Ludgero Cardoso Galli Vieira

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.

Influence of spatial complexity on the density and diversity of periphytic rotifers, microcrustaceans and testate amoebae

Species richness, diversity and density in periphytic communities generally increase with substratum complexity. Aquatic macrophytes are often a main component of habitat complexity in lentic ecosystems, and the texture of aquatic macrophytes may alter the structure of periphytion. Here, we tested the hypothesis that even a subtle increase in complexity promotes an increase in species richness and density of periphytic organisms by means of a paired experiment with artificial plants. Artificial leaves were constructed simulating leaves of submerged aquatic macrophytes with veins (0.01 cm tall) and without veins (with the same foliar area). Nineteen pairs of artificial leaves, with two levels of complexity (with or without veins), were submerged during three weeks in Samambaia Lake, a small (ca. 4 ha) pond localized in Central Brazil. Species richness and density were significantly higher in the more complex leaves for rotifers and small bodied organisms (< 100 μm). Species composition as determined by ordination was not altered by complexity. The results suggest that even subtle differences in complexity of aquatic macrophytes (i.e. more complex venation) can influence the diversity of periphytic communities.

Using lower taxonomic resolution and ecological approaches as a surrogate for plankton species

Abstract 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.

Determinants of chlorophyll-a concentration in tropical reservoirs

Predictive models for chlorophyll-a concentration are the most common ecological tools for water-quality management. However, the interactions among factors driving eutrophication processes remain poorly understood. In addition to nutrient concentrations, other variables such as, for instance, hydrology, land use and biotic interactions may also be included as explanatory variables. Here, we compared a set of a priori models (which included local, morphological, and landscape variables) with respect to their power to predict chlorophyll-a concentration in 21 reservoirs of central Brazil. The best model, selected according to the Akaike information criterion, explained 67.7% of the variation in chlorophyll-a concentration, and indicated a positive relationship with total phosphorus concentration (the main predictor in our model) and depth. Turbidity was negatively correlated with chlorophyll-a concentration. Contrary to recent studies indicating the importance of landscape predictors, our results suggested a preponderance of local factors in determining chlorophyll-a concentration, and that the control of phosphorus sources in tropical reservoirs is as important as it is in temperate ecosystems. We also detected a substantial uncertainty regarding the best model, suggesting that further studies should focus on explicitly modeling the variation in the strength of the relationships between chlorophyll-a and explanatory variables.

Use of phytoplankton functional groups as a model of spatial and temporal patterns in reservoirs: a case study in a reservoir of central Brazil

We analyzed the temporal (dry and rainy periods) and spatial (zones) phytoplankton biomass variation (FGs—functional groups) in a tropical reservoir, and determined the main drivers. We hypothesized that water flow negatively affects the FG–environment relationship because high flow promotes dispersal stochasticity. Our results indicated that the FG–environment relationship was affected mainly by the rainfall regime. Periods with intermediate precipitation showed greater predictability than periods with extreme precipitation. This suggests that the effect of stochastic processes on the phytoplankton community is more important in both the highest and lowest water flow, and deterministic processes are more important at intermediate flow. The longitudinal gradient of nutrients, light, and water-column mixing influenced the distribution of the FG biomass. The riverine zone showed high nutrient concentrations, low light availability, and a high biomass of organisms related to highly enriched systems (FG J—chlorophyceans) and shade-adapted taxa (FG S1—cyanobacteria). The lacustrine zone showed high light availability and a high biomass of heterocytous cyanobacteria (FGs SN and H1) and meroplanktonic diatoms (FG MP). The functional approach can be applied to understand the processes responsible for species coexistence and for the organization of aquatic ecosystems.

Bird communities in different phytophysiognomies of the cerrado biome

The Brazilian cerrado is a global biodiversity hotspot and one of the most poorly sampled regions in the Neotropics. We describe the bird community structure among the distinct cerrado phytophysiognomies and among different periods of the day, in five environments of this biome. Bird observations were carried out from October 2003 to March 2005, by visual and acoustical records, using transect and point-count surveys. We found a total of 128 species in the area, including six species endemic to the cerrado biome, and found evidence of breeding in nine species. The bird community differed significantly among phytophysiognomies. Our data show that, even at a small spatial scale, high richness, endemism and nesting are likely to be found in the cerrado. The variation in species occurrence also reveals the unique community structure of each cerrado habitat type over time, even if the same vegetal formations were considered between habitats. Our results support the decision to convert the study site into the first university cerrado conservation unit, since this will protect a broad range of species and will guarantee habitats for some endemic birds.

The role of limnological variables and habitat complexity in impacted tropical streams as regulatory factors on the flagellate protozoa community

OBJETIVO: Contribuir para o conhecimento dos padroes de distribuicao espacial e sazonal da composicao e riqueza de especies de protozoarios flagelados de riachos tropicais impactados e ainda identificar quais variaveis (fisicas e quimicas ou descritoras de complexidade de habitat) regulam esses atributos nestes ambientes. METODOS: As coletas foram realizadas em 10 riachos tropicais (5 urbanos e 5 rurais), em dois periodos diferentes (verao e inverno). As variaveis limnologicas foram determinadas em campo (exceto a concentracao de nutrientes), a macroestrutura do habitat foi estimada visualmente in situ, com auxilio de um quadrat e a identificacao das especies foi realizada in vivo, sob microscopio optico. RESULTADOS: Foram identificados 106 taxons e a Ordem Euglenida foi a que mais contribuiu para a riqueza de especies, provavelmente, devido a sua alta tolerância as alteracoes ambientais. Analises multivariadas (ANOSIM e MDS) evidenciaram diferencas espaciais e sazonais significativas tanto para a composicao quanto para a riqueza de especies. A Bioenv e o Teste de Mantel mostraram que os padroes de composicao e riqueza de especies foram regulados pelas variaveis fisicas e quimicas da agua descritoras da qualidade da agua (pH, condutividade eletrica e concentracao de nutrientes). Entretanto, a riqueza de especies tambem foi influenciada pela complexidade estrutural do habitat e por sua estabilidade que pode ser perturbada pelo regime de chuvas. CONCLUSOES: Em suma, os resultados obtidos mostraram que os protozoarios flagelados sao bastante sensiveis as alteracoes ambientais e por isso podem ser usados como eficientes bioindicadores da qualidade da agua, como ja tem sido feito com outros organismos aquaticos. Alem disso, ficou evidente que atividades antropicas que causam mudancas na morfologia do canal dos ecossistemas loticos podem determinar a ocorrencia das especies de flagelados, pois a simplificacao da estrutura do habitat acarreta a diminuicao de especies presentes no ambiente.

Effects of Seasonality and Dispersal on the Ciliate Community Inhabiting Bromeliad Phytotelmata in Riparian Vegetation of a Large Tropical River

This study evaluated the influence of rainfall amount on the abundance, species richness, and species occurrence and abundance distribution of the ciliate community associated with the bromeliad Aechmea distichantha. The plants were collected from a rock wall of about 10‐km long at the left bank of Paraná River. We assessed the effects of both spatial and temporal variables on the community attributes, as well as whether plants geographically closer have a similar abundance distribution and species composition. The ciliate community was substantially distinct between both hydrological periods, with greater values of species richness and abundance in the rainy period. No spatial structuring (differences in the species occurrence and abundance distribution among strata) or geographical similarity (similarity in ciliate species composition among the plants) was found. Multiple regression analysis showed a positive relationship only between the ciliate abundances and water volumes for both periods. Although few of the formulated predictions were confirmed, our study provides valuable information on the ecological aspects of the ciliate community inhabiting bromeliad phytotelmata.

Two practical approaches to monitoring the zooplanktonic community at Lago Grande do Curuai, Pará, Brazil

The use of substitute groups in biomonitoring programs has been proposed to minimize the high financial costs and time for samples processing. The objectives of this study were to evaluate the correlation between (i) the spatial distribution among the major zooplankton groups (cladocerans, copepods, rotifers, and testaceans protozoa), (ii) the data of density and presence/absence of species, and (iii) the data of species, genera, and families from samples collected in the Lago Grande do Curuai, Para, Brazil. A total of 55 sample of the zooplanktonic community was collected, with 28 samples obtained in March and 27 in September, 2013. The agreement between the different sets of data was assessed using Mantel and Procrustes tests. Our results indicated high correlations between genus level and species level and high correlations between presence/absence of species and abundance, regardless of the seasonal period. These results suggest that zooplankton community could be incorporated in a long-term monitoring program at relatively low financial and time costs.

Environmental factors affecting chlorophyll-a concentration in tropical floodplain lakes, Central Brazil.

Chlorophyll-a (Chl-a) has been widely used in the assessment and monitoring of aquatic environments. Local and regional factors can influence Chl-a concentrations; moreover, the connection between terrestrial and aquatic ecosystems is a major paradigm within aquatic ecology. Here, we investigate the spatial distribution of Chl-a concentrations in a tropical savannah floodplain in Central Brazil using a broad spatial data set (a 900-km north-south transect; 30 lakes). We determine the relative importance of local environmental variables (limnological and morphometric) and regional (land use) and spatial distances (spatial eigenvector) on Chl-a concentrations using partial linear regression. We evaluate the direct and indirect effects of local and regional variables on Chl-a with a path analysis. Our results indicate spatially autocorrelated patterns wherein lakes in closer proximity showed more similar levels of Chl-a than more distant lakes. Local environmental factors explained most variance in Chl-a (R2adj = 0.28; P = 0.02); more specifically, both lake area and total nitrogen significantly (P < 0.05) explained Chl-a concentrations (direct effects). Meanwhile, regional factors neither directly nor indirectly predicted Chl-a. Thus, internal processes, such as the resuspension of sediment (which is frequent in tropical floodplains), rather than external influences, were the main factors that explained Chl-a concentrations in this study. The importance of local variables in structuring Chl-a concentration may be used to guide the conservation of the aquatic ecosystems in these tropical floodplain lakes.