Local Contribution To Beta Diversity Research Articles

Patterns and drivers of prokaryotic communities in thermokarst lake water across Northern Hemisphere

AbstractAimThe formation of thermokarst lakes could make a large amount of carbon accessible to microbial degradation, potentially intensifying the permafrost carbon‐climate feedback via carbon dioxide/methane emissions. Because of their diverse functional roles, prokaryotes could strongly mediate biogeochemical cycles in thermokarst lakes. However, little is known about the large‐scale patterns and drivers of these communities.LocationPermafrost regions in the Northern Hemisphere.Time periodPresent day.Major taxa studiedProkaryotes.MethodsBased on a combination of large‐scale measurements on the Tibetan Plateau and data syntheses in pan‐Arctic regions, we constructed a comprehensive dataset of 16S rRNA sequences from 258 thermokarst lakes across Northern Hemisphere permafrost regions. We also used the local contributions to beta diversity (LCBD) to characterize the variance of prokaryotic species composition and screened underlying drivers by conducting a random forest modelling analysis.ResultsProkaryotes in thermokarst lake water were dominated by the orders Burkholderiales, Micrococcales, Flavobacteriales and Frankiales. The relative abundance of dominant taxa was positively associated with dissolved organic matter (DOM) properties, especially for the chromophoric/aromatic compounds. Microbial structure differed between high‐altitude and high‐latitude thermokarst lakes, with the dominance of Flavobacterium in high‐altitude lakes, and the enrichment of Polynucleobacter in high‐latitude lakes. More importantly, climatic variables were among the main drivers shaping the large‐scale variation of prokaryotic communities. Specifically, mean annual precipitation was the best predictor for prokaryotic beta diversity across the Northern Hemisphere, as well as in the high‐altitude permafrost regions, while mean annual air temperature played a key role in the high‐latitude thermokarst lakes.Main conclusionsOur findings demonstrate significant associations between dominant taxa and DOM properties, as well as the important role of climatic factors in affecting prokaryotic communities. These findings suggest that climatic change may alter DOM conditions and induce dynamics in prokaryotic communities of thermokarst lake water in the Northern Hemisphere.

The effects of longitudinal fragmentation on riverine beta diversity are modulated by fragmentation intensity

The loss of longitudinal connectivity affects river systems globally, being one of the leading causes of the freshwater biodiversity crisis. Barriers alter the dispersal of aquatic organisms and limit the exchange of species between local communities, disrupting metacommunity dynamics. However, the interplay between connectivity losses due to dams and other drivers of metacommunity structure, such as the configuration of the river network, needs to be explored. In this paper, we analyzed the response of fish communities to the network position and the fragmentation induced by dams while controlling for human pressures and environmental gradients. We studied three large European catchments covering a fragmentation gradient: Upper Danube (Austrian section), Ebro (Spain), and Odra/Oder (Poland). We quantified fragmentation through reach-scaled connectivity indices that account for the position of barriers along the dendritic network and the dispersal capacity of the organisms. We used generalized linear models to explain species richness and Local Contributions to Beta Diversity (LCBD) and multilinear regressions on the distance matrix to describe Beta Diversity and its Replacement and Richness Difference components. Results show that species richness was not affected by fragmentation. Network centrality metrics were relevant drivers of beta diversity for catchments with lower fragmentation (Ebro, Odra), and fragmentation indices were strong beta diversity predictors for the catchment with higher fragmentation (Danube). We conclude that in highly fragmented catchments, the effects of network centrality/isolation on biodiversity could be masked by the effects of dam fragmentation. In such catchments, metapopulation and metacommunity dynamics can be strongly altered by barriers, and the restoration of longitudinal connectivity (i.e. the natural centrality/isolation gradient) is urgent to prevent local extinctions.

Limitations of beta diversity in conservation site selection

Preservation of diversity is a key issue in many conservation efforts. It has recently been suggested that beta diversity should be considered in conservation planning and that sites with high local contribution to beta diversity (LCBD) may be valuable for conservation. Yet, such an approach has not been applied to freshwater mussels, a highly imperiled group of organisms. We used a dataset on freshwater mussel from the five largest rivers of southwestern Ontario, Canada to examine whether LCBD would be an efficient approach for assessing the conservation value of sites and compared it to more traditional conservation approaches (biomonitoring, high richness, high abundance). Sites with high LCBD value were associated with low mussel richness and were often characterized by mussels that are regionally widespread and usually abundant in lentic systems or smaller streams, limiting site selection based on beta diversity. Species at risk (including IUCN categories of Critically Endangered through Near Threatened) were more likely to occur in communities with high richness and abundance at sites chosen by the more traditional approaches. Thus, protecting sites with higher alpha diversity of mussels would also support higher gamma diversity of mussels. The provision of important ecosystem services by higher abundances of mussels which was also correlated with local richness should be considered as well. Our study suggests that there likely is an important link between high richness and abundance of mussels and the presence of species at risk which we argue is driven by facilitation (i.e., positive species interaction), an important, yet understudied, process that deserves more attention in conservation.

Hydrological changes regulate fish metacommunity structures and β-diversity patterns in the floodplain lake, China

The metacommunity structures are continuously dynamic, and understanding the temporal species distribution patterns and biodiversity variations will elucidate the metacommunity theory. To examine whether the idealized metacommunity structuring, diversity patterns, and potential driving mechanisms vary among different seasons, we assessed seasonal fish data (i.e., normal, wet, and dry seasons) in the Poyang Lake, the largest freshwater lake in China, by incorporating the Elements of Metacommunity Structure (EMS), β-diversity partitioning, and variance partitioning. The results suggested fish metacommunity displayed quasi-structures, with the quasi-Clemensian paradigm in the normal season and the quasi-Gleasonian paradigm in the wet and dry seasons, indicating the unity of species groups and individualistic species responded weakly to latent environmental gradients, respectively. The highest fish β-diversity occurred in the normal season and the lowest in the wet season with a humped trend. The species abundance replacement process contributed more to the total β-diversity than the nestedness-resultant component among seasons. The variation of the highest Local Contribution to Beta Diversity (LCBD) across seasons indicated the significance of protecting unique habitats. The relative importance of environment and spatial factors on fish metacommunity structure depended on discharge alternation, with a more significant role of spatial structuring occurring in the wet season, whereas predominant environmental filtering in the normal and dry seasons. The seasonal shifts in EMS patterns, β-diversity, and metacommunity assembly rules result from the change in hydrological conditions in the Poyang Lake. This work helps understand seasonal metacommunity dynamics and provides essential information for systematic biodiversity conservation planning in freshwater lakes.

Biogeographic patterns of hydrozoans in the Gulf of Mexico and adjacent waters: biological assemblages, beta diversity, and endemism

The biogeography of hydrozoans encompasses a broad scope of study that involves various challenges due to their diverse distributional strategies and life cycle characteristics. This work aims to study the biogeographic patterns of hydrozoans in the Gulf of Mexico. Occurrence records on hydrozoans were compiled through the Global Biodiversity Facility Information database and peer-reviewed literature. Biogeographic patterns were addressed through (1) the identification of biological assemblages, using hierarchical clustering with contiguity constraint; (2) the decomposition of beta diversity into species replacement, nestedness, and local contribution to beta diversity (LCBD); and (3) the identification of areas of endemism with a parsimony analysis of endemicity (PAE). The northern Gulf of Mexico and the Yucatán Peninsula contain a large hydrozoan assemblage that splits into smaller groups at different levels, characterized by species replacement and high LCBD values. By contrast, the southern Gulf of Mexico contains a homogenous assemblage, which exhibits low LCBD values and contributes strongly to nestedness. PAE identified 19 areas of higher-level endemism, concentrated mainly in shelf zones of the Yucatán and Florida peninsulas. The distribution patterns of hydrozoans in the Gulf of Mexico may be shaped by the life cycle characteristics of the taxa and the geological history of the region, relating either to neritic or oceanic zones. The northern Gulf reflects a heterogeneous biological composition with a complex biogeographical history, which makes this area of particular interest for future studies, as it likely represents a transition zone. This premise must be corroborated in the future.

Taxonomic dependency of beta diversity for bacteria, archaea, and fungi in a semi-arid lake

Microbial beta diversity has been recently studied along the water depth in aquatic ecosystems, however its turnover and nestedness components remain elusive especially for multiple taxonomic groups. Based on the beta diversity partitioning developed by Baselga and Local Contributions to Beta Diversity (LCBD) partitioning by Legendre, we examined the water-depth variations in beta diversity components of bacteria, archaea and fungi in surface sediments of Hulun Lake, a semi-arid lake in northern China, and further explored the relative importance of environmental drivers underlying their patterns. We found that the relative abundances of Proteobacteria, Chloroflexi, Euryarchaeota, and Rozellomycota increased toward deep water, while Acidobacteria, Parvarchaeota, and Chytridiomycota decreased. For bacteria and archaea, there were significant (p < 0.05) decreasing water-depth patterns for LCBD and LCBDRepl (i.e., species replacement), while increasing patterns for total beta diversity and turnover, implying that total beta diversity and LCBD were dominated by species turnover or LCBDRepl. Further, bacteria showed a strong correlation with archaea regarding LCBD, total beta diversity and turnover. Such parallel patterns among bacteria and archaea were underpinned by similar ecological processes like environmental selection. Total beta diversity and turnover were largely affected by sediment total nitrogen, while LCBD and LCBDRepl were mainly constrained by water NO2 --N and NO3 --N. For fungal community variation, no significant patterns were observed, which may be due to different drivers like water nitrogen or phosphorus. Taken together, our findings provide compelling evidences for disentangling the underlying mechanisms of community variation in multiple aquatic microbial taxonomic groups.

Evaluating ecological uniqueness over broad spatial extents using species distribution modelling

Local contributions to beta diversity (LCBD) can be used to identify sites with high ecological uniqueness and exceptional species composition within a region of interest. Yet, these indices are typically used on local or regional scales with relatively few sites, as they require information on complete community compositions difficult to acquire on larger scales. Here, we investigated how LCBD indices can be predicted over broad spatial extents using species distribution modelling and examined the effect of scale changes on beta diversity quantification. We used Bayesian additive regression trees (BARTs) to predict warbler species distributions in North America based on observations recorded in the eBird database. We then calculated LCBD indices for observed and predicted data and compared the site‐wise difference using direct comparison, a spatial association test and generalized linear regression. We also examined the relationship between LCBD values and species richness in different regions and at various spatial extents. Our results showed that species distribution models provided uniqueness estimates highly correlated with observed data. The form and variance of the LCBD–richness relationship varied according to the region and the total extent size. The relationship was also affected by the proportion of rare species in the communities. Therefore, sites identified as unique over broad spatial extents may vary according to regional characteristics. These results show that species distribution modelling can be used to predict ecological uniqueness over broad spatial extents, which could help identify beta diversity hotspots and important targets for conservation purposes in unsampled locations.

Eutrophication causes microbial community homogenization via modulating generalist species

Eutrophication substantially influences the community structure of aquatic organisms and has become a major threat to biodiversity. However, whether eutrophication is linked to homogenization of microbial communities and the possible underlying mechanisms are poorly understood. Here, we studied bacterial and fungal communities from water and sediments of 40 shallow lakes in the Yangtze-Huaihe River basin, a representative area characterized by intensifying eutrophication in China, and further examined the beta diversity patterns and underlying mechanisms under eutrophication conditions. Our results indicate that eutrophication generally caused biotic homogenization of bacterial and fungal communities in both habitats showing decreased community variations for the sites with a higher trophic state index (TSI). In the two habitats, community dissimilarities were positively correlated with TSI changes for both taxonomic groups, while the local contribution to beta diversity (LCBD) remarkably declined with increasing TSI for the fungal community. These phenomena were consistent with the pivotal importance of the TSI in statistically accounting for beta diversity of bacterial and fungal communities in both habitats. In addition, we found that physicochemical factors such as water temperature and pH were also important for bacterial and fungal communities in water, while heavy metal elements were important for the communities in sediments. Interestingly, generalist species, rather than specialist species, were revealed to more dominantly affect the variations in beta diversity along the trophic gradient, which were quantified by Bray-Curtis dissimilarity and LCBD. Collectively, our findings reveal the importance of generalist species in contributing to the change of beta diversity of microbial communities along trophic gradients, which have profound implications for a comprehensive understanding of the effects of eutrophication on microbial community.

Temperature and Precipitation Drive Elevational Patterns of Microbial Beta Diversity in Alpine Grasslands.

Understanding the mechanisms underlying biodiversity patterns is a central issue in ecology, while how temperature and precipitation jointly control the elevational patterns of microbes is understudied. Here, we studied the effects of temperature, precipitation and their interactions on the alpha and beta diversity of soil archaea and bacteria in alpine grasslands along an elevational gradient of 4300-5200 m on the Tibetan Plateau. Alpha diversity was examined on the basis of species richness and evenness, and beta diversity was quantified with the recently developed metric of local contributions to beta diversity (LCBD). Typical alpine steppe and meadow ecosystems were distributed below and above 4850 m, respectively, which was consistent with the two main constraints of mean annual temperature (MAT) and mean annual precipitation (MAP). Species richness and evenness showed decreasing elevational patterns in archaea and nonsignificant or U-shaped patterns in bacteria. The LCBD of both groups exhibited significant U-shaped elevational patterns, with the lowest values occurring at 4800 m. For the three diversity metrics, soil pH was the primary explanatory variable in archaea, explaining over 20.1% of the observed variation, whereas vegetation richness, total nitrogen and the K/Al ratio presented the strongest effects on bacteria, with relative importance values of 16.1%, 12.5% and 11.6%, respectively. For the microbial community composition of both archaea and bacteria, the moisture index showed the dominant effect, explaining 17.6% of the observed variation, followed by MAT and MAP. Taken together, temperature and precipitation exerted considerable indirect effects on microbial richness and evenness through local environmental and energy supply-related variables, such as vegetation richness, whereas temperature exerted a larger direct influence on LCBD and the community composition. Our findings highlighted the profound influence of temperature and precipitation interactions on microbial beta diversity in alpine grasslands on the Tibetan Plateau.

Monitoring of Neotropical Streams Using Macroinvertebrate Communities: Evidence from Honduras

Assessing the water quality by using biological indicators is a reliable and economically feasible way to promote environmental conservation in developing tropical countries. Here, we report one of the few examples of river biomonitoring in Honduras. In June 2005, benthic macroinvertebrates were collected from six sites in the Río Cangrejal basin. An adapted version of the Biological Monitoring Working Party index (BMWP) was used to assess the water quality because it is simple, consolidated, relatively easy to use, and needs a family-level identification. Moreover, two other community metrics were calculated, namely the total taxon richness and local contribution to beta diversity (LCBD). Differences in the biomonitoring and diversity metrics among sites and their correlations were statistically tested. Thirty-nine macroinvertebrate taxa were collected and, despite significant differences in the BMWP score, all sampling sites were classified in the high environmental quality class. A very strong and positive correlation between the BMPW and taxon richness was found, while LCBD did not vary significantly and did not correlate with the other metrics. Our results suggest that taxon richness could be used as a surrogate indicator to assess the water quality when consolidate biomonitoring methods are not available.

Local contributions to beta diversity in urban pond networks: Implications for biodiversity conservation and management

AbstractAimAn understanding of how biotic communities are spatially organized is necessary to identify and prioritize habitats within landscape‐scale biodiversity conservation. Local contribution to beta diversity (LCBD) identifies individual habitats that make a significant contribution to beta diversity and may have important practical implications, particularly for conservation of habitat networks. In this study, we develop and apply a conservation prioritization approach based on LCBD in aquatic invertebrate communities from 132 ponds.LocationFive urban settlements in the UK: Halton, Loughborough, Stockport, Birmingham and Huddersfield.MethodsWe partition LCBD into richness difference (nestedness: RichDiffLCBD) and species replacement (turnover: ReplLCBD) and identify key environmental variables driving LCBD. We examine LCBD at two scales relevant to conservation planning: within urban settlements and nationally across the UK.ResultsSignificant differences in LCBD values were recorded among the five settlements. In four of the five urban settlements studied, pond sites with the greatest LCBD values typically showed high replacement values. Significant LCBD sites and sites with high taxonomic diversity together supported more of the regional species pool (70%–97%) than sites with high taxonomic diversity alone (54%–94%) or what could be protected by the random selection of sites. LCBD was significantly associated with vegetation shading, surface area, altitude and macrophyte cover.Main conclusionsConservation prioritization that incorporates LCBD and sites with high taxonomic diversity improves the effectiveness of conservation actions within pond habitat networks, ensures sites supporting high biodiversity are protected and provides a method to define a spatial network of protected sites. Identifying new, effective conservation approaches, particularly in urban areas where resources may be scarce and conflicts regarding land use exist, is essential to ensure biodiversity is fully supported, and detrimental anthropogenic effects are reduced.

The anthropic gradient determines the taxonomic diversity of aquatic insects in Amazonian streams

Anthropic activities are one of the main drivers of change in the environmental characteristics of streams and the diversity of aquatic macroinvertebrates. We evaluated the influence of an anthropic gradient (varying degrees of impact) on the genera level alpha and beta diversity of the Ephemeroptera, Plecoptera, and Trichoptera (EPT) in 48 eastern Amazonian streams. These insects were sampled using a dipnet, and the anthropic gradient was represented by the activities observed in the channel and the catchment of each stream. We found that increasing anthropic impact reduced the alpha diversity of the EPT. The Total Beta Diversity (BDTotal) showed a moderate degree of variation in streams. The streams with the greatest Local Contribution to Beta Diversity (LCBD) had the lowest alpha diversity of EPT, while the genera with the greatest Species Contribution to Beta Diversity (SCBD) were the most abundant and widely distributed among the streams. Thus, the increase in anthropic impacts reduced the alpha diversity of the EPT and indirectly influenced the uniqueness, emphasizing the importance of using different components of the diversity to understand the effects of anthropic impacts on Amazonian streams.

Effects of urbanization and environmental heterogeneity on fish assemblages in small streams

Abstract The structure of freshwater assemblages may be driven directly by urbanization or indirectly by a reduction in environmental heterogeneity (EH). Disentangling the effects of urbanization and EH requires uncorrelated proxies of each of these factors. We assessed the effects of the degree of urbanization and EH on the structure of fish assemblages. We sampled fish in 45 streams located in the urban area of Cuiabá. We assessed the effects of urbanization and EH on rarefied fish species richness (Srarefied), the local contribution to beta diversity (LCBD), and composition with linear models and distance-based redundancy analysis. Our indexes of urbanization and EH were not correlated. We found that both Srarefied and the LCBD decreased with an increasing degree of urbanization, but were not associated with EH. We also noted that few native fish species abundances were associated with the EH. Serrapinnus microdon, S. calliurus, Hemigrammus tridens, and Astyanax lacustris were abundant in streams with a lower degree of urbanization. The non-native Poecilia reticulata was more abundant in streams with a higher degree of urbanization. Our results highlight that urbanization leads in negative impacts on fish assemblages, such as decreases in diversity and the dominance of non-native species.

Anuran diversity of four taxocenoses of the subtropical Atlantic Forest from Santa Catarina and Paraná states Brazil

Local fauna inventories provide primary key information on diversity and distribution of species for conservation purposes. The Atlantic Forest holds 50% of anuran species in the country and the main threats to the conservation of this fauna are habitat reduction and fragmentation. The present study brings information on the local richness and species composition of four anuran taxocenoses from the subtropical Atlantic Forest of Paraná and Santa Catarina states, Brazil. Data collection included breeding sites surveys (N = 56) and literature review. Richness and beta diversity were compared through rarefaction/extrapolation curves, local contribution to beta diversity (LCBD), beta partitioning and cluster analysis. Anuran from 46 species were registered and local richness differences were observed on the rarefaction/extrapolation curves and on asymptotic analysis. Nevertheless, the LCBD did not detect differences in species composition among the four taxocenoses. The turnover was the predominant component of beta diversity. The geographical distances explain species composition for all localities compiled in this study. The differences among local richness may be related to environmental impacts, emphasizing the need for conservation of biodiversity in the remnants of Atlantic forest.

Seasonal patterns of ecological uniqueness of anuran metacommunities along different ecoregions in Western Brazil

Beta diversity can be portioned into local contributions to beta diversity (LCBD), which represents the degree of community composition uniqueness of a site compared to regionally sampled sites. LCBD can fluctuate among seasons and ecoregions according to site characteristics, species dispersal abilities, and biotic interactions. In this context, we examined anuran seasonal patterns of LCBD in different ecoregions of Western Brazil, and assessed their correlation with species richness and if environmental (climatic variables, pond area and ecoregions) and/or spatial predictors (spatial configuration of sampling sites captured by distance-based Moran's Eigenvector Maps) would drive patterns of LCBD. We sampled anurans in 19 ponds in different ecoregions in the Mato Grosso do Sul state, Western Brazil, during one dry and one rainy season. We found that LCBD patterns were similar between seasons with sites tending to contribute in the same way for community composition uniqueness during the dry and rainy season. Among studied ecoregions, Cerrado showed higher LCBD values in both seasons. In addition, LCBD was negatively correlated with species richness in the dry season. We also found that LCBD variation was explained by ecoregion in the dry season, but in the rainy season both environmental and spatial global models were non-significant. Our results reinforce the compositional uniqueness of the Cerrado ecoregion when compared to the other ecoregions in both seasons, which may be caused by the presence of species with different requirements that tolerate different conditions caused by seasonality.

Spatial and Temporal Ecological Uniqueness of Andean Diatom Communities Are Correlated With Climate, Geodiversity and Long-Term Limnological Change

National Socio-Environmental Synthesis Center (SESYNC) from the US NSF DBI-1639145 National Geographic Society 8672-09 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT LIFE14/IPE/FI/023 project FRESHABIT LIFE IP LIFE14/IPE/FI/023 National Science Foundation (NSF) EAR-1338694

Spatial processes determine planktonic diatom metacommunity structure of headwater streams

Headwater streams are interesting ecological systems for studies of metacommunities given their high degrees of isolation, unidirectionality of water flow and hierarchical organization in the drainage network. In addition, for passively dispersing aquatic organisms (e.g. planktonic diatoms), connectivity between sites is unidirectional, which implies a higher isolation of headwaters, leading to a greater dispersal limitation between streams. The aim of this study was to evaluate the relative importance of local environmental (i.e., physicochemical variables) and spatial (i.e., distance between sites) components to the planktonic diatom community in 28 headwater streams of the Cerrado, central region of Brazil. Due the fact that each sampling point was located in a different headwater stream, we expected that spatial components (a proxy for diatom dispersal) were more important than local environmental conditions to the structure of the diatom metacommunity. We found 51 morphospecies of diatoms (Bacillariophyceae). The community composition of diatoms showed strong spatial variation, which was also indicated by high beta diversity (mainly contributed by the turnover component). The variation in diatom community composition, species richness, total density, and Local Contribution to Beta Diversity (LCBD) of headwaters streams was explained solely by spatial factors. Based on these results, we inferred that due to dispersal limitation, the diatom communities of these headwaters tend to show distinct species composition, with high species turnover among the local communities. We highlight the importance of headwater streams as reservoirs of biodiversity for a riverine diatom metacommunity.

Local environmental, geo-climatic and spatial factors interact to drive community distributions and diversity patterns of stream benthic algae, macroinvertebrates and fishes in a large basin, Northeast China

Understanding processes and mechanisms driving patterns of species distribution and diversity is a vital theme in community ecology and conservation biology. There has been a continuous increase in studies focusing on diversity patterns in freshwater ecosystems during the last few decades. However, comparative studies of species distributions, diversity patterns and underlying processes across trophic levels remain limited. The unique characteristics of the study area (i.e. Hun-Tai River in Northeast China) generates a wide range of environmental conditions to advance our understanding of what drives community assembly and diversity pattern of three stream organism groups. We applied variance partitioning (VPA) to correlate community compositions with environmental and spatial factors to infer stochastic and deterministic assembly processes, respectively. Linear regression (LR) models were used to identify the main drivers of species richness and local contributions to beta diversity (LCBD) as a function of different factors, including local environmental (e.g., in situ parameters, hydrology, nutrients), geo-climatic variables (e.g., land use, topography, climate) and spatial factors. Results indicated that species compositions of stream biota showed significant correlations with local environmental, geo-climatic and spatial factors. VPA demonstrated that both paradigms (i.e. deterministic and stochastic processes) interact to influence the biota distributions with stochastic process contributing more than deterministic process. In addition, the strongest stochastic process was found in fishes (10%), followed by benthic algae and macroinvertebrates with the same effects (8%). Notably, geo-climatic factors explained a substantial fraction of species composition, richness and beta diversity, although their effects were partially manifested via local and spatial variables. We demonstrate the relative importance of both stochastic and deterministic processes in shaping community composition and biodiversity of three stream organism groups in a large basin. This emphasizes the need to move beyond observed patterns and consider metacommunity theory into river management and conservation practices.

Taxonomic dependency of beta diversity components in benthic communities of bacteria, diatoms and chironomids along a water-depth gradient

Community variation (i.e., beta diversity) along geographical gradients is a well-known ecological pattern, but the corresponding variation in beta diversity components (e.g., species turnover and nestedness) and underlying drivers remain poorly understood. Based on two alternative approaches (that is, the beta diversity partitioning proposed by Baselga and the Local Contributions to Beta Diversity (LCBD) partitioning proposed by Legendre), we examined the patterns of beta diversity components of lacustrine benthos, from bacteria to diatoms and chironomids, in the surface sediments along a 100-m water-depth gradient in Lugu Lake. We further quantified the relative importance of spatial, environmental and biotic variables in explaining water-depth patterns in beta diversity. Based on the Baselga's framework, there was a taxonomic dependency for the patterns of beta diversity components with water-depth, showing a significant species turnover pattern for bacteria, while diatoms and chironomids showed significant nestedness. This dependency was also evident in the patterns of community uniqueness with water-depth because based on Legendre's framework, the LCBD decreased with water depth for bacteria whereas increased with depth for diatoms. The total beta diversity and species turnover of bacteria could be explained by the pure effects of spatial, environmental and biotic variables. A total of 26.8% and 23.6% of the nestedness component of diatoms and chironomids was explained by environmental variables, respectively, while species turnover was mostly related to spatial variables. Bacteria total LCBD and species replacement were driven only by environmental variables. For diatoms and chironomids, however, most of the total LCBD and its two components were explained by spatial variables, and biotic variables were most important for the diatom replacement component. Our findings provide insights into the mechanisms responsible for community organizations along water-depth gradients from the perspective of beta diversity components.

Untangling the determinants of macrophyte beta diversity in tropical floodplain lakes: insights from ecological uniqueness and species contributions

Deconstructing beta diversity patterns into site or species contributions is a modern approach to understand the factors affecting variation in biodiversity. In this context, estimating the Local Contribution to Beta Diversity (LCBD) and the individual Species Contribution to Beta diversity (SCBD) have been shown to be a good approach to improve knowledge of the drivers of beta diversity. We examined the beta diversity of macrophytes surveyed at 49 floodplain lakes in the Pantanal Wetlands in Brazil during the dry season. We found that, unexpectedly, total species richness was not correlated to LCBD values, but the number of rare species per site was possibly related to LCBD values. Three variables from Moran’s Eigenvector Maps (MEM), water transparency and organic matter were the main variables related to LCBD values. The species with highest contributions to beta diversity were those that occurred at approximately half of the surveyed sites. The same patterns were observed when analysing macrophyte data divided by life forms. Of the life forms, floating macrophytes contributed most to beta diversity. The understanding of which factors drive variation in LCBD and which kind of species most contribute to SCBD are fundamental to performing efficient conservation and restoration programs to maintain the structural, functional and ecological diversity of the macrophyte communities in dynamic floodplain ecosystems.