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In river–floodplain systems, the construction of dams causes environmental changes in the natural dynamics of rivers and the associated wetlands, which can affect both the taxonomic and functional composition of communities, and, consequently, ecosystem functioning. We evaluated zooplankton taxonomic and functional β‐diversity in sets of lakes associated with a preserved and a dammed river in a Neotropical floodplain. We expected that both β‐diversity measures would be lower in lakes associated with a dammed river than in lakes associated with a preserved river. β‐Diversity was partitioned into turnover and nestedness components, through multiple‐site dissimilarity measures, and compared with expected null models. We expected that nestedness would be more important for both the β‐diversity measures in lakes associated with the dammed river, whereas species and trait turnover would be more important in lakes associated with the preserved river. Functional β‐diversity was higher among lakes of the preserved river than of the dammed river, while taxonomic β‐diversity was not different between the rivers. Contributions of turnover and nestedness components were similar in the preserved river, whereas that of nestedness was higher in the dammed river, revealing the loss of extreme trait combinations from the functional space. Comparisons between observed and expected β‐diversity revealed a higher trait turnover than would be expected by species turnover in the preserved river, and no differences from the null models were observed in lakes associated with the dammed river. Our results suggest that dissimilarity in trait composition is influenced more by environmental changes associated with river damming than by dissimilarity in species composition such that a functional homogenisation occurs without a change in taxonomic β‐diversity. We propose the maintenance of preserved tributaries in floodplains, which sustain environmental heterogeneity, primarily if the nearby environments are already dammed. Furthermore, we reinforce the necessity of a pluralistic approach, considering both taxonomic and functional aspects of biodiversity in ecosystem management.

Aim: This study presents length-weight regressions adjusted for the most representative microcrustacean species and young stages of copepods from tropical lakes, together with a comparison of these results with estimates from the literature for tropical and temperate regions; Methods: Samples were taken from six isolated lakes, in summer and winter, using a motorized pump and plankton net. The dry weight of each size class (for cladocerans) or developmental stage (for copepods) was measured using an electronic microbalance; Results: Adjusted regressions were significant. We observed a trend of under-estimating the weights of smaller species and overestimating those of larger species, when using regressions obtained from temperate regions; Conclusion: We must be cautious about using pooled regressions from the literature, preferring models of similar species, or weighing the organisms and building new models.Keywords: dry weight, cladocerans, copepods, biomass, secondary productivity.Resumo: Objetivo: Este estudo apresenta as regressões peso-comprimento elaboradas para as espécies mais representativas de microcrustáceos e formas jovens de copépodes em lagos tropicais, bem como a comparação desses resultados com as estimativas da literatura para as regiões tropical e temperada; Métodos: As amostragens foram realizadas em seis lagoas isoladas, no verão e no inverno, usando moto-bomba e rede de plâncton. O peso seco de cada classe de tamanho (para cladóceros) e estágio de desenvolvimento (copépodes) foi medido em microbalança eletrônica; Resultados: As regressões ajustadas foram significativas. Observamos uma tendência em subestimar o peso das espécies de menor porte e superestimar as espécies de maior porte, quando se utiliza regressões pesocomprimento obtidas para a região de clima temperado; Conclusão: Devemos ter cautela no uso de regressões peso-comprimento existentes na literatura, preferindo modelos para as mesmas espécies, ou pesar os organismos e construir os próprios modelos.Palavras-chave: peso seco, cladóceros, copépodes, biomassa, produtividade secundária.

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We investigated the hierarchical importance of local factors including lake area, macrophyte cover, and phytoplankton chlorophyll a (Chl-a) influencing zooplankton diversity (i.e., number of species) and the response of planktonic and littoral zooplankton species to these factors in 23 lakes in a Neotropical floodplain. Results of a regression tree clustered 4 groups of lakes separated according to the following factors in order of importance: percentage of macrophyte cover (environmental complexity), lake area (size of environment), and phytoplankton Chl-a (food resource). Macrophytes were significantly related to species diversity, as found by simple regression, whereas area and Chl-a were not significantly related to total zooplankton diversity. Planktonic species diversity correlated positively with area and Chl-a but negatively with macrophyte cover. By contrast, the opposite occurred for the littoral species, which correlated positively with macrophyte cover but negatively with lake area and Chl-a. We conclude that, in tropical shallow lakes, macrophytes are the most important factor influencing total zooplankton diversity; thus, maintenance and management of macrophytes should increase and promote conservation of aquatic biodiversity in these lakes.

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