Marine ecosystems are experiencing rapid and pervasive changes in biodiversity and species composition. Understanding the ecosystem consequences of these changes is critical to effectively managing ...these systems. Over the last several years, numerous experimental manipulations of species richness have been performed, yet existing quantitative syntheses have focused on a just a subset of processes measured in experiments and, as such, have not summarized the full data available from marine systems. Here, we present the results of a meta-analysis of 110 marine experiments from 42 studies that manipulated the species richness of organisms across a range of taxa and trophic levels and analysed the consequences for various ecosystem processes (categorised as production, consumption or biogeochemical fluxes).
Our results show that, generally, mixtures of species tend to enhance levels of ecosystem function relative to the average component species in monoculture, but have no effect or a negative effect on functioning relative to the ‘highest-performing' species. These results are largely consistent with those from other syntheses, and extend conclusions to ecological functions that are commonly measured in the marine realm (e.g. nutrient release from sediment bioturbation). For experiments that manipulated three or more levels of richness, we attempted to discern the functional form of the biodiversity–ecosystem functioning relationship. We found that, for response variables related to consumption, a powerfunction best described the relationship, which is also consistent with previous findings. However, we identified a linear relationship between richness and production. Combined, our results suggest that changes in the number of species will, on average, tend to alter the functioning of marine ecosystems. We outline several research frontiers that will allow us to more fully understand how, why, and when diversity may drive the functioning of marine ecosystems.
Synthesis
The oceans host an incredible number and variety of species. However, human activities are driving rapid changes in the marine environment. It is imperative we understand ecosystem consequences of any associated loss of species. We summarized data from 110 experiments that manipulated species diversity and evaluated resulting changes to a range of ecosystem responses. We show that losing species, on average, decreases productivity, growth, and a myriad of other processes related to how marine organisms capture and utilize resources. Finally, we suggest that the loss of species may have stronger consequences for some processes than others.
Evidence is mounting that extinctions are altering key processes important to the productivity and sustainability of Earth's ecosystems. Further species loss will accelerate change in ecosystem ...processes, but it is unclear how these effects compare to the direct effects of other forms of environmental change that are both driving diversity loss and altering ecosystem function. Here we use a suite of meta-analyses of published data to show that the effects of species loss on productivity and decomposition--two processes important in all ecosystems--are of comparable magnitude to the effects of many other global environmental changes. In experiments, intermediate levels of species loss (21-40%) reduced plant production by 5-10%, comparable to previously documented effects of ultraviolet radiation and climate warming. Higher levels of extinction (41-60%) had effects rivalling those of ozone, acidification, elevated CO(2) and nutrient pollution. At intermediate levels, species loss generally had equal or greater effects on decomposition than did elevated CO(2) and nitrogen addition. The identity of species lost also had a large effect on changes in productivity and decomposition, generating a wide range of plausible outcomes for extinction. Despite the need for more studies on interactive effects of diversity loss and environmental changes, our analyses clearly show that the ecosystem consequences of local species loss are as quantitatively significant as the direct effects of several global change stressors that have mobilized major international concern and remediation efforts.
The importance of biodiversity for the integrated functioning of ecosystems remains unclear because most evidence comes from analyses of biodiversity's effect on individual functions. Here we show ...that the effects of biodiversity on ecosystem function become more important as more functions are considered. We present the first systematic investigation of biodiversity's effect on ecosystem multifunctionality across multiple taxa, trophic levels and habitats using a comprehensive database of 94 manipulations of species richness. We show that species-rich communities maintained multiple functions at higher levels than depauperate ones. These effects were stronger for herbivore biodiversity than for plant biodiversity, and were remarkably consistent across aquatic and terrestrial habitats. Despite observed tradeoffs, the overall effect of biodiversity on multifunctionality grew stronger as more functions were considered. These results indicate that prior research has underestimated the importance of biodiversity for ecosystem functioning by focusing on individual functions and taxonomic groups.
Summary
Extensive research shows that more species‐rich assemblages are generally more productive and efficient in resource use than comparable assemblages with fewer species. But the question of how ...diversity simultaneously affects the wide variety of ecological functions that ecosystems perform remains relatively understudied. It presents several analytical and empirical challenges that remain unresolved. In particular, researchers have developed several disparate metrics to quantify multifunctionality, each characterizing different aspects of the concept and each with pros and cons.
We compare four approaches to characterizing multifunctionality and its dependence on biodiversity, quantifying (i) magnitudes of multiple individual functions separately, (ii) the extent to which different species promote different functions, (iii) the average level of a suite of functions and (iv) the number of functions that simultaneously exceeds a critical threshold.
We illustrate each approach using data from the pan‐European BIODEPTH experiment and the R multifunc package developed for this purpose, evaluate the strengths and weaknesses of each approach and implement several methodological improvements.
We conclude that an extension of the fourth approach that systematically explores all possible threshold values provides the most comprehensive description of multifunctionality to date. We outline this method and recommend its use in future research.
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.
The rapidly rising CO₂ level in the atmosphere has led to proposals of climate stabilization by "geoengineering" schemes that would mitigate climate change by intentionally reducing solar radiation ...incident on Earth's surface. In this article we address the impact of these climate stabilization schemes on the global hydrological cycle. By using equilibrium climate simulations, we show that insolation reductions sufficient to offset global-scale temperature increases lead to a decrease in global mean precipitation. This occurs because solar forcing is more effective in driving changes in global mean evaporation than is CO₂ forcing of a similar magnitude. In the model used here, the hydrological sensitivity, defined as the percentage change in global mean precipitation per degree warming, is 2.4% K⁻¹ for solar forcing, but only 1.5% K⁻¹ for CO₂ forcing. Although other models and the climate system itself may differ quantitatively from this result, the conclusion can be understood based on simple considerations of the surface energy budget and thus is likely to be robust. For the same surface temperature change, insolation changes result in relatively larger changes in net radiative fluxes at the surface; these are compensated by larger changes in the sum of latent and sensible heat fluxes. Hence, the hydrological cycle is more sensitive to temperature adjustment by changes in insolation than by changes in greenhouse gases. This implies that an alteration in solar forcing might offset temperature changes or hydrological changes from greenhouse warming, but could not cancel both at once.
Lung cancer screening using low-dose CT (LDCT) was shown to reduce lung cancer mortality by 20% in the National Lung Screening Trial.
The pilot UK Lung Cancer Screening (UKLS) is a randomised ...controlled trial of LDCT screening for lung cancer versus usual care. A population-based questionnaire was used to identify high-risk individuals. CT screen-detected nodules were managed by a pre-specified protocol. Cost effectiveness was modelled with reference to the National Lung Cancer Screening Trial mortality reduction.
247 354 individuals aged 50-75 years were approached; 30.7% expressed an interest, 8729 (11.5%) were eligible and 4055 were randomised, 2028 into the CT arm (1994 underwent a CT). Forty-two participants (2.1%) had confirmed lung cancer, 34 (1.7%) at baseline and 8 (0.4%) at the 12-month scan. 28/42 (66.7%) had stage I disease, 36/42 (85.7%) had stage I or II disease. 35/42 (83.3%) had surgical resection. 536 subjects had nodules greater than 50 mm(3) or 5 mm diameter and 41/536 were found to have lung cancer. One further cancer was detected by follow-up of nodules between 15 and 50 mm(3) at 12 months. The baseline estimate for the incremental cost-effectiveness ratio of once-only CT screening, under the UKLS protocol, was £8466 per quality adjusted life year gained (CI £5542 to £12 569).
The UKLS pilot trial demonstrated that it is possible to detect lung cancer at an early stage and deliver potentially curative treatment in over 80% of cases. Health economic analysis suggests that the intervention would be cost effective-this needs to be confirmed using data on observed lung cancer mortality reduction.
ISRCTN 78513845.
Summary
Background
A high total body naevus count is the highest risk factor for melanoma; the phenotype of red hair colour, freckling and pale skin that burns easily, produced by MC1R R alleles, ...also predisposes to melanoma.
Objectives
To determine whether the known melanoma risk factors of high naevus count and red hair or MC1R R alleles act synergistically to increase melanoma risk.
Methods
The Brisbane Naevus Morphology Study involved 1267 participants from volunteers presenting at a melanoma unit, dermatology outpatient clinic, private dermatology clinics, the Brisbane Longitudinal Twin Study and the QSkin Study. We examined pigmentation characteristics, total body naevus ≥ 5 mm count, and MC1R, ASIP and CDKN2A genotype in participants with and without a personal history of melanoma, living in Queensland, Australia, which is an area of high ultraviolet radiation.
Results
Cases were older than controls (median 57 vs. 33 years). Compared with individuals with dark brown hair and zero to four naevi, individuals with red hair and ≥ 20 naevi had a melanoma odds ratio of 10·0 (95% confidence interval 4·2–24·3). Individuals with MC1R R/R genotype and ≥ 20 naevi (≥ 5 mm diameter) had a melanoma odds ratio of 25·1 (95% confidence interval 8·4–82·7) compared with wild‐type (WT)/WT individuals with zero to four naevi. The highest risk group is Australian men with the MC1R R/R genotype and ≥ 20 moles, who have an absolute risk of melanoma to age 75 years of 23·3%, compared with 0·8% for men with the WT/WT genotype and zero to four naevi.
Conclusions
Patients who live in areas of high ultraviolet radiation, and have many large naevi and the red hair colour phenotype, particularly those with the MC1R R/R genotype, have a high risk of melanoma above the threshold recommended for screening in other cancers. Therefore, they should undergo intensive physician‐led surveillance.
What's already known about this topic?
A high number of acquired melanocytic naevi, the red hair phenotype and MC1R R alleles all independently increase melanoma risk.
Women with atypical naevi have an increasing melanoma risk gradient from darker hair to lighter hair.
Women with many naevi have an increasing melanoma risk gradient from those with no elements of the red hair phenotype, to those with freckles but not red hair, to those with red hair.
What does this study add?
In Queensland, Australia, people with ≥ 20 naevi (≥ 5 mm diameter) and MC1R R/R genotype have a 25‐fold increased melanoma risk, relative to people with zero to four naevi and the MC1R WT/WT genotype.
In Queensland, individuals with ≥ 20 naevi and the MC1R R/R genotype have an absolute melanoma risk to age 75 years of 23·3% for men and 19·3% for women. This effect is independent of CDKN2A genotype.
Further research is required to determine the effect of areas of lower ultraviolet radiation, as this study took place in the Queensland, Australia, which is an area of high ultraviolet radiation.
MC1R R/r genotype is associated with increased total body naevus count but this is not the case for R/R.
What is the translational message?
Patients with many large naevi and the red hair colour phenotype, particularly those with an MC1R R/R genotype, have an unusually high risk of melanoma.
In a high ultraviolet environment, this risk exceeds the threshold recommended for screening in other cancers, and such individuals should undergo intensive, regular, physician‐led surveillance.
Patients with many large naevi but with non‐red colour hair may benefit further from clinical MC1R genotyping.
Plain language summary available online
Linked Comment: Ribero. Br J Dermatol 2019; 181:889–890.
Respond to this article
Summary
Background
Skin phenotype, host genotype and ultraviolet (UV) damage play a role in the development of melanoma.
Objectives
To ascertain whether the level of UV damage at the site of ...melanomas was associated with genetic polymorphisms.
Methods
Deep phenotyping was performed on 1244 individuals; 281 with multiple primary melanomas (MPMs), 304 with single primary melanoma (SPM) and 659 convenience controls. Genotype data was generated using the Illumina CoreExome microarray platform, assaying over 500 000 single‐nucleotide polymorphisms. A subset of variants were combined to assess a polygenic risk score (PRS) for melanoma.
Results
Most MPM cases were diagnosed in patients aged > 40 years, in sites with visible chronic UV damage. Women and those diagnosed at age ≤ 40 years were less likely to have perilesional UV damage. Patients with MPM had higher frequencies of MITF E318K, MC1R R‐alleles and the ASIP risk haplotype. Individuals who had melanoma in a visibly UV‐damaged site were more likely to carry MC1R rs75570604 odds ratio (OR) 2·5, 9q31.2 rs10816595 (OR 1·4) and MTAP rs869329 (OR 1·4). These same alleles were more common in patients with MPM who were diagnosed at age ≤ 40 years. The mean PRS was significantly higher in MPM than in SPM and controls. Naevus count was comparable in early‐onset MPM cases and those diagnosed at age > 40 years.
Conclusions
Our cohort demonstrated higher frequencies of previously reported alleles associated with melanoma. MPM melanomas more commonly occur in UV‐damaged areas, and these individuals are more likely to carry MC1R red hair colour alleles. Awareness of the interplay of genetic vulnerability with UV damage can stratify risk and guide recommendations for melanoma screening.
What's already known about this topic?
Skin phenotype, host genotype and ultraviolet (UV) damage all play a role in melanoma development.
One of the main risk factors is a personal history of melanoma; second and subsequent primary melanomas account for over 20% of all melanomas registered in Queensland.
Multiple loci are associated with melanoma risk, including many low‐penetrance loci, which may have a cumulatively significant risk.
Population‐wide screening programmes for melanoma are not yet economically viable.
What does this study add?
Patients diagnosed with melanoma at age ≤ 40 years were more likely than older patients to have melanomas in non‐UV‐damaged sites.
Patients with multiple melanomas had higher frequencies of MITF E318K, MC1R R‐alleles, and the ASIP extended risk haplotype than patients with single melanoma.
CDKN2A, MC1R and MTAP variants were more frequent in patients who developed melanomas at a younger age, but also in those whose melanomas were all on visibly UV‐damaged sites.
What is the translational message?
Incorporating these genetic findings into the known risk factors of skin phenotype and visible UV damage may allow for a more customized and economically feasible approach to early detection of melanoma, particularly in younger patients.
Plain language summary available online
Although there is growing interest in mental health problems in university students there is limited understanding of the scope of need and determinants to inform intervention efforts.
To ...longitudinally examine the extent and persistence of mental health symptoms and the importance of psychosocial and lifestyle factors for student mental health and academic outcomes.
Undergraduates at a Canadian university were invited to complete electronic surveys at entry and completion of their first year. The baseline survey measured important distal and proximal risk factors and the follow-up assessed mental health and well-being. Surveys were linked to academic grades. Multivariable models of risk factors and mental health and academic outcomes were fit and adjusted for confounders.
In 1530 students surveyed at entry to university 28% and 33% screened positive for clinically significant depressive and anxiety symptoms respectively, which increased to 36% and 39% at the completion of first year. Over the academic year, 14% of students reported suicidal thoughts and 1.6% suicide attempts. Moreover, there was persistence and overlap in these mental health outcomes. Modifiable psychosocial and lifestyle factors at entry were associated with positive screens for mental health outcomes at completion of first year, while anxiety and depressive symptoms were associated with lower grades and university well-being.
Clinically significant mental health symptoms are common and persistent among first-year university students and have a negative impact on academic performance and well-being. A comprehensive mental health strategy that includes a whole university approach to prevention and targeted early-intervention measures and associated research is justified.
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