We studied the trait diversity and structure in the fish communities of two floodplain lakes of the Caura River: Aricagua and Paramuto, during one hydrological cycle. We calculated taxonomic and a functional alpha and beta diversities and made comparisons among hydrological seasons and among habitats within each lake based on rarefactions. The trait structure was explored with an RLQ (analysis of a table R of environmental conditions, a table L of abundances of species and a table Q of species traits) analysis, and pairwise relationships between environmental variables and traits were explored with fourth-corner analyses. Despite its smaller extension, Paramuto showed higher alpha taxonomic and trait diversities. The substrates of open sand and those covered by leaf litter were the most diverse habitats in terms of both species and traits. The trait structure of the fish communities was influenced by the hydrological seasons, the lakes as well as water pH and temperature, and in a lesser degree dissolved oxygen, habitat type and total dissolved solids in the water. These factors constitute the habitat templet for the fish community's composition and trait structure. K E Y W O R D Scomponents of beta diversity, fourth-corner analysis, neotropical freshwater fish communities, RLQ analysis

Twenty nine species have been added to the annotated checklists of the ichthyofauna of the Caura River Basin, Guiana Shield, Venezuela. Of these, 18 were found in two floodplain lagoons in the lower Caura, corresponding to the orders Characiformes, Clupeiformes, Gymnotiformes, Siluriformes and Perciformes and one species of Tetraodontiformes in the port of Maripa. The others 11 species were found in the upper Caura, representing the orders Characiformes, Gymnotiformes and Siluriformes. Previous ichthyofaunal surveys in the Caura river Basin recorded a total of 514 species, including 150 species for the upper Caura and 492 for the lower Caura. After our recent survey the total number of fish species in the whole drainage basin increased to 543 species, of which 172 and 510 belong to the upper and lower Caura, respectively.

The Caura National Park encompasses the entire basin of the River Caura, one of the most biodiverse hydrographic systems of Venezuela, yet the ichthyofauna, particularly in the upper basin, has been poorly studied. In this study, the taxonomic and functional diversity of fishes in mesohabitats of the River Kakada, a main tributary of the upper River Caura in Southern Venezuela, are described. The fishes were sampled in four mesohabitat types with seines during four different occasions, representing the hydrological seasons of rising waters, high waters, falling waters and low waters. Functional diversity indices were calculated based on four traits: size, trophic guild, mouth orientation and body shape. A total of 56 fish species were registered. There were significant differences in species composition of the fish assemblages and their taxonomic diversities among mesohabitats and across hydrological seasons, and the taxonomic and functional diversities were higher in the mesohabitats with presence of riparian forest. However, there were no seasonal variations in functional composition or functional diversities. The rocky substrates had unique assemblages of habitat specialist species with a particular array of traits. On the other hand, the presence of riparian forest and more structurally complex substrates favors the coexistence of a high diversity of fishes with a variety of trait combinations, whereas the seasonal fluctuations in the water level might propitiate stochastic processes of dispersion and colonisation that generate variations in species composition and taxonomic diversity. Considering the spread of artisanal gold mines in the Caura National Park, the results of this investigation might serve as a reference for future studies that assess the impacts of the gold mining activities on the river integrity and their fish communities.

Abstract:The study of co-occurrence patterns has been extensively applied to propose assembly rules for community organization. Recently, a new interest has grown in the effect of gradients on these patterns and to analyze them through new approximations such as co-occurrence networks, through which keystone species can be identified. Neotropical floodplains represent interesting systems to study such patterns, because of their spatial heterogeneity, temporal variability and their high fish species richness. With this in mind, our goal was to study the co-occurrence patterns of fish in a segment of the Arauca River's floodplain and the influence of the spatial and temporal variability on them. One stream and one floodplain lake were sampled with gill nets during 2014 -2015 across a hydrological cycle and 5 matrices for each 5 sampled months in each water body were prepared to explore the co-occurrence patterns in each water body across months and 2 for the entire period, through a probabilistic pair-wise analysis of species co-occurrence that identified aggregated and segregated species pairs. With the observed cooccurrences × water body × month, the species weighted degrees and betweenness were calculated, and co-occurrence networks were constructed. The networks structures, in terms of the degrees of every species, were compared spatially and temporally through a generalized linear model. The stream showed the highest numbers of aggregated species pairs, and in general showed the most complex networks in terms of nodes, edges and degrees. The habitat type and the hydrological phases significantly influenced the structure of the fish co-occurrence networks. Two species, Loricariichthys brunneus and Pygocentrus cariba were identified as the core of the fish communities of the floodplain and as keystone species because they contribute to the connection of the networks by having a series of links with less frequent species.