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16 pages, 7 figures, 3 tables, supplementary data https://doi.org/10.1093/plankt/fbz019, The aquatic microbiota plays key roles in ecosystem processes; however, the mechanisms that influence their biogeographic patterns are not yet fully understood. Using high-throughput 18S rDNA gene sequencing, we investigated the composition of planktonic microeukaryotes (organisms sampled using a 68-μm plankton net) in 27 floodplain lakes of the Araguaia River, central Brazil and explored the influence of environmental and spatial factors for communities considering taxonomic and trophic groups. Of the 807 operational taxonomic units (OTUs) observed, Chlorophyta and Charophyta were the groups with greater abundance. Beta diversity was high, and the similarity of communities decreased as the geographic distance increased. We found a shared explanation between environmental and spatial predictors for total and autotrophic microbiota. Environmental variables influence only mixotrophic microbiota. These results suggest an OTU turnover along the floodplain and a spatially structured composition. This spatial pattern can be derived from the association with extrinsic factors, such as spatially structured environmental variables, that generate spatial dependence. However, the relationship between the composition of microbiota and environmental conditions is still unclear, Conselho Nacional de Desenvolvimento Científico e Tecnológico and research productivity grant (project nos. 473730/2013-8; 563834/2010-2; 563839/2010-4 to T.N.S., M.P.C.T., V.L.M.H. and J.C.N.); Fundação de Amparo a Pesquisa do Estado de Goiás (FAPEG; project no. 201212267001071); National Institutes for Science and Technology in Ecology, Evolution and Biodiversity Conservation, supported by MCTIC/CNPq (proc. 465610/2014–5) and FAPEG for the PhD scholarship to K.B.M. and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (R.L., as a visiting researcher in the Science without Borders Program)

Variation in phytoplankton functional diversity is partioned and mapped using several indices and linkage methods based on dendrograms. The relationships between diversity metrics and major environmental predictors, including zooplankton density, were assessed in 29 phytoplankton communities of floodplain lakes distributed along the Middle Araguaia River in central Brazil. The dendrogram-based functional diversity indices were Functional Group Richness, Functional Diversity, Mean Pairwise Distance and Mean Nearest Taxon Distance, whereas seven different hierarchical agglomerative linkage methods we used. The performance of indices were compared using ANOVA and their spatial variation in response to major environmental predictors evaluated. The results indicate that variation in functional diversity values is primarily a product of the type of index chosen. This variation was statistically significant in 90 % of the floodplain lakes studied; however, a spatial pattern of variation in index values along the river was not detected. Furthermore, environmental constraints, including zooplankton density, were weak predictors of functional diversity indices. Therefore, the mathematical characteristics of indices are of primary importance in explaining variation among functional diversity values.

This study focuses on determining how many samples are needed to effectively assess the species richness of a community. Zooplankton samples at 40 sampling sites distributed among four lakes in the floodplain of the middle Araguaia River (Central-West region of Brazil) were evaluated to determine the effect of the accumulation of collecting points by lake on species richness estimates. The results indicated the zooplankton community has high spatial heterogeneity. Thus, using a single sampling unit per lake would not be sufficient to accurately estimate their diversity (i.e. the zooplankton composition in these cases would be represented mainly by abundant species). Sampling designs that include a minimum of seven sampling sites in each lake are needed to record 70% of the total species richness. It is recommended, therefore, that researchers use a larger number of sampling sites per lake or, alternatively, that the water obtained and filtered through plankton nets is extracted from a wide area and in different lake compartments, rather than from a single site.

Understanding how species are structured in space and time and how they are functionally related to environmental conditions is still a challenge in ecology. In this study, we assessed the predictive power of lake morphometry, physical and chemical conditions of the water, and zooplankton density in relation to phytoplankton taxonomic and functional diversity in Amazonian floodplain lakes during low- and high-water periods. We also examined to what extent taxonomic and functional indexes were coupled. Taxonomic diversity was evaluated by species richness and Shannon index, and functional diversity by functional richness (FRic) and community-weighted mean trait value (CWM). The relative importance of predictive factors was evaluated by model selection, multi-model inference and correlations. We found that phytoplankton taxonomic and functional diversity indexes were mostly related to the same factors within the low- and high-water periods. Total phosphorus was the main driving factor in the low water, while euphotic zone depth and zooplankton density were the main driving factors in the high water. Taxonomic and functional diversity indexes were weakly coupled in the low water, but strongly coupled in the high water. Our results highlight that phytoplankton taxonomic and functional diversity can differ between periods, but respond similarly to environmental driving factors.

Aim This study aimed to investigate the relative influence of climate (temperature and precipitation) and land use on limnological features of 30 floodplain lakes in the Araguaia River, in Central Brazil, an important river that drains in the Brazilian Cerrado. Methods The lakes were sampled in one same period, at a large spatial scale (900 km along the river) covering climate and landscape variability. For decomposing the relative importance of land use and climate, we used the RDA and partitioning variance techniques. Results The lakes presented limnological gradient along the floodplain; in general, the lakes presented low transparency, nutrients concentrations ​​(total nitrogen and total phosphorus) and oxygen saturation. The water pH was considered weakly acidic. Considering land use in Araguaia river basin, lakes in downstream presented more remnant vegetation and lakes in upstream presented more livestock and agriculture soil use. The climate conditions were the most important in explaining the variation in limnological characteristics of the lakes, while the individual analysis of limnological variables showed that land use was important to explain to the pH and transparency of the water. Conclusions Finally, this study showed the importance of investigating regional climatic attributes and land use information to explain the limnological characterization of floodplain lakes. Thus, it highlights the importance of the possible impacts of global climate change on limnological conditions. Objetivo O objetivo desse estudo foi investigar a influência relativa do clima (temperatura e precipitação) e do uso da terra nas características limnológicas de 30 lagoas da planície de inundação do Rio Araguaia, no Brasil Central, um importante rio que drena no Cerrado brasileiro. Métodos As lagoas foram amostradas em um mesmo período, em uma grande extensão espacial (900 km ao longo do rio) cobrindo uma variabilidade climática e de paisagem. Para decompor o efeito relativo do clima e do uso do solo foi utilizada uma RDA seguida da partição da variância. Resultados As lagoas apresentaram um gradiente limnológico ao longo da planície de inundação. Em geral, as lagoas possuem baixa transparência, concentração de nutrientes (nitrogênio total e fósforo total) e saturação de oxigênio. O pH da água pode ser considerado fracamente ácido. Considerando o uso do solo na bacia do Rio Araguaia, as lagoas a jusante da planície apresentaram maior percentual de vegetação remanescente, ao passo que lagoas a montante da planície apresentaram maior uso do solo em pastagem em agricultura. As características climáticas foram o principal fator para explicar a variação das características limnológicas das lagoas estudadas, enquanto que análises individuais das variáveis limnológicas evidenciaram que o uso do solo foi importante para explicar a variação no pH e transparência da água. Conclusões O presente estudo evidenciou a importância de investigar os atributos climáticos regionais e o uso do solo para explicar as características limnológicas de lagoas na planície de inundação. Portanto, destacamos a importância de possíveis impactos das mudanças climáticas globais sobre as características limnológicas.

The use of lower taxonomic resolutions and ecological classifications can function as a strategy to minimize difficulties in plankton identification. To assess this issue, we evaluated the concordance of the spatial ordering of lakes in a floodplain using phytoplankton and zooplankton densities scaled at three taxonomic levels (species, genus, and family) and two exclusive ecological classifications for phytoplankton [Reynolds functional groups (RFGs) and morphology-based functional groups]. Furthermore, we evaluated the concordance of environmental variables with each taxonomic resolution/ecological classification. Procrustes and Mantel tests (simple and partial) were used for the concordance analysis. The correlations between species and higher taxonomic levels were found for phytoplankton and zooplankton. For the ecological classifications, significant r values, greater than 0.70, were obtained only for the Mantel test between species and RFGs. The relationship between species and genus and between species and family for phytoplankton can be explained by the environmental structure. For zooplankton, only species were related to environmental variables. These results indicate that it is possible to adopt a lower taxonomic resolution for identification of phytoplankton and zooplankton without a significant loss of information. However, the use of ecological classifications for phytoplankton is not recommended for this purpose.

The relative importance of local and regional processes in shaping natural communities within a metacommunity context has been a focus of intense debate in recent years. Floodplain lakes provide a good system for testing this theoretical approach, as they undergo seasonal variations in physical, chemical and biological factors, as well as in their degree of connectivity. Here, we investigated how local phytoplankton communities in lakes of a tropical river-floodplain system (Araguaia River floodplain – Central Brazil) were affected by environmental and spatial (dispersal) predictors in two rainy and two dry seasons (two consecutive years). Partial redundancy analysis indicated that during the periods analyzed the effects of neither predictor were significant. Although we cannot exclude the possibility that these tropical phytoplankton communities could be regulated by stochastic events, we suggested that further studies will have greater explanatory power if they include other variables related to biotic interactions (e.g., abundance of grazers) and fine-scale environmental variation.

Alpha, beta and gamma are three components of species diversity. Knowing these attributes in floodplain lake phytoplankton communities is vital when selecting conservation areas. Species diversity is commonly used with other taxonomic groups, but rarely with phytoplankton. We compared the number of phytoplankton species (alpha diversity) from 21 Middle Araguaia River floodplain lakes in the 2000 and 2001 rainy and dry seasons. From these samples we estimated complete survey species richness (gamma diversity), quantified differences in species composition between lakes (beta diversity) and assessed the influence of abiotic variables on beta diversity. We recorded a total of 577 taxa. The Sjack1 estimator indicated that 62.31% of taxa were sampled in the 2000 rainy and 67.65% dry seasons, and 68.36% in the 2001 rainy and 73.5% dry seasons. In almost all seasons, alpha diversity negatively correlated with latitude. Beta diversity (β-1) was higher in high water periods, especially in 2000. This may have been caused by isolated heavy rainfall, which would have increased environmental heterogeneity and raised beta diversity. DCA showed differences in phytoplankton composition between rainy and dry seasons in 2000 and 2001, reflecting the influence of flood pulses on phytoplankton composition. The Mantel test indicated spatial distribution patterns where geographically more distant lakes had less-similar phytoplankton communities.

This work analyses the attributes of the phytoplankton community (species richness, biovolume, diversity, equitability, abundance, dominance and size structure) associated with some physical, chemical and climatic variables of floodplain lakes of the Araguaia River, central Brazil, in the rainy and dry seasons of 2000 and 2001. The lakes in 2000 and 2001 presented different limnological characteristics between the periods of high and low water. The phytoplankton comprised 292 taxa, mainly Chlorophyceae and nanoplankton. In the dry seasons of both years, the functional group Y (Cryptophyceae) was the most prominent association. In high-water periods, different functional groups dominated the lakes. The canonical correspondence analysis (CCA) demonstrated a separation between the rainy and dry seasons of both years. The high and low water presented different dynamics in 2 years due to the influence of the flood pulse.

OBJETIVO: A diversidade beta é definida como as mudanças na composição de espécies ao longo de um gradiente ambiental, e atualmente, ecólogos têm investigado a influência de fatores locais (i.e. ambiente) e regionais (i.e. dispersão) na estrutura de comunidades. Os objetivos desse trabalho foram avaliar a diversidade beta da comunidade fitoplanctônica da planície de inundação do Curuaí e determinar a importância relativa dos processos ambientais e espaciais em sua estrutura; MÉTODO: A comunidade fitoplanctônica foi amostrada em 16 lagos da planície de inundação do Curuaí (Bacia Amazônica) durante o período de águas altas em 2002 e 2003. Usou-se a análise de redundância parcial (pRDA) para avaliar o efeito do ambiente (seis variáveis) e espacial (filtros espaciais) na variabilidade da composição da comunidade fitoplanctônica; RESULTADO: Foram registradas 156 espécies em dois anos de estudos, 122 espécies em 2002 e 66 espécies em 2003. A beta diversidade (índice βSIM) foi 0.889 em 2002 e 0.789 em 2003. A análise de partição da variância revelou que a maior parte da variação da comunidade fitoplanctônica não foi significativamente explicada pelos únicos efeitos ambientais e espaciais. No entanto, as variáveis ambientais no presente estudo apresentaram maior coeficiente de determinação do que as variáveis espaciais; CONCLUSÃO: Outros fatores afetaram a ausência de resultados significativos nos presentes dados, como variáveis locais não mensuradas (i.e. interações biológicas, hidrologia e outros) e eventos estocásticos. Dessa forma, sugerimos que variáveis como interações biológicas e outras variáveis locais sejam consideradas nesse tipo de análise para aumentar o poder de explicação e elucidar a variação da diversidade biológica. AIM: Beta diversity is defined as the change in species composition along environmental gradients, and in the present study, we investigated the influence of local (i.e., environmental) and regional (i.e., dispersal) factors in community structure. The aims of this study were to evaluate the beta diversity of phytoplankton communities in the Curuaí floodplain and to determine the relative importance of environmental and spatial processes in shaping phytoplankton community structure; METHOD: The phytoplankton communities were sampled in 16 lakes of the Curuaí floodplain (Amazon Basin) during high-water periods in 2002 and 2003. We used partial redundancy analysis (pRDA) to evaluate the pure effect of environmental (six variables) and spatial (spatial filter) variability on phytoplankton community composition; RESULTS: There were 156 taxa recorded in the two study years, including 122 algae species in 2002 and 66 algae species in 2003. The beta diversity that we measured (βSIM index) was 0.889 in 2002 and 0.789 in 2003. The partitioning variation demonstrated that the majority of variation in phytoplankton community structure was not significantly explained by pure environmental and pure spatial components. However, environmental variables presented a larger coefficient of determination than the spatial variable; CONCLUSION: Other factors than those we measured in this study, such as local variables (i.e., biotic interactions, hydrology, etc.) and stochastic events, affected the absence of significant results in our data. Therefore, we suggest that additional variables, such as biological interactions and other local factors, should be considered in this type of analysis to increase its explanatory power for understanding the variation of diversity in these communities.

O objetivo deste trabalho foi avaliar a estrutura e dinâmica das populações de fitoflagelados nos períodos de chuva e estiagem dos anos de 2000 e 2001 nas lagoas de inundação do rio Araguaia. As análises foram baseadas na riqueza específica, composição florística e biovolume dos fitoflagelados que estão associadas a determinadas variáveis climáticas, físicas e químicas da água. O teste de Mantel evidenciou um fraco padrão espacial das populações de fitoflagelados, além disso, o teste de Mantel corroborou a importância do componente local na estrutura dessas populações. Os escores derivados da DCA, aplicadas aos dados biológicos demonstram que os períodos de águas altas e baixas não se diferenciaram fortemente em 2000 e 2001, entretanto foi possível notar variação interanual das populações de fitoflagelados. Os dados de biovolume indicaram que existiu um fitoplâncton predominado por Chryptophyceae (grupo funcional Y) e Euglenophyceae (grupo funcional W1) em 2000 e 2001. A riqueza especifica e o biovolume responderam ao pulso de inundação, tanto as águas altas como as águas baixas apresentaram dinâmicas distintas nos dois anos o que pode indicar a importância do pulso de inundação sobre os fitoflagelados.

This study emphasizes that syntheses on biodiversity should consider the functional aspect of the species towards better understanding of the processes involved in community ecology and ecosystem functioning. This study is the first to assess the functional diversity and the functional and taxonomic beta diversity of periphytic algae in floodplain. For this, periphytic algae were evalueted on natural substrates, in two consecutive years in floodplain lakes. In a first approach the environmental filters were tested as structuring the functional diversity of these communities in two hydrological periods. In consecutive approaches, the objectives aimed to evaluate the functional and taxonomic beta diversity of these communities, what was the relationship between them and their partitioned components, and if environmental dissimilarity of the lakes was related to the functional and taxonomic beta dissimilarity. For the entire thesis the functional matrix comprised four functional traits of the species, and was used for construction of functional dendrograms. The main patterns demonstrated by this study were: i) that higher values of periphytic algae functional diversity are related to high-water period and less impacted environments; ii) there is no evidence that environmental filters are structure for the periphytic algae functional diversity in floodplain, and that dispersion-restricting is an important factor in this structure; iii) the taxonomical and functional beta diversity of these organisms may reveal different patterns; iv) surprisingly high taxonomic beta diversity not reveals high functional beta diversity, because there is a large redundancy in functional traits among species, even between dissimilar lakes. That way, was proved the necessity of to incorporate functional approach in studies of periphytic algae, and is an incentive to continue the evaluation of the periphytic algae functional traits on floodplains and other aquatic ecosystems. Sínteses sobre biodiversidade devem considerar o aspecto funcional das espécies para uma melhor compreensão dos processos envolvidos em ecologia de comunidades e funcionamento ecossistêmico. Esta análise é pioneira em avaliar a diversidade funcional e diversidade beta taxonômica e funcional de algas perifíticas em planície de inundação. A comunidade de algas perifíticas foi avaliada em substratos naturais em dois anos consecutivos em lagos de planície de inundação. Em uma primeira abordagem os filtros ambientais foram testados como estruturadores da diversidade funcional destas comunidades em dois períodos hidrológicos. Nas demais abordagens foram avaliadas as diversidades beta funcional e taxonômica das algas perifíticas, a relação entre elas e a suas desconstruções (turnover e resultante de aninhamento), e se a dissimilaridade ambiental dos lagos relacionava-se com as dissimilaridades beta funcional e taxonômica. A matriz funcional foi composta de quatro características funcionais das espécies, utilizada para a construção dos dendrogramas funcionais. Os principais padrões demonstrados foram que maiores valores de diversidade funcional de comunidades de algas perifíticas estão relacionados com período de águas altas e com ambientes menos impactados; que não houve indícios de que os filtros ambientais estruturam a diversidade funcional de algas perifíticas em lagos planície de inundação, e que a limitação da dispersão é um fator importante nesta estruturação; que a diversidade beta funcional e taxonômica nestas comunidades podem revelar tendências diferenciadas, com alta diversidade beta taxonômica e baixa diversidade beta funcional, porque há grande redundância nas características funcionais entre as espécies, mesmo entre lagos dissimilares limnologicamente. Constatamos a importância da determinação de padrões de diversidade beta taxonômica e funcional de algas perifíticas, e que o uso de características funcionais deve ser feito de forma cautelosa, com características que representem seu nicho. Incentiva-se a continuidade da avaliação das características funcionais desses organismos em planícies de inundação e em outros ecossistemas aquáticos. 64 f