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Unravelling patterns and mechanisms of biogeographical transitions is crucial if we are to understand compositional gradientsat large spatial extents, but no studies have thus far examined breakpoints in community composition of freshwater plants acrosscontinents. Using a dataset of almost 500 observations of lake plant community composition from six continents, we examined,for the first time, if such breakpoints in geographical space exist for freshwater plants and how well a suite of ecological factors(including climatic and local environmental variables) can explain transitions in community composition from the subtropicsto the poles. Our combination of multivariate regression tree (MRT) analysis and k-means partitioning suggests that the mostabrupt breakpoint exists between temperate to boreal regions on the one hand and freshwater plant communities harbouringmainly subtropical or Mediterranean assemblages on the other. The spatially structured variation in current climatic conditionsis the most likely candidate for controlling these latitudinal patterns, although one cannot rule out joint effects of eco-evolutionary constraints in the harsher high-latitude environments and post-glacial migration lags after Pleistocene Ice Ages. Overall, ourstudy supports the foundations of global regionalisation for freshwater plants and anticipates further biogeographical researchon freshwater plant communities once datasets have been harmonised for conducting large-scale spatial analyses.

Rationale: New isolation of Pseudomonas aeruginosa (Pa) is generally treated with inhaled antipseudomonal antibiotics such as tobramycin inhalation solution (TIS). A therapeutic approach that complements traditional antimicrobial therapy by reducing the risk of pulmonary exacerbation and inflammation may ultimately prolong the time to Pa recurrence. Objectives: To test the hypothesis that the addition of azithromycin to TIS in children with cystic fibrosis and early Pa decreases the risk of pulmonary exacerbation and prolongs the time to Pa recurrence. Methods: The OPTIMIZE (Optimizing Treatment for Early Pseudomonas aeruginosa Infection in Cystic Fibrosis) trial was a multicenter, double-blind, randomized, placebo-controlled, 18-month trial in children with CF, 6 months to 18 years of age, with early Pa. Azithromycin or placebo was given 3× weekly with standardized TIS. Measurements and Main Results: The primary endpoint was the time to pulmonary exacerbation requiring antibiotics and the secondary endpoint was the time to Pa recurrence, in addition to other clinical and safety outcomes. A total of 221 participants (111 placebo, 110 azithromycin) out of a planned 274 were enrolled. Enrollment was stopped early by the NHLBI because the trial had reached the prespecified interim boundary for efficacy. The risk of pulmonary exacerbation was reduced by 44% in the azithromycin group as compared with the placebo group (hazard ratio, 0.56; 95% confidence interval, 0.37–0.83; P = 0.004). Weight increased by 1.27 kg in the azithromycin group compared with the placebo group (95% confidence interval, 0.01–2.52; P = 0.046). No significant differences were seen in microbiological or other clinical or safety endpoints. Conclusions: Azithromycin was associated with a significant reduction in the risk of pulmonary exacerbation and a sustained improvement in weight, but had no impact on microbiological outcomes in children with early Pa. Clinical trial registered with clinicaltrials.gov (NCT02054156).

Documenting the patterns of biological diversity on Earth has always been a central challenge in macroecology and biogeography. However, for the diverse group of freshwater plants, such research program is still in its in- fancy. Here, we examined global variation in taxonomic, functional and phylogenetic beta diversity patterns of lake macrophytes using regional data from six continents. A data set of ca. 480 lake macrophyte community ob- servations, together with climatic, geographical and environmental variables, was compiled across 16 regions worldwide. We (a) built the very first phylogeny comprising most freshwater plant lineages; (b) exploited a wide array of functional traits that are important to macrophyte autoecology or that relate to lake ecosystem functioning; (c) assessed if different large-scale beta diversity patterns show a clear latitudinal gradient from the equator to the poles using null models; and (d) employed evolutionary and regression models to first identify the degree to which the studied functional traits show a phylogenetic signal, and then to estimate community- environment relationships at multiple spatial scales. Our results supported the notion that ecological niches evolved independently of phylogeny in macrophyte lineages worldwide. We also showed that taxonomic and phylogenetic beta diversity followed the typical global trend with higher diversity in the tropics. In addition, we were able to confirm that species, multi-trait and lineage compositions were first and foremost structured by climatic conditions at relatively broad spatial scales. Perhaps more importantly, we showed that large-scale processes along latitudinal and elevational gradients have left a strong footprint in the current diversity patterns and community-environment relationships in lake macrophytes. Overall, our results stress the need for an inte- grative approach to macroecology, biogeography and conservation biology, combining multiple diversity facets at different spatial scales. JGG appreciates financial support from the Spanish Ministry of Economy and Industry [project METAPONDS, grant CGL2017- 84176R], the Junta de Castilla y León [grant LE004G18] and from the Fundación Biodiversidad (Spanish Ministry for Ecological Transi- tion and Demographic Challenge). BAL was supported by National Research, Development and Innovation Fund [grant NKFIH, OTKA PD120775] and by the Bolyai János Research Scholarship of the Hun- garian Academy of Sciences. S.K. was supported by NWO Veni [grant 86312012]. Sampling of the coastal Brazilian lakes was financed by NWO [grant W84-549]; The National Geographic Society [grant 7864-5]; and CNPq [grants 480122, 490409, 311427]. We thank the SALGA team, especially Gissell Lacerot, Nestor Mazzeo, Vera Huszar, David da Motta Marques, and Erik Jeppesen for organizing and exe- cuting the SALGA field sampling campaign and Bruno Irgang† and Eduardo Alonso Paz for helping with identification. We thank Minne- sota and Wisconsin Departments of Natural Resources for collecting the macrophyte data. We are grateful to Carol Reschke for her work in combining and performing quality control for the Minnesota mac- rophyte data used in the analysis. This is contribution no. 607 of the Natural Resources Research Inst. of the Univ. of Minnesota Duluth. Provision of New Zealand macrophyte data was possible via NIWA SSIF funding. JGG appreciates financial support from the Spanish Ministry of Economy and Industry [project METAPONDS, grant CGL2017- 84176R], the Junta de Castilla y León [grant LE004G18] and from the Fundación Biodiversidad (Spanish Ministry for Ecological Transi- tion and Demographic Challenge). BAL was supported by National Research, Development and Innovation Fund [grant NKFIH, OTKA PD120775] and by the Bolyai János Research Scholarship of the Hun- garian Academy of Sciences. S.K. was supported by NWO Veni [grant 86312012]. Sampling of the coastal Brazilian lakes was financed by NWO [grant W84-549]; The National Geographic Society [grant 7864-5]; and CNPq [grants 480122, 490409, 311427]. We thank the SALGA team, especially Gissell Lacerot, Nestor Mazzeo, Vera Huszar, David da Motta Marques, and Erik Jeppesen for organizing and exe- cuting the SALGA field sampling campaign and Bruno Irgang† and Eduardo Alonso Paz for helping with identification. We thank Minne- sota and Wisconsin Departments of Natural Resources for collecting the macrophyte data. We are grateful to Carol Reschke for her work in combining and performing quality control for the Minnesota mac- rophyte data used in the analysis. This is contribution no. 607 of the Natural Resources Research Inst. of the Univ. of Minnesota Duluth. Provision of New Zealand macrophyte data was possible via NIWA SSIF funding.

Documenting the patterns of biological diversity on Earth has always been a central challenge in macroecology and biogeography. However, we are only beginning to generate an understanding of the global patterns and determinants of macrophyte diversity. Here, we studied large-scale variation and community-environment relationships of lake macrophytes along climatic and geographical gradients using regional data from six continents. We applied statistical routines typically used in the context of metacommunity studies to provide novel insights into macrophyte community compositional patterns within regions worldwide. We found that lake macrophyte metacommunities followed clumped species replacement structures, suggesting that two or more species groups were responding similarly to the environment within regions. Underlying such general convergence, our results also provided evidence that community-environment relationships were largely context-dependent, stressing that no single mechanism is enough to account for the complex nature of compositional variation. Surprisingly, we found no general relationships between functional or phylogenetic composition and main metacommunity types, suggesting that linking multi-trait and evolutionary information to the elements of metacommunity structure is not straightforward. Our findings highlight that global conservation initiatives and biodiversity protection need to capture environmental variation at the metacommunity level, and acknowledge the highly context-dependent patterns in the community-environment relationships of lake macrophytes. Overall, we emphasize the need to embrace the potential complexity of ecological inferences in metacommunity organization across the globe.

The biodiversity of aquatic ecosystems is under threat and there is an urgent need to quantify the various facets of biodiversity to assess the conservation value of freshwater ecosystems. The effects of taxonomic relatedness have so far not been taken into account in biodiversity assessments of lake macrophytes. We therefore tested the response of species richness and average taxonomic distinctness (AvTD) of aquatic macrophytes along environmental gradients using linear regression models and Bayesian Information Criterion variable selection method. We selected data from four regions, each with 50–60 lakes, situated in northern Europe (Finland and Sweden) and northern America (Minnesota and Wisconsin). We separately studied all macrophyte species, hydrophytes and helophytes. Species richness and AvTD of aquatic macrophytes were generally negatively related in all regions, although it was not statistically significant. Both biodiversity measures responded to environmental gradients to various degrees among the studied macrophyte groups and regions. Species richness was best explained by alkalinity and lake area in Finland, by elevation, annual mean temperature and total phosphorus in Minnesota, and by alkalinity in Wisconsin. AvTD was best explained by alkalinity, annual mean temperature and total phosphorus in Finland and by alkalinity in Wisconsin. Very weak relationships were found in Sweden. Our findings strongly suggest that complementary indices are needed to indicate more comprehensively the effects of environmental conditions on freshwater biodiversity. Species richness was found to be a better measure than AvTD to account for conservation value in freshwaters. However, further research is required to evaluate the usefulness of AvTD to indicate conservation value (e.g. randomisation tests), because alternative measures are clearly needed for those freshwater taxa lacking complete information on true phylogenetic diversity.

Different species' niche breadths in relation to ecological gradients are infrequently examined within the same study and, moreover, species niche breadths have rarely been averaged to account for variation in entire ecological communities. We investigated how average environmental niche breadths (climate, water quality and climate-water quality niches) in aquatic macrophyte communities are related to ecological gradients (latitude, longitude, altitude, species richness and lake area) among four distinct regions (Finland, Sweden and US states of Minnesota and Wisconsin) on two continents. We found that correlations between the three different measures of average niche breadths and ecological gradients varied considerably among the study regions, with average climate and average water quality niche breadth models often showing opposite trends. However, consistent patterns were also found, such as widening of average climate niche breadths and narrowing of average water quality niche breadths of aquatic macrophytes along increasing latitudinal and altitudinal gradients. This result suggests that macrophyte species are generalists in relation to temperature variations at higher latitudes and altitudes, whereas species in southern, lowland lakes are more specialised. In contrast, aquatic macrophytes growing in more southern nutrient-rich lakes were generalists in relation to water quality, while specialist species are adapted to low-productivity conditions and are found in highland lakes. Our results emphasise that species niche breadths should not be studied using only coarse-scale data of species distributions and corresponding environmental conditions, but that investigations on different kinds of niche breadths (e.g., climate vs. local niches) also require finer resolution data at broad spatial extents.

One of the most intriguing questions in current ecology is the extent to which the ecological niches of species are conserved in space and time. Niche conservatism has mostly been studied using coarse-scale data of species' distributions, although it is at the local habitat scales where species' responses to ecological variables primarily take place. We investigated the extent to which niches of aquatic macrophytes are conserved among four study regions (i.e. Finland, Sweden and the US states of Minnesota and Wisconsin) on two continents (i.e. Europe and North America) using data for 11 species common to all the four study areas. We studied how ecological variables (i.e. local, climate and spatial variables) explain variation in the distributions of these common species in the four areas using species distribution modelling. In addition, we examined whether species' niche parameters vary among the study regions. Our results revealed large variation in both species' responses to the studied ecological variables and in species' niche parameters among the areas. We found little evidence for niche conservatism in aquatic macrophytes, though local environmental conditions among the studied areas were largely similar. This suggests that niche shifts, rather than different environmental conditions, were responsible for variable responses of aquatic macrophytes to local ecological variables. Local habitat niches of aquatic macrophytes are mainly driven by variations in local environmental conditions, whereas their climate niches are more or less conserved among regions. This highlights the need to study niche conservatism using local-scale data to better understand whether species' niches are conserved, because different niches (e.g. local versus climate) operating at various scales may show different degrees of conservatism. The extent to which species' niches are truly conserved has wide practical implications, including for instance, predicting changes in species' distributions in response to global change.

Este artículo contiene 16 páginas, 3 tablas, 2 figuras., We studied community–environment relationships of lake macrophytes at two metacommunity scales using data from 16 regions across the world. More specifically, we examined (a) whether the lake macrophyte communities respond similar to key local environmental factors, major climate variables and lake spatial locations in each of the regions (i.e., within-region approach) and (b) how well can explained variability in the community–environment relationships across multiple lake macrophyte metacommunities be accounted for by elevation range, spatial extent, latitude, longitude, and age of the oldest lake within each metacommunity (i.e., across-region approach). In the within-region approach, we employed partial redundancy analyses together with variation partitioning to investigate the relative importance of local variables, climate variables, and spatial location on lake macrophytes among the study regions. In the across-region approach, we used adjusted R2 values of the variation partitioning to model the community–environment relationships across multiple metacommunities using linear regression and commonality analysis. We found that niche filtering related to local lake-level environmental conditions was the dominant force structuring macrophytes within metacommunities. However, our results also revealed that elevation range associated with climate (increasing temperature amplitude affecting macrophytes) and spatial location (likely due to dispersal limitation) was important for macrophytes based on the findings of the across-metacommunities analysis. These findings suggest that different determinants influence macrophyte metacommunities within different regions, thus showing context dependency. Moreover, our study emphasized that the use of a single metacommunity scale gives incomplete information on the environmental features explaining variation in macrophyte communities., Open access funding provided by University of Oulu including Oulu University Hospital. JA appreciates financial support from the Ella and Georg Ehrnrooth Foundation. BAL was supported by National Research, Development and Innovation Office—NKFIH, OTKA PD120775 Grant and by the Bolyai János Research Scholarship of the Hungarian Academy of Sciences. S.K. was supported by NWO Veni grant 86312012. Sampling of the coastal Brazilian lakes was financed by NWO grant W84-549; The National Geographic Society grant 7864-5; and CNPq grants 480122, 490409, 311427.

Este artículo contiene 14 páginas, 3 tablas, 3 figuras., Aim: We studied global variation in beta diversity patterns of lake macrophytes using regional data from across the world. Specifically, we examined (1) how beta diversity of aquatic macrophytes is partitioned between species turnover and nestedness within each study region, and (2) which environmental characteristics structure variation in these beta diversity components. Location: Global. Methods: We used presence–absence data for aquatic macrophytes from 21 regions distributed around the world. We calculated pairwise-site and multiple-site beta diversity among lakes within each region using Sørensen dissimilarity index and partitioned it into turnover and nestedness coefficients. Beta regression was used to correlate the diversity coefficients with regional environmental characteristics. Results Aquatic macrophytes showed different levels of beta diversity within each of the 21 study regions, with species turnover typically accounting for the majority of beta diversity, especially in high-diversity regions. However, nestedness contributed 30–50% of total variation in macrophyte beta diversity in low-diversity regions. The most important environmental factor explaining the three beta diversity coefficients (total, species turnover and nestedness) was elevation range, followed by relative areal extent of freshwater, latitude and water alkalinity range. Main conclusions: Our findings show that global patterns in beta diversity of lake macrophytes are caused by species turnover rather than by nestedness. These patterns in beta diversity were driven by natural environmental heterogeneity, notably variability in elevation range (also related to temperature variation) among regions. In addition, a greater range in alkalinity within a region, likely amplified by human activities, was also correlated with increased macrophyte beta diversity. These findings suggest that efforts to conserve aquatic macrophyte diversity should primarily focus on regions with large numbers of lakes that exhibit broad environmental gradients., The gathering of the Finnish data was partly supported by Biological Monitoring of Finnish Freshwaters under diffuse loading -project (XPR3304) financed by Ministry of Agriculture and Forestry and partly by national surveillance monitoring programs of lakes. S.H. and M.M. were supported by the EU-funded MARS-project (7th EU Framework Programme, Contract No.: 603378).Swedish macrophyte data were collected within the Swedish Monitoring Program of macrophytes in lakes funded by the Swedish Agency for Marine and Water Management. S.K. was supported by NWO Veni grant 86312012. Macrophyte data from Brazilian Amazon were collected within a limnological monitoring program funded by Vale S.A. The vast majority of macrophyte data from Polish lakes were collected within the State Environmental Monitoring Programme and were provided by the Inspection for Environmental Protection. Macrophyte data for British lakes were collated by the Joint Nature Conservation Committee from surveys resourced by the national conservation agencies. Swiss macrophytes data were collected during a study financially supported by the Swiss Federal Office for the Environment. Wisconsin data collection was funded by the Wisconsin Department of Natural Resources and supported by the Wisconsin Cooperative Fishery Research Unit. The Norwegian macrophyte data were collected within the European Union project ‘LAKES – Long distance dispersal of Aquatic Key Species’, contract no. env4-ct-97-0585.

Gangs have risen to the level of a broad social problem, yet, to date, research has neglected the influence of school factors on gang membership. Although gang involvement leads to many negative outcomes, such as incarceration, drug and alcohol use, injury, and death, gangs may also serve a protective influence to those who join them. For this reason, it is important to take a risk and resilience framework to understanding and ultimately preventing gang involvement. By examining various theories of gang involvement, as well as the risk and protective factors identified in current literature, a model to explain gang involvement and inform school-based prevention efforts was conceptualized. We suggest that schools can compensate for the attraction of gangs by addressing the hierarchical needs of at-risk youth. Our discussion includes a focus on three critical policy issues regarding schools' ability to implement the interventions necessary to protect youth from gang involvement: resource allocation, zero tolerance policies, and tracking.

Aquatic macrophyte communities were assessed in 53 lakes in Wisconsin, U.S.A. along environmental and land use development gradients to determine effects human land use perturbations have on aquatic macrophytes at the watershed and riparian development scales. Species richness and relative frequency were surveyed in lakes from two ecoregions: the Northern Lakes and Forests Ecoregion and the Southeastern Wisconsin Till Plain Ecoregion. Lakes were selected along a gradient of watershed development ranging from undeveloped (i.e., forested), to agricultural to urban development. Land uses occurring in the watershed and in perimeters of different width (0–100, 0–200, 0–500, and 0–1000 m from shore, in the watershed) were used to assess effects on macrophyte communities. Snorkel and SCUBA were used to survey aquatic macrophyte species in 18 quadrats of 0.25 m2 along 14 transects placed perpendicular to shore in each lake. Effects of watershed development (e.g., agriculture and/or urban) were tested at whole-lake (entire littoral zone) and near-shore (within 7 m of shore) scales using canonical correspondence analysis (CCA) and linear regression. Overall, species richness was negatively related to watershed development, while frequencies of individual species and groups differed in level of response to different land use perturbations. Effects of land use in the perimeters on macrophytes, with a few exceptions, did not provide higher correlations compared to land use at the watershed scale. In lakes with higher total watershed development levels, introduced species, particularly Myriophyllum spicatum, increased in abundance and native species, especially potamids, isoetids, and floating-leaved plants, declined in abundance. Correlations within the northern and southeastern ecoregions separately were not significant. Multivariate analyses suggested species composition is driven by environmental responses as well as human development pressures. Both water chemistry and land use variables loaded positively with the first CCA axis indicating that these factors are correlated. Land use pressures in Wisconsin are greater in the southeastern portion of the state where lakes have higher concentrations of water chemistry variables including alkalinity, conductivity, pH, calcium, magnesium, and nitrogen. This creates a complex gradient that influences species composition of macrophyte communities from lake to lake.

It has been suggested that shallow lakes in warm climates have a higher probability of being turbid, rather than macrophyte dominated, compared with lakes in cooler climates, but little field evidence exists to evaluate this hypothesis. We analyzed data from 782 lake years in different climate zones in North America, South America, and Europe. We tested if systematic differences exist in the relationship between the abundance of submerged macrophytes and environmental factors such as lake depth and nutrient levels. In the pooled dataset the proportion of lakes with substantial submerged macrophyte coverage (430% of the lake area) decreased in a sigmoidal way with increasing total phosphorus (TP) concentration, falling most steeply between 0.05 and 0.2mgL � 1 . Substantial submerged macrophyte coverage was also rare in lakes with total nitrogen (TN) concentrations above 1‐2mgL � 1 , except for lakes with very low TP concentrations where macrophytes remain abundant until higher TN concentrations. The deviance reduction of logistic regression models predicting macrophyte coverage from nutrients and water depth was generally low, and notably lowest in tropical and subtropical regions (Brazil, Uruguay, and Florida), suggesting that macrophyte coverage was strongly influenced by other factors. The maximum TP concentration allowing substantial submerged macrophyte coverage was clearly higher in cold regions with more frost days. This is in agreement with other studies which found a large influence of ice cover duration on shallow lakes’ ecology through partial fish kills that may improve light conditions for submerged macrophytes by cascading effects on periphyton and phytoplankton. Our findings suggest that, in regions where climatic warming is projected to lead to fewer frost days, macrophyte cover will decrease unless the nutrient levels are lowered.

Change in plants as bicarbonate rises Freshwater plants can be broadly divided into two major categories according to their photosynthetic traits: Some use carbon dioxide as their carbon source, whereas others use bicarbonate. Iversen et al. found that the relative concentrations of these two inorganic carbon forms in water determine the functional composition of plant communities across freshwater ecosystems (see the Perspective by Marcé and Obrador). They created global maps revealing that community composition is structured by catchment geology and not climate (in contrast to the terrestrial realm, where the trait composition is structured by temperature and rainfall). Anthropogenic influences from land-use change are causing large-scale increases in bicarbonate concentrations in freshwater catchments and are thus leading to wholesale changes in the composition of their aquatic plant communities. Unlike in land plants, photosynthesis in many aquatic plants relies on bicarbonate in addition to carbon dioxide (CO2) to compensate for the low diffusivity and potential depletion of CO2 in water. Concentrations of bicarbonate and CO2 vary greatly with catchment geology. In this study, we investigate whether there is a link between these concentrations and the frequency of freshwater plants possessing the bicarbonate use trait. We show, globally, that the frequency of plant species with this trait increases with bicarbonate concentration. Regionally, however, the frequency of bicarbonate use is reduced at sites where the CO2 concentration is substantially above the air equilibrium, consistent with this trait being an adaptation to carbon limitation. Future anthropogenic changes of bicarbonate and CO2 concentrations may alter the species compositions of freshwater plant communities. One sentence summary: The widespread photosynthetic trait of freshwater plants, bicarbonate use, has a global biogeography controlled by catchment characteristics