Jean Carlo Gonçalves Ortega

Spatio-temporal organization patterns in the fish assemblages of a Neotropical floodplain

Communities can be structured over time by deterministic, stochastic, or both mechanisms. This study evaluated whether the fish assemblages of the Upper Paraná River floodplain were spatio-temporally structured and examined the mechanisms driving these organizational patterns. The floodplain ichthyofauna was sampled quarterly with seines and gillnets. The structure of the assemblage was assessed using the C-Score co-occurrence index and null models. The influence of both the environment (physical and chemical variables and hydrometric levels) and time on the species’ organization patterns was assessed via principal component analysis, multiple and simple regressions, and analyses of variance. Assemblages with larger species showed patterns of species segregation at both spatial and temporal scales, while those composed of smaller species often exhibited random patterns. The physical and chemical variables did not predict co-occurrence among species. For assemblages of large species, the patterns of co-occurrence tended to be random when the river level increased but only during high-water months. Therefore, the life history traits of the species, such as body size, may predict the structure of the assemblages in floodplains, but this effect depends on variations in the hydrometric level.

Interchange between flooding and drying, and spatial connectivity control the fish metacommunity structure in lakes of the Pantanal wetland

We evaluated if the homogenizing effect of flooding and the environmental differentiation during the dry period, as reflected in fish communities, are related to the type of connection between floodplain lakes and rivers. In order to do this, we sampled fish in the early dry and the early flood hydroperiods. We estimated the fish assemblage structure, as fish species richness, abundance, biomass, and beta diversity. We found that biomass varied among connectivity levels and hydroperiods, while richness varied among hydroperiods and density was influenced by an interaction between connectivity and hydroperiod. Species composition varied as a function of both connection type and hydroperiod, but the interaction between these factors was not observed. The fish assemblage in isolated lakes differed from those in temporarily and permanently connected lakes. Beta diversity increased from the early dry to the early flood period and was higher in temporarily connected lakes than in permanently connected lakes. These results indicated that the spatio-temporal variations in local fish communities of floodplain lakes can be attributed to differences in connectivity. Consequently, they strengthen the hypothesis that dispersal plays a fundamental role in shaping the pattern of fish species diversity in floodplain lakes.

Environmental filters predict the trait composition of fish communities in reservoir cascades

Dam construction alters flow regimes and can change the composition of aquatic communities. Using data from three Brazilian hydrographic basins, we tested the hypothesis that reservoir cascades act as environmental filters for fish traits. This dataset included information on different environmental variables and fish traits (diet, migration, fecundation, parental care, position in the water column, and body size), and we used multivariate analysis (partial RLQ) to quantify the relationships between environmental variables, species abundance and traits. We found that the abundance of migratory species declined towards downstream reservoirs, which tend to be smaller and less turbid with a shorter water residence time than upstream reservoirs. We also found evidence of an association between reservoir age and the domination of fish communities by small-sized species with parental care, external fecundation, and benthic habits. Our findings suggest that particular fish traits are selected for across reservoir cascades.

Experiments reveal that environmental heterogeneity increases species richness, but they are rarely designed to detect the underlying mechanisms

Environmental heterogeneity (EH) plays a central role in hypotheses used to explain distributions of species diversity. Here, we conducted a meta-analysis of species richness–EH (S–EH) relationships reported for experimental or quasi-experimental studies. We controlled for the lack of independence among effect sizes and additionally performed a cumulative meta-analysis. We found that EH has a consistent positive effect on species richness. This pattern was consistent across spatial scales, methodological issues and among taxonomic groups and realms. Furthermore, our cumulative meta-analysis highlighted that a positive S–EH relationship has been evident for nearly two decades. However, experiments often did not deeply explore the mechanisms underlying the positive relationship between EH and species richness. Taken together, our results present a robust pattern for the S–EH relationship, but our understanding of the main mechanisms is still in its infancy.