Cumulative Effects Of Multiple Stressors Research Articles

Water‐level fluctuations and nutrient enrichment interact to alter ecosystem structure in distinct ways at different water depths

Abstract Aquatic ecosystems are often impacted by several human‐derived pressures simultaneously. A key challenge for ecologists is to develop mechanistic understanding of the cumulative effects of multiple stressors on freshwater biodiversity. We established an outdoor mesocosm experiment to examine the individual and combined effects of two key stressors on lake ecosystems globally—nutrient enrichment and amplified water‐level fluctuations—on benthic algal and macroinvertebrate assemblages along a gradient in littoral water depth. We found that nutrient enrichment and water‐level fluctuations not only altered the structure of littoral communities when acting individually, but also interacted to dynamically alter biomass and community structure in different ways at different depths. As expected, enrichment increased benthic algal biomass significantly in very shallow waters. Yet, when enrichment co‐occurred with water‐level fluctuations, this pattern was reversed, with algal biomass increasing significantly in deeper waters, but not in the shallows that were exposed to fluctuating water levels. This pattern occurred across all algal groups that we examined except for green algae. Green algae biomass increased with nutrient enrichment, was greatest in the shallows, and remained unaffected by fluctuating water levels. Water‐level fluctuations modified the functional feeding group structure of benthic macroinvertebrate communities, reducing relative densities of collector‐gatherers and increasing those of predators. However, these changes occurred only in the shallow‐most regions exposed directly to fluctuating water levels. Our results reveal how two globally important stressors of standing water systems can interact in different ways in different ecological contexts and show how stressors can combine to have unanticipated impacts that vary in space. Our findings underscore the potentially highly multifaceted and complex nature of stressor combinations that present a major and growing challenge to ecosystem management, particularly in light of accelerating global environmental change.

Cumulative effects of multiple stressors impact an endangered seagrass population and fish communities

Coastal ecosystems are becoming increasingly threatened by human activities and there is growing appreciation that management must consider the impacts of multiple stressors. Cumulative effects assessments (CEAs) have become a popular tool for identifying the distribution and intensity of multiple human stressors in coastal ecosystems. Few studies, however, have demonstrated strong correlations between CEAs and change in ecosystem condition, questioning its management use. Here, we apply a CEA to the endangered seagrass Posidonia australis in Pittwater, NSW, Australia, using spatial data on known stressors to seagrass related to foreshore development, water quality, vessel traffic and fishing. We tested how well cumulative effects scores explained changes in P. australis extent measured between 2005 and 2019 using high-resolution aerial imagery. A negative correlation between P. australis and estimated cumulative effects scores was observed (R2 = 22 %), and we identified a threshold of cumulative effects above which losses of P. australis became more likely. Using baited remote underwater video, we surveyed fishes over P. australis and non-vegetated sediments to infer and quantify how impacts of cumulative effects to P. australis extent would flow on to fish assemblages. P. australis contained a distinct assemblage of fish, and on non-vegetated sediments the abundance of sparids, which are of importance to fisheries, increased with closer proximity to P. australis. Our results demonstrate the negative impact of multiple stressors on P. australis and the consequences for fish biodiversity and fisheries production across much of the estuary. Management actions aimed at reducing or limiting cumulative effects to low and moderate levels will help conserve P. australis and its associated fish biodiversity and productivity.

Context and Neuroendocrine Interplay in the Lab and Everyday Experiences: From Early Life to Adulthood

Whereas many other disciplines tend to overlook the role of context—that is, the environment—from its earliest days, the field of psychoneuroendocrinology has appreciated the connection between context and neurobiological functioning. Context shapes neurobiological systems in development, evokes neurobiological responses, and moderates the magnitude and even the directionality of those neurobiological responses. In the present symposium, four speakers will present talks that use samples and environmental measures spanning from early life to adulthood to: demonstrate a central role for the environment, point us toward which environments matter most in the prediction of health and well-being, and yield new insights about the functioning of neuroendocrine systems. First, Dr. Catherine B. Stroud will present novel evidence that the impact of threat adversity (e.g., assault) on latent trait cortisol (LTC) is modified by co-occurring adversities, including deprivation (e.g., neglect) and other non-threat adversities. Though prior work has linked threat adversity to hypothalamic pituitary adrenal (HPA) axis activity, it remains to be examined whether threat adversity is related to trait cortisol and whether this effect is modified by co-occurring adversities. Emerging adults (n=90) provided 36 saliva samples over 13 weeks, and early adversity was assessed with contextual stress interviews. Results showed that greater frequency of threat adversity was related to lower LTC, regardless of level of co-occurring deprivation. Further, greater severity of threat adversity was negatively associated with LTC, but only when co-occurring deprivation was low in severity. Finally, the effect of threat adversity on LTC was stronger when co-occurring non-threat adversity was lower in severity and frequency. Findings provide novel evidence that the effect threat adversity on LTC depends upon the context in which it occurs. Such results underscore the importance of simultaneously examining multiple co-occurring dimensions of early adversity to elucidate their unique and interactive effects on HPA axis regulation. Second, Dr. Suzanne Vrshek-Schallhorn will present a newly developed objective measure of performance, the Behavioral Indicators of Trier Engagement (BITE) scale for use during the Trier Social Stress Test (TSST), to reveal relationships with biomarkers. The authors report good psychometric properties for the BITE, then report how it related to affect and salivary cortisol and alpha amylase (AA). Emerging adults (n=109) completed one of three versions of the TSST that manipulated the context level of negative evaluation—a non-evaluative Control Condition, an ambiguously evaluative Intermediate Condition similar to the original TSST, and an explicitly negative evaluative Challenge Condition. The BITE was not related to negative affect, but as condition intensified, the BITE increasingly predicted positive affect preservation. More importantly, for both biomarkers, the relationship between baseline levels and behavioral engagement on the BITE varied significantly by condition: under milder conditions, elevated biomarkers predicted greater engagement, but under explicit negative evaluation, they predicted behavioral withdrawal. Results (a) provide a new measure of behavioral engagement, (b) show that two biomarkers are involved in heightened behavioral engagement under less threatening contexts but in behavioral withdrawal under more threatening contexts, and (c) highlight the importance of utilizing a full range of negative evaluation. Third, Ms. Jeri Sasser will present a study examining the role of environmental factors (e.g., stress) in predicting “wear and tear” on HPA-axis functioning in daily life in an understudied cultural context. The college transition is a time of socio-contextual change, and may be especially stressful for Latino students, who often experience both minority-specific and general life stress. Despite this, little is known regarding the cumulative impact of multiple contextual stressors on Latino students’ HPA-axis functioning. This study utilized rigorous methodological (e.g., naturalistic assessment of cortisol, ecological momentary assessment) and analytical approaches (e.g., multi-risk model, multilevel growth curve modeling) to examine the additive, common, and cumulative effects of multiple stressors (e.g., general, college, minority-specific) on diurnal cortisol in a sample of first-year Latino college students (N=180; 64.4% female; Mage=18.95). Results indicated that general stress was linked to a flatter diurnal cortisol slope (DCS) whereas bicultural stress was linked to a steeper DCS. College stress and cumulative risk were both associated with lower cortisol awakening response (CAR). Findings highlight the physiological correlates of various stressors experienced by Latino college students, emphasizing the importance of not only an array of forms of stress, but also culture, as context. Fourth, Dr. Frances Chen will present a study of the cross-system coordination of the HPA axis and the autonomic nervous system (ANS) in response to stress. Cross-system coordination captures the degree of co-changing between systems within a person and has implications for behavior problems. One prior study showed that greater HPA axis-ANS coordination (indexed by cortisol and AA, respectively) is linked to more behavior problems in youth. This study aimed to extend these findings to adults and a new context—disadvantageous urban neighborhoods—and tested whether cortisol-AA coordination was associated with negative urgency and antisocial behavior. An urban sample of 124 adults (college students, active offenders, and matched controls) completed a modified Trier Social Stress Test (mTSST). Results showed that antisocial behavior and negative urgency were each associated with greater cortisol-AA stress coordination. Further, cortisol-AA stress coordination was stronger among offenders than other groups. Findings (a) support the interpretation that high cortisol-AA coordination may indicate an overshooting of the ANS response in response to distress, (b) highlight the importance of the multisystem approach, and (c) extend prior work to a new context, disadvantageous urban neighborhoods. Taken together, these four talks will highlight how context—the environment—both shapes and reveals the functioning of neuroendocrine stress-response systems across early life, emerging adulthood, and adulthood. Findings emphasize the importance of co-occurring adversities, negative evaluation, daily cultural proximal processes, and disadvantageous urban neighborhoods as critical contexts in revealing the role of neuroendocrine systems in behavior. The speakers will provide suggestions for future research examining how context shapes the impact of stressful experiences on neuroendocrine stress-response systems.

The cumulative impacts of anthropogenic stressors vary markedly along environmental gradients.

Understanding the cumulative effects of multiple stressors on biodiversity is key to managing their impacts. Stressor interactions are often studied using an additive/antagonistic/synergistic typology, aimed at identifying situations where individual stressor effects are reduced or amplified when they act in combination. Here, we analysed variation in the family richness of stream macroinvertebrates in the groups Ephemeroptera, Plecoptera and Trichoptera (EPT) at 4658 sites spanning a 32° latitudinal range in eastern Australia in relation to two largely human-induced stressors, salinity and turbidity, and two environmental gradients, temperature and slope. The cumulative and interactive effect of salinity and turbidity on EPT family richness varied across the landscape and by habitat (edge or riffle) such that we observed additive, antagonistic and synergistic outcomes depending on the environmental context. Our findings highlight the importance of understanding the consistency of multiple stressor impacts, which will involve higher-order interactions between multiple stressors and environmental factors.

Global Swimways for the conservation of migratory freshwater fishes

AbstractAnthropogenic activities have severely degraded the ecological integrity of global freshwater systems. Migratory freshwater fishes are especially threatened by the cumulative effects of multiple stressors and fragmentation, particularly those that impede access to critical habitats. To stimulate the conservation and protection of these species, we propose a “Global Swimways” program to identify rivers that support the migration routes of biologically and/or socioeconomically important freshwater fishes. We test the utility of the International Union for Conservation of Nature Red List data to support the identification of Global Swimways and present case study regions containing rivers with either high species richness (west‐central Africa and Southeast Asia), high numbers of threatened species (Eastern Europe and Central Asia), or multiple endemic species (the Rift Valley lakes in East Africa). We hope the Global Swimways program will provide metrics that can be used to identify rivers requiring increased protection or restoration, track trends, and stimulate the greater inclusion of migratory freshwater fishes in global policy mechanisms.Front Ecol Environ 2022;

The effects of a half century of warming and fire exclusion on montane forests of the Klamath Mountains, California, USA

AbstractClimate warming and altered disturbance regimes are changing forest composition and structure worldwide. Given that species often exhibit individualistic responses to change, making predictions about the cumulative effects of multiple stressors across environmental gradients is challenging, especially in diverse communities. For example, warming temperatures are predicted to drive species upslope, whereas fire exclusion promotes the expansion of species at lower elevations where fire was historically frequent. We resampled 148 vegetation plots to assess 46 years (1969–2015) of species and community‐level response to warming and fire exclusion in a topographically complex landscape in the Klamath Mountains, California, USA, a diverse region that served as a climate refugia throughout the Holocene. We compared cover and assessed change in the elevational distributions of 12 conifer species at different life stages (i.e., seedlings, saplings, canopy). We observed consistent but non‐significant shifts upward in elevation for eight species, and a significant shift upward for one species, all of which were far less than expectations based on recent warming. Six species declined in total cover and another five declined in at least one life stage, whereas the drought‐ and fire‐intolerant Abies concolor increased by 30.7%. The largest declines were at lower elevations in drought‐tolerant, early‐seral species (Pinus lambertiana and Pinus ponderosa) and at higher elevations for the shade‐tolerant Abies magnifica var. shastensis and the regionally rare Abies lasiocarpa. Regionally rare (Picea engelmannii) and endemic (Picea breweriana) species had reductions in early life stages, portending future declines. Multivariate analyses revealed a high degree of inertia with a minor, but significant, shift in composition and a slight decrease in species turnover along the elevation gradient driven by the expansion of A. concolor. Our results indicate that most species are declining, especially at lower and mid‐elevations where fire exclusion has increased the cover of shade‐tolerant species and reduced the recruitment for fire‐adapted species. Collectively, declines in most species, insufficient upward movement to track warming, reductions in drought‐ and fire‐tolerant early‐seral species, and an increase in a single, shade‐tolerant species will leave these communities maladapted to projected climate scenarios and questions the potential for future climate refugia in this region.

Rapidly declining body size in an insectivorous bat is associated with increased precipitation and decreased survival.

Reduced food availability is implicated in declines in avian aerial insectivores, but the effect of nutritional stress on mammalian aerial insectivores is unclear. Unlike birds, insectivorous bats provision their young through lactation, which might protect nursing juveniles when prey availability is low but could increase the energetic burden on lactating females. We analyzed a 15-year capture-mark-recapture data set from 5312 individual little brown myotis (Myotis lucifugus) captured at 11 maternity colonies in northwestern Canada, to test the hypothesis that nutritional stress is impacting these mammalian aerial insectivores. We used long-bone (forearm [FA]) length as a proxy for relative access to nutrition during development, and body mass as a proxy for access to nutrition prior to capture. Average FA length and body mass both decreased significantly over the study period in adult females and juveniles, suggesting decreased access to nutrition. Effect sizes were very small, similar to those reported for declining body size in avian aerial insectivores. Declines in juvenile body mass were only observed in individuals captured in late summer when they were foraging independently, supporting our hypothesis that lactation provides some protection to nursing young during periods of nutritional stress. Potential drivers of the decline in bat size include one or both of (1) declining insect (prey) abundance, and (2) declining prey availability. Echolocating insectivorous bats cannot forage effectively during rainfall, which is increasing in our study area. The body mass of captured adult females and juveniles in our study was lower, on average, after periods of high rainfall, and higher after warmer-than-average periods. Finally, survival models revealed a positive association between FA length and survival, suggesting a fitness consequence to declines in body size. Our study area has not yet been impacted by bat white-nose syndrome (WNS), but research elsewhere has suggested that fatter bats are more likely to survive infection. We found evidence for WNS-independent shifts in the body size of little brown myotis, which can inform studies investigating population responses to WNS. More broadly, the cumulative effects of multiple stressors (e.g., disease, nutritional stress, climate change, and other pressures) on mammalian aerial insectivores require urgent attention.

Perception and consideration of cumulative effects and multiple stressors by marine managers in Canada

The cumulative effects of multiple stressors are a pressing global concern for marine ecosystems. The effectiveness of marine management can be improved by considering three key elements that can affect their impacts: stressor interaction types, non-linear stressor–effect relationships, and ecosystem tipping points. Little is known about the degree to which cumulative effects, or these key elements, are considered in marine management in Canada. We surveyed Canadian federal government managers involved in managing either marine conservation areas or commercial fisheries, and asked (1) if they currently assess cumulative effects in decision-making, (2) if so, how and which elements are considered, and (3) the perceived importance of considering the three key elements. We also compared approaches among federal departments, management type, oceans, experience levels, and position types. We found that most managers (84%, n = 80) consider cumulative effects in decision-making. Responses clustered into either a structured approach, which included using an assessment framework and considering the three key elements of cumulative effects, or an intuitive approach, characterized by the absence of a formal framework or consideration of key elements. Neither was strongly linked with demographic categories. Despite most managers (97%, n = 37) believing that the three key elements of cumulative effects are important to consider, only 21% actually did so in decision-making. This discrepancy appears to be underpinned by barriers such as a lack of guidelines for assessing cumulative effects and data quality, quantity, and availability. We provide recommendations to overcome these challenges.

How psychosocial stress profile influences the subsequent occurrence of neuropsychiatric comorbidities: A longitudinal population-based cohort study

BackgroundThe role of psychosocial stressors in psychiatric disorders and executive dysfunction has been reported, separately. The literature has also suggested the involvement of social support and coping strategies in these relationships. However, there is a lack of research conducted to examine the relationships among multiple stressors and neuropsychiatric comorbidities while considering the presence of social support and coping strategies. This study aims to articulate the roles of multiple psychosocial stressors, social support, and coping strategies in the subsequent occurrence of neuropsychiatric comorbidities. MethodsData analyzed were from the 6th data collection of a large-scale, longitudinal population-based cohort from Southwest Montreal in Canada. The cumulative effects of multiple stressors were separately examined by a composite score and latent profile analysis. Multinomial logistic regression models were used to test the relationship between cumulative stressors and neuropsychiatric comorbidities. ResultsA total of 210 participants were included in the analyses. The LPA identified a 2-class model for psychosocial stressors (low and high) and executive function (executive dysfunction and no executive dysfunction), respectively. There were 11.8% of participants with neuropsychiatric comorbidities. Both the composite stress score (RR = 1.08, 95%CI = 1.01–1.15) and latent stress groups (RR = 3.65, 95%CI = 1.15–11.57) were associated with neuropsychiatric comorbidities after adjusting for social support and coping strategies. The risk of developing neuropsychiatric comorbidities decreased when the level of social support was high (P < 0.05). ConclusionsExposures to multiple stressors increased the risk of subsequent neuropsychiatric comorbidities, but the risk can be modified by a higher level of social support.

Same Space, Different Standards: A Review of Cumulative Effects Assessment Practice for Marine Mammals

Marine mammals are vulnerable to a variety of acute and chronic anthropogenic stressors, potentially experiencing these in isolation, successively and/or simultaneously. Formal assessment of the likely impact(s) of the cumulative effects of multiple stressors on a defined population is carried out through a Cumulative Effects Assessment (CEA), which is a mandatory component of the Environmental Impact Assessment (EIA) process in many countries. However, for marine mammals, the information required to feed into CEA, such as thresholds for disturbance, frequency of multiple (and simultaneous) exposures, interactions between stressors, and individual variation in response, is extremely limited, though our understanding is slowly improving. The gaps in knowledge make it challenging to effectively quantify and subsequently assess the risk of individual and population consequences of multiple disturbances in the form of a CEA. To assess the current state of practice for assessing cumulative effects on marine mammals within UK waters, 93 CEAs were reviewed across eleven maritime industries. An objective framework of thirteen evaluative criteria was used to score each assessment on a scale of 13-52 (weak - strong). Scores varied significantly by industry. On average, the aquaculture industry produced the lowest scoring CEAs, whilst the large offshore windfarm industry (≥ 20 turbines) scored highest, according to the scoring criteria used. There was a significant increase in scores over the sample period (2009-2019), though this was mostly attributed to five industries (cable, large and small offshore wind farms, tidal and wave energy). There was inconsistency in the language used to define and describe cumulative effects and a lack of routinely applied methodology. We use the findings presented here, along with a wider review of the literature, to provide recommendations and discussion points aimed at supporting the standardisation and improvement of CEA practice. Although this research focused on how marine mammals were considered within UK CEAs, recommendations made are broadly applicable to assessments conducted for other receptors, countries and/or environments. Adoption of these proposals would help to ensure a more consistent approach, and would aid decision-makers and practitioners in mitigating any potential impacts, to ensure conservation objectives of marine mammal populations are not compromised.

Science Alone Won’t Do It! South Africa’s Endangered Humpback Dolphins Sousa plumbea Face Complex Conservation Challenges

The Indian Ocean humpback dolphin (Sousa plumbea) is “endangered” with likely less than 500 animals remaining in South African waters. Established in 2016, the SouSA Consortium is a formalised network of scientists and conservationists to combine knowledge and research efforts, and make coordinated decisions with the aim of conserving the species. The first collaborative project collated available photo-identification data in an attempt to refine a national population estimate and investigate movements between research sites. This work was able to identify 250 uniquely marked individuals, with the population divided into the south-coast (Agulhas bioregion) and east-coast (Natal bioregion) populations. Environmental factors almost certainly play a role in the declining numbers of the species in South African waters. However, individual threats and solutions are challenging to identify as the South African marine environment is undergoing significant natural and anthropogenic changes with major shifts in the distribution and numbers of some prey, competitor and predator species. Therefore, we believe that a continued investigation of potential contributing factors and their interaction will take too long, inevitably resulting in another case of documenting extinction. With this in mind, we present the results of a SWOT (Strengths, Weaknesses, Opportunities, and Threats) analysis in an effort to help us identify the next steps to take toward the conservation of humpback dolphins in South African waters. We unanimously conclude that no single cause for the rapid decline of humpback dolphins in South African waters can be identified, and that the cumulative effects of multiple stressors, which are difficult to pinpoint and mitigate, are impacting population numbers. While highlighting the need for continued research, we suggest a shift toward more action-focused conservation efforts, the first concrete steps being the development of a Conservation Management Plan with input from other stakeholders.

Forecasting the Cumulative Effects of Multiple Stressors on Breeding Habitat for a Steeply Declining Aerial Insectivorous Songbird, the Olive-sided Flycatcher (Contopus cooperi)

To halt ongoing loss in biodiversity, there is a need for landscape-level management recommendations that address cumulative impacts of anthropogenic and natural disturbances on wildlife habitat. We examined the cumulative effects of logging, roads, land-use change, fire, and bark beetle outbreaks on future habitat for olive-sided flycatcher (Contopus cooperi), a steeply declining aerial insectivorous songbird, in Canada’s western boreal forest. To predict the occurrence of olive-sided flycatcher we developed a suite of habitat suitability models using point count surveys (1997–2011) spatially- and temporally-matched with forest inventory data. Flycatcher occurrence was positively associated with small (∼10 ha) 10- to 20-year-old clearcuts, and with 10–100% tree mortality due to mountain pine beetle (Dendroctonus ponderosae) outbreaks, but we found no association with roads or distance to water. We used the parameter estimates from the best-fit habitat suitability models to inform spatially explicit state-and-transition simulation models to project change in habitat availability from 2020 to 2050 under six alternative scenarios (three management × two fire alternatives). The simulation models projected that the cumulative effects of land use conversion, forest harvesting, and fire will reduce the area of olive-sided flycatcher habitat by 16–18% under Business As Usual management scenarios and by 11–13% under scenarios that include protection of 30% of the land base. Scenarios limiting the size of all clearcuts to ≤10 ha resulted in a median habitat loss of 4–6%, but projections were highly variable. Under all three management alternatives, a 50% increase in fire frequency (expected due to climate change) exacerbated habitat loss. The projected losses of habitat in western boreal forest, even with an increase in protected areas, imply that reversing the ongoing population declines of olive-sided flycatcher and other migratory birds will require attention to forest management beyond protected areas. Further work should examine the effects of multiple stressors on the demographic mechanisms driving change in aerial insectivore populations, including stressors on the wintering grounds in South America, and should aim to adapt the design of protected areas and forest management policies to projected climate-driven increases in the size and frequency of wildfires.

Investigating the cumulative effects of multiple stressors on fish assemblages in a semi-enclosed bay

The growing intensity of anthropogenic activities has led to an increase in the number of studies assessing the effects of stressors on marine ecosystems. Yet, the cumulative effects of multiple stressors are rarely studied although they seldom operate in isolation of each other. Our study aimed to investigate the effects of multiple stressors on fish assemblages in a series of semi-enclosed bays. We quantified fish assemblages using baited remote underwater video across five sites with varying environmental and anthropogenic stressors. We also sampled across two seasons and in protected and unprotected areas. We found that fish assemblages were most influenced by effluent input and aquaculture, but not fishing pressure. Relief, season, salinity, and pH were also included in the best model highlighting the importance of environmental variables in structuring fish assemblages. Total abundance was not affected by anthropogenic stressors but individual species showed variable responses from reduced abundance (e.g. Neoodax balteatus and Cyanea rosella) to increased abundances (e.g. Arripis spp.). We found no evidence that increased number or intensity of stressors affected overall fish abundance or diversity. Our findings highlight the diverse effects anthropogenic stressors can have on fishes with both environmental and anthropogenic influences playing a role in structuring fish assemblages over both short temporal and spatial scales.

The Cumulative Effects of Fishing, Plankton Productivity, and Marine Mammal Consumption in a Marine Ecosystem

The marine ecosystem off British Columbia (BC), Canada, has experienced various changes in the last two decades, including reduced lipid-rich zooplankton biomass, increased marine mammals, and deteriorated commercial fisheries, particularly those targeting pelagic species such as Pacific Herring (Clupea pallasii). Understanding how stressors interactively and cumulatively affect commercially important fish species is key to moving toward ecosystem-based fisheries management. Because it is challenging to assess the cumulative effects of multiple stressors by using empirical data alone, a dynamic, individual-based spatially explicit ecosystem modeling platform such as Object-oriented Simulator of Marine Ecosystems (OSMOSE) represents a valuable tool to simulate ecological processes and comprehensively evaluate how stressors cumulatively impact modeled species. In this study, we employed OSMOSE to investigate the cumulative effects of fishing, plankton biomass change, and marine mammal consumption on the dynamics of some fish species and the BC marine ecosystem as a whole. We specifically simulated ecosystem dynamics during the last 20 years under two sets of scenarios: (1) unfavorable conditions from the perspective of commercial fish species (i.e., doubling fishing mortality rates, halving plankton biomass, and doubling marine mammal biomass, acting individually or collectively); and (2) favorable conditions with the three factors having opposite changes (i.e., halving fishing mortality rates, doubling plankton biomass, and halving marine mammal biomass, acting individually or collectively). Our results indicate that, under unfavorable conditions, the degree to which species biomass was reduced varied among species, and that negative synergistic and negative dampened effects were dominant under historical and doubled fishing mortality rates, respectively. Under favorable conditions, species biomasses did not increase as much as expected due to the existence of complex predator-prey interactions among fish species, and positive synergistic and positive dampened effects were prevailing under historical and halved fishing mortality rates, respectively. The ecosystem total biomass and the biomass to fisheries yield ratio were found to be good ecological indicators to represent ecosystem changes and track the impacts from the multiple drivers of change. Our research provides insights on how fisheries management should adapt to prepare for potential future impacts of climate change.

Patterns and variation in the mammal parasite-glucocorticoid relationship.

Parasites are ubiquitous and can strongly affect their hosts through mechanisms such as behavioural changes, increased energetic costs and/or immunomodulation. When parasites are detrimental to their hosts, they should act as physiological stressors and elicit the release of glucocorticoids. Alternatively, previously elevated glucocorticoid levels could facilitate parasite infection due to neuroimmunomodulation. However, results are equivocal, with studies showing either positive, negative or no relationship between parasite infection and glucocorticoid levels. Since factors such as parasite type, infection severity or host age and sex can influence the parasite-glucocorticoid relationship, we review the main mechanisms driving this relationship. We then perform a phylogenetic meta-analysis of 110 records from 65 studies in mammalian hosts from experimental and observational studies to quantify the general direction of this relationship and to identify ecological and methodological drivers of the observed variability. Our review produced equivocal results concerning the direction of the relationship, but there was stronger support for a positive relationship, although causality remained unclear. Mechanisms such as host manipulation for parasite survival, host response to infection, cumulative effects of multiple stressors, and neuro-immunomodulatory effects of glucocorticoids could explain the positive relationship. Our meta-analysis results revealed an overall positive relationship between glucocorticoids and parasitism among both experimental and observational studies. Because all experimental studies included were parasite manipulations, we conclude that parasites caused in general an increase in glucocorticoid levels. To obtain a better understanding of the directionality of this link, experimental manipulation of glucocorticoid levels is now required to assess the causal effects of high glucocorticoid levels on parasite infection. Neither parasite type, the method used to assess parasite infection nor phylogeny influenced the relationship, and there was no evidence for publication bias. Future studies should attempt to be as comprehensive as possible, including moderators potentially influencing the parasite-glucocorticoid relationship. We particularly emphasise the importance of testing hosts of a broad age range, concomitantly measuring sex hormone levels or at least reproductive status, and for observational studies, also considering food availability, host body condition and social stressors to obtain a better understanding of the parasite-glucocorticoid relationship.

Cumulative Effects of Thermal and Fisheries Stressors Reveal Sex-Specific Effects on Infection Development and Early Mortality of Adult Coho Salmon (Oncorhynchus kisutch).

Multiple stressors are commonly encountered by wild animals, but their cumulative effects are poorly understood, especially regarding infection development. We conducted a holding study with repeated gill and blood sampling to characterize the effects of cumulative stressors on infection development in adult coho salmon. Treatments included chronic thermal stress (15°C vs. 10°C) and acute gill net entanglement with an air exposure (simulating fisheries bycatch release). The potential loadings of 35 infectious agents and the expression of 17 host immune genes were quantified using high-throughput quantitative polymerase chain reaction, while host physiology was characterized with chemical analysis of blood. Temporal increases in infectious agent richness and loads were concurrent with decreased expression of immune genes in fish sampled in the river. In the laboratory, mortality was minimal in cool water regardless of fishery treatment (<15%). Elevated water temperature under laboratory conditions increased mortality of males and females (8% and 28% mortality, respectively, delayed by >1 wk) and enhanced mortality associated with handling and biopsy (∼40% both sexes). Experimental gillnetting at high temperature further enhanced female mortality (73%). Fish held at high temperature demonstrated heavier infectious agent loads, osmoregulatory impairment, suppressed female maturation, and upregulation of inflammatory and extracellular immune genes. At high temperature, heavy Parvicapsula minibicornis loads were associated with premature mortality. Females exhibited physiological impairment from both stressors after 1 wk, and infection burdens correlated poorly with immune gene regulation compared with males. Cumulative effects of multiple stressors on female mortality are likely a function of physiological impairment and enhanced infections at high temperature.

A new method to evaluate the vulnerability of watersheds facing several stressors: A case study in mediterranean Chile

Freshwater systems are subjected to multiple anthropogenic stressors and natural disturbances that act as debilitating agents and modifiers of river systems, causing cumulative and synergistic effects that deteriorate their health and result in watershed vulnerability. This study proposes an easy-to-apply spatial method of watershed vulnerability evaluation using Geographic Information Systems (GIS) in the Andalién River watershed, located in the Chilean mediterranean. A watershed vulnerability index (WVI) based on three sub-indices – anthropogenic stressors, environmental fragility and natural disturbances – was developed. To determine the index grouping weights, expert surveys were carried out using the Delphi method. We subsequently normalized and integrated the factors of each sub-index with relative weights. The ranges of each thematic layer were re-classified to establish vulnerability scores. The watershed was divided into three sections: headwaters zone, transfer zone and depositional zone. The watershed vulnerability index showed that 41% of the watershed had very low vulnerability and 42% had medium vulnerability, while only 1% – in the depositional zone – had high vulnerability. A one-way ANOVA was carried out to analyze the vulnerability differences among the three sections of the watershed; it showed significant differences (F (2, 16) = 8.15: p < 0.05). The a posteriori test showed differences between the headwaters and depositional zones (Tukey test, p = 0.005) and between the transfer and depositional zones (Tukey test, p = 0.014). To validate the WVI, water quality was measured at 16 stations in the watershed; there was a significant correlation between vulnerability level and NO2− levels (r = 0.8; p = 0.87; α = 0.05) and pH (r = 0.8; p = 0.80; α = 0.05). The WVI showed the cumulative effects of multiple stressors in the depositional zone of the watershed. This is the first study to evaluate and validate non-regulated watershed vulnerability with GIS using multiple anthropogenic and natural stressors.

Crossing boundaries for cetacean conservation: Setting research priorities to guide management of harbour porpoises

Effective management of natural resources involves a multidisciplinary perspective to address complex issues in data poor-environments. With mobile species that do not conform to human-defined borders a cross-boundary approach is essential. There is a continuing concern of ecological sustainability of marine environments, which demands monitoring of ecosystem indicators. Such indicators are increasingly derived from monitoring sentinel species. Harbour porpoises (Phocoena phocoena) are included as indicator species in several national and international agreements. Increasing exposure to anthropogenic stressors may impact harbour porpoise populations. To investigate these risks, a better understanding of threats and their effect is required. This study aimed to identify current knowledge gaps, to predict future pressures or threats, and to define useful conservation indicators to facilitate future research on harbour porpoises in the North Sea, through expert elicitation gained in a two-round Delphi approach. The three most important knowledge gaps addressed were bycatch, population dynamics, and the cumulative effects of multiple stressors. Bycatch was predicted as the highest concern for porpoises in the next 20 years, followed by chemical and noise pollution, respectively. A list of essential indicators aiming to increase understanding of harbour porpoises’ health status was established and studying causes of death, distribution, abundance, habitat use and diet composition were scored as most relevant. These results should guide research focus and management objectives of harbour porpoise populations and the study design could be translated to serve managers in other geographical areas aiming to identify knowledge gaps and defining research priorities for other wildlife species.

Cumulative effects of climate and landscape change drive spatial distribution of Rocky Mountain wolverine (Gulo gulo L.).

Contemporary landscapes are subject to a multitude of human‐derived stressors. Effects of such stressors are increasingly realized by population declines and large‐scale extirpation of taxa worldwide. Most notably, cumulative effects of climate and landscape change can limit species’ local adaptation and dispersal capabilities, thereby reducing realized niche space and range extent. Resolving the cumulative effects of multiple stressors on species persistence is a pressing challenge in ecology, especially for declining species. For example, wolverines (Gulo gulo L.) persist on only 40% of their historic North American range. While climate change has been shown to be a mechanism of range retractions, anthropogenic landscape disturbance has been recently implicated. We hypothesized these two interact to effect declines. We surveyed wolverine occurrence using camera trapping and genetic tagging at 104 sites at the wolverine range edge, spanning a 15,000 km2 gradient of climate, topographic, anthropogenic, and biotic variables. We used occupancy and generalized linear models to disentangle the factors explaining wolverine distribution. Persistent spring snow pack—expected to decrease with climate change—was a significant predictor, but so was anthropogenic landscape change. Canid mesocarnivores, which we hypothesize are competitors supported by anthropogenic landscape change, had comparatively weaker effect. Wolverine population declines and range shifts likely result from climate change and landscape change operating in tandem. We contend that similar results are likely for many species and that research that simultaneously examines climate change, landscape change, and the biotic landscape is warranted. Ecology research and species conservation plans that address these interactions are more likely to meet their objectives.

Visual analytics of high-frequency lake monitoring data

In recognizing the cumulative effects of multiple stressors on altering aquatic ecosystem function, scientists have become increasingly interested in capturing high-frequency response variables using a variety of sensors. This practice has led to a demand for novel ways to visualize and analyze the wealth of data in order to meet policy and management goals. Time series data collected as part of these monitoring activities are not easily analyzed with traditional methods. In this paper, a visual analytics system is described that leverages humans’ innate capability for pattern recognition and feature detection. High-frequency monitoring of weather and water conditions in Lake Nipissing, a large, shallow, inland lake in northeastern Ontario, Canada, is used as a case study. These visualizations are presented as Web-based tools to facilitate community-based participatory research among scientists, government agencies, and community stakeholders. These analytics techniques contribute to collaborative research endeavors and to the understanding of the response of lake conditions to environmental change.