Multiple Stressors Research Articles

The environmental cellular stress response: the intertidal as a multistressor model.

The wild poses a multifaceted challenge to the maintenance of cellular function. Therefore, a multistressor approach is essential to predict the cellular mechanisms which promote homeostasis and underpin whole-organism tolerance. The intertidal zone is particularly dynamic, and thus, its inhabitants provide excellent models to assess mechanisms underpinning multistressor tolerance. Here, we critically review our current understanding of the regulation of the cellular stress response (CSR) under multiple abiotic stressors in intertidal organisms and consider to what extent a multistressor approach brings us closer to understanding responses in the wild. The function of theCSR has been well documented in laboratory and field exposures with a view to understanding single-stressor thermal effects. Multistressor studies still remain relatively limited in comparison but have applied three main approaches: (i) laboratory application of multiple stressors in isolation, (ii) multiple stressors applied in combination, and (iii) field-based correlation of multiple stressors against the CSR. The application of multiple stressors in isolation has allowed the identification of putative,shared stress pathways but overlooks non-additive stressor interactions on the CSR. Combined stressor studies are relatively limited in number but already highlight variable effects onthe CSR dependent upon stressor type, timing, and magnitude. Field studies have allowed the identification of responsive components ofthe CSR to various stressors in situ but are correlative, not causative. A combined approach involving laboratory multistressor studies linkingthe CSR to whole-organism tolerance as well as field studies is required if we are to understand the role ofthe CSR in the natural environment.

Freshwater-related species richness in Natura 2000 sites strongly depends on the surrounding land use besides local habitat conditions

The Birds and Habitats Directive are the cornerstones of Europe's nature conservation policy and the resulting Natura 2000 (N2k) sites form the largest coordinated network of protected areas in the world. Despite the ambitious targets of these directives and decades of efforts, biodiversity, especially of freshwater-related species, continues to decline in Europe. While multiple stressors at larger spatial scales are known to limit the effect of river restoration projects, the importance of surrounding land use outside the N2k sites for freshwater-related species richness inside N2k sites has rarely been studied. Conditional inference forests were used to assess the importance of land use in the surrounding and upstream of the German N2k sites compared to local habitat conditions inside. Freshwater-related species richness depended on land use in the surrounding besides local habitat conditions. Results indicated that this was especially true for birds in small N2k sites embedded in a wet, diverse, and patchy landscape and for non-birds due to the provision of additional habitats outside the N2k sites. Given that most N2k sites in Europe are rather small, the surrounding habitat conditions and land use potentially influences and affects freshwater-related species in many N2k sites across Europe. The additional conservation and restoration areas to be designated under the EU Biodiversity Strategy and upcoming EU restoration law should either be large enough or surrounded by extensive land use to optimize their effect on freshwater-related species.

The identification of the new species Nitratireductor thuwali sp. nov. reveals the untapped diversity of hydrocarbon-degrading culturable bacteria from the arid mangrove sediments of the Red Sea.

The geological isolation, lack of freshwater inputs and specific internal water circulations make the Red Sea one of the most extreme-and unique-oceans on the planet. Its high temperature, salinity and oligotrophy, along with the consistent input of hydrocarbons due to its geology (e.g., deep-sea vents) and high oil tankers traffic, create the conditions that can drive and influence the assembly of unique marine (micro)biomes that evolved to cope with these multiple stressors. We hypothesize that mangrove sediments, as a model-specific marine environment of the Red Sea, act as microbial hotspots/reservoirs of such diversity not yet explored and described. To test our hypothesis, we combined oligotrophic media to mimic the Red Sea conditions and hydrocarbons as C-source (i.e., crude oil) with long incubation time to allow the cultivation of slow-growing environmentally (rare or uncommon) relevant bacteria. This approach reveals the vast diversity of taxonomically novel microbial hydrocarbon degraders within a collection of a few hundred isolates. Among these isolates, we characterized a novel species, Nitratireductor thuwali sp. nov., namely, Nit1536T. It is an aerobic, heterotrophic, Gram-stain-negative bacterium with optimum growth at 37°C, 8 pH and 4% NaCl, whose genome and physiological analysis confirmed the adaptation to extreme and oligotrophic conditions of the Red Sea mangrove sediments. For instance, Nit1536T metabolizes different carbon substrates, including straight-chain alkanes and organic acids, and synthesizes compatible solutes to survive in salty mangrove sediments. Our results showed that the Red Sea represent a source of yet unknown novel hydrocarbon degraders adapted to extreme marine conditions, and their discovery and characterization deserve further effort to unlock their biotechnological potential.

Cumulative Pandemic Stressors, Psychosocial Resources, and Psychological Distress: Toward a More Comprehensive Test of a Pandemic Stress Process

Although the mental health consequences of individual COVID-19 stressors (e.g., bereavement, job loss, or financial strain) have been well-documented, little is known about the cumulative toll of multiple pandemic stressors. Using national data from the Crime, Health, and Politics Survey (May–June 2021), we test whether the accumulation of pandemic stressors is associated with greater psychological distress. We also consider whether this association is moderated by psychosocial resources (i.e., mastery, self-esteem, and social support). Our findings suggest that individuals who report three or more pandemic stressors tend to exhibit greater psychological distress than those who report fewer pandemic stressors or no pandemic stressors. While mastery offsets the impact of pandemic stressors at higher levels of stress exposure (i.e., two or more COVID-19 stressors), social support and self-esteem played a stress-buffering role to a point, but became ineffective at the highest levels of pandemic stress. The current study provides new insights into the pandemic stress process by conceptualizing and operationalizing the cumulative impact of COVID-19 stressors. We also confirm the continued significance of traditional coping resources in the context of novel pandemic stressors.

Expansion and adaptive evolution of the WRKY transcription factor family in Avicennia mangrove trees

Mangroves are adapted to intertidal zones, which present extreme environmental conditions. WRKYs are among the most prominent transcription factors (TFs) in higher plants and act through various interconnected networks to regulate responses to multiple abiotic stressors. Here, based on omic data, we investigated the landscape and evolutionary patterns of WRKYs in the main mangrove genus Avicennia. We found that both the number and the proportion of TFs and WRKYs in Avicennia species exceeded their inland relatives, indicating a significant expansion of WRKYs in Avicennia. We identified 109 WRKY genes in the representative species Avicennia marina. Comparative genomic analysis showed that two recent whole-genome duplication (WGD) events played a critical role in the expansion of WRKYs, and 88% of Avicennia marina WRKYs (AmWRKYs) have been retained following these WGDs. Applying comparative transcriptomics on roots under experimental salt gradients, we inferred that there is high divergence in the expression of WGD-retained AmWRKYs. Moreover, we found that the expression of 16 AmWRKYs was stable between freshwater and moderately saline water but increased when the trees were exposed to high salinity. In particular, 14 duplicates were retained following the two recent WGD events, indicating potential neo- and sub-functionalization. We also found that WRKYs could interact with other upregulated genes involved in signalling pathways and natural antioxidant biosynthesis to enhance salt tolerance, contributing to the adaptation to intertidal zones. Our omic data of the WRKY family in A. marina broadens the understanding of how a TF family relates to the adaptive evolution of mangroves.

Thermal tolerance limits and physiological traits as indicators of Hediste diversicolor's acclimation capacity to global and local change drivers

Global projections predict significant increases in ocean temperature and changes in ocean chemistry, including salinity variations by 2100. This has led to a substantial interest in the study of thermal ecophysiology, as temperature is a major factor shaping marine ectotherm communities. However, responses to temperature may be influenced by other factors such as salinity, highlighting the relevance of multiple stressor studies. In the present work, we experimentally evaluated the thermal tolerance of the marine ragworm Hediste diversicolor under predicted global change scenarios. Organisms were subjected to an experimental trial under control (24 °C), and two temperature treatment scenarios (ocean warming +3 °C – (27 °C) and heat wave +6 °C – (30 °C)), combined with salinity variations (20 and 30) in a full factorial design for 29 days. Environmental data from the field were collected during 2019 and 2020. At day 30 post exposure, upper thermal limits (Critical Thermal Maximum - CTMax), thermal safety margins (TSM) and acclimation capacity were measured. Higher acclimation temperatures led to higher thermal tolerance limits, confirming that H. diversicolor features some physiological plasticity, acclimation capacity and a positive thermal safety margin. This margin was greater considering in situ temperature data from 2019 than maximum temperatures for 2020 (CTMax > maximum habitat temperature–MHT). Moreover, smaller organisms displayed higher upper thermal limits suggesting that thermal tolerance is size dependent. Ragworms subjected to higher salinity also showed a higher CTMax than those acclimated to lower salinity. However, temperature and salinity showed an additive effect on CTMax, as no significant interaction was detected. We conclude that H. diversicolor can easily acclimate to increased water temperature, independently of salinity variations. Given the key role of ragworms in food webs in estuaries and coastal lagoons, substrate bioturbation and aquaculture, this information is relevant to support conservation actions, optimize culture protocols and identify thermal resistant strains.

Non-interactive effects drive multiple stressor impacts on the taxonomic and functional diversity of atlantic stream macroinvertebrates

Freshwaters are considered among the most endangered ecosystems globally due to multiple stressors, which coincide in time and space. These local stressors typically result from land-use intensification or hydroclimatic alterations, among others. Despite recent advances on multiple stressor effects, current knowledge is still limited to manipulative approaches minimizing biological and abiotic variability. Thus, the assessment of multiple stressor effects in real-world ecosystems is required.Using an extensive survey of 50 stream reaches across North Portugal, we evaluated taxonomic and functional macroinvertebrate responses to multiple stressors, including marked gradients of nutrient enrichment, flow reduction, riparian vegetation structure, thermal stress and dissolved oxygen depletion. We analyzed multiple stressor effects on two taxonomic (taxon richness, Shannon-diversity) and two trait-based diversity indices (functional richness, functional dispersion), as well as changes in trait composition.We found that multiple stressors had additive effects on all diversity metrics, with nutrient enrichment identified as the most important stressor in three out of four metrics, followed by dissolved oxygen depletion and thermal stress. Taxon richness, Shannon-diversity and functional richness responded similarly, whereas functional dispersion was driven by changes in flow velocity and thermal stress.Functional trait composition changed along a major stress gradient determined by nutrient enrichment and oxygen depletion, which was positively correlated with organisms possessing fast-living strategies, aerial respiration, adult phases, and gathering-collector feeding habits.Overall, our results reinforce the need to consider complementary facets of biodiversity to better identify assembly processes in response to multiple stressors. Our data suggest that stressor interactions may be less frequent in real-word streams than predicted by manipulative experiments, which can facilitate mitigation strategies. By combining an extensive field survey with an integrative consideration of multiple biodiversity facets, our study provides new insights that can help to better assess and manage rivers in a global change context.

Culturing for conservation: the need for timely investments in reef aquaculture

Temperate oyster and tropical coral reefs are analogous systems that create habitat for economically, ecologically, and culturally important species, and they provide countless ecosystem services to human coastal communities. Globally, reefs are imperiled by multiple anthropogenic stressors, particularly climate impacts. Using aquaculture to support conservation goals - known as conservation aquaculture - is a relatively new approach for many reef building species, but it shows great promise for promoting species recovery and bolstering resilience to stressors. Concerns about aquaculture-associated risks, both known and potential, have often restricted the implementation of this tool to an emergency intervention following dramatic declines on reefs, when species or systems were unlikely to recover. Here, we combine expertise from coral and oyster reef ecosystems to consider the role of aquaculture as a conservation intervention for reefs, and provide recommendations for its timely development and targeted implementation. We highlight the importance of evaluating reef systems - alongside local stakeholders and Indigenous communities - to determine where and when the benefits of using aquaculture are most likely to outweigh the risks. We spotlight the importance of proactive monitoring to detect reef population declines, and the value of early aquaculture interventions to increase efficacy. Novel aquaculture approaches and technologies specifically designed for reef builders are considered, including techniques for building complex, multi-generational and multi-species reefs. We address the need for scaling up aquaculture-assisted reef recovery, particularly of corals, using high volume methods like those that have been successfully employed for oysters. We also recommend the immediate assessment and development of techniques to increase climate resilience of reef builders and we identify the challenges and trade-offs of these approaches. We highlight the use of proof-of-concept projects to test these promising methods, and we advise tracking of all interventions over time to determine their long-term efficacy. Finally, we outline opportunities to leverage novel partnerships among conservation, industry, and community interests that utilize aquaculture to facilitate the conservation of reefs. Developing conservation aquaculture approaches now is critical to position managers, scientists, and restoration practitioners to implement this intervention in timely and effective ways to support resilient reef and human communities worldwide.

OsHSP 17.9, a Small Heat Shock Protein, Confers Improved Productivity and Tolerance to High Temperature and Salinity in a Natural Paddy Field in Transgenic Rice Plants

Various abiotic stress factors, such as high temperatures and salinity, have a significant impact on the development and growth of crop plants and ultimately impact crop yield. Previous studies have reported that overexpression of heat-shock-protein (HSP) genes in transgenic plants can enhance stress tolerance under controlled conditions in laboratories and greenhouses. Despite the significance of multiple environmental stressors on plants in natural paddy fields, there is still a lack of research regarding the contribution of HSP genes to stress tolerance and crop yield. In this study, we cloned and characterized the function of OsHSP 17.9, an HSP gene from Oryza sativa, in rice plants grown under diverse conditions. Our results showed that overexpressing OsHSP 17.9 in rice plants enhanced the activity of antioxidant enzymes under high-temperature and salinity stresses. Moreover, transgenic rice plants overexpressing OsHSP 17.9 exhibited significantly improved adaptability after transplantation from greenhouses to natural paddy fields. In particular, OsHSP 17.9-overexpressing transgenic rice plants established improved agronomic traits and increased grain yields even under unfavorable natural-paddy-field conditions. These results suggest that OsHSP 17.9 transgenic plants can be a promising strategy for cultivating crops in adverse environmental conditions.

The Relationship between Occupational Stress, Mental Health and COVID-19-Related Stress: Mediation Analysis Results

The COVID-19 pandemic led to serious psychological consequences that negatively affect workers’ mental health, leading to post-traumatic symptoms. In this scenario, employees may be exposed to multiple stressors that ultimately drain their resources. Drawing on the Conservation of Resources Theory (COR) and the stress–strain perspective, we analyzed the relationship between different dimensions of work-related stress and psychological distress in a sample of 294 workers in the industrial sector. Specifically, we hypothesized a series of mediation models in which the dimensions of work-related stress are associated with a lower level of mental health directly and indirectly through higher levels of COVID-19-related post-traumatic symptoms. The results partially support the hypotheses, showing that COVID-19-related trauma plays a mediating role between the stress experienced and the resulting decrease in mental health, except in the case of job control and colleague support. These results will hopefully offer insights into possible organizational interventions for the promotion of workers’ well-being in the postpandemic setting.

Decreased feeding rates of the copepod Acartia tonsa when exposed to playback harbor traffic noise

IntroductionCopepods present the largest and most diverse group of zooplankton and their feeding behavior can affect top-down and bottom-up processes. Thus, how efficient feeding is executed determines the abundance of copepods’ prey and their predators and, with that, carbon transfer and storage in ecosystems. The rise of anthropogenic underwater noise from shipping, oil exploration and exploitation, wind farm construction and operation, and more, is increasingly changing the marine acoustic environment. This acoustic pollution can have detrimental effects on biological life. Studies on this topic increasingly indicate that anthropogenic underwater noise adversely affects primary producers, marine mammals, fish, and invertebrates. However, little data exist on the effects of anthropogenic underwater noise on the feeding behavior of zooplankton.MethodsHere, we investigated the ingestion and clearance rates of the copepodAcartia tonsaon a motile phytoplankton as a function of prey density under ambient aquarium sound conditions and, when exposed to playback, harbor traffic noise.ResultsWe measured significantly decreased ingestion rates and clearance rates ofA. tonsawhen exposed to harbor noise compared to ambient conditions. The negative impact of noise on the ingestion rates was found at all given phytoplankton cell densities between 1k to 10k cells ml−1. Clearance rates were fitted to the Rogers random predator equation which revealed significantly decreased capture rates on phytoplankton under the exposure of harbor noise while handling times remained the same in both sound treatments.DiscussionOur results call for follow-up studies to focus on noise driven community-effects in field experiments to confirm laboratory results and to predict the outcome of a changing world with multiple stressors. Further, the underlying mechanism on how noise affects the feeding behavior of copepods is still unknown. Noise may distract copepods or mask hydromechanical cues of the prey. Noise may also adversely affect copepod physiology or morphology that would lead to changes in the feeding behavior. All potential mechanisms need to be investigated rigorously in future experiments.

Identifying ecological risk and cost–benefit value for supporting habitat restoration: a case study from Sansha Bay, southeast China

BackgroundCoastal wetlands with high biodiversity and productivity provide essential ecosystem services that have a significant positive socio-economic impact. However, coastal reclamation, pollution, and climate change are threatening coastal wetlands. Thus, it is critical to identify priority areas for restoration and improve habitat resilience to adapt to environmental changes. Here, we propose a general analysis framework integrating nature-based solutions (NbS) into habitat restoration to increase coastal resilience to multiple stressors in Sansha Bay, southeast China.ResultsThe total loss of value in ecosystem services due to reclamation in Sansha Bay was US$162.18 million from 2000 to 2015. The coastal habitats were at medium risk of degradation, with some high-risk areas concentrated in the northwest and along the west coasts, which were prioritized for restoration.ConclusionsOur proposed framework, which integrates hard and soft engineering such as mudflat renovation, mangrove afforestation, and an ecological seawall, can aid in the improvement of coastal resilience. The project cost was US$12.71 million and was estimated to generate US$36.75 million in environmental services. We recommend evaluating and monitoring shoreline changes, environmental factors, and marine biological resources using long-term sampling surveys and remote sensing methods. Our findings can serve as a guide for government decision-making in coastal restoration planning and management.

Applying propensity score matching to assess the impact of the pandemic on intimate relationships

AbstractThe COVID‐19 pandemic produced multiple stressors that risk relationship conflict and dissatisfaction. We extended prior studies that yielded inconsistent effects of the pandemic on relationships by using propensity score matching to (1) compare levels of relationship conflict and satisfaction during the pandemic (pandemic group; N = 7268) to similar people immediately before the pandemic (matched control group; N = 7268), and (2) compare pandemic groups facing different types of restrictions, beginning with lockdowns involving household isolation to returning to normal life. Results reveal that relationship conflict increased and relationship satisfaction decreased in response to the pandemic, but these effects were very small and primarily occurred in the initial stages of the pandemic when lockdown involved household isolation. The results add to evidence of resilience in personal and relationship well‐being in 2020, but also indicate the importance of understanding the effects of varying pandemic‐related conditions across the years of the pandemic.

Dietary exposure to nTiO2 reduces byssus performance of mussels under ocean warming

Nano‑titanium dioxide (nTiO2) is a widely used nanomaterial posing potential ecological risk for marine ecosystems that might be enhanced by elevated temperatures such as expected during climate change. nTiO2 may affect benthic filter feeders like mussels through waterborne exposures and via food chain due to the adsorption on/in algae. Mussel byssus are proteinaceous fibers secreted by byssal glands of the mussels for attachment. Byssus production and mechanical properties are sensitive to environmental stressors but the combined effects of warming and nTiO2 on byssus performance of mussels are unclear hampering our understanding of the predation and dislodgement risk of mussels under the multiple stressor scenarios. We explored the effects of a short-term (14-day) single and combined exposures to warming (28 °C) and 100 μg L−1 nTiO2 (including food co-exposure) on the byssus performance of the thick shell mussel Mytilus coruscus. The mechanical strength (measured as the breaking force) of the byssal threads was impaired by warming and nTiO2 (including food co-exposure), but the number and length of the byssal threads were increased. The mRNA expression levels of mussel foot proteins (mfp-3, mfp-5) and pre-collagens (preCOL-D, preCOL-P, preCOL-NG) were up-regulated to varying degrees, with the strongest effects induced by warming. This indicates that the physiological and molecular mechanisms of byssus secretion are plastic. However, downregulation of the mRNA expression of preCOL-D and preCOL-P under the combined warming and nTiO2 exposures indicate the limits of these plasticity mechanisms and suggest that the attachment ability and survival of the mussels may be impaired if the pollution or temperature conditions further deteriorate.

DNA repair enzymes of the Antarctic Dry Valley metagenome.

Microbiota inhabiting the Dry Valleys of Antarctica are subjected to multiple stressors that can damage deoxyribonucleic acid (DNA) such as desiccation, high ultraviolet light (UV) and multiple freeze-thaw cycles. To identify novel or highly-divergent DNA-processing enzymes that may enable effective DNA repair, we have sequenced metagenomes from 30 sample-sites which are part of the most extensive Antarctic biodiversity survey undertaken to date. We then used these to construct wide-ranging sequence similarity networks from protein-coding sequences and identified candidate genes involved in specialized repair processes including unique nucleases as well as a diverse range of adenosine triphosphate (ATP) -dependent DNA ligases implicated in stationary-phase DNA repair processes. In one of the first direct investigations of enzyme function from these unique samples, we have heterologously expressed and assayed a number of these enzymes, providing insight into the mechanisms that may enable resident microbes to survive these threats to their genomic integrity.

Survival, Growth Performance, and Hepatic Antioxidant and Lipid Profiles in Infected Rainbow Trout (Oncorhynchus mykiss) Fed a Diet Supplemented with Dihydroquercetin and Arabinogalactan.

Natural feed supplements have been shown to improve fish viability, health, and growth, and the ability to withstand multiple stressors related to intensive cultivation. We assumed that a dietary mix of plant-origin substances, such as dihydroquercetin, a flavonoid with antioxidative, anti-inflammatory, and antimicrobial properties, and arabinogalactan, a polysaccharide with immunomodulating activity, would promote fish stress resistance and expected it to have a protective effect against infectious diseases. Farmed rainbow trout fish, Oncorhynchus mykiss, received either a standard diet or a diet supplemented with 25 mg/kg of dihydroquercetin and 50 mg/kg of arabinogalactan during a feeding season, from June to November. The fish in the control and experimental groups were sampled twice a month (eight samplings in total) for growth variable estimations and tissue sampling. The hepatic antioxidant status was assessed via the quantification of molecular antioxidants, such as reduced glutathione and alpha-tocopherol rates, as well as the enzyme activity rates of peroxidase, catalase, and glutathione-S-transferase. The lipid and fatty acid compositions of the feed and fish liver were analyzed using thin-layer and high-performance liquid chromatography. The viability, size, and biochemical indices of the fish responded to the growth physiology, environmental variables such as the dissolved oxygen content and water temperature, and sporadic factors. Due to an outbreak of a natural bacterial infection in the fish stock followed by antibiotic treatment, a higher mortality rate was observed in the fish that received a standard diet compared to those fed supplemented feed. In the postinfection period, reduced dietary 18:2n-6 and 18:3n-3 fatty acid assimilation contents were detected in the fish that received the standard diet in contrast to the supplemented diet. By the end of the feeding season, an impaired antioxidant response, including reduced glutathione S-transferase activity and glutathione content, and a shift in the composition of membrane lipids, such as sterols, 18:1n-7 fatty acid, and phospholipids, were also revealed in fish fed the standard diet. Dietary supplementation with plant-origin substances, such as dihydroquercetin and arabinogalactan, decreases lethality in fish stocks, presumably though the stimulation of natural resistance in farmed fish, thereby increasing the economic efficacy during fish production. From the sustainable aquaculture perspective, natural additives also diminish the anthropogenic transformation of aquaculture-bearing water bodies and their ecosystems.

Tipping points and interactive effects of chronic human disturbance and acute heat stress on coral diversity.

Multiple anthropogenic stressors co-occur ubiquitously in natural ecosystems. However, multiple stressor studies often produce conflicting results, potentially because the nature and direction of stressor interactions depends upon the strength of the underlying stressors. Here, we first examine how coral α- and β-diversities vary across sites spanning a gradient of chronic local anthropogenic stress before and after a prolonged marine heatwave. Developing a multiple stressor framework that encompasses non-discrete stressors, we then examine interactions between the continuous and discrete stressors. We provide evidence of additive effects, antagonistic interactions (with heatwave-driven turnover in coral community composition diminishing as the continuous stressor increased), and tipping points (at which the response of coral Hill-richness to stressors changed from additive to near synergistic). We show that community-level responses to multiple stressors can vary, and even change qualitatively, with stressor intensity, underscoring the importance of examining complex, but realistic continuous stressors to understand stressor interactions and their ecological impacts.

Climate change, wildfire, and past forest management challenge conservation of Canada lynx in Washington, USA

AbstractThe synergistic effects of climate change, wildfires, fire suppression, and past forest management are challenging efforts to protect and recover Canada lynx (Lynx canadensis) in the North Cascades of Washington, USA. Canada lynx is a threatened species in the United States and a focal species used to gain insights into the structure and function of boreal forest ecosystems. To understand how multiple stressors are influencing lynx populations and the boreal forest in Washington, we developed a spatially explicit carrying capacity model in HexSim using local data on lynx resource selection and life history. We used this model to estimate changes in carrying capacity and population persistence for 3 time steps: year 2000, which represented limited historical wildfire and aggressive fire suppression; year 2013, after nearly 2,000 km2 of wildfires burned about 17% of lynx habitat; and year 2020, after an additional 2,000 km2 of wildfires burned another 15% of lynx habitat in our study area. Fires altered habitat distribution and landscape capacity to support Canada lynx. There was a 66–73% reduction in lynx carrying capacity in our study area because of large, high‐severity fires that have occurred from 2000–2020, despite aggressive fire suppression. This reduction in carrying capacity was concurrent with decreases in the probability of lynx persistence from year 2000 to year 2020 simulations and was most pronounced for simulations that included no immigration and the largest home range size. The negative synergistic influences of long‐term fire suppression, timber harvest, increased drought, longer wildfire seasons, declining mountain snowpack, and increasingly frequent large fires pose considerable challenges to the conservation and recovery of Canada lynx and the boreal forest ecosystem upon which they depend. We discuss an alternative approach to vegetation and fire management to conserve and restore lynx habitat and populations in Washington.

Accelerated Event Times with Multiple Thresholds

In some systems lowering any one of several stress variables limits the extent to which the others are able to accelerate random event times. That is, each stress variable can cap acceleration of the time to failure distribution, independent of the others. For example, repeated electrostatic shocks will set off a high-explosive detonator within the first few attempts only if voltage and energy are both sufficiently large. This article presents a class of time-to-event models with soft thresholds on multiple stressors. These models are fit to data obtained from an experiment performed at Los Alamos National Laboratory to estimate probabilities that detonators will fire from accidental electrostatic discharge. The models include a limited failure component to account for the possibility that a fraction of units is completely unable to produce the event of interest regardless of how long one waits or how many trials are attempted.

Effects of structural complexity on epifaunal assemblages associated with two intertidal Mediterranean seaweeds

Brown foundation seaweeds are key elements increasing substrate heterogeneity and shaping the biodiversity in rocky coastal ecosystems. They are, however, vulnerable species that are declining due to multiple anthropogenic and climate change stressors, leading to a shift to less structural complex habitats. We investigate the role of structural attributes of two intertidal macroalgae, Ericaria amentacea and Laurencia obtusa, in shaping the abundance and diversity of their associated epifaunal assemblages. For this aim, we measured seaweeds’ biomass, thallus volume and length (used here as proxy of substrate complexity), and explored which seaweeds’ substrate attribute explained better variation of epifaunal assemblages. Results showed that E. amentacea was more complex than L. obtusa and hosted a higher number of epifaunal individuals. However, unlike that expected, the epifaunal assemblage of L. obtusa was more structured with higher Shannon–Wiener diversity and Pielous’ evenness. Our findings indicate that, besides seaweed’s substrate attributes, other mechanisms such as wave action and chemical defense might play a role in structuring epifaunal assemblages. We suggest that a shift from E. amentacea to L. obtusa population could have effect on structure and abundance of associated epifaunal assemblages. Certainly, further investigations are needed to clear up the consequences of these changes.