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Understanding how species are structured in space and time and how they are functionally related to environmental conditions is still a challenge in ecology. In this study, we assessed the predictive power of lake morphometry, physical and chemical conditions of the water, and zooplankton density in relation to phytoplankton taxonomic and functional diversity in Amazonian floodplain lakes during low- and high-water periods. We also examined to what extent taxonomic and functional indexes were coupled. Taxonomic diversity was evaluated by species richness and Shannon index, and functional diversity by functional richness (FRic) and community-weighted mean trait value (CWM). The relative importance of predictive factors was evaluated by model selection, multi-model inference and correlations. We found that phytoplankton taxonomic and functional diversity indexes were mostly related to the same factors within the low- and high-water periods. Total phosphorus was the main driving factor in the low water, while euphotic zone depth and zooplankton density were the main driving factors in the high water. Taxonomic and functional diversity indexes were weakly coupled in the low water, but strongly coupled in the high water. Our results highlight that phytoplankton taxonomic and functional diversity can differ between periods, but respond similarly to environmental driving factors.

A limnological investigation involving physical, chemical and biological aspects was undertaken in five tropical upland lakes (Violao − Vl, Amendoim − Am, and Tres Irmas − TI1, TI2 and TI3) from Serra dos Carajas, Brazil. Results show that these lakes are shallow, weakly stratified, and of polymictic type. These characteristics may have caused vertical mixing of limnological parameters. Seasonal changes were minor for most parameters, except for chlorophyll-a (Chl-a ) and cyanobacteria, which also showed considerable variation between lakes. In general, waters of these lakes were mostly acidic in nature (avg. pH 4.9–5.9), with high total Fe (up to 1.52 mg/L) and low electrolytic conductivity (avg. 8.13–14 μS/cm) and total phosphorus (TP) (avg. 10–35.5 μg/L). Although the water bodies have good quality and classified as class I and II types according to CONAMA Resolution No. 357/05, trophic state index (TSI) varies from ultra-oligotrophic to eutrophic state, with higher trophic state observed for Vl, TI1 and TI2. Limnological characteristics of these lakes is highly influenced by lithological and morphological parameters. Principal component analysis (PCA) reveals that Chl-a and cyanobacteria are not solely influenced by TP and lower concentrations of all these parameters in Am lake are probably due to specificities of its catchment lithology. Phytoplankton taxa in the lakes are characterized by small chroococcales groups and desmids together with filamentous algae, more commonly observed in the dry season. The zooplankton community in the lakes is mainly dominated by rotifers, followed by cladocerans and copepods. Regarding species richness, zooplankton was highest in Vl, while phytoplankton is highest in TI1, and this aspect is most likely related to lake water levels.

Little effort has been devoted to charac- terizing the resting egg banks in tropical lakes. In this study, we evaluated the structure of egg banks across 26 Brazilian lakes located in four geographical regions. We also evaluated cross-taxon concordance in species richness and community similarity between dormant rotifers and dormant cladocerans, and searched for concordant patterns between dormant and active communities. We observed 88 taxa among all the hatchlings that belonged mainly to rotifers and cladocerans. Lakes located in the same geographical region displayed more similar dormant communities. Overall, no concordance was observed between dormant rotifers and dormant cladocerans. Concor- dance in community similarity was observed between dormant and active organisms but only for rotifers and the entire zooplankton community. Resting egg banks were not associated to a set of environmental variables. Our results demonstrate the occurrence of resting egg banks in several tropical lakes. Due to the weak concordant patterns, rotifers or cladocerans found in egg banks should be used cautiously as a surrogate of the other group in zooplankton surveys. Finally, the lack of strong concordance between the active and dormant stages of cladocerans suggests that some species may not receive appropriate cues to induce diapause.

Floods are major determinants of ecological patterns and processes in river-floodplain systems. Although some general predictions of the effects of water level changes on ecological attributes have been identified, specific tests using the flood pulse concept are scarce, mainly in tropical areas, where large river-floodplain systems abound. We tested the hypothesis that floods decrease environmental and biological variability using data from a near-pristine floodplain in Central Amazon (Brazil). We recorded nine limnological variables and the zooplankton community structure at eleven sites during one low and one high water period. During the low water period, when the levels of hydrological connectivity were low, asynchronous processes (e.g., sediment disturbance by biota, decomposition, and predation) likely determined the large environmental and biological heterogeneity in the floodplain. On the other hand, environmental variability and zooplankton beta diversity were significantly decreased by the flood. We postulate that floods act as “rubber erasers”, reducing the environmental and ecological idiosyncrasies created during low water periods. Also, we suggest that dilution effects and enhanced connectivity during the high water period, along with species sorting during the low water period, may determine zooplankton beta diversity patterns in river-floodplain systems.

After much debate, there is an emerging consensus that the composition of many ecological communities is determined both by species traits, as proposed by niche theory, as well as by chance events. A critical question for ecology is, therefore, which attributes of species predict the dominance of deterministic or stochastic processes. We outline two hypotheses by which organism size could determine which processes structure ecological communities, and we test these hypotheses by comparing the community structure in bromeliad phytotelmata of three groups of organisms (bacteria, zooplankton, and macroinvertebrates) that encompass a 10 000-fold gradient in body size, but live in the same habitat. Bacteria had no habitat associations, as would be expected from trait-neutral stochastic processes, but still showed exclusion among species pairs, as would be expected from niche-based processes. Macroinvertebrates had strong habitat and species associations, indicating niche-based processes. Zooplankton, with body size between bacteria and macroinvertebrates, showed intermediate habitat associations. We concluded that a key niche process, habitat filtering, strengthened with organism size, possibly because larger organisms are both less plastic in their fundamental niches and more able to be selective in dispersal. These results suggest that the relative importance of deterministic and stochastic processes may be predictable from organism size.

Conservation planning and biodiversity monitoring rely exclusively on the use of surrogate groups. However, the effectiveness of these groups in representing unknown biodiversity is rarely tested. These tests can be based on cross-taxon concordance (or congruence) analysis. In a second step, the main mechanisms underlying concordance can be investigated. Here, we evaluated the relative influence of local environmental factors and spatial processes on the patterns of beta-diversity exhibited by phytoplankton, zooplankton and benthic invertebrates and the strength of assemblage concordance among these assemblages in 38 upland Amazonian lakes (northern Brazil) over four years. Zooplankton and benthic invertebrates responded exclusively to environmental variables. These results are in accordance with the expected under the species sorting model, where local factors are the main mechanisms shaping assemblage structure. In general, patterns of concordance between the assemblages were weak and varied through time, indicating that the use of surrogates in freshwater ecosystems may be a flawed approach.

Aquatic coastal systems are affected by high fluctuations in salinity and the zooplankton may rely on dispersal or dormancy to recolonise these environments. Here, we analysed the long-term dynamics of the zooplankton community over 6 years during large salinity fluctuations in a coastal lagoon (Garças Lagoon, Brazil) and the effect of salinity on the hatching patterns of the resting egg bank. We hypothesised that salinity is the main driving factor of the zooplankton community structure, and that increases in salinity reduce the species richness and the abundance of hatchlings. Multiple regression analysis showed that salinity was associated negatively with species richness in the open water, whereas total phosphorus and chlorophyll-a concentrations were negatively and positively related to abundance respectively. Redundancy analysis demonstrated that temporally structured environmental variables (total phosphorus and salinity) were important for zooplankton composition. Periods of low salinity allowed the presence of freshwater organisms, changing the zooplankton composition over the years. However, our hatchling experiment showed a depauperate resting egg bank. Overall, our results showed a strong influence of salinity on the structure and dynamics of the zooplankton at Garças Lagoon, and that the resting egg bank likely plays a minor role in the zooplankton colonisation during low-salinity periods.

Human activities are exposing freshwater ecosystems to a wide range of stressors, whose direct and indirect effects can be alleviated or exacerbated through interactive effects with dynamic environmental drivers. This study used long-term data from two Neotropical lacustrine freshwater systems (Batata Lake, an Amazonian floodplain lake and Imboassica lagoon, an Atlantic coastal lagoon) subjected to different kinds of environmental fluctuations (i.e., flood pulse and sandbar opening) and anthropogenic impacts (i.e., siltation and eutrophication). Our objective was to determine whether the effects of human perturbations are contingent on modifications of important biotic and abiotic characteristics through environmental variability. For both ecosystems, environmental variability consistently interacted with anthropogenic perturbations to alter most of the variables analyzed, such as nutrient dynamics, chlorophyll- a concentration, zooplankton and benthic invertebrate species richness, and temporal community stability, which indicates that interactive effects between environmental variability and anthropogenic perturbations may impact a myriad of ecosystem properties. Furthermore, the nature of these interactive effects was highly dependent on the variable considered and on the ecosystem analyzed. For example, at Imboassica lagoon, sandbar openings interacted synergistically with trophic state to increase the phosphorus concentration in the water column. At Batata Lake, flooding generally alleviated the negative effects of siltation on species richness by both diluting inorganic suspended material concentration and by promoting local recruitment from the regional species pool. Such results indicate that our ability to understand and predict the outcome of anthropogenic impacts on inland aquatic systems can be hampered if we consider human stressors as “static” phenomena disconnected from dynamic interactions with major local environmental drivers.