Fábio Amodêo Lansac-Tôha

Biodiversity of zooplankton communities in the Upper Paraná River floodplain: interannual variation from long-term studies

We investigated the effect of interannual variation of hydrosedimentological regime and connectivity on the zooplankton biodiversity in the Upper Paraná River floodplain. Zooplankton samplings were undertaken between 2000 and 2007, in different environments of the floodplain, including connected and isolated floodplain lakes, backwaters, rivers and channels. The zooplankton included 541 species. Rotifers showed the highest species richness and abundance. Among the zooplankton species, 71 represent new occurrence records for the floodplain. The species accumulation curve showed a continuous increase in gamma diversity, demonstrating the importance of long-term research for accurate knowledge of biodiversity in heterogeneous and dynamic ecosystems, such as the floodplains. Interannual beta diversity among studied years indicated a lesser alteration in community composition in 2001, when a long limnophase period was observed. In most of the environments, the highest species richness values were related to the greatest flooding amplitudes. Flooding amplitude, which is associated with connectivity, favors faunal exchange amongst the environments and between the pelagic and littoral zones. This explains the occurrence of both planktonic and non-planktonic species within the community. On the other hand, mean zooplankton abundance values were higher when a long isolation period occurred. Differences between the potamophase and limnophase amplitude associated with connectivity among the environments were the most important factors for the structure and dynamics of the zooplankton community in the Upper Paraná River floodplain.

Dispersal Ability Determines the Role of Environmental, Spatial and Temporal Drivers of Metacommunity Structure

Recently, community ecologists are focusing on the relative importance of local environmental factors and proxies to dispersal limitation to explain spatial variation in community structure. Albeit less explored, temporal processes may also be important in explaining species composition variation in metacommunities occupying dynamic systems. We aimed to evaluate the relative role of environmental, spatial and temporal variables on the metacommunity structure of different organism groups in the Upper Paraná River floodplain (Brazil). We used data on macrophytes, fish, benthic macroinvertebrates, zooplankton, periphyton, and phytoplankton collected in up to 36 habitats during a total of eight sampling campaigns over two years. According to variation partitioning results, the importance of predictors varied among biological groups. Spatial predictors were particularly important for organisms with comparatively lower dispersal ability, such as aquatic macrophytes and fish. On the other hand, environmental predictors were particularly important for organisms with high dispersal ability, such as microalgae, indicating the importance of species sorting processes in shaping the community structure of these organisms. The importance of watercourse distances increased when spatial variables were the main predictors of metacommunity structure. The contribution of temporal predictors was low. Our results emphasize the strength of a trait-based analysis and of better defining spatial variables. More importantly, they supported the view that “all-or- nothing” interpretations on the mechanisms structuring metacommunities are rather the exception than the rule.

CLADOCERA FAUNA COMPOSITION IN A RIVER-LAGOON SYSTEM OF THE UPPER PARANÁ RIVER FLOODPLAIN, WITH A NEW RECORD FOR BRAZIL

Cladocera communities were studied in lotic and lentic environments of the Upper Paraná River floodplain, State of Mato Grosso do Sul, Brazil. A total of 63 species of Cladocera were identified in 108 samples. Of these, 24 species are considered new records for that floodplain, and one is a new record for Brazil. Chydoridae was the most representative family with 19 genera and 39 species.

Diversity and abundance of the planktonic rotifers in different environments of the Upper Paraná River floodplain (Paraná State — Mato Grosso do Sul State, Brazil)

This study proposes that diversity and abundance of rotifers show spatial and temporal variations in the Upper Parana River floodplain due to heterogeneity of the environment and hydrological level fluctuations of the main river. The structure and dynamics of rotifer assemblages were investigated by samplings carried out during the rainy (February) and dry period (August) of the year 2000, in 36 environments (rivers, channels, backwaters, open and isolated floodplain lakes). The influence of phytoplankton biomass on rotifer diversity and abundance was also investigated. 104 taxa of rotifers were identified. The highest species richness was found in rivers and open floodplain lakes, the highest abundances in the isolated floodplain lakes, and the highest values of species diversity in the channels, especially during the rainy period. β2-diversity values were higher in the channels, especially during the dry period. Flow differences and food availability were predominant factors influencing the structure and dynamics of the rotifer communities.

Community structure of rotifers in two environments of the upper River Paraná floodplain (MS) - Brazil

We evaluate the influence of abiotic and biotic factors on the community structure of rotifers across a regional hydrological cycle in lotic and lentic environments of the upper River Paraná. Depth, transparency, temperature, pH, electrical conductivity, dissolved oxygen, chlorophyll a and densities of rotifers were measured at two stations in Lake Guaraná (littoral and open water regions) and at one station in the River Baía (open water region). Highest densities of rotifers were found at the lake littoral. Canonical correlation analysis related environmental variables with the densities of the most abundant rotifers. The strongest relationship was with chlorophyll a, dissolved oxygen, hydrological level and water temperature. Diversity of rotifers at each station was mainly explained by fluctuations in hydrological level. Results of grouping analysis suggested the formation of groups according to phases of the hydrological cycle.

Correlates of Zooplankton Beta Diversity in Tropical Lake Systems

The changes in species composition between habitat patches (beta diversity) are likely related to a number of factors, including environmental heterogeneity, connectivity, disturbance and productivity. Here, we used data from aquatic environments in five Brazilian regions over two years and two seasons (rainy and dry seasons or high and low water level periods in floodplain lakes) in each year to test hypotheses underlying zooplankton beta diversity variation. The regions present different levels of hydrological connectivity, where three regions present lakes that are permanent and connected with the main river, while the water bodies of the other two regions consist of permanent lakes and temporary ponds, with no hydrological connections between them. We tested for relationships between zooplankton beta diversity and environmental heterogeneity, spatial extent, hydrological connectivity, seasonality, disturbance and productivity. Negative relationships were detected between zooplankton beta diversity and both hydrological connectivity and disturbance (periodic dry-outs). Hydrological connectivity is likely to affect beta diversity by facilitating dispersal between habitats. In addition, the harsh environmental filter imposed by disturbance selected for only a small portion of the species from the regional pool that were able to cope with periodic dry-outs (e.g., those with a high production of resting eggs). In summary, this study suggests that faunal exchange and disturbance play important roles in structuring local zooplankton communities.

Planktonic and non-planktonic rotifers in two environments of the Upper Paraná River floodplain, state of Mato Grosso do Sul, Brazil

Investigations were carried out for the composition and occurrence of rotifer taxa of different forms and sizes during two distinct hydrological periods, in two environments (river and lake). Two sampling stations were established in open water of each environments. Surface samples were taken daily for 14 days. The faunistic similarity between the environments was established using Jaccards index. One hundred and fourty three taxa were identified. The largest number of taxa was recorded in the river. Faunistic similarity between these environments was greater during high water. The planktonic taxa predominated and the difference for the non-planktonic ones was not marked. Non-planktonic taxa predominated in the river, while both types were numerous in the lake. We observed a larger number of smaller-sized taxa in both environments (> 200µm to 600µm in length). This was related to the shallowest depths and to current velocity, which moved benthic and periphytic taxa from the bottom and littoral zone into the water column.

Zooplankton assemblage concordance patterns in Brazilian reservoirs

The main goal of this study was to evaluate the assemblage concordance among three zooplankton groups (Rotifera, Cladocera and Copepoda) in 30 Brazilian reservoirs. According to Mantel tests and Procrustean analyses, there was a high level of assemblage concordance. Highest assemblage concordance was observed between cladocerans and copepods, while the lowest level of concordance was detected between copepods and rotifers. Based on environmental or biotic data, patterns of among-reservoir dissimilarities were fairly stable across the two seasonal periods analyzed in this study. Multiple Mantel tests were used to model the between-reservoir dissimilarities (Bray–Curtis distance) in zooplankton assemblage structure as a function of the limnological, geographical and morphological distances between pairs of reservoirs. The best predictor of faunistic dissimilarities was the matrix containing the limnological distances among the reservoirs. In general, these results are important for monitoring purposes because they supported the use of surrogate taxa and indicate that community concordance analysis may be a powerful tool for enhancing the efficiency of monitoring programs, ensuring their long-term sustainability.

Spatial and temporal variation in densities of testate amoebae in the plankton of the Upper Paraná River floodplain, Brazil

The occurrence and abundance of testate amoebae in the zooplankton of the floodplain of the Upper Paraná River was studied and compared with other zooplankton groups. Results showed that testate amoebae were dominant zooplankters in littoral zones of lentic and lotic environments. Species of Arcellidae were most abundant, followed by Difflugidae and Centropyxidae. The influence of environmental heterogeneity (lakes or river, littoral or pelagic zones and abiotic variables) on testate amoebae abundance was significant. Although significant differences were observed between different months, the patterns of abundance variation did not appear to be synchronously related to hydrological cycle. The results suggest that the high abundance of testate amoebae in the planktonic environment of Upper Paraná River floodplain is not determined only by stochastic process (washing out from the bottom and from the shoreline vegetation).

Floods control the influence of environmental gradients on the diversity of zooplankton communities in a neotropical floodplain

Floodplains show a high biodiversity due to their spatial heterogeneity and temporal variability, which are governed by environmental dynamics resulting from the flood pulse. We evaluated the importance of this driving force, the flood pulse, in the structuring of environmental gradients that influence species diversity in a neotropical floodplain. Gamma (γ) and alpha (α) zooplankton diversities were higher in the year with a typical flood pulse (2010), indicating that flood dynamics contributed to high diversity component values. We found significant relationships between α- and β-diversity and local environmental gradients, indicating that in years with a flood pulse, environmental filters might be the dominant mechanisms that structure the zooplankton community. Additive partitioning of γ-diversity showed that even in 2000 with atypical flood conditions, zooplankton diversities showed non-random patterns of spatial distribution and temporal variation in the floodplain. Our results indicate that the driving force of a floodplain can determine the spatial distribution of α- and β-diversity of aquatic communities owing to its primary effect on environmental filters. Therefore, if human activities that influence this driving force, such as water regulation, affect those environmental filters, floodplain biodiversity may decline.