Structure of Fish Assemblages Along Environmental Gradients in Floodplain Lakes of the Orinoco River

Abstract

Fish assemblages of temperate lakes are structured primarily by an interaction between piscivory and a small number of environmental variables, but tropical floodplain assemblages have often been viewed as unpredictably structured. We tested the predictability of fish assemblage structure in floodplain lakes of the Orinoco River, Venezuela, in relation to 22 variables describing environmental variation at the microhabitat, habitat, and supra‐lake levels. Fish species abundances were estimated through electrofishing surveys of 20 lakes in three regions for the early and late dry seasons of each of two consecutive years. Canonical correspondence analyses indicated that assemblage structure was predictably related to only four descriptors of lakes: transparency, conductance, depth, and area. Discriminant function analyses revealed that transparency (“clear”: Secchi transparency >20 cm; or “turbid”: Secchi transparency ≤20 cm) was tightly associated with the numerical density of six major taxa (82% classification accuracy) and the numerical density of piscivorous species (89% accuracy). Depth and area probably derived their significance from causal relationships to transparency and availability of cover, whereas the influence of conductance arose incidentally through an association with biogeographical zonation. Mantel tests indicated that similarity in structure of assemblages was not strongly related to the distance between lakes. Transparency was a remarkably reliable predictor of species composition. Fish with sensory adaptations to low light were dominant in turbid lakes, whereas visually oriented fishes predominated in clear lakes; seasonal change involved decline in the proportion of visually oriented fishes concomitant with a decline in transparency. The effect of transparency on assemblage structure was probably mediated by the relationship of transparency to visibility of prey. The structuring of Orinoco fish assemblages by piscivory, under the influence of transparency as controlled by depth and area, contrasts with previous views emphasizing random assemblage variation in neotropical floodplain lakes and extends the applicability of a conceptual model originally developed for temperate lakes.

Predicting diversity of juvenile neotropical fish communities: patch dynamics versus habitat state in floodplain creeks

“…Predation upon young ®sh would have occurred during the dry season, when ®sh densities in the creeks increased with decreasing water levels. Piscivores are known to modify the young ®sh assemblage structure by culling the most vulnerable prey species during low water in¯oodplain lakes of the Orinoco river (Rodriguez and Lewis 1997). In the Sinnamary Basin, some ®sh species are specialised in preying upon ®sh at very early stages (Me rigoux and ).…”

Lake connectivity and fish species richness in southern Brazilian coastal lakes

“…In aquatic habitats, the influence of habitat connectivity on biological communities has been generally analyzed using only structural connectivity metrics (the presence/absence of connections, connection length). These metrics do not take into account that the movement of an aquatic organism may be favored or limited by habitat characteristics (channel morphology, depth, flow direction, vegetation cover), water characteristics (salinity, oxygen), and predation (but see Rodríguez & Lewis, 1997;Hoffman et al, 2006;Macedo-Soares et al, 2010;Sepulveda & Marczak, 2012). Consequently, fish species dispersal between lakes depends not only on the length of connections, but also on the kinds of habitats along the connections (and their heterogeneity).…”

Five Cryptic Species in the Amazonian Catfish Centromochlus existimatus Identified Based on Biogeographic Predictions and Genetic Data

“…In terms of contemporary conditions, the Amazon Basin sustains dramatic hydrochemical and ecological gradients that impose physiological constraints upon its aquatic communities [38], [39], [40], [41], [42]. For instance, based primarily on optical and sedimentary characteristics, the Amazon and Madeira Rivers (Figure 1) are known as ‘white’ water rivers, characterised by a high content of dissolved solids and a neutral pH (Table 1).…”