Temporal dynamics and environmental predictors on the structure of planktonic testate amoebae community in four Neotropical floodplains

<p>Understanding the environmental factors that control community structure has become a major focus of ecological research in recent decades. Here, we aimed to analyze the structure of planktonic testate amoebae community and the impact of environmental variables on the diversity of planktonic species in four floodplains of Brazil (Amazonian, Araguaia, Paraná, and Pantanal) over two hydrological periods (2011 and 2012). We hypothesized that biological diversity (richness, abundance, and diversity) of the testate amoebae community is higher during drought periods. Samples were collected from the subsurface of the limnetic region of 72 lakes in the four floodplains during both drought and flood periods in both years. We identified 109 species, belonging to 11 families. Difflugiidae and Arcellidae exhibited higher species composition and abundance. ANOVA results showed noticeable temporal variation in testate amoebae community structure. We confirmed that the highest richness, abundance, and diversity were primarily recorded during drought periods, with significant differences being documented among floodplains and across the two hydrological periods. Multiple regression analysis also indicated that testate amoebae diversity is related to the productivity of the environments in the Amazonian, Araguaia, and Paraná floodplains. Depth of lakes and phosphorus appeared to be limiting factors in the Paraná and Araguaia floodplains, while dissolved oxygen limited species diversity in the Pantanal floodplain. Our results highlight that testate amoebae community exhibit the greatest biological diversity during drought periods, while species diversity is influenced by the environmental conditions (primarily productivity) of each floodplain.</p

Adjacent environments contribute to the increase of zooplankton species in a neotropical river

<div><p> Abstract Aim: The distribution of the zooplankton community along the Paraná River and in adjacent environments (tributaries and lakes) was evaluated, as well as the contribution of the community present in these environments to the species composition of the Paraná River. It was expected that the ensemble of species found in the last sampling site of the Paraná River would represent the accumulation of species found in the upstream sites. Methods The community was sampled at 25 sites, during 2013 and 2014, and the species richness and composition were determined. The similarity in the composition of the community between the environments was evaluated using cluster analysis, and the contribution of the species to the Paraná River was evaluated using nestedness analysis, using the NODF index. Results Overall, 193 species were registered (116 rotifers, 48 cladocerans and 29 copepods), with the majority of species considered as rare (163 species). In general, the composition of the community in the river was dissimilar to the adjacent environments, although there was a relationship among communities. Rotifers presented broad distribution throughout the area. As expected, the zooplanktonic species presented a nested distribution, with the last river site representing a set of the species registered in the upstream sites. Conclusion The results show the importance of the tributaries and lakes to the occurrence of species along the river. The distinct hydrological characteristics of the environments, as well as flow velocity, depth and connectivity, were responsible for the development of planktonic populations in the lakes that arrived in the main river through tributaries. With these results, we suggest the importance of the conservation of adjacent environments of the Paraná River for the maintenance of the zooplanktonic species in this system.</p></div

Main predictors of periphyton species richness depend on adherence strategy and cell size

<div><p>Periphytic algae are important components of aquatic ecosystems. However, the factors driving periphyton species richness variation remain largely unexplored. Here, we used data from a subtropical floodplain (Upper Paraná River floodplain, Brazil) to quantify the influence of environmental variables (total suspended matter, temperature, conductivity, nutrient concentrations, hydrology, phytoplankton biomass, phytoplankton species richness, aquatic macrophyte species richness and zooplankton density) on overall periphytic algal species richness and on the richness of different algal groups defined by morphological traits (cell size and adherence strategy). We expected that the coefficients of determination of the models estimated for different trait-based groups would be higher than the model coefficient of determination of the entire algal community. We also expected that the relative importance of explanatory variables in predicting species richness would differ among algal groups. The coefficient of determination for the model used to predict overall periphytic algal species richness was higher than the ones obtained for models used to predict the species richness of the different groups. Thus, our first prediction was not supported. Species richness of aquatic macrophytes was the main predictor of periphyton species richness of the entire community and a significant predictor of the species richness of small mobile, large mobile and small-loosely attached algae. Abiotic variables, phytoplankton species richness, chlorophyll-a concentration, and hydrology were also significant predictors, depending on the group. These results suggest that habitat heterogeneity (as proxied by aquatic macrophytes richness) is important for maintaining periphyton species richness in floodplain environments. However, other factors played a role, suggesting that the analysis of species richness of different trait-based groups unveils relationships that were not detectable when the entire community was analysed together.</p></div

Intercept, partial regression coefficients (± SE)and associated <i>t</i>-tests for the species richness of small and large firmly attached algae regressed against our explanatory variables in the Upper Paraná River floodplain.

<p>Significant results are highlighted in bold.</p

Minimum (Min), maximum (Max), mean values and coefficients of variation of the limnological variables and of the phytoplankton, macrophyte and zooplankton datasets in environments of the Upper Paraná River floodplain (<i>n</i> = 30).

<p>The first five variables in this Table were summarized by a Principal Component Analysis (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0181720#sec008" target="_blank">Results</a> section).</p

Intercept, partial regression coefficients (± SE) and associated <i>t</i>-tests for periphytic species richness regressed against our explanatory variables in the Upper Paraná River floodplain.

<p>Significant results are highlighted in bold.</p

Species richness variation of periphytic algae from the Upper Paraná River floodplain and of the groups formed according to morphological traits (<i>n</i> = 30).

<p>Species richness variation of periphytic algae from the Upper Paraná River floodplain and of the groups formed according to morphological traits (<i>n</i> = 30).</p

Intercept, partial regression coefficients (± SE) and associated <i>t</i>-tests for the species richness of small and large mobile algae regressed against our explanatory variables in the Upper Paraná River floodplain.

<p>Significant results are highlighted in bold.</p