Community-level Effects Research Articles

Vulnerability to HIV infection among the Borana pastoral community of Southern Ethiopia: a persisting challenge.

BackgroundVulnerability to HIV infection is a major concern in an effort to control further infections. What drives vulnerability among pastoral settings of Ethiopia is not well documented.ObjectivesThis study aims to identify drivers of vulnerability to HIV infection among the Borana pastoral community of Ethiopia.MethodsData were collected during 2008–2009 as part of a PhD work and subsequently in 2014 and 2016, during a follow-up visit to Borana. Data on perceived threats of HIV, facilitators of vulnerability, coping mechanisms and perceived consequences were collected by trained research assistants using topic guides developed for this purpose. In-depth and key informant interviews and Focus Group Discussions (FGDs) with selected married men and women, opinion leaders, and HIV focal persons of public sectors and Non Governmental Organizations in Teltele, Arero, Yabelo and Moyale were carried out. Sample transcripts were checked for consistency and completeness before data collection was completed. Two qualitative researchers read transcripts and suggested themes and subthemes in reference to the objective of the study. Transcripts were imported to MAXQDA software. Thematic analysis was applied to reduce data into defined themes. Findings were interpreted following the objective of the study.FindingsThe results show that HIV is a major threat in Borana with individual and community level consequences. Concurrent extramarital sexual practices, men’s role in the selling of livestock and consequent encounters with “other” women facilitate vulnerability to HIV. Lack of information about HIV, availability and use of condoms, and failure to use local resources for HIV prevention were key limitations to coping with the problem. After nearly 40 years of HIV intervention in Ethiopia, coping mechanisms are not exploited in Borana.ConclusionVulnerability to HIV among the Borana pastoral community is facilitated by multiple factors that work in tandem, thus calling for interventions that address the different factors at the same time.

Flatworm mucus as the base of a food web

BackgroundBy altering their habitats, engineering species can improve their own fitness. However, the effect of this strategy on the fitness of coexisting species or on the structure of the respective food web is poorly understood. In this study, bacteria and bacterivorous nematodes with short (Caenorhabditis elegans) and long (Plectus acuminatus) life cycles were exposed to the mucus secreted by the freshwater flatworm Polycelis tenuis. The growth, reproduction, and feeding preferences of the nematodes in the presence/absence of the mucus were then determined. In addition, confocal laser scanning microscopy (CLSM) was used to examine the structural footprint of the mucus and the mucus colonization dynamics of bacteria and protozoans.ResultsMucus exposure resulted in a greater reproductive output in P. acuminatus than in C. elegans. In a cafeteria experiment, both nematode species were attracted by bacteria-rich patches and were not deterred by mucus. CLSM showed that the flatworms spread a layer of polysaccharide-rich mucus ca. 15 µm thick from their tails. Subsequent colonization of the mucus by bacteria and protozoans resulted in an architecture that progressively resembled a complex biofilm. The presence of protozoans reduced nematode reproduction, presumably due to competition for their bacterial food supply.ConclusionAnimal secretions such as mucus may have broader, community-level consequences and contribute to fueling microbial food webs.

Community-level effects of spatial management in the California drift gillnet Fishery

Fisheries management interventions that protect certain species by redistributing fishing effort may generate unintended consequences for other species. In the California drift gillnet fishery for swordfish and sharks, a large spatial closure was implemented in 2001 to protect endangered leatherback turtles, which limited fishing effort to the Southern California Bight. Leatherback bycatch has since decreased, but the effects on other species have not been comprehensively examined. Here, we explore the effects of this closure on the community catch composition in the fishery and find that other protected species may have benefited, while catch per unit effort of major target species increased or was not significantly affected over the long term. However, a time-series analysis reveals that changes in catch trends across twenty species began at least five years before the closure was implemented, suggesting that previous regulatory measures or other drivers may also contribute to these trends. These results highlight the importance of comprehensive approaches that include the historical context when evaluating management outcomes.

Detection and removal efficiency of invasive lionfish in the northern Gulf of Mexico

Mitigating the negative impacts of invasive lionfish (Pterois volitans/miles complex) is a top priority for marine reef fisheries management, with human removals considered the most viable approach to population control. Control efforts via diver spearfishing removals have annually removed tens of thousands of lionfish throughout their invasive range, but the effectiveness of removal efforts to remove 100% or achieve target lionfish densities in a given reef system has not been fully evaluated. Accounting for detection and removal efficacy is necessary for developing and evaluating lionfish management targets, as population- and community-level effects of lionfish removals may be diminished by undetected lionfish remaining in the system. This study quantified lionfish detection, catchability, and removal efficiency to evaluate the effectiveness of lionfish surveys and removal efforts on northern Gulf of Mexico (nGOM) artificial and natural reefs. Detection was assessed during crepuscular and midday time periods via diver and remotely operated vehicle (ROV) video surveys, with covariates for time of day and survey methodology assessed using generalized linear mixed models. Catchability and removal efficiency were estimated via depletion models based on serial removals via spearfishing on 6 artificial reefs and 9 natural reefs. A priori, we had expected lionfish detection to be higher during crepuscular periods given lionfish in the Caribbean and in their native range have been shown to forage more actively away from reefs then. However, we found lionfish detection was not significantly different between midday and crepuscular periods. Survey methodology affected detection, with 24% fewer lionfish being detected via ROV surveys versus diver surveys at artificial reefs and 72% fewer lionfish detected via ROV surveys at natural reefs. Therefore, density estimates on nGOM natural reefs, which constitute of >99% of the region’s habitat, may be higher than previously reported and problematic for lionfish management. Mean catchability for spearfishing lionfish was 0.88 on artificial reefs and 0.69 on natural reefs standardized for area. Mean removal efficiency for the first removal event was 87% on artificial reefs and 67% on natural reefs, higher than removal efficiency computed for Caribbean reefs (47%). Incomplete detection and <100% removal efficiency, in concert with density-dependent processes, may explain recent findings that sustained lionfish removal efforts had no discernible positive impacts on native reef fish communities.

A Common Yardstick to Measure the Effects of Different Extreme Climatic Events on Soil Arthropod Community Composition Using Time-Series Data

Extreme climatic events can have profound effects on ecosystems. Climate change is causing an increase in the frequency and intensity of extreme events, which raises the probability that natural ecosystems will be exposed to subsequent or simultaneous extreme events. Exposure to multiple extreme events may involve very different abiotic stressors, which makes it hard to compare their consequences for more than a single or a few species, limiting our knowledge of community level effects. Here, we propose a novel approach to assess how different abiotic stressors influenced soil arthropod communities in a coastal ecosystem, using a species abundance time series of more than two years. We first correlated shifts in community composition with the climatic conditions preceding the sampling dates. Temperature was found to be the most important factor influencing community composition in both locations. Based on local meteorological data, we then defined five types of extreme events which occurred during our monitoring period: heat, cold, drought, heavy precipitation and high sea water levels. To compare the effect of different types of extreme climatic events on community composition, we calculated the multidimensional Hellinger distance between two subsequent sampling dates, which is a measure for the compositional dissimilarity between communities. Extreme events were expected to result in a larger change in community composition between sampling dates and thus a larger Hellinger distance. However, no significant difference in Hellinger distance was found for intervals with or without extreme events in three out of the four location-vegetation combinations. In the saline location with an open vegetation type we found that Hellinger’s distance was reduced when extreme events had occurred, which is discussed in the light of the buffering potential of different vegetation types. Our study illustrates the novel use of an established method from the community ecological toolbox to facilitate direct comparison of different types of extreme climatic events on community composition. We highly encourage other ecologists with long-term monitoring datasets to perform similar analyses and test the general applicability of this method.

Multilevel analysis of factors associated with assistance during delivery in rural Nigeria: implications for reducing rural-urban inequity in skilled care at delivery

BackgroundStudies have observed rural-urban inequity in the use of skilled delivery in Nigeria. A number of studies have explicitly examined associated factors of assistance during delivery in rural areas. However, the studies so far conducted in rural Nigeria have investigated mainly individual-level characteristics with near exclusion of community-level characteristics. Also, most of the studies that have investigated community-level influence on use of maternal healthcare services in Nigeria did not isolate rural areas for specific research attention. The objective of this study was to investigate the individual-level and community-level characteristics associated with assistance during delivery in rural Nigeria.MethodsThe study analysed women data of 2013 Nigeria Demographic and Health Survey. A weighted sample size of 12,665 rural women was analysed. The outcome variable was assistance during delivery, dichotomised into ‘skilled assistance’ and ‘unskilled assistance’. The explanatory variables are selected individual-level characteristics (maternal education, parity, age at first birth, religion, healthcare decision, employment status, access to mass media, and means of transportation); and selected community-level characteristics (community literacy level, community childcare burden, proportion of women employed outside agriculture, proportion of women who perceived distance to facility as a big problem, community poverty level, and geographical region). The mixed-effects logistic regression was applied.ResultsDuring the most recent deliveries, 23.0% of rural women utilised skilled assistance compared with 77.0% who utilised unskilled assistance. Maternal education, parity, religion, healthcare decision, access to mass media, and means of transportation were the individual-level characteristics that revealed significant effects on the likelihood of utilising skilled assistance during delivery, while community literacy level, community poverty level, community perception of distance to health facility, and geographic region were the community-level characteristics that revealed significant effects on the odds of using skilled assistance during delivery. Results of Intra-Class Correlation (ICC) supported significant community-level effects on the likelihood of using skilled assistance during delivery.ConclusionsAssistance during delivery is influenced by individual-level and community-level characteristics. Health policies and programmes seeking to reduce rural-urban inequity in skilled delivery should endeavour to identify and address important factors at both the individual and community levels of the social environment.

Sexual dimorphism in a top predator (Notophthalmus viridescens) drives aquatic prey community assembly.

Intraspecific variation can have important consequences for the structure and function of ecological communities, and serves to link community ecology to evolutionary processes. Differences between the sexes are an overwhelmingly common form of intraspecific variation, but its community-level consequences have never been experimentally investigated. Here, we manipulate the sex ratio of a sexually dimorphic predacious newt in aquatic mesocosms, then track their impact on prey communities. Female and male newts preferentially forage in the benthic and pelagic zones, respectively, causing corresponding reductions in prey abundances in those habitats. Sex ratio differences also explained a large proportion (33%) of differences in the composition of entire pond communities. Ultimately, we demonstrate the impact of known patterns of sexual dimorphism in a predator on its prey, uncovering overlooked links between evolutionary adaptation and the structure of contemporary communities. Given the extreme prevalence of sexual dimorphism, we argue that the independent evolution of the sexes will often have important consequences for ecological communities.

The effect of group involvement on post-disaster mental health: A longitudinal multilevel analysis

Involvement in voluntary associations is a key form of social capital and plays an especially important role following disaster as a venue for coordination and decision-making for the wider community. Yet, relatively little attention has been paid to how group involvement affects mental health, at either the individual or community level. The aim of this study was to assess the impact of involvement in voluntary associations on mental health among residents of bushfire-affected communities. A longitudinal sample of 642 individuals affected by the 2009 Victorian bushfires in south-eastern Australia were surveyed in 2012 and 2014 (3- and 5-years post-disaster). A further subsample (n = 552) of residents residing continuously within 22 bushfire-affected communities were examined for community-level effects using multilevel regression methods. After adjusting for demographics, disaster exposure, and network variables, group involvement at time 1 bore a curvilinear relationship with PTSD at both time points: moderate involvement was most beneficial, with no participation, or high amounts, yielding poorer outcomes. High amounts of group involvement was likewise linked to a greater risk of major depression. Furthermore, communities with higher median levels of group involvement reported lower levels of PTSD symptoms and major depression two years later. With respect to group involvement, more is not always better. For individuals, moderation – if possible – is key. Meanwhile, community-level health benefits come when most people participate to some extent, suggesting that the distribution of involvement across the community is important.

Demographic and epidemic transitions in peri-urban areas of Colombia: a multilevel study of malaria in the Amazonian city of San José del Guaviare

Migration to urban centres is among the most important forces in contemporary urban studies. In this paper, we study how the demography and epidemic profile of a community are altered when they transition from living in nomadic conditions in a forested environment to a peri-urban settlement in a city of the Amazon basin. We analyse demographic and epidemic data with a multilevel model to understand individual and community-level effects in terms of the risk of malarial infection. We show that malaria becomes endemic when the population settles in the peri-urban area of the city. We also show that the reproductive rate of women in the group increases as they become sedentary, and that while individual fertility rates have no effect on risk of contracting malaria, population-level fertility rates are associated with malaria endemicity.

Effects of clothianidin-treated seed on the arthropod community in a mid-Atlantic no-till corn agroecosystem.

Nearly all corn seed in the US is coated with neonicotinoid insecticides to protect against soil and foliar arthropod pests. Exposure in the soil and the systemic activity in the plant can pose non-target risks. We assessed the community-level effects of clothianidin-treated seed on the diversity and abundance of arthropod communities in a no-till corn agroecosystem over a single growing season. Epigeal and foliage-dwelling communities were disturbed by the clothianidin seed treatment, with significant negative and positive changes in taxa abundances. Clothianidin reduced the abundance of minute pirate bugs by 66.2%, lady beetles by 44.7%, ants by 43.4%, ground beetle adults and larvae by 31.7%, and rove beetles by 44.1% during the early corn growth stages. Herbivores, particularly thrips, were more negatively affected by clothianidin than other trophic groups. In contrast, some groups, such as collembolans and leafhoppers, exhibited significantly higher abundances in the seed treated plots. Clothianidin primarily influenced arthropod communities during the 4 weeks following planting, with disruptions to major natural enemy taxa, but communities showed trends toward recovery at the later corn stages. While the insecticide suppressed multiple herbivores, none were economically damaging to corn; thus, the pest suppression benefits of clothianidin observed in this study did not justify the non-target impacts. © 2018 Society of Chemical Industry.

Individual, Household and Community-Level Effects of Infant and Child Mortality in Nigeria: A Logistic Regression Approach

Research has shown that knowledge about the determinants of childhood mortality at the individual level is not enough to address the problem because the characteristics of the environment where a child is born tend to alter individual level characteristics and thereby affect child survival. The study used data from the 2013 Nigeria Demographic and Health Survey (NDHS). The fact that a child was either dead or alive was assumed to be accurately recorded. Hence, logistic regression model was used to model whether a child is dead or alive with respect to the selected predictor variables. Results from the study reveal that infant and child mortality in Nigeria is determined more by individual household than by community, and that geographical variations also exist. This study has identified significant risk factors that will help policy makers to formulate policies that will improve childhood survival.

The effects of a mixture of copper, nickel, and zinc on the structure and function of a freshwater planktonic community.

It is generally assumed that as long as the majority of species experiences no direct adverse effects attributable to a single substance (i.e., potentially affected fraction [PAF] <5%), no significant structural or functional effects at the community level are expected to occur. Whether this assumption holds for mixed metal contamination is not known. In the present study, we tested this by performing a microcosm experiment in which a naturally occurring freshwater planktonic community was exposed to a copper-nickel-zinc (Cu-Ni-Zn) mixture for 8 wk and various structural and functional community-level traits were assessed. In the low mixture concentration treatments (i.e., Ni-Zn mixtures, because there was no difference in Cu concentrations in these treatments with the control), community-level effects were relatively simple, only involving phytoplankton species groups. In the high mixture concentration treatments (Cu-Ni-Zn mixtures), community-level effects were more complex, involving several phytoplankton and zooplankton species groups. Multisubstance PAF (msPAF) values for all mixture treatments were calculated by applying the concentration addition model to bioavailability-normalized single-metal species sensitivity distributions (SSDs). Consistent effects on the structural traits community composition, abundance of zooplankton species groups, species diversity, and species richness and on the functional trait dissolved organic carbon (DOC) concentration (as a proxy for the microbial loop and pelagic food web interactions) were only observed at msPAF values >0.05 (i.e., in the Cu-Ni-Zn mixture). However, consistent effects on the abundance of various phytoplankton species groups (structural traits) and on 2 measures of community respiration, overnight Δ dissolved oxygen (ΔDO) and ΔpH (functional traits), were already observed at msPAF values of ≤0.05 (i.e., in the Ni-Zn mixture). This indicates that the threshold msPAF value of 0.05 was not protective against metal mixture exposure for all community-level structural and functional endpoints in the present study. A possible explanation for this result is the mismatch between the species in the SSD and those in our microcosm community. Indeed, our data suggest that the presence of one single dominant and very Zn- and/or Ni-sensitive species in the investigated community (i.e., a cyanobacteria of the genus Oscillatoria), which is not represented in the SSD of these metals, was probably the driver of all observed effects at or below an msPAF of 0.05. Overall, the present results show that SSDs are not necessarily a good predictor of community-level effects for all types of communities and that the presence of dominant sensitive species may result in significant, consistent effects on certain structural and functional community-level endpoints at msPAF values ≤0.05, which is generally considered protective in many regulatory frameworks. Environ Toxicol Chem 2018;37:2380-2400. © 2018 SETAC.

Education is the antidote: Individual- and community-level effects of maternal education on child immunizations in Nigeria

Nigeria is an interesting case study because it outperforms other lower middle-income countries in economic development, yet ranks among the lowest in the world in immunization coverage rates. Combining multi-level modeling with spatial data techniques, this study investigates the individual- and community-level factors that influence the likelihood that a child is fully immunized, underscoring the importance of maternal education for improving child health. Drawing on data from the Demographic and Health Surveys and the Global Administrative Areas database, the analysis pools data on children aged 12–24 months across 455 communities. The spatial analysis reveals substantial geographic gaps in immunization coverage across Nigeria, demonstrating that not everyone benefits from the purported benefits of economic growth. Results from the multi-level models indicate that women's education has a robust association with vaccinations at the individual level and at the community level, even net of a variety of other household and community characteristics. The education level of a child's own mother influences the likelihood of being immunized, but above and beyond that, living in a community in which many women are educated also influences that likelihood. This suggests that education has a protective effect on child health not only because more individual women are going to school, but also because everyone benefits from the education and empowerment of women in the community. As broad societal transformations take place, education may shape women's capacity to take advantage of better access to power and resources, resulting in a dispersion effect of expanded women's education on health.

Ontogeny and Consistent Individual Differences Mediate Trophic Interactions.

Ecologists use species traits to predict responses to environmental change and, ultimately, to understand the composition of biological communities. However, this ignores known and substantial intraspecific variation that can have important consequences for species interactions and community composition. This within-species variation results from two distinct sources: ontogeny and consistent individual differences. Ontogeny and consistent differences interact to produce phenotypes, but the community-level consequences of this interaction have not been studied. Using larval dragonfly communities, I investigate patterns of intraguild predation by manipulating (1) consistent individual differences in activity rate and (2) the ontogeny of the focal and interacting species. I show that activity rate is a consistent individual trait but that the effect of activity rate on intraguild predation depends on the functional role of an organism in the community (predator or prey). An organism's functional role itself varies across ontogeny of both the focal and interacting individuals. I suggest that ontogeny and consistent individual differences interact to produce intraspecific variation, with consequences for species interactions, communities, and eco-evolutionary dynamics.

Assessing the gang-level and community-level effects of the Philadelphia Focused Deterrence strategy

Violence reduction initiatives based on focused deterrence strategies have gained attention in recent years due to their empirical support. The evaluations have generally assessed the impact of this intervention on trends in gun violence at the aggregate level, but not at the gang level. The current study evaluates both the community- and gang-level impacts of the Philadelphia Focused Deterrence strategy. The intervention was assessed using a quasi-experimental design that measured trends in shootings over a twelve-year period, including two years after the implementation of the initiative. Propensity scoring and matching techniques were used to match neighborhoods and gangs, and a number of regression models were run to assess impact. Although a statistically significant reduction in total shootings across the treated neighborhoods was observed when compared to matched neighborhoods, the findings at the gang level were mixed. Models comparing shootings around gang territories showed significant reductions when compared to shootings around the territories of matched gangs, but pre-post-only models of treated gangs using the more rigorous measure of gang-involved shootings did not show evidence of impact. The findings suggest that focused deterrence may provide a mechanism for general deterrence among a broad pool of potential offenders. Specifically, violent gangs, even when targeted, may not be affected similarly for a variety of reasons. To better understand who is receiving the deterrence message and responding to it, future evaluations of focused deterrence strategies, when assessing impact, should include measures of the dosage of the message and other components relative to individuals and their groups.

Oyster aquaculture impacts Zostera marina epibiont community composition in Akkeshi-ko estuary, Japan.

Coastal fisheries are in decline worldwide, and aquaculture has become an increasingly popular way to meet seafood demand. While finfish aquaculture can have substantial adverse effects on coastal ecosystems due mostly to necessary feed inputs, bivalves graze on natural phytoplankton and are often considered for their positive ecosystem services. We conducted two independent studies to investigate the effects of long-line Crassostrea gigas oyster aquaculture on Zostera marina seagrass beds and associated epibiont communities in Akkeshi-ko estuary, Japan. Results from both studies yielded no evidence of an effect of oyster aquaculture on the morphology, density, or biomass of Z. marina, but significant differences were apparent in the epibiont community. Reference seagrass beds located away from aquaculture had higher seagrass epiphyte loads and higher abundances of amphipods. Conversely, seagrass beds below aquaculture lines had higher sessile polychaete biomass and higher isopod abundances. Our results suggest that the presence of oyster aquaculture may have indirect effects on seagrass by changing epibiont community composition and relative abundances of species. One proposed mechanism is that cultured oysters feed on epiphytic diatoms and epiphyte propagules before they can settle on the seagrass, which reduces epiphyte loads and influences subsequent faunal settlement. If carefully implemented and monitored, long-line oyster aquaculture may be a sustainable option to consider as bivalve aquaculture expands to meet global seafood demand, but further work is needed to fully assess and generalize the community-level effects on seagrass epibionts.

Assessment of community-level effects of intermittent preventive treatment for malaria in schoolchildren in Jinja, Uganda (START-IPT trial): a cluster-randomised trial

SummaryBackgroundIntermittent preventive treatment (IPT) is a well established malaria control intervention. Evidence that delivering IPT to schoolchildren could provide community-level benefits is limited. We did a cluster-randomised controlled trial to assess the effect of IPT of primary schoolchildren with dihydroartemisinin-piperaquine (DP) on indicators of malaria transmission in the community, in Jinja, Uganda.MethodsWe included 84 clusters, each comprising one primary school and the 100 closest available households. The clusters were randomly assigned 1:1 to receive IPT with DP or standard care (control) by restricted randomisation to ensure balance by geography and school type. Children in intervention schools received IPT monthly for up to six rounds (June to December, 2014). We did cross-sectional community surveys in randomly selected households at baseline and in January to April, 2015, during which we measured participants' temperatures and obtained finger-prick blood smears for measurement of parasite prevalence by microscopy. We also did entomological surveys 1 night per month in households from 20 randomly selected IPT and 20 control clusters. The primary trial outcome was parasite prevalence in the final community survey. The primary entomological survey outcome was the annual entomological inoculation rate (aEIR) from July, 2014, to April, 2015. This trial is registered at ClinicalTrials.gov, number NCT02009215.FindingsAmong 23 280 students registered in the 42 intervention schools, 10 079 (43%) aged 5–20 years were enrolled and received at least one dose of DP. 9286 (92%) of 10 079 received at least one full course of DP (three doses). Community-level parasite prevalence was lower in the intervention clusters than in the control clusters (19% vs 23%, adjusted risk ratio 0·85, 95% CI 0·73–1·00, p=0·05). The aEIR was lower in the intervention group than in the control group, but not significantly so (10·1 vs 15·2 infective bites per person, adjusted incidence rate ratio 0·80, 95% CI 0·36–1·80, p=0·59).InterpretationIPT of schoolchildren with DP might have a positive effect on community-level malaria indicators and be operationally feasible. Studies with greater IPT coverage are needed.FundingUK Medical Research Council, UK Department for International Development, and Wellcome Trust.

Fitness variation among host species and the paradox of ineffective rhizobia.

Legumes can preferentially select beneficial rhizobial symbionts and sanction ineffective strains that fail to fix nitrogen. Yet paradoxically, rhizobial populations vary from highly beneficial to ineffective in natural and agricultural soils. Classic models of symbiosis focus on the single dimension of symbiont cost-benefit to sympatric hosts, but fail to explain the widespread persistence of ineffective rhizobia. Here, we test a novel framework predicting that spatio-temporal and community dynamics can maintain ineffective strains in rhizobial populations. We used clonal and multistrain inoculations and quantitative culturing to investigate the relative fitness of four focal Bradyrhizobium strains varying from effective to ineffective on Acmispon strigosus. We found that an ineffective Bradyrhizobium strain can be sanctioned by its native A.strigosus host across the host's range, forming fewer and smaller nodules compared to beneficial strains. But the same ineffective Bradyrhizobium strain exhibits a nearly opposite pattern on the broadly sympatric host Acmispon wrangelianus, forming large nodules in both clonal and multistrain inoculations. These data suggest that community-level effects could favour the persistence of ineffective rhizobia and contribute to variation in symbiotic nitrogen fixation.

Stalin’s terror and the long-term political effects of mass repression

Repression has a long-term negative effect on political participation. Using millions of arrest records from archival documents, and polling station-level election results, we examine how exposure to Stalin-era repression affects voter turnout in Putin’s Russia. To estimate the effect of repression on voting, we exploit exogenous variation in repression due to the structure of mid-century Soviet railroads, and travel distances to prison camps. We find that communities more heavily repressed under Stalin are less likely to vote today. The electoral legacy of Stalin’s terror – decades after the Soviet collapse, and across multiple election cycles (2003–12) – is systematically lower turnout. To show that our result is not unique to the Putin regime, we replicate our analysis in Ukraine (2004–14), and find similar patterns. These results highlight the negative consequences of repression for political behavior, and challenge the emerging view that exposure to violence increases political engagement. While past research has emphasized the short-term effects of repression over several months or years, we show that these effects may be durable over generations and even changes of political regime. Our findings also demonstrate that repression need not be collective or indiscriminate to have community-level effects.

Positive diversity-functioning relationships in model communities of methanotrophic bacteria.

Biodiversity enhances ecosystem functions such as biomass production and nutrient cycling. Although the majority of the terrestrial biodiversity is hidden in soils, very little is known about the importance of the diversity of microbial communities for soil functioning. Here, we tested effects of biodiversity on the functioning of methanotrophs, a specialized group of soil bacteria that plays a key role in mediating greenhouse gas emissions from soils. Using pure strains of methanotrophic bacteria, we assembled artificial communities of different diversity levels, with which we inoculated sterile soil microcosms. To assess the functioning of these communities, we measured methane oxidation by gas chromatography throughout the experiment and determined changes in community composition and community size at several time points by quantitative PCR and sequencing. We demonstrate that microbial diversity had a positive overyielding effect on methane oxidation, in particular at the beginning of the experiment. This higher assimilation of CH4 at high diversity translated into increased growth and significantly larger communities towards the end of the study. The overyielding of mixtures with respect to CH4 consumption and community size were positively correlated. The temporal CH4 consumption profiles of strain monocultures differed, raising the possibility that temporal complementarity of component strains drove the observed community-level strain richness effects; however, the community niche metric we derived from the temporal activity profiles did not explain the observed strain richness effect. The strain richness effect also was unrelated to both the phylogenetic and functional trait diversity of mixed communities. Overall, our results suggest that positive biodiversity-ecosystem-function relationships show similar patterns across different scales and may be widespread in nature. Additionally, biodiversity is probably also important in natural methanotrophic communities for the ecosystem function methane oxidation. Therefore, maintaining soil conditions that support a high diversity of methanotrophs may help to reduce the emission of the greenhouse gas methane.