Nadson Ressyé Simões

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.

Focando na variação: métodos e aplicações do conceito de diversidade beta em ecossistemas aquáticos

Ecologists usually estimate means, but devote much less attention to variation. The study of variation is a key aspect to understand natural systems and to make predictions regarding them. In community ecology, most studies focus on local species diversity (alpha diversity), but only in recent decades have ecologists devoted proper attention to variation in community composition among sites (beta diversity). This is in spite of the fact that the first attempts to estimate beta diversity date back to the pioneering work by Koch and Whittaker in the 1950s. Progress in the last decade has been made in the development both of methods and of hypotheses about the origin and maintenance of variation in community composition. For instance, methods are available to partition total diversity in a region (gamma diversity), in a local component (alpha), and several beta diversities, each corresponding to one scale in a hierarchy. The popularization of the so-called raw-data approach (based on partial constrained ordination techniques) and the distance-based approach (based on correlation of dissimilarity/distance matrices) have allowed many ecologists to address current hypotheses about beta diversity patterns. Overall, these hypotheses are based on niche and neutral theory, accounting for the relative roles of environmental and spatial processes (or a combination of them) in shaping metacommunities. Recent studies have addressed these issues on a variety of spatial and temporal scales, habitats and taxonomic groups. Moreover, life history and functional traits of species such as dispersal abilities and rarity have begun to be considered in studies of beta diversity. In this article we briefly review some of these new tools and approaches developed in recent years, and illustrate them by using case studies in aquatic ecosystems.

Biodiversity of testate amoebae (Arcellinida and Euglyphida) in different habitats of a lake in the Upper Paraná River floodplain

This study aimed to investigate the testate amoebae (Arcellinida and Eugliphida) species diversity in plankton, macrophytes and aquatic sediment samples from a shallow lake of the Upper Paraná River floodplain. Samples were carried out from April 2007 to March 2008. We recorded 89 taxa, belonging to 10 families. Eighty-two taxa were found in the aquatic sediment, 71 in the macrophytes and 53 in the plankton. Highest values of alpha diversity were observed in the aquatic sediment. Although the plankton had the highest number of accidental species, accessory and constant species were also observed in this habitat. Most of the species classified as constant for the plankton belonged to the genus Arcella. Most of the constant species in the macrophytes and aquatic sediment belonged to the genus Difflugia. This study supports the idea that the presence of these protists in the plankton should not be attributed only to stochastic processes because (i) the species diversity recorded in this habitat was remarkably high in relation to the total biodiversity of the lake, and (ii) we also recorded frequent and constant species in the plankton.

Impact of reservoirs on zooplankton diversity and implications for the conservation of natural aquatic environments

Reservoirs are intermediate ecosystems between rivers and lakes. These ecosystems break up the landscape by forming artificial lakes connected by rivers and change important ecological processes of lotic ecosystems (e.g. organic matter production and nutrient cycling) and thus have direct effects on aquatic biodiversity. We test the hypothesis that damming water courses exerts a negative effect on the zooplankton community by decreasing the alpha diversity. Samplings were conducted in 30 reservoirs and 29 natural lakes in the Neotropics, during two hydrological periods (dry and rainy) in 2001. The study analysed differences in alpha diversity, the number of rare, accessory and constant species, and species composition between the types of lakes. Alpha diversity was significantly higher in natural lakes and species composition differed between natural lakes and reservoirs. Zooplankton alpha diversity was positively related to total phosphorus (best model), indicating that productive environments (natural lakes) gather more species. Our results suggest that reservoirs have negative effect on community structure, whereas natural lakes have an important ecological function for biodiversity conservation because they are refuges for biodiversity.

Hydrological dynamics drives zooplankton metacommunity structure in a Neotropical floodplain

The maintenance of biodiversity in dynamic landscapes can be explained through the unifying concept of the metacommunity, an ecological system with a changing structure that arises from both the biotic features of its component species and from changing temporal processes. We evaluated the relative importance of environmental factors and spatial factors on the structure of metacommunities of zooplankton in a Neotropical floodplain system, in relation to hydrological dynamics and potential connections among lakes. Zooplankton was sampled from 16 to 22 shallow lakes during droughts and floods in two hydrologically contrasting years. Copepods appeared to be more limited by their dispersal potential, while testate amoebae and rotifers seemed to be controlled mostly by environmental variables. These findings stress the importance of the species sorting metacommunity paradigm for groups with the smallest propagules and adult body sizes. The importance of environmental factors rather than spatial factors was apparent during floods, likely due to the facilitation of animal dispersal by floods. Our results demonstrate that the importance of these factors depends on both the functional traits of major zooplankton groups and the hydrological dynamics of the region.

Structure of the testate amoebae community in different habitats in a neotropical floodplain

This study evaluated the differences in composition, abundance and morphology of testate amoebae among different habitats of the same aquatic environment (plankton, aquatic macrophyte and sediment) in the Upper Paraná River floodplain. Triplicate samplings were undertaken monthly at each habitat from April 2007 to March 2008. The structure of the community of testate amoebae was different among the habitats. The species typical for each habitat, according to Indval, were classified by their shell morphology. Arcella species together with Difflugia gramen and Difflugia pseudogramem were more abundant for plankton. Trinema and Phryganella stood out by their abundance and frequency in aquatic macrophytes. Centropyxis was an indicator of sediment. The results indicated a higher frequency of hemispherical and spherical shells in plankton and spherical and elongated shells in aquatic macrophytes. In the sediment, there was a high frequency of elongated species. Our results support the hypothesis that the community of testate amoebae has different structures among the habitats, refuting the idea that the organization of this community in plankton is guided by random events like the resuspension of organisms from the sediment and their displacement from marginal vegetation.

Zooplankton body-size structure and biomass in tropical floodplain lakes: relationship with planktivorous fishes

AIM: This study evaluated whether the size structure of the zooplankton community, as analyzed from density and biomass, would be influenced by bottom-up and/or top-down mechanisms in isolated lakes from the Upper Parana River floodplain during dry and rainy periods. METHODS: zooplankton individuals were classified as: smaller-sized ( 0.05), but it was associated to the increase in fish density during the dry season. The percentage of individuals with intermediate sizes (301 to 600 µm), in both biomass and density, was positively related to the fish density (R2 = 0.78 for biomass, p 600 µm), in both biomass (R2 = 0.86, p < 0.001) and density (R2 = 0.69, p = 0.02) was negatively associated to the fish density, reflecting a decrease of this size class with the increase of fish in the environment. CONCLUSIONS: This can implicate a direct and negative effect of the predation on larger-sized individuals, as well as indirect and positive effect on the intermediate-sized individuals, but it occurred only on dry season. Thus, different mechanisms act on the size structure of the zooplankton community between dry and rainy season.

Diversity and structure of microcrustacean assemblages (Cladocera and Copepoda) and limnological variability in perennial and intermittent pools in a semi-arid region, Bahia, Brazil

Ambientes temporarios sofrem secas periodicas devido a escassez de agua que interrompe a conectividade hidrologica com sistemas aquaticos adjacentes. No entanto, alguns ambientes retem agua por mais tempo permitindo uma maior persistencia das comunidades. Este estudo avaliou diferencas nas assembleias de microcrustaceos e na variabilidade limnologica entre pocas perenes e temporarias em um rio intermimente na regiao semiarida da Bahia. As caracteristicas abioticas das pocas temporarias (temperatura da agua, pH, alcalinidade total, condutividade eletrica e profundidade) foram mais afetadas do que nas pocas perenes devido a perda total do volume de agua. Isso pode ter contribuido para maior riqueza e indice de diversidade medio de microcrustaceos em alguns ambientes intermitentes, e a diferencas encontradas na estrutura das assembleias. Menores valores de diversidade e riqueza de especies foram registrados nos locais com fatores fisicos e quimicos restritivos que tornaram o ambiente improprio para os organismos, tais como: maior quantidade de solidos em suspensao e condutividade eletrica da agua e amplitude de variacao do pH. Estes resultados sugerem que nos ambientes intermitentes, o desenvolvimento da comunidade e interrompido pela estacao seca. Quando a agua retorna, devido as chuvas ou soerguimento do lencol freatico, cada ambiente apresenta um processo diferente de colonizacao. Nestas circunstâncias, a importância biologica dos ambientes aquaticos temporarios e destacada, ja que esses locais fornecem abrigos e tem um papel importante na manutencao da diversidade regional de ambientes aquaticos.

Distinct responses of Copepoda and Cladocera diversity to climatic, environmental, and geographic filters in the La Plata River basin

The distribution of freshwater cladocerans and copepods and the drivers of beta diversity along La Plata basin were studied. We propose that local environmental conditions, dispersal limitation, and climate affect cladocerans and copepods differently owing to their variances in terms of life strategies. We calculated beta diversity using four dissimilarity metrics, and also the relative importance of spatial, environmental, and climatic variables by partitioning variance and forward selection procedure coupled with a partial redundancy analysis. Beta diversity patterns were characterized by a high turnover in the subbasins and a small contribution of nestedness. Forward selection evidenced the influence of total nitrogen and total suspended matter for both copepods and cladocerans, suggesting a strong role of eutrophication in controlling their turnover, but spatial distance, precipitation, and mean temperature of winter were related only to copepods. The last one suggests a likely role of geographic isolation driving speciation and endemism in Copepoda and reinforces the strong effect of climatic variation resulting in the high endemism patterns one finds in the Neotropical region.