Managing for Interactions between Local and Global Stressors of Ecosystems

Global stressors, including climate change, are a major threat to ecosystems, but they cannot be halted by local actions. Ecosystem management is thus attempting to compensate for the impacts of global stressors by reducing local stressors, such as overfishing. This approach assumes that stressors interact additively or synergistically, whereby the combined effect of two stressors is at least the sum of their isolated effects. It is not clear, however, how management should proceed for antagonistic interactions among stressors, where multiple stressors do not have an additive or greater impact. Research to date has focussed on identifying synergisms among stressors, but antagonisms may be just as common. We examined the effectiveness of management when faced with different types of interactions in two systems – seagrass and fish communities – where the global stressor was climate change but the local stressors were different. When there were synergisms, mitigating local stressors delivered greater gains, whereas when there were antagonisms, management of local stressors was ineffective or even degraded ecosystems. These results suggest that reducing a local stressor can compensate for climate change impacts if there is a synergistic interaction. Conversely, if there is an antagonistic interaction, management of local stressors will have the greatest benefits in areas of refuge from climate change. A balanced research agenda, investigating both antagonistic and synergistic interaction types, is needed to inform management priorities.     

Starvation of bacteria as a stress caused by substrate limitation

The analysis of literature has made it possible to establish the priority of Russian research works made in the 1970-80s on the subject of starvation of bacteria caused by substrate limitation as well as research made in the 1990s concerning starvation of bacteria. This state is characterized by synthesis of additional proteins, so-called stress proteins, which not only ensure the survival of bacteria under the conditions of substrate limitation, but also protect them from a number of other stressors. In spite of the fact that genetic mechanisms regulating the synthesis of some stressor proteins have been revealed their significance for microbiological technology is not yet clear.     

Patterns of benthic algae and cyanobacteria along twin‐stressor gradients of nutrients and fine sediment: a stream mesocosm experiment

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Interactive and cumulative effects of multiple human stressors in marine systems

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.     

Evidence for multiple stressor interactions and effects on coral reefs

Concern is growing about the potential effects of interacting multiple stressors, especially as the global climate changes. We provide a comprehensive review of multiple stressor interactions in coral reef ecosystems, which are widely considered to be one of the most sensitive ecosystems to global change. First, we synthesized coral reef studies that examined interactions of two or more stressors, highlighting stressor interactions (where one stressor directly influences another) and potentially synergistic effects on response variables (where two stressors interact to produce an effect that is greater than purely additive). For stressor‐stressor interactions, we found 176 studies that examined at least 2 of the 13 stressors of interest. Applying network analysis to analyze relationships between stressors, we found that pathogens were exacerbated by more costressors than any other stressor, with ca. 78% of studies reporting an enhancing effect by another stressor. Sedimentation, storms, and water temperature directly affected the largest number of other stressors. Pathogens, nutrients, and crown‐of‐thorns starfish were the most‐influenced stressors. We found 187 studies that examined the effects of two or more stressors on a third dependent variable. The interaction of irradiance and temperature on corals has been the subject of more research (62 studies, 33% of the total) than any other combination of stressors, with many studies reporting a synergistic effect on coral symbiont photosynthetic performance (n = 19). Second, we performed a quantitative meta‐analysis of existing literature on this most‐studied interaction (irradiance and temperature). We found that the mean effect size of combined treatments was statistically indistinguishable from a purely additive interaction, although it should be noted that the sample size was relatively small (n = 26). Overall, although in aggregate a large body of literature examines stressor effects on coral reefs and coral organisms, considerable gaps remain for numerous stressor interactions and effects, and insufficient quantitative evidence exists to suggest that the prevailing type of stressor interaction is synergistic.     

Feeding is inhibited by sublethal concentrations of toxicants and by heat stress in the nematode Caenorhabditis elegans: relationship to the cellular stress response.

We report that the free-living nematode Caenorhabditis elegans can respond to a variety of stressors (compounds known to induce the production of cellular stress proteins in model biological systems), by ceasing pharyngeal pumping. This phenomenon results in both a reduction in intake of the stressor and a cessation of feeding. The effect of stressors can therefore be conveniently assayed by monitoring the decrease in the density of the bacterial food in liquid cultures of nematodes. A great range of stressors induced this response including alcohols, heavy metals, sulfhydryl-reactive compounds, salicylate, and heat. For several of these stressors, inhibition of pharyngeal pumping occurred at stressor concentrations below the threshold required for the induction of the 16-kDa heat shock proteins. Salicylate, which did not induce 16-kDa heat shock proteins at any concentration, nevertheless inhibited pharyngeal pumping. Heat was also inhibitory, at a temperature where 16-kDa heat shock protein production was near maximal. Some compounds caused only a partial inhibition of feeding while with others the effect was complete. Upon removal of the stressor, the nematodes resumed pharyngeal pumping with a residual inhibitory effect that depended on the concentration and type of stressor that had been applied. A number of C. elegans neurosensory mutant strains also exhibited a cessation of pharyngeal pumping when exposed to stressors suggesting that the mechanism underlying this inhibition was not entirely neurosensory and may be intrinsic to the pharynx. In C. elegans and other invertebrates, stress-induced inhibition of feeding may be an important survival mechanism that limits the intake of toxic solutes.     

Ventilatory frequency of Nile tilapia subjected to different stressors

Ventilatory frequency (VF) was investigated in the fish Nile tilapia, Oreochromis niloticus, subjected to confinement, electroshock or social stressor. Fish were allowed to acclimatize to tank conditions for 10 days (1 fish/aquarium). VF baseline was determined 5 days after adjustment had been started. At the 10th day of isolation, stressor effects on VF were assessed. The stressors were imposed during 60 min: pairing with a larger resident animal (social stressor), or gentle electroshock (AC, 20 V, 15 mA, 100 Hz for 1 min every 4 min), or space restriction (confinement). VF was quantified immediately after the end of the stressor imposition. Baseline of VF was not statistically different among groups. Social stressor clearly induced VF to increase, while an increased or decreased VF can be observed for both confinement and electroshock. However, fish tend to increase their VF in response to confinement and decrease in the case of electroshock. These results suggest that VF is a sensitive behavioural indicator for distinguishing stress responses in the fish Nile tilapia among different stressors.     

多重压力下重点生态功能区农户生计脆弱性——以甘南黄河水源补给区为例

农户作为农村社会中最小的生计单元,面临着多重压力的冲击,这些压力不仅加剧了重点生态功能区农户的生计脆弱性,更威胁到该区生态服务功能的提升,当前亟需准确评估多重压力下农户的生计脆弱性,为制定可持续的生计政策提供借鉴。以甘南黄河水源补给区为例,利用入户调查数据,评估了多重压力下农户的生计脆弱性,分析了多重压力下农户生计脆弱性的形成过程。结果发现：（1）家人患病、子女学费开支高和自然灾害三种生计压力对甘南黄河水源补给区农户生计的影响最为剧烈,经济压力是该区农户面临最频繁的压力类型,但自然压力对该区农户的生计脆弱性影响最大;（2）经济示范区农户的生计敏感性最高,重点保护区农户的适应能力最低;（3）重点保护区农户的生计脆弱性最高,经济示范区次之,恢复治理区最低,自然压力冲击下农户的生计脆弱性最高;（4）不同类型的生计压力影响农户生计脆弱性的路径不同,自然压力通过影响自然资源依赖度与自然资本、社会压力通过影响饮水条件与社会资本、经济压力通过影响家庭抚养比与金融资本来影响生计脆弱性,生计压力之间的交互作用会增强农户的生计脆弱性。     

Stressor richness intensifies productivity loss but mitigates biodiversity loss

Ecosystems are subject to a multitude of anthropogenic environmental changes. Experimental research in the field of multiple stressors has typically involved varying the number of stressors, here termed stressor richness, but without controlling for total stressor intensity. Mistaking stressor intensity effects for stressor richness effects can misinform management decisions when there is a trade‐off between mitigating these two factors. We incorporate multiple stressors into three community models and show that, at a fixed total stressor intensity, increasing stressor richness aggravates joint stressor effects on ecosystem functioning, but reduces effects on species persistence and composition. In addition, stressor richness weakens the positive selection and negative complementarity effects on ecosystem function. We identify the among‐species variation of stressor effects on traits as a key determinant of the resulting community‐level stressor effects. Taken together, our results unravel the mechanisms linking multiple environmental changes to biodiversity and ecosystem function.     

Biotic interactions modify multiple‐stressor effects on juvenile brown trout in an experimental stream food web

Agricultural land use results in multiple stressors affecting stream ecosystems. Flow reduction due to water abstraction, elevated levels of nutrients and chemical contaminants are common agricultural stressors worldwide. Concurrently, stream ecosystems are also increasingly affected by climate change. Interactions among multiple co‐occurring stressors result in biological responses that cannot be predicted from single‐stressor effects (i.e. synergisms and antagonisms). At the ecosystem level, multiple‐stressor effects can be further modified by biotic interactions (e.g. trophic interactions). We conducted a field experiment using 128 flow‐through stream mesocosms to examine the individual and combined effects of water abstraction, nutrient enrichment and elevated levels of the nitrification inhibitor dicyandiamide (DCD) on survival, condition and gut content of juvenile brown trout and on benthic abundance of their invertebrate prey. Flow velocity reduction decreased fish survival (?12% compared to controls) and condition (?8% compared to initial condition), whereas effects of nutrient and DCD additions and interactions among these stressors were not significant. Negative effects of flow velocity reduction on fish survival and condition were consistent with effects on fish gut content (?25% compared to controls) and abundance of dominant invertebrate prey (?30% compared to controls), suggesting a negative metabolic balance driving fish mortality and condition decline, which was confirmed by structural equation modelling. Fish mortality under reduced flow velocity increased as maximal daily water temperatures approached the upper limit of their tolerance range, reflecting synergistic interactions between these stressors. Our study highlights the importance of indirect stressor effects such as those transferred through trophic interactions, which need to be considered when assessing and managing fish populations and stream food webs in multiple‐stressor situations. However, in real streams, compensatory mechanisms and behavioural responses, as well as seasonal and spatial variation, may alter the intensity of stressor effects and the sensitivity of trout populations.     

Is heat shock protein re-induction during tolerance related to the stressor-specific induction of heat shock proteins?

The existence of stressor-specific induction programs of heat shock proteins (hsps) leads us to analyze the possible occurrence of a stressor-specific tolerance induced by either heat shock, arsenite, or cadmium. As a measure of this tolerance re-induction of hsps was studied. In this paper, we tested whether the refractory state is either valid for each specific hsp (implying independent regulation of every member of the heat shock protein family) or extends from small subsets of the hsp-family to even larger groups of proteins (indicating a more common denominator in their regulation). (Re-)induction of hsps does not seem to be regulated at the level of each individual hsp since differences in induced synthesis of hsps between two stressor conditions are not supplemented systematically upon the sequential application of the two stressors. The most notable example in this respect is hsp60. A pretreatment with cadmium, which hardly induces synthesis of this hsp, does induce a tolerance to (re)-induction by heat shock, which normally induces hsp60. This suggests the existence of a more common denominator regulating the coordinate expression of at least some hsps. From our data we conclude that the degree, but not the pattern, of hsp re-induction is influenced by the type of stressor used in the pretreatment. The pattern of hsps induced by a secondary applied stressor still shows most of its stressor-specificity and seems to be independent of any pretreatment. The possible implications of stressor-specificity are discussed. © 1996 Wiley-Liss, Inc.     

Multiple‐stressor effects on stream invertebrates: a mesocosm experiment manipulating nutrients,fine sediment and flow velocity

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Using a newly introduced framework to measure ecological stressor interactions

Understanding how stressors combine to affect population abundances and trajectories is a fundamental ecological problem with increasingly important implications worldwide. Generalisations about interactions among stressors are challenging due to different categorisation methods and how stressors vary across species and systems. Here, we propose using a newly introduced framework to analyse data from the last 25 years on ecological stressor interactions, for example combined effects of temperature, salinity and nutrients on population survival and growth. We contrast our results with the most commonly used existing method – analysis of variance (ANOVA) – and show that ANOVA assumptions are often violated and have inherent limitations for detecting interactions. Moreover, we argue that rescaling – examining relative rather than absolute responses – is critical for ensuring that any interaction measure is independent of the strength of single‐stressor effects. In contrast, non‐rescaled measures – like ANOVA – find fewer interactions when single‐stressor effects are weak. After re‐examining 840 two‐stressor combinations, we conclude that antagonism and additivity are the most frequent interaction types, in strong contrast to previous reports that synergy dominates yet supportive of more recent studies that find more antagonism. Consequently, measuring and re‐assessing the frequency of stressor interaction types is imperative for a better understanding of how stressors affect populations.     

Can biological traits of stream invertebrates help disentangle the effects of multiple stressors in an agricultural catchment?

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Eutrophic status influences the impact of pesticide mixtures and predation on Daphnia pulex populations

Pesticides, nutrients, and ecological stressors such as competition or predation co‐occur in freshwater ecosystems impacted by agriculture. The extent to which combinations of these stressors affect aquatic populations and the role of nutrients availability in modulating these responses requires further understanding. In this study, we assessed how pesticides affecting different taxonomic groups and predation influence the response of Daphnia pulex populations under different trophic conditions. An outdoor experiment was designed following a factorial design, with the insecticide chlorpyrifos, the herbicide diuron, and the predation by Notonecta sp. individuals as key stressors. The single impact of each of these stressors, and their binary and tertiary combinations, was evaluated on D. pulex abundance and population structure under mesotrophic and eutrophic conditions for 21 days. Data were analyzed using generalized linear mixed models estimated by means of a novel Bayesian shrinkage technique. Our study shows a significant influence of each of the evaluated stressors on D. pulex abundance; however, the impacts of the herbicide and predation were lower under eutrophic conditions as compared to the mesotrophic ones. We found that binary stressor interactions were generally additive in the mesotrophic scenario, except for the herbicide–predation combination, which resulted in synergistic effects. The impacts of the binary stressor combinations in the eutrophic scenario were classified as antagonistic, except for the insecticide–herbicide combination, which was additive. The tertiary interaction resulted in significant effects on some sampling dates; however, these were rather antagonistic and resembled the most important binary stressor combination in each trophic scenario. Our study shows that the impact of pesticides on freshwater populations depends on the predation pressure, and demonstrates that the combined effect of pesticides and ecological stressors is influenced by the food availability and organism fitness related to the trophic status of freshwater ecosystems.     

Urban stream denitrifier communities are linked to lower functional resistance to multiple stressors associated with urbanization

The microbial communities in urban stream ecosystems are subject to complex combinations of stressors. These same microbial communities perform the critical ecosystem service of removing excess reactive nitrogen. We asked whether the denitrifying microbial communities in urban streams differ in their functional resistance to common urban stressors from communities from nonurban streams. We exposed inocula from a highly polluted urban stream and a nearby nonurban stream to three different stressors, added alone and in combination. Stressors represent the common urban impacts of thermal pollution (10°C), trace metal exposure (ionic silver (Ag⁺)), and salinization (addition of NaCl). We used reduction in nitrite (NO₂ ^?) concentrations under anaerobic conditions as a proxy for denitrification potential. Nonurban stream denitrifying microbial communities were more diverse than their urban counterparts. Denitrification potential for both communities was unaffected by exposure to any individual stressor. However, denitrification rates by the less diverse urban microbial inoculum decreased in response to combined heavy metal and salt stress, while nonurban communities were unaffected. These findings support the hypothesis that higher diversity may confer greater functional resistance in response to multiple stressors and do not support the idea that stressful conditions select for communities that are functionally resilient to multiple stressors.     

Adaptive Amplification

ABSTRACT

Modern techniques are revealing that repetition of segments of the genome, called amplification or gene amplification, is very common. Amplification is found in all domains of life, and occurs under conditions where enhanced expression of the amplified genes is advantageous. Amplification extends the range of gene expression beyond that which is achieved by control systems. It also is reversible because it is unstable, breaking down by homologous recombination. Amplification is believed to be the driving force in the clustering of related functions, in that it allows them to be amplified together. Amplification provides the extra copies of genes that allow evolution of functions to occur while retaining the original function. Amplification can be induced in response to cellular stressors. In many cases, it has been shown that the genomic regions that are amplified include those genes that are appropriate to upregulate for a specific stressor. There is some evidence that amplification occurs as part of a broad, general stress response, suggesting that organisms have the capacity to induce structural changes in the genome. This then allows adaptation to the stressful conditions. The mechanisms by which amplification arises are now being studied at the molecular level, but much is still unknown about the mechanisms in all organisms. Recent advances in our understanding of amplification in bacteria suggests new interpretations of events leading to human copy number variation, as well as evolution in general.     

Stress-inducible bacterial proteins and virulence

Different species of pathogenic bacteria, including Salmonella, Neisseria, Listeria and Francisella have been used to demonstrate relationship between the synthesis of stressor induced proteins by cells and the phenotypic manifestation of their virulence. The impact of such external factors as high temperature, low pH, osmolarity, substrate limitation, the content of active forms of oxygen, etc. is accompanied by the synthesis of different stressor induced proteins playing a complex role. Under unfavorable environmental conditions the synthesis of these proteins ensures the survival of the infective agents. Under conditions of a macroorganism synthesis of some stressor induced proteins promotes the survival of infective agents and their resistance to the action of humoral and cell-mediated protective factors of the host. As is known, the expression of virulence genes is not constitutive. The expression of these genes greatly depends on environmental conditions and its induction is determined by extra- or intracellular location of the infective agent. Several systems of the regulation of bacterial pathogenicity factors have been described that are relatively not numerous, conservative and respond to external signals. The relevance of a number of stressor induced proteins of bacteria to virulence associated factors is discussed.     

Microbial stress priming: a meta‐analysis

Microbes have to cope with complex and dynamic environments, making it likely that anticipatory responses provide fitness benefits. Mild, previous stressors can prepare microbes (stress priming) to further and potentially damaging stressors (triggering). We here quantitatively summarize the findings from over 250 trials of 34 studies including bacteria and fungi, demonstrating that priming to stress has a beneficial impact on microbial survival. In fact, survival of primed microbes was about 10‐fold higher compared with that in non‐primed microbes. Categorical moderators related to microbial taxonomy and the kind of stress applied as priming or as triggering revealed significant differences of priming effect size among 14 different microbial species, 6 stress categories and stressor combination. We found that priming by osmotic, physiological and temperature stress had the highest positive effect sizes on microbial response. Cross‐protection was evident for physiological, temperature and pH stresses. Microbes are better prepared against triggering by oxidative, temperature and osmotic stress. Our finding of an overall positive mean effect of priming regardless of the microbial system and particular stressor provides unprecedentedly strong evidence of the broad ecological significance of microbial stress priming. These results further suggest that stress priming may be an important factor in shaping microbial communities.     

Impact of multiple stressors on juvenile fish in estuaries of the northeast Pacific

A key step in identifying global change impacts on species and ecosystems is to quantify effects of multiple stressors. To date, the science of global change has been dominated by regional field studies, experimental manipulation, meta‐analyses, conceptual models, reviews, and studies focusing on a single stressor or species over broad spatial and temporal scales. Here, we provide one of the first studies for coastal systems examining multiple stressor effects across broad scales, focused on the nursery function of 20 estuaries spanning 1,600 km of coastline, 25 years of monitoring, and seven fish and invertebrate species along the northeast Pacific coast. We hypothesized those species most estuarine dependent and negatively impacted by human activities would have lower presence and abundances in estuaries with greater anthropogenic land cover, pollution, and water flow stress. We found significant negative relationships between juveniles of two of seven species (Chinook salmon and English sole) and estuarine stressors. Chinook salmon were less likely to occur and were less abundant in estuaries with greater pollution stress. They were also less abundant in estuaries with greater flow stress, although this relationship was marginally insignificant. English sole were less abundant in estuaries with greater land cover stress. Together, we provide new empirical evidence that effects of stressors on two fish species culminate in detectable trends along the northeast Pacific coast, elevating the need for protection from pollution, land cover, and flow stressors to their habitats. Lack of response among the other five species could be related to differing resistance to specific stressors, type and precision of the stressor metrics, and limitations in catch data across estuaries and habitats. Acquiring improved measurements of impacts to species will guide future management actions, and help predict how estuarine nursery functions can be optimized given anthropogenic stressors and climate change scenarios.