Ecological stressors (i.e., environmental factors outside their normal range of variation) can mediate each other through their interactions, leading to unexpected combined effects on communities. ...Determining whether the net effect of stressors is ecologically surprising requires comparing their cumulative impact to a null model that represents the linear combination of their individual effects (i.e., an additive expectation). However, we show that standard additive and multiplicative null models that base their predictions on the effects of single stressors on community properties (e.g., species richness or biomass) do not provide this linear expectation, leading to incorrect interpretations of antagonistic and synergistic responses by communities. We present an alternative, the compositional null model, which instead bases its predictions on the effects of stressors on individual species, and then aggregates them to the community level. Simulations demonstrate the improved ability of the compositional null model to accurately provide a linear expectation of the net effect of stressors. We simulate the response of communities to paired stressors that affect species in a purely additive fashion and compare the relative abilities of the compositional null model and two standard community property null models (additive and multiplicative) to predict these linear changes in species richness and community biomass across different combinations (both positive, negative, or opposite) and intensities of stressors. The compositional model predicts the linear effects of multiple stressors under almost all scenarios, allowing for proper classification of net effects, whereas the standard null models do not. Our findings suggest that current estimates of the prevalence of ecological surprises on communities based on community property null models are unreliable, and should be improved by integrating the responses of individual species to the community level as does our compositional null model.
Our findings highlight how current additive and multiplicative null models, which predict combined effects of stressors based on single stressor effects on community properties, can erroneously generate nonlinear predictions, leading to incorrect interpretations of multiple stressor effects on communities. Here, we present a new compositional null model that predicts combined effects of stressors using single stressor effects on populations and then scales them up to community‐level properties. Using a simulation model, we show that the compositional null model provides more accurate linear predictions of stressor effects on community properties (e.g., species richness) across different patterns of species co‐tolerance (i.e., positive, random, negative), and different combinations of positive and negative stressors across a range of stressor intensities.
Bottom current activity has been responsible for the formation of a multitude of erosional and depositional features recorded in chalk. Advanced knowledge on the mobility and transport of unlithified ...calcareous nannofossil ooze by bottom currents is increasingly important not only for understanding the deposition of ancient chalk, but also for modelling the behaviour of modern pelagic carbonate sediments. Whereas the erosional behaviour of very pure calcareous nannofossil ooze has recently been investigated, the effect of organic matter and clay minerals on the erosional behaviour of calcareous nannofossil ooze is as yet unquantified. The results of the present study are based on laboratory flume studies utilizing chalk ooze with varying concentrations of smectite clay (1 to 30 wt.%), two types of organic matter and bed porosity. Phytoplankton (Pavlova lutheri) was used as a proxy for particulate marine organic matter, and xanthan gum as a proxy for extracellular polymeric substances. The results show a significant decrease in nannofossil ooze mobility with increasing content of clay or marine organic matter. Organic matter is found to reduce erodibility at much lower concentrations than clay minerals at porosities equivalent to those of the seafloor. At lower porosities, corresponding to some depth below the seafloor, organic matter and clay minerals are less effective in bed stabilization. This suggests that clay minerals and especially organic matter will affect the likelihood of initiation of severe erosion on the seafloor, whereas their inhibiting effect will decrease as erosion scours progressively deeper into the sediment column. The effect of extracellular polymeric substances is more complex than marine organic matter, probably due to detachment of large aggregates from the bed and resulting increase in bed roughness. The choice of organic matter in sedimentological experiments may lead to significant differences in sediment behaviour and should therefore involve careful consideration.
Species diversity affects the functioning of ecosystems, including the efficiency by which communities capture limited resources, produce biomass, recycle and retain biologically essential nutrients. ...These ecological functions ultimately support the ecosystem services upon which humanity depends. Despite hundreds of experimental tests of the effect of biodiversity on ecosystem function (BEF), it remains unclear whether diversity effects are sufficiently general that we can use a single relationship to quantitatively predict how changes in species richness alter an ecosystem function across trophic levels, ecosystems and ecological conditions. Our objective here is to determine whether a general relationship exists between biodiversity and standing biomass. We used hierarchical mixed effects models, based on a power function between species richness and biomass production (Y = a × Sb), and a database of 374 published experiments to estimate the BEF relationship (the change in biomass with the addition of species), and its associated uncertainty, in the context of environmental factors. We found that the mean relationship (b = 0.26, 95% CI: 0.16, 0.37) characterized the vast majority of observations, was robust to differences in experimental design, and was independent of the range of species richness levels considered. However, the richness–biomass relationship varied by trophic level and among ecosystems; in aquatic systems b was nearly twice as large for consumers (herbivores and detritivores) compared to primary producers; in terrestrial ecosystems, b for detritivores was negative but depended on few studies. We estimated changes in biomass expected for a range of changes in species richness, highlighting that species loss has greater implications than species gains, skewing a distribution of biomass change relative to observed species richness change. When biomass provides a good proxy for processes that underpin ecosystem services, this relationship could be used as a step in modeling the production of ecosystem services and their dependence on biodiversity.
Eelgrass (
Zostera marina
) meadows are important fish habitats in temperate coastal areas. Understanding the relationships between seascape patterns—the spatial and temporal variability of ...biological and physiochemical drivers—and fish diversity in eelgrass meadows is crucial to conserving and managing these important habitats. The main objective of this study was to determine the environmental variables that influence the diversity of fish in eelgrass meadows in British Columbia, and whether a rich mosaic of edge habitats is positively associated with species richness and diversity, owing to the increased niche dimensionality and foraging opportunities provided by heterogeneous adjacent habitats. Using a spatiotemporal multispecies model based on long-term eelgrass fish diversity monitoring program data (2004–2020), we found that seascape variables, particularly those derived from unmanned aerial vehicles (meadow area, edge habitat heterogeneity), explained the most variation in species occurrence and abundance. We also found a positive effect of edge habitat heterogeneity on species richness in small and medium-sized meadows, with higher species richness and diversity in small and medium-sized meadows with high edge habitat heterogeneity. The relationship between edge habitat heterogeneity and species richness and diversity in large meadows was less clear. We also found that species richness has declined through time while diversity has been variable through time, remaining relatively stable in one region and generally decreasing in the other region. This analysis provides key insights into how seascape variables influence the distribution of species and the diversity of fish assemblages in nearshore eelgrass habitats in British Columbia.
Prone position ventilation (PPV) is resource-intensive, yet the optimal strategy for PPV in intubated patients with COVID-19 is unclear.
Does a prolonged (24 or more h) PPV strategy improve mortality ...in intubated COVID-19 patients compared with intermittent (∼16 h with daily supination) PPV?
Multicenter, retrospective cohort study of consecutively admitted intubated COVID-19 patients treated with PPV between March 11 and May 31, 2020. The primary outcome was 30-day all-cause mortality. Secondary outcomes included 90-day all-cause mortality and prone-related complications. Inverse probability treatment weights (IPTW) were used to control for potential treatment selection bias.
Of the COVID-19 patients who received PPV, 157 underwent prolonged and 110 underwent intermittent PPV. Patients undergoing prolonged PPV had reduced 30-day (adjusted hazard ratio aHR, 0.475; 95% CI, 0.336-0.670; P < .001) and 90-day (aHR, 0.638; 95% CI, 0.461-0.883; P = .006) mortality compared with intermittent PPV. In patients with Pao2/Fio2 ≤ 150 at the time of pronation, prolonged PPV was associated with reduced 30-day (aHR, 0.357; 95% CI, 0.213-0.597; P < .001) and 90-day mortality (aHR, 0.562; 95% CI, 0.357-0.884; P = .008). Patients treated with prolonged PPV underwent fewer pronation and supination events (median, 1; 95% CI, 1-2 vs 3; 95% CI, 1-4; P < .001). PPV strategy was not associated with overall PPV-related complications, although patients receiving prolonged PPV had increased rates of facial edema and lower rates of peri-proning hypotension.
Among intubated COVID-19 patients who received PPV, prolonged PPV was associated with reduced mortality. Prolonged PPV was associated with fewer pronation and supination events and a small increase in rates of facial edema. These findings suggest that prolonged PPV is a safe, effective strategy for mortality reduction in intubated COVID-19 patients.
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Humans have elevated global extinction rates and thus lowered global scale species richness. However, there is no a priori reason to expect that losses of global species richness should always, or ...even often, trickle down to losses of species richness at regional and local scales, even though this relationship is often assumed. Here, we show that scale can modulate our estimates of species richness change through time in the face of anthropogenic pressures, but not in a unidirectional way. Instead, the magnitude of species richness change through time can increase, decrease, reverse, or be unimodal across spatial scales. Using several case studies, we show different forms of scale‐dependent richness change through time in the face of anthropogenic pressures. For example, Central American corals show a homogenization pattern, where small scale richness is largely unchanged through time, while larger scale richness change is highly negative. Alternatively, birds in North America showed a differentiation effect, where species richness was again largely unchanged through time at small scales, but was more positive at larger scales. Finally, we collated data from a heterogeneous set of studies of different taxa measured through time from sites ranging from small plots to entire continents, and found highly variable patterns that nevertheless imply complex scale‐dependence in several taxa. In summary, understanding how biodiversity is changing in the Anthropocene requires an explicit recognition of the influence of spatial scale, and we conclude with some recommendations for how to better incorporate scale into our estimates of change.
Challenges in evaluating surgical innovation Ergina, Patrick L, Dr; Cook, Jonathan A, PhD; Blazeby, Jane M, Prof ...
The Lancet,
09/2009, Letnik:
374, Številka:
9695
Journal Article
Recenzirano
Odprti dostop
Summary Research on surgical interventions is associated with several methodological and practical challenges of which few, if any, apply only to surgery. However, surgical evaluation is especially ...demanding because many of these challenges coincide. In this report, the second of three on surgical innovation and evaluation, we discuss obstacles related to the study design of randomised controlled trials and non-randomised studies assessing surgical interventions. We also describe the issues related to the nature of surgical procedures—for example, their complexity, surgeon-related factors, and the range of outcomes. Although difficult, surgical evaluation is achievable and necessary. Solutions tailored to surgical research and a framework for generating evidence on which to base surgical practice are essential.
In the coming decades, warming and deoxygenation of marine waters are anticipated to result in shifts in the distribution and abundance of fishes, with consequences for the diversity and composition ...of fish communities. Here, we combine fisheries-independent trawl survey data spanning the west coast of the USA and Canada with high-resolution regional ocean models to make projections of how 34 groundfish species will be impacted by changes in temperature and oxygen in British Columbia (BC) and Washington. In this region, species that are projected to decrease in occurrence are roughly balanced by those that are projected to increase, resulting in considerable compositional turnover. Many, but not all, species are projected to shift to deeper depths as conditions warm, but low oxygen will limit how deep they can go. Thus, biodiversity will likely decrease in the shallowest waters (less than 100 m), where warming will be greatest, increase at mid-depths (100-600 m) as shallow species shift deeper, and decrease at depths where oxygen is limited (greater than 600 m). These results highlight the critical importance of accounting for the joint role of temperature, oxygen and depth when projecting the impacts of climate change on marine biodiversity. This article is part of the theme issue 'Detecting and attributing the causes of biodiversity change: needs, gaps and solutions'.
A marine protected area (MPA) network of multiple reserves can protect biodiversity across space, but to be effective, network configuration should support dispersal among MPAs as well as spillover ...to unprotected habitats. The ability of MPAs to function as an interacting network of populations connected by dispersal, however, is difficult to estimate at broad spatial scales, and therefore, connectivity is often not integrated in MPA design. Here, we simulate passive larval dispersal using a biophysical model to estimate potential transboundary network connectivity of MPAs in western Canada and United States. Drift time was varied to represent generic functional groups of nearshore species with planktonic larvae and sedentary adult stages. We found that MPAs potentially act as an interacting network and meet connectivity design criteria for nearshore invertebrate species, many MPAs (65%–90%) possibly exchange individuals, and a third of larvae from MPAs (25%–32%) source areas of the unprotected coast. This analysis provides a first approximation of multispecies connectivity to inform ongoing transboundary MPA design, and it can be used as a foundation for future model development.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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