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This study investigates the marriage protection and selection effects among middle-aged and elderly Japanese. Using 9 years of a longitudinal data set from a nationally representative survey in Japan from 2005 to 2013, we extract 15,242 respondents aged 50–59 years in the baseline year. We utilize positive self-rated health to present subjective health status and lifestyle diseases to present objective health status. Using dynamic panel data approach to control for endogeneity issue, we find that being married does protect respondents’ subjective health, in terms of a higher probability of self-ratings of “very good” or “good” health statuses. Nonetheless, we find that marriage deteriorated their objective health in terms of a higher probability of having lifestyle diseases. Regarding the selection effect, better subjective health is found to select middle-aged and elderly Japanese into marriage, but such influence is fairly modest. Although objective health status also selects respondents into marriage, it positively affects women but adversely affects men. The findings provide a more comprehensive understanding of the relationship between marriage and health, which may have substantial implications for health-related public policies for middle-aged and elderly people in Japan.

Although the relationship between species diversity and biomass productivity has been extensively studied in grasslands, the impact of tree species diversity on forest productivity, as well as the main drivers of this relationship, are still under discussion. It is widely accepted that the magnitude of the relationship between tree diversity and forest stand productivity is context specific and depends on environmental conditions, but the underlying mechanisms of this relationship are still not fully understood. Competition reduction and facilitation have been identified as key mechanisms driving the diversity–productivity relationship. However, contrasting results have been reported with respect to the extent to which competition reduction and facilitation determine the diversity–productivity relationship. They appear to depend on regional climate, soil fertility, functional diversity of the tree species involved, and developmental stage of the forest. The purpose of this review is to summarize current knowledge and to suggest a conceptual framework to explain the various processes leading to higher productivity of species-rich forests compared with average yields of their respective monocultures. This framework provides three pathways for possible development of the diversity–productivity relationship under a changing climate.

1. Forest productivity may be determined not only by biodiversity but also by environmental factors and stand structure attributes. However, the relative importance of these factors in determining productivity is still controversial for subtropical forests. 2. Based on a large dataset from 600 permanent forest inventory plots across subtropical China, we examined the relationship between biodiversity and forest productivity and tested whether stand structural attributes (stand density in terms of trees per ha, age and tree size) and environmental factors (climate and site conditions) had larger effects on productivity. Furthermore, we quantified the relative importance of environmental factors, stand structure and diversity in determining forest productivity. 3. Diversity, together with stand structure and site conditions, regulated the variability in forest productivity. The relationship between diversity and forest productivity did not vary along environmental gradients. Stand density and age were more important modulators of forest productivity than diversity. 4. Synthesis. Diversity had significant and positive effects on productivity in species rich subtropical forests, but the effects of stand density and age were also important. Our work highlights that while biodiversity conservation is often important, the regulation of stand structure can be even more important to maintain high productivity in subtropical forests.

Deciphering the mechanisms that drive variation in biomass production across plant communities of contrasting species composition and diversity is a main challenge of biodiversity–ecosystem functioning research. Niche complementarity and selection effect have been widely investigated to address biodiversity–productivity relationships. However, the overlooking of the specific role played by key species has limited so far our capacity to comprehensively assess the relative importance of other potential drivers of biodiversity effects. Here, we conducted a grassland diversity–productivity experiment to test how four potential facets of biodiversity effects, namely species richness, functional diversity, species identity and the relaxation of intraspecific competition, account for variations in above and root biomass production. We grew six plant species in monoculture, as well as in every combination of two, three and six species. Plant density was kept constant across the richness gradient but we additionally grew each species in half‐density monoculture to estimate the strength of intraspecific competition for each studied species. We characterized eight functional traits, including root traits, related to nutrient and light acquisition and computed both the functional dissimilarity and the community‐weighted mean (CWM) of each trait. We further partitioned above‐ground biodiversity effect into complementarity and selection effects. We observed strong positive biodiversity effects on both above‐ground and root biomass as well as strong positive complementarity effect. These arose largely from the presence of a particular species (Plantago lanceolata) and from CWM trait values more than from a higher functional dissimilarity in plant mixtures. P. lanceolata displayed the highest intraspecific competition, which was strongly relaxed in species mixtures. By contrast, the presence of Sanguisorba minor negatively affected the productivity of plant mixtures, this species suffering more from interspecific than intraspecific competition. This study provides strong evidences that the search for key species is critical to understand the role of species diversity on ecosystem functioning and demonstrates the major role that the balance between intraspecific and interspecific competition plays in biodiversity–ecosystem functioning relationships. Developing more integrative approaches in community and ecosystem ecology can offer opportunities to better understand the role that species diversity plays on ecosystem functioning. A free Plain Language Summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

Aims Resident plants can exert allelopathic effects on introduced exotic plants, and resistance to exotic plant invasions usually increases with diversity and density of the resident plant communities. We hypothesize that allelopathic effects increase with increasing diversity and density of the community, and thereby contribute to the community’s resistance against invaders. Methods To test these hypotheses, we conducted two greenhouse experiments in which we grew five individuals of the exotic invasive plant Solidago canadensis in pots without residents and in artificially assembled resident plant communities either with two levels of diversity (4 or 8 resident plant species) or two levels of density (8 or 32 individuals, representing 8 species). We used activated carbon as the allelopathy-neutralizer treatment in both the diversity and the density experiment. Results In the absence of activated carbon, S. canadensis grew worse in the presence of residents, and when diversity or density of the residents increased. These negative effects, however, largely disappeared in the presence of activated carbon, and at the highest resident density S. canadensis even performed better with than without activated carbon. Conclusions Low invasibility of species-rich and dense plant communities is likely to be at least in part associated with increased allelopathy. Our study provides the first evidence that increasing allelopathy could be a mechanism underlying the diversity and density effects on community invasibility.

This paper develops a model of Bayesian learning from online reviews and investigates the conditions for learning the quality of a product and the speed of learning under different rating systems. A rating system provides information about reviews left by previous customers. observe the ratings of a product and decide whether to purchase and review it. We study learning dynamics under two classes of rating systems: full history, where customers see the full history of reviews, and summary statistics, where the platform reports some summary statistics of past reviews. In both cases, learning dynamics are complicated by a selection effect—the types of users who purchase the good, and thus their overall satisfaction and reviews depend on the information available at the time of purchase. We provide conditions for complete learning and characterize and compare its speed under full history and summary statistics. We also show that providing more information does not always lead to faster learning, but strictly finer rating systems do.

1. Forest ecosystems are critical for the global regulation of carbon (C), a substantial portion of which is stored in above-ground biomass (AGB). While it is well understood that taxonomic and functional composition, stand structure and environmental gradients influence spatial variation in AGB, the relative strengths of these drivers at landscape scales have not been investigated in temperate forests. Furthermore, when biodiversity enhances C storage, it is unclear whether it is through mass-ratio effects (i.e. the dominant trait in communities regulates AGB) or through niche complementarity (i.e. increased AGB due to interspecific resource partitioning). 2. To address these mechanisms, we analysed data from a census of 28,262 adult trees sampled across 900 ha of temperate deciduous forest in southwestern Pennsylvania. We used data on four key plant functional traits to determine if (1) there is a positive relationship between species diversity and AGB and (2) whether this is due to mass-ratio effects or niche complementarity. We also sought to (3) identify the physical stand structural attributes and topographic variables that influence AGB across this landscape. 3. We found AGB was positively related to species richness and negatively related to species evenness, albeit weakly, while functional diversity indices had neutral effects. Above-ground biomass was enhanced in communities dominated by traits related to greater maximum tree height, deeper minimum rooting depths and larger seeds. Most importantly, areas with high AGB were dominated by Acer saccharum and Liriodendron tulipifera. Overall, these results support mass-ratio effects, with little evidence for niche complementarity. 4. Synthesis. Stand structure, topography, and species and functional composition, but not taxonomic or functional diversity, were found to be key drivers of above-ground biomass at landscape scales (<900 ha) in this temperate deciduous forest. Our findings suggest that simultaneously managing for both high diversity and for above-ground carbon storage may prove challenging in some forest systems. Our results further indicate that the impact of tree biodiversity loss on above-ground carbon stocks will depend greatly on the identity of the species that are lost.

Plant biodiversity loss in riparian forests is known to alter key stream ecosystem processes such as leaf litter decomposition. One potential mechanism mediating this biodiversity–decomposition relationship is the increased variability of plant functional traits at higher levels of biodiversity, providing more varied resources for decomposers and thus improving their function. We explored this in a field experiment exposing litter from different assemblages with low or high trait variability (measured through phylogenetic distance, PD) to microbial decomposers and invertebrate detritivores within litterbags in a low-order stream. Litter assemblages generally lost less mass but more phosphorus (P) than expected from monocultures, and nitrogen (N) tended to increase in the absence of detritivores and decrease in their presence, with little effect of PD. In contrast, there were strong influences of mean values and variability of specific traits (mostly N, P and condensed tannins) on decomposition and on net diversity effects. The negative diversity effect on litter mass loss was mainly driven by negative complementarity (that is, physical or chemical interference among species or traits), although there was positive selection (that is, particular species or traits with large effects on decomposition) in high-PD assemblages with detritivores. High-PD assemblages tended to have more invertebrates and attracted more typical litter-consuming detritivores. Our study suggests that decomposition of litter assemblages is mainly driven by concentration and variability of several key litter traits, rather than overall trait heterogeneity (measured through PD). However, differences in invertebrates colonizing high-PD and low-PD assemblages pointed to potential long-term effects of PD on decomposition.

Background The potential benefits of intercropping are manifold and have been repeatedly demonstrated. Intercropping has the potential to create more productive and resilient agroecosystems, by improving land utilisation, yield and yield stability, soil quality, and pest, disease and weed suppression. Despite these potential benefits, significant gaps remain in the understanding of ecological mechanisms that govern the outcomes when crop species are grown together. A major part of plant-plant interactions takes place belowground and these are often overlooked. Scope This review synthesises current evidence for belowground plant-plant interactions of competition, niche differentiation and facilitation, with the aim of identifying root traits that influence the processes contributing to enhanced performance of intercrops compared with monocultures. We identify a suite of potentially complementary root traits for maximising the benefits of intercropping. These traits underpin improved soil exploration, more efficient resource use, and suppression of soil-borne pathogens and pests in intercrops. Conclusion This review brings together understanding of the mechanisms underpinning interactions between intercropped roots, and how root traits and their plasticity can promote positive outcomes. Root trait ‘ideotypes’ for intercropped partners are identified that could be selected for crop improvement. We highlight the importance of examining belowground interactions and consider both spatial and temporal distribution of roots and rhizosphere mechanisms that aid complementarity through niche differentiation and facilitation. Breeding of crop ideotypes with specific beneficial root traits, combined with considerations for optimal spatio-temporal arrangement and ratios of component crops, are essential next steps to promote the adoption of intercropping as a sustainable farming practice.

Previous reviews have often shown a link between digital media ADHD symptom levels. However, longitudinal studies are needed to find stronger evidence of a causal effect as well as to determine the direction of effects. The aim of the present review (PROSPERO CRD42021262695) was therefore to provide a systematic review of studies meeting the following inclusion criteria: (1) include longitudinal data investigating associations between digital media (i.e., gaming and social media) and later ADHD symptoms or vice versa, (2) be published within the past 10 years (i.e., 2011 until June 2021), (3) be published in a peer-reviewed journal in English, and (4) include children or adolescents (age 0–17 years). After a systematic search in the Web of Science and PsycInfo databases, we included 28 studies, all with adequate or high quality. Results showed support for reciprocal associations between digital media and ADHD symptoms, with associations being more consistent for problematic use of digital media than for screen time. Thus, children with ADHD symptoms appear more vulnerable to developing high or problematic use of digital media (i.e., selection effects), and digital media also have effects on later ADHD symptom levels, either because of specific characteristics of digital media or because of indirect effects on, for example, sleep and social relations (i.e., media effects). However, it should be emphasized that further studies investigating potential moderators and mediators are needed if we are to better understand the complex associations between digital media and ADHD symptom levels.