels; long-term increases in DOC concentrations, which may provide refuge for daphniids from visual predators; and long-term declines in TP concentrations which may contribute to the dominance of species that are more efficient grazers, such as daphniids. Overall, this study provides field-based evidence that the modern-day cladoceran communities in south-central Ontario lakes are different than they were prior to human settlement in the region, and therefore these paleolimnological data provide a long-term, historical component to contemporary cladoceran datasets and an extended perspective on how multiple environmental stressors have impacted aquatic organisms from Boreal Shield lakes.

Understanding the relative importance of multiple stressors is valuable to prioritize conservation and restoration measures. Yet, the effects of multiple stressors on ecosystem functioning remain largely unknown in many fresh waters. Here, we provided a methodology combining ecosystem modeling with linear regression to disentangle the effects of multiple stressors on matter flow, an important ecosystem function. Treating a shallow lake as the model ecosystem, we simulated matter flow dynamics during 1950s–2010s with different combinations of stressors by Ecopath with Ecosim (EwE) modeling and determined the relative importance of each stressor by generalized linear mixed models. We found that matter flow of the lake food web was highly dynamic, attributing to effects of multiple anthropogenic stressors. Biological invasion played the strongest role in driving the matter flow dynamics, followed by eutrophication, while biomanipulation (i.e., phytoplankton control by planktivorous fish stocking) was of little importance. Eutrophication had a stronger role on primary producers, pelagic food chain, and top predators, while biological invasion on consumers in the middle of food chains. The former was more important in driving the quantity of matter flow, while the latter on trophic transfer efficiencies. Scenario forecasting showed that reducing nutrients contents could largely shape the matter flow pattern, while biomanipulation had little effect. Our findings provided new insights into understanding the mechanistic links between anthropogenic stressors and ecosystem functioning by combining ecosystem modeling with linear regression.

Humans impact natural systems in a multitude of ways, yet the cumulative effect of multiple stressors on ecological communities remains largely unknown. Here we synthesized 171 studies that manipulated two or more stressors in marine and coastal systems and found that cumulative effects in individual studies were additive (26%), synergistic (36%), and antagonistic (38%). The overall interaction effect across all studies was synergistic, but interaction type varied by response level (community: antagonistic, population: synergistic), trophic level (autotrophs: antagonistic, heterotrophs: synergistic), and specific stressor pair (seven pairs additive, three pairs each synergistic and antagonistic). Addition of a third stressor changed interaction effects significantly in two-thirds of all cases and doubled the number of synergistic interactions. Given that most studies were performed in laboratories where stressor effects can be carefully isolated, these three-stressor results suggest that synergies may be quite common in nature where more than two stressors almost always coexist. While significant gaps exist in multiple stressor research, our results suggest an immediate need to account for stressor interactions in ecological studies and conservation planning.

Responses of stream microbes to multiple anthropogenic stressors in a mesocosm study

Ecosystems are strongly influenced by multiple anthropogenic stressors, including a wide range of chemicals and their mixtures. Studies on the effects of multiple stressors have largely focussed on nonchemical stressors, whereas studies on chemical mixtures have largely ignored other stressors. However, both research areas face similar challenges and require similar tools and methods to predict the joint effects of chemicals or nonchemical stressors, and frameworks to integrate multiple chemical and nonchemical stressors are missing. We provide an overview of the research paradigms, tools, and methods commonly used in multiple stressor and chemical mixture research and discuss potential domains of cross-fertilization and joint challenges. First, we compare the general paradigms of ecotoxicology and (applied) ecology to explain the historical divide. Subsequently, we compare methods and approaches for the identification of interactions, stressor characterization, and designing experiments. We suggest that both multiple stressor and chemical mixture research are too focused on interactions and would benefit from integration regarding null model selection. Stressor characterization is typically more costly for chemical mixtures. While for chemical mixtures comprehensive classification systems at suborganismal level have been developed, recent classification systems for multiple stressors account for environmental context. Both research areas suffer from rather simplified experimental designs that focus on only a limited number of stressors, chemicals, and treatments. We discuss concepts that can guide more realistic designs capturing spatiotemporal stressor dynamics. We suggest that process-based and data-driven models are particularly promising to tackle the challenge of prediction of effects of chemical mixtures and nonchemical stressors on (meta-)communities and (meta-)food webs. We propose a framework to integrate the assessment of effects for multiple stressors and chemical mixtures. Environ Toxicol Chem 2023;42:1915-1936. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Surface soils are highly vulnerable to multiple global change stressors associated with climate change and human activity; however, whether the impacts of this increasing number of stressors penetrate deeper soils remains virtually unknown. Here, we conducted a continental-scale survey of soil profiles (0-100 cm). Results showed that multiple stressors jointly affect multiple soil functions (from soil carbon sequestration to pathogen control) across top (0-30 cm), subsurface (30-60 cm) and deep soils (60-100 cm). An increasing number of stressors was especially detrimental to the capacity of ecosystems to support productivity and regulate soil-borne pathogens across all depths. Further analyses revealed that climatic stressors interact with multiple environmental stressors, diminishing multifunctionality across the soil profile. Our work demonstrates that the effects of multiple stressors can permeate the entire soil profile, highlighting that an increasing number of global change stressors at low levels significantly threaten multiple functions supported by deep soils.

Chapter 17 - Managing Ecosystem Services Under Multiple Stresses

Second International Symposium on Ionising Radiation:`Environmental Protection Approaches for Nuclear Facilities', Ottawa, Canada, 10-14 May 1999

Evaluating the effects of multiple stressors on ecosystems is becoming increasingly vital with global changes. The role of species interactions in propagating the effects of stressors, although widely acknowledged, has yet to be formally explored. Here, we conceptualise how stressors propagate through food webs and explore how they affect simulated three-species motifs and food webs of the Canadian St.Lawrence System. We find that overlooking species interactions invariably underestimate the effects of stressors, and that synergistic and antagonistic effects through food webs are prevalent. We also find that interaction type influences a species' susceptibility to stressors; species in omnivory and tri-trophic food chain interactions in particular are sensitive and prone to synergistic and antagonistic effects. Finally, we find that apex predators were negatively affected and mesopredators benefited from the effects of stressors due to their trophic position in the St.Lawrence System, but that species sensitivity is dependent on food web structure. In conceptualising the effects of multiple stressors on food webs, we bring theory closer to practice and show that considering the intricacies of ecological communities is key to assess the net effects of stressors on species.