Local Abiotic Variables Research Articles

Mosses and vascular plants show diverging diversity patterns along a latitudinal gradient in boreal bogs and fens

AbstractQuestionsThe latitudinal biodiversity gradient; i.e., the increase in biodiversity towards the equator, is one of the most prominent biodiversity patterns. Nevertheless, many questions remain to be answered about the influence of multiple environmental factors on the latitudinal biodiversity gradient, especially for mosses, and the functional diversity of mosses and vascular plants. This study aims at evaluating the influence of latitude, climate, environmental variables, and habitat types (bog vs fen) on taxonomic and functional diversity (α‐diversity and β‐diversity) and the composition of vascular plant and moss species.Location49° N to 55° N in Northwestern Quebec, Canada.TaxonMosses, vascular plants.MethodsWe used a database containing 376 phytosociological plots (400 m2) sampled in boreal peatlands located along a 600‐km latitudinal gradient. We evaluated changes in α‐diversity and β‐diversity in response to latitude, longitude, climate, and local abiotic variables for both taxonomic groups using linear mixed effect models. We evaluated the effects of these variables on taxonomic and functional composition using variance partitioning by redundancy analysis.ResultsMoss diversity increased with latitude, although the effects were masked by environmental variables, whereas vascular plant diversity decreased with latitude in fens and did not vary with latitude in bogs. We observed a decrease in taxonomic and functional uniqueness with latitude. Moss and vascular plant taxonomic and functional composition were primarily structured by contrasting local conditions in bogs and fens, whereas climatic variations along the latitudinal gradient played a secondary role.ConclusionsOur results highlight the contrasting biodiversity patterns in both peatland types and the importance of local habitat conditions in structuring vascular plant and moss diversity. These patterns varied depending on the diversity indicator used, as α‐ and β‐diversity and functional and taxonomic diversity were often decoupled. Future studies should therefore include more than one diversity indicator and consider the differences between ecosystems and taxon groups.

Plant functional traits are dynamic predictors of ecosystem functioning in variable environments

Abstract A central goal at the interface of ecology and conservation is understanding how the relationship between biodiversity and ecosystem function (B–EF) will shift with changing climate. Despite recent theoretical advances, studies which examine temporal variation in the functional traits and mechanisms (mass ratio effects and niche complementarity effects) that underpin the B–EF relationship are lacking. Here, we use 13 years of data on plant species composition, plant traits, local‐scale abiotic variables, above‐ground net primary productivity (ANPP), and climate from the alpine tundra of Colorado (USA) to investigate temporal dynamics in the B–EF relationship. To assess how changing climatic conditions may alter the B–EF relationship, we built structural equation models (SEMs) for 11 traits across 13 years and evaluated the power of different trait SEMs to predict ANPP, as well as the relative contributions of mass ratio effects (community‐weighted mean trait values; CWM), niche complementarity effects (functional dispersion; FDis) and local abiotic variables. Additionally, we coupled linear mixed effects models with Multimodel inference methods to assess how inclusion of trait–climate interactions might improve our ability to predict ANPP through time. In every year, at least one SEM exhibited good fit, explaining between 19.6% and 57.2% of the variation in ANPP. However, the identity of the trait which best explained ANPP changed depending on winter precipitation, with leaf area, plant height and foliar nitrogen isotope content (δ15N) SEMs performing best in high, middle and low precipitation years, respectively. Regardless of trait identity, CWMs exerted a stronger influence on ANPP than FDis and total biotic effects were always greater than total abiotic effects. Multimodel inference reinforced the results of SEM analysis, with the inclusion of climate–trait interactions marginally improving our ability to predict ANPP through time. Synthesis. Our results suggest that temporal variation in climatic conditions influences which traits, mechanisms and abiotic variables were most responsible for driving the B–EF relationship. Importantly, our findings suggest that future research should consider temporal variability in the B–EF relationship, particularly how the predictive power of individual functional traits and abiotic variables may fluctuate as conditions shift due to climate change.

High-latitude invasion and environmental adaptability of the freshwater mussel Limnoperna fortunei in Beijing, China.

The invasive freshwater mussel Limnoperna fortunei (Dunker, 1857) has spread widely throughout Asia and South America, especially via interbasin water diversion and navigation. The middle route of the South-to-North Water Transfer Project (SNWTP), whose terminal is Beijing, has diverted more than 60 billion m3 of water from the Yangtze River Basin to Northern China since December 2014. L. fortunei has spread north to Beijing along the SNWTP, biofouling its channels and tunnels. To determine the status of L. fortunei's invasion in Beijing, we systematically inspected the water bodies receiving southern water, including all branches of the SNWTP, water treatment plants, lakes, reservoirs, and rivers. We measured the densities of adults and veligers of L. fortunei and conducted eDNA analyses of water samples. A generalized linear model and canonical correspondence analysis were adopted to investigate the correlations between environmental (e.g., water temperature, conductivity, pH, total nitrogen, and phosphorus) and biological (e.g., chlorophyll a, plankton density, and community composition) variables and the densities of adults and veligers of L. fortunei. Water temperature is the most important factor in determining the densities of D-shaped and pediveliger veligers, with explanatory variable contributions of 56.2% and 43.9%, respectively. The pH affects the densities of D-shaped, umbonated, and pediveliger veligers. The density of plantigrade veligers is negatively correlated with the conductivity and positively correlated with the concentration of chlorophyll a. Canonical correspondence analysis shows a weak correlation between the dominant phytoplankton taxa and the density of veligers. The densities of D-shaped, umbonated, and pediveliger veligers are positively correlated with the density of small phytoplankton (12.54 ± 4.33 μm), and the density of plantigrade veligers is positively correlated with the density of large (16.12 ± 5.96 μm) phytoplankton. The density of planktonic veligers is well correlated with local abiotic variables, and that of plantigrade veligers is less correlated with local abiotic variables. This finding implies that controlling early-stage veligers by altering water temperature, pH, and food size might effectively control the establishment of further L. fortunei colonies.

Growing at the forest edges: how natural regeneration develops under fragmentation

Environmental changes caused by edge effects and matrix land use can interfere with plant community resilience and, consequently, alter forest succession. Here, we aimed to (i) investigate whether species composition, density and richness in a forest’s regeneration layer vary in its edge-to-interior gradient and (ii) analyze the relationship between regeneration and local abiotic variables. We conducted the study in the lowland rainforest of the Atlantic Forest biodiversity hotspot at the Córrego Grande Biological Reserve, Espírito Santo state, Brazil. We sampled the regeneration layer in two edge environments with different matrices (forest and road) and the fragmented interior to link vegetation structure with environmental variables. In each environment, we set up 12 plots of 5 × 10 m size and recorded, in each plot, the height and stem base diameter of all living individuals above 50 cm of height and below 2.5 cm of diameter at breast height (1.30 m height). We applied different multivariate analyses to assess the influence of environmental data, such as canopy openness and physical-chemical soil variables. The three environments shared 22 out of the 174 morphospecies recorded, and the forest-side edge had the lowest species richness among all environments. The environmental variables that better explained the distribution of species across the three environments were: canopy openness, soil penetration resistance, zinc, and calcium content. Our results revealed significant environmental differences among the forest edges and the forest interior of the study site, highlighting the relevant role of the forest surrounding matrix for the maintenance of protected remnants.

Observing diatom diversity and community composition along environmental gradients in subarctic mountain ponds

Abstract Cold subarctic pond ecosystems will be threatened due to the increase in global temperatures. Therefore, it is important to gain more knowledge on how their biota may respond to global warming. The aim of this research was to illustrate the variability in diatom species richness and community composition along environmental gradients in northernmost Finland and Norway and reveal the variables most strongly associated with diatom biodiversity. We also compared diatom biodiversity among different biotope types and placed emphasis on the distribution of rare diatom taxa. A total of 100 subarctic ponds from the Finnish and Norwegian Lapland covering an elevational gradient of 8–887 m above sea level were sampled. A generalised linear model and hierarchical partitioning were used to identify variables associated with diatom species richness. To identify variables associated with diatom community composition, a non‐metric multidimensional scaling ordination was performed. Finally, a principal component analysis and permutational multivariate analysis of variance were used for the investigation of environmental and biotic differences among biotope types. Water pH, aluminium concentration, and air temperature best explained the variation in species richness and community composition. Diatom species richness and community composition did not differ among the biotope types, but environmental variables in pine forests differed significantly from other biotope types. Many diatom species occupied the entire elevational gradient, while rare taxa seemed to appear at the ends of the elevational gradient as well around the mid‐elevational zone. We found that elevation was not sufficient to explain the variation in diatom species richness and community composition, but diatom biodiversity was shaped by a variety of local‐scale environmental variables, some of which are in turn correlated with elevation. Our findings suggest that local abiotic factors and especially water chemistry are important factors in describing the variability in diatom community composition and species richness in subarctic ponds. It seems that the lowest and the highest elevations provide suitable habitats for rare diatom taxa that have unique environmental preferences but some of the rare taxa were also constrained to mid elevations. Our study provides new insights into the role of local abiotic variables in shaping subarctic mountain pond biodiversity. We urge researchers not only to study elevational gradients per se in mountain areas, but also pay special attention to environmental covariates that may play a notable role in maintaining freshwater biodiversity in the subarctic.

Anthropogenic factors overrule local abiotic variables in determining non-native plant invasions in mountains

The factors that determine patterns of non-native species richness and abundance are context dependent in both time and space. Global change has significantly boosted plant invasions in mountains, therefore, understanding which factors determine the invasion and at what scale they operate are fundamental for decision-making in the conservation of mountain ecosystems. Although much evidence has been gathered on the patterns of non-native species in mountain ecosystems, little is known about what specific abiotic, biotic, or anthropogenic factors are driven such patterns. Here, we assessed the importance of anthropogenic, biotic, and abiotic factors at two spatial scales as drivers of plant invasions along three roads in south-central Chile. We sampled non-native plant richness and abundance, and each of these explanatory factors, in-situ in 60 transects in disturbed areas and adjacent undisturbed vegetation. Low elevation areas were the most invaded, with patterns of richness and abundance driven mainly by anthropogenic factors, explaining between 20 and 50% of the variance for the three roads. Only for the abundance of non-native species along the road in the Malalcahuello National Reserve, biotic factors were more important (45% of the variance). At the regional scale, the abundance of non-native species was again explained best by anthropogenic factors (24% of the variance), yet non-native richness was driven most strongly by abiotic factors such as soil nitrogen content and pH (15% of the variance). Our results confirm the conclusions from experimental studies that anthropogenic factors override abiotic factors and are important drivers of non-native species at local and regional scales and that non-native plant invasion in mountains is currently not strongly limited by climate.

Seasonal and long-term trends in the spatial heterogeneity of lake phytoplankton communities over two decades of restoration and climate change

World-wide, reducing the external nutrient loading to lakes has been the primary priority of lake management in the restoration of eutrophic lakes over the past decades, and as expected this has resulted in an increase in the local environmental heterogeneity, and thus biotic heterogeneity, within lakes. However, little is known about how the regional spatial heterogeneity of lake biotic communities changes with restoration across a landscape. Using a long-term monitoring dataset from 20 Danish lakes, we elucidated the seasonal and long-term trends in the spatial heterogeneity of climate, local abiotic variables and phytoplankton communities over two decades of restoration and climate change at landscape level. We found significant seasonality in the spatial heterogeneity of most climatic and local drivers as well as in the total beta diversity (Sørensen coefficient) and its turnover components (Simpson coefficient) of phytoplankton communities among the lakes. The seasonality tended to be less marked in deep than in shallow lakes. We found significant spatial homogenisation of most local drivers (except for alkalinity) and phytoplankton communities after two decades of restoration and that turnover dominated the temporal responses of the total beta diversity of phytoplankton communities. Path analyses showed that the homogenisation of phytoplankton communities was mainly due to a decrease in spatial heterogeneity of total phosphorus and Schmidt stability in shallow lakes and to a decrease in spatial total phosphorus and total nitrogen heterogeneity in deep lakes. However, albeit weakly, the spatial heterogeneity of the phytoplankton communities was affected indirectly by climatic warming in both shallow and deep lakes and directly by wind speed in shallow lakes. We conclude that restoration of eutrophic lakes may lead to an increase in the local heterogeneity of phytoplankton communities at lake scale and an increase in homogeneity at landscape scale.

Functional traits determine why species belong to the dark diversity in a dry grassland fragmented landscape

A challenge for nature conservation is to know why many species are absent from suitable habitats and whether they might be able to disperse and to establish. Here, we used 272 dry grassland patches within a fragmented landscape to investigate the role of local abiotic conditions and dispersal filtering in determining the likelihood of vascular plants to belong to the dark diversity (i.e. absent portion of the species pool). First, we quantified the species (SD), functional (FD) and phylogenetic (PD) diversity of both observed and dark communities. Second, we determined the roles of abiotic, present‐day and historical landscape configuration variables in shaping their patterns. Third, we evaluated the importance of each variable in determining their species. Environmental filtering was assessed as effects of local abiotic conditions and dispersal filtering as the effects of present‐day and historical landscape configuration. Dispersal filtering was also estimated by comparing dispersal traits of observed and dark diversity. Finally, we assessed community completeness to determine how much of the species pool was realized within a local community. We found higher SD in the observed compared to the dark communities, but PD did not differ. Contrary to expectations, dark communities resembled higher FD compared to the observed communities. Species with low dispersal capacity, low competitive abilities and high stress‐tolerance were more often absent. Observed and dark diversities were mostly affected by local abiotic variables. In the observed communities, present‐day landscape configuration variables affected SD while historical landscape configuration variables explained FD and PD. In the dark communities, we found the opposite pattern. Completeness was affected by present‐day and historical patch size. Our results explain why dry grassland species may belong to the dark diversity and highlight the importance of local abiotic and dispersal traits of the species to conserve dry grasslands in changing landscapes.

Cell size and acid tolerance constrain pond diatom distributions in the subarctic

AbstractNiche characteristics and traits affect species distributions. However, their effects on the distribution of microorganisms remain understudied, especially in subarctic regions. Our aim was to determine the effects of species niche characteristics and traits on benthic diatom (Bacillariophyceae) elevational distributions, and to identify the key drivers of trait diversity across climate‐sensitive subarctic ponds.We sampled 102 ponds along an elevational gradient of 10 to 1,038 m a.s.l. in subarctic Finland and Norway. We calculated the niche characteristics by Outlying Mean Index analysis using an independent data set collected from 141 lakes in northern Fennoscandia. We ran generalised linear models to identify traits most strongly affecting the distribution of individual species, and used a functional dispersion metric to explore trait diversity at community level.Benthic diatom distributions correlated positively with niche breadth, implying that generalists were more widely distributed than specialists, but negatively with niche position, suggesting that marginal species had narrow distributions. Cell size and acid tolerance were the key traits affecting diatom distributions: small size and strong acid tolerance were associated with a wider distribution.Local abiotic variables were more important than elevation in shaping trait diversity, which increased withpHand decreased with conductivity. Several acidic wetland ponds located at low elevations exhibited functionally clustered communities, reflecting stressful conditions that comprised a filter that selected acid‐tolerant species.Our results suggest that benthic diatom distributions across subarctic ponds are jointly driven by species cell size and tolerance towards water chemistry variables, especially acidity. Although elevation summarises the effects of several environmental factors, local abiotic variables were more strongly associated with trait diversity than were elevation effects. Our findings provide new insights into the key mechanisms associated with aquatic microbial distributions in highly sensitive climatic regions.

Linking nutrient loading, local abiotic variables, richness and biomasses of macrophytes, and associated invertebrate species in the north-eastern Baltic Sea

Abstract. We studied relationships between nutrient loading, local abiotic variables, richness and biomasses of macrophytes, and associated invertebrate species in the north-eastern Baltic Sea. The study showed that nutrient load strongly correlated to the richness and biomass of macroalgal and invertebrate species and functions and often interacted with local abiotic variables such as salinity and depth. Generally elevated nutrient loads increased the species richness of macrophytes and benthic invertebrates and the biomass of annual macroalgae and of the majority of invertebrate feeding groups, but reduced the biomass of perennial macroalgae. The study also showed that the effect of nutrient loading was scale-specific, i.e. different responses to nutrients were observed at water-body and gulf scales. The biomass of the majority of species and functions was a function of the gulf-scale nutrient loading whereas the variability of annual algae and chironomidae reflected changes in the water-body level nutrient loading.

Advancing plant phenology and reduced herbivore production in a terrestrial system associated with sea ice decline

The contribution of declining Arctic sea ice to warming in the region through Arctic amplification suggests that sea ice decline has the potential to influence ecological dynamics in terrestrial Arctic systems. Empirical evidence for such effects is limited, however, particularly at the local population and community levels. Here we identify an Arctic sea ice signal in the annual timing of vegetation emergence at an inland tundra system in West Greenland. According to the time series analyses presented here, an ongoing advance in plant phenology at this site is attributable to the accelerating decline in Arctic sea ice, and contributes to declining large herbivore reproductive performance via trophic mismatch. Arctic-wide sea ice metrics consistently outperform other regional and local abiotic variables in models characterizing these dynamics, implicating large-scale Arctic sea ice decline as a potentially important, albeit indirect, contributor to local-scale ecological dynamics on land.

Potential effects of climate change on the distribution of the common frog Rana temporaria at its northern range margin

Climate change is projected to be particularly strong in northern latitudes, and subarctic species are thus likely to be especially susceptible to the effects of climate warming. We forecast potential effects of climate change on the extent of the suitable habitat of the common frog,Rana temporaria,at the margin of its northern range. We investigated 179 potential breeding sites in subarctic Finland and subjected the data to detailed bioclimate envelope modelling using three state-of-the-art techniques: generalized additive models, maximum entropy and generalized boosting methods. Moreover, we included local environmental factors in the models to investigate whether they improve model performance. Under all tested climate change projections and irrespective of the modelling method, the suitable habitat forR. temporariaincreased in warming climate. The inclusion of local abiotic variables significantly improved the performance of the models. However, June temperature appeared to be the most informative variable in all modelling approaches: a major increase in the extent of suitable habitat occurred when it increased by 1°C. Overall, the modelling results indicate that the distribution of northernR. temporariais likely to be very sensitive to climate warming. The results also highlight the fact that overlooking local abiotic variation can significantly bias bioclimatic modelling results.

Identification of fish nursery areas in a free tributary of an impoundment region, upper Uruguay River, Brazil

This study aims to determine the importance of different environments of the Ligeiro River (upper Uruguay River, Brazil) in fish reproduction. For this purpose, three environments (sampling sites) were selected: rapids, a pool, and the mouth of the Ligeiro River. Ichthyoplankton, zooplankton, and benthos were sampled six times per month from September, 2006 to March, 2007. Zooplankton and ichthyoplankton samples were collected early in the evening with plankton nets (64 µm and 500 µm, respectively). Benthos samples were also collected early in the evening with a Van Veen dredge. Local abiotic variables (temperature, dissolved oxygen, pH, electrical conductivity, water speed, alkalinity, water hardness, and water transparency) were measured simultaneously with the biotic data sampling and were complemented by regional variables (water flow and precipitation). A total of 43,475 eggs and 2,269 larvae were captured. Of these larvae, 80.1% were in the pre-flexion and larval yolk stages. Digestive tract content showed that the greatest degree of repletion among the larvae in more advanced phases occurred in the pool environment. Water speed was the main characteristic used to differentiate the river's rapids and mouth from the pool. The abundance of zooplankton and benthos was not related to the distribution of densities among the different components of the ichthyoplankton. A greater abundance of eggs and larvae with yolk was found in the rapids and river mouth. Ordination analyses showed a connection between the advanced stage larvae and the pool environment. In conclusion, the rapids and river mouth of the Ligeiro River's are important locations for fish reproduction, particularly in regard to spawning and drifting of the ichthyoplankton's initial stages, whereas the pool represents a nursery place for larval growth.

The recovery of acid‐damaged zooplankton communities in Canadian Lakes: the relative importance of abiotic, biotic and spatial variables

Summary1. Acidification has damaged biota in thousands of lakes and streams throughout eastern North America. Fortunately, reduced emissions of sulphur dioxide and nitrogen oxides beginning in the 1960s have allowed pH levels in many affected systems to increase. Determining the extent of biological and pH recovery in these systems is necessary to assess the success of emissions reductions programmes.2. Although there have been promising signs of biological recovery in many systems, recovery has occurred more slowly than expected for some taxa. Past studies with crustacean zooplankton indicate that a mixture of local abiotic variables, biotic variables and dispersal processes may influence the structure of recovering communities. However, most studies have been unable to determine the relative importance of these three groups of variables.3. We assessed chemical and biological recovery of acid‐damaged lakes in Killarney Park, Ontario. In addition, we assessed the relative importance of local abiotic variables, biotic variables and dispersal processes for structuring recovering communities. We collected zooplankton community data, abiotic and biotic data from 45 Killarney Park lakes. To assess the recovery of zooplankton communities, we compared zooplankton data collected in 2005 to a survey conducted for the same lakes in 1972–73 using several univariate measures of community structure, as well as multivariate methods based on relative species abundances. To determine the factors influencing the structure of recovering zooplankton communities, we used hierarchical partitioning for univariate measures and spatial modelling and variation partitioning techniques for multivariate analyses.4. Our survey revealed significant pH increases for the majority of sampled lakes but univariate measures of community structure, such as species richness and diversity, indicated that only minor changes have occurred in many acid‐damaged lakes. Hierarchical partitioning identified several variables that may influence our univariate measures of recovery, including pH, dissolved organic carbon (DOC) levels, fish presence/absence, lake surface area and lake elevation.5. Multivariate methods revealed a shift in communities through time towards a structure more typical of neutral lakes, providing some evidence for recovery. Variation partitioning suggested that the structure of recovering copepod communities was influenced most by dispersal processes and abiotic variables, while biotic (Chaoborus densities, fish presence/absence) and abiotic variables were more important for cladoceran zooplankton.6. Our results indicate that the recovery of zooplankton communities in Killarney Park is not yet complete, despite decades of emission reductions. The importance of variables related to acidification, such as pH and DOC, indicates that further chemical recovery may be necessary. The differing importance of abiotic, biotic and dispersal processes for structuring copepod versus cladoceran zooplankton might indicate that different management approaches and expectations for recovery are needed for these groups.

Species pool versus site limitations of macrophytes in urban waters

Biodiversity in urban areas is affected by a multitude of stressors. In addition to physico-chemical stress factors, the native regional species pool can be greatly reduced in highly urbanized landscapes due to area loss and fragmentation. In this study, we investigated how macrophyte composition and diversity in urban water systems are limited by the regional species pool and local environmental conditions. Canonical correspondence analysis of the macrophyte species composition revealed that urban and semi-natural water systems differed and differences could be related to local abiotic variables such as pH and iron concentrations. Macrophytes in the semi-natural area were typical for slightly acid and oligotrophic conditions. In urban water systems, exotic species characteristic of eutrophic conditions were present. In the semi-natural areas, the number of macrophyte species exceeded the number of species expected from species–area relationships of artificial water bodies in rural areas. In urban areas, the number of macrophyte species was similar to artificial water systems in rural areas. Macrophyte species present in the study areas also were generally found within 20–30 km distance to the study area. Macrophyte species composition in urban water systems and semi-natural water systems appeared to be influenced by the regional species pool within approximately 30 km of the locations. Nevertheless, site limitation ultimately determined the local macrophyte species composition and diversity in urban water systems and in semi-natural water systems.

Characterising functional trait diversity and trait–environment relationships in fish assemblages of boreal lakes

Summary1. Characterisation of biodiversity is typically based on taxonomic approaches, while much less is known about other related aspects. Functional trait diversity is one such component of biodiversity that has not been addressed rigorously in ecological research until recently. We tested the congruence between taxonomic‐ and trait‐based approaches, and examined how spatial configuration, local abiotic environmental factors and biotic effects interact to influence taxonomic‐ and trait‐based characterisation of freshwater fish assemblages.2. Fish assemblage data were compiled for 124 lakes in southern Finland. Variance partitioning in both linear regression analyses and redundancy analysis was used to quantify the relative contribution of spatial and environmental variables to taxonomic and functional trait diversity and structure. Additionally, a null model analysis was used to test for the potential effects of interspecific segregation and biotic interactions on the co‐occurrence of species.3. The species pool was relatively poor. However, trait‐based classification of species indicated that most species belonged to unique functional entities, which suggested low redundancy in species composition. Correlation analysis indicated a very strong relationship between species richness (SR) and the number of unique trait combinations (UTC). Ecoregion‐level heterogeneity in SR and UTC were well represented in a relatively small group of randomly selected lakes (c. 30 lakes). Multiple regressions indicated moderate roles for abiotic environmental variables (i.e. lake surface area, depth, total phosphorous, colour and pH) in determining SR, UTC and the distribution of single trait categories, whereas geographical location was not generally influential.4. Redundancy analysis revealed similar patterns to those of diversity analyses for taxonomic and associated trait‐based structure, emphasising the effect of abiotic environmental variables and the negligible effect of geographical position.5. Co‐occurrence analysis indicated significant checkerboard distribution at the whole assemblage level, but interspecific segregation proved to be of relatively minor importance in the constrained analyses, where species pair combinations within trait category groups were evaluated.6. Our results suggest that taxonomic‐ and trait‐based patterns of boreal lake fish assemblages are strongly interrelated. Environmental filtering through the effects of local abiotic variables seems to have the most prominent role in determining trait‐based assemblage patterns among lakes, which may also be secondarily shaped by biotic interactions.7. From the applied perspective, it may not necessarily matter whether traditional taxonomic or more novel trait‐based approaches are used in characterising spatial patterns in boreal fish assemblages. However, trait‐based approaches may provide complementary information which cannot be directly revealed by taxonomic data.

Long-term changes in a northern Baltic macrophyte community

Over the last 45 years significant changes in the floristic composition, distribution pattern, and dominance structure of phytobenthos were observed in Haapsalu Bay. Although the species composition of macroalgae did not change much over the course of this study, we observed notable changes in the community structure, i.e. algal shares. Some species, e.g. Tolypella nidifica, disappeared, other species such as Chara connivens and Chara baltica appeared for the first time in the study area. Besides, many prevailing species were relocated within the observed area over the course of the study. Another distinct feature of the recent years is that the vegetation had no dominant species. In general decadal variability exceeded yearly variability. There was no single abiotic variable that exerted major influence on phytobenthic communities. Instead we observed a combined effect of multiple environmental variables on phytobenthos communities. This study indicated that the changes in phytobenthic communities in Haapsalu Bay over the last 45 years were mainly due to large-scale weather patterns that determined regional salinity and ice conditions. Salinity sets the dominance pattern of phytobenthic species of freshwater and marine origin within communities. The intensity of ice scrape in turn created new unvegetated substrate and determined the overall phytobenthic cover in the study area. Within these large-scale patterns exposure, depth, and spatial salinity gradients contributed to the variability of small-scale patterns of macrophyte communities. Regional nutrient loading had weak effects on macrophyte communities, mainly in interactions with local abiotic variables and regional weather patterns.

Elevation and local refuges ensure persistence of mountain specific vegetation in the Nigerien Sahara

The inselberg structure and the local habitats of the Aïr mountains (Niger) are hypothesized to generate the coexistence of geographically isolated plant species with high conservation values. By studying the diversity and the distribution of plants on the highest peak of these mountains, we aimed to identify the respective effects of local and regional abiotic factors on isolated species. We estimated the regional effects of elevation by comparing 103 floristic quadrats with existing data in the adjacent lowlands, and we tested the effects of local abiotic variables on species distribution with ordination methods. Among the 151 species identified, 12 were recorded for the first time in Niger and 53 were not found in the adjacent lowlands, thus evidencing true mountain specificity. A five-class habitat variable separated a relatively high portion of Saharan-Mediterranean species (8%) located in volcanic gullies, and Guinean-Sudanian-Zambezian species (13%) located in granite boulders. These two habitats provided local abiotic refuges (boulders, gullies), which protected a pool of relictual species from aridity, and probably from grazers. Species persistence may thus be dependent both on regional and local abiotic variables. With probable high genetic divergence because of the surrounding desert matrix, their conservation value may be particularly high.