Simultaneous abrupt shifts in hydrology and fish assemblage structure in a floodplain lake in the central Amazon

Combined effects of climate change and deforestation have altered precipitation patterns in the Amazon. This has led to changes in the frequency of extreme events of flood and drought in recent decades and in the magnitude of the annual flood pulse, a phenomenon that influences virtually all aspects of river-floodplain ecosystem dynamics. Analysis of long-term data revealed abrupt and synchronous changes in hydrology and fish assemblage structure of a floodplain lake near the confluence of Amazon and Negro rivers. After an intense drought in 2005, the assemblage assumed a different and fairly persistent taxonomic composition and functional structure. Declines in abundance after 2005 were more pronounced for species of all sizes having equilibrium life history strategy, large species with periodic life history strategy, and for all trophic levels except primary consumers. Our results suggest that the extreme drought triggered changes in the fish assemblage and subsequent anomalous hydrological conditions have hampered assemblage recovery. These findings stress the need to account for climatic-driven hydrological changes in conservation efforts addressing aquatic biodiversity and fishery resources in the central Amazon

Diet and trophic structure of the fish assemblage in the mid-course of the Teles Pires River, Tapajós River basin, Brazil

ABSTRACT This study was carried out in a section of the middle course of the Teles Pires River, a clear water river that drains ancient and highly eroded geological formations, and where five hydropower plants are planned or in construction. In this study we tested the hypothesis that local fish fauna is mainly sustained by autochthonous food resources, with modest changes in the trophic structure of fish assemblages along the hydrometric cycle. Sampling was performed every three months between July 2008 and May 2009 at seven sites distributed along a 50-km section of the river. Piscivores was the most representative group in terms of biomass, abundance and species richness, followed by herbivores, insectivores and omnivores. The trophic structure did not change significantly during the hydrometric cycle, only omnivores showed significant temporal variation in abundance. The main food resources consumed by the ichthyofauna were of autochthonous origin, mainly immature aquatic insects and fish. Eight of 34 species showed temporal variations of the food resources consumed. Our results corroborate the hypothesis that the fish fauna of large, clear water rivers can be sustained by autochthonous resources. This contributes to understanding some determinants of fish production in large Neotropical rivers

Diet and trophic structure of the fish assemblage in the mid-course of the Teles Pires River, Tapajós River basin, Brazil

<div><p>ABSTRACT This study was carried out in a section of the middle course of the Teles Pires River, a clear water river that drains ancient and highly eroded geological formations, and where five hydropower plants are planned or in construction. In this study we tested the hypothesis that local fish fauna is mainly sustained by autochthonous food resources, with modest changes in the trophic structure of fish assemblages along the hydrometric cycle. Sampling was performed every three months between July 2008 and May 2009 at seven sites distributed along a 50-km section of the river. Piscivores was the most representative group in terms of biomass, abundance and species richness, followed by herbivores, insectivores and omnivores. The trophic structure did not change significantly during the hydrometric cycle, only omnivores showed significant temporal variation in abundance. The main food resources consumed by the ichthyofauna were of autochthonous origin, mainly immature aquatic insects and fish. Eight of 34 species showed temporal variations of the food resources consumed. Our results corroborate the hypothesis that the fish fauna of large, clear water rivers can be sustained by autochthonous resources. This contributes to understanding some determinants of fish production in large Neotropical rivers.</p></div

Reproductive allocation by Amazon fishes in relation to feeding strategy and hydrology

Seasonal environments favor the evolution of capital breeding, whereby reproduction uses surplus energy from resources acquired during an earlier period. Consequently, reproductive effort in capital breeders is expected to depend on traits associated with energy storage rather than environmental conditions at the time of reproduction. Based on a 15-year dataset, we investigate the effect of phenotype (body size and condition) and environmental conditions (intensity of hydrological seasons, predator density, and density of conspecifics) on fecundity three capital breeding fish species from the strongly seasonal Amazon River floodplain: Psectrogaster rutiloides, Triportheus angulatus, and Acestrorhynchus falcirostris. Fecundity of all three species was strongly correlated with phenotype and modulated by unfavorable environmental conditions during the period of reproduction, especially high density of conspecifics. Fecundity was negatively affected by the density of conspecifics for small females of A. falcirostris, and for T. angulatus females with poor body condition. Fecundity of P. rutiloides declined during periods of drought when density of conspecifics was highest. A clear tradeoff between quantity and quality of oocytes was found only for P. rutiloides. This study highlights that reproductive allocation of capital breeders in seasonal environments is strongly linked to environmental conditions before and during the reproductive period

Testing Wallace's intuition: water type, reproductive isolation and divergence in an Amazonian fish

Alfred Russel Wallace proposed classifying Amazon rivers based on their colour and clarity: white, black and clear water. Wallace also proposed that black waters could mediate diversification and yield distinct fish species. Here, we bring evidence of speciation mediated by water type in the sailfin tetra (Crenuchus spilurus), a fish whose range encompasses rivers of very distinct hydrochemical conditions. Distribution of the two main lineages concords with Wallace's water types: one restricted to the acidic and nutrient-poor waters of the Negro River (herein Rio Negro lineage) and a second widespread throughout the remaining of the species’ distribution (herein Amazonas lineage). These lineages occur over a very broad geographical range, suggesting that despite occurring in regions separated by thousands of kilometres, individuals of the distinct lineages fail to occupy each other's habitats, hundreds of metres apart and not separated by physical barrier. Reproductive isolation was assessed in isolated pairs exposed to black-water conditions. All pairs with at least one individual of the lineage not native to black waters showed significantly lower spawning success, suggesting that the water type affected the fitness and contributed to reproductive isolation. Our results endorse Wallace's intuition and highlight the importance of ecological factors in shaping diversity of the Amazon fish fauna. © 2018 European Society For Evolutionary Biology. Journal of Evolutionary Biology © 2018 European Society For Evolutionary Biolog

Fish species and functional guild composition, and environmental predictor variables from Amazonian streams

This is the complete dataset used in the manuscript. It includes fish species composition per stream site, functional guild composition per stream site and environmental predictor variables per stream site. For dataset descriptions see the file 'README.docx'

Data from: Is environmental legislation conserving tropical stream faunas? a large-scale assessment of local, riparian and catchment-scale influences on Amazonian stream fish

1.Agricultural expansion and intensification are major threats to tropical biodiversity. In addition to the direct removal of native vegetation, agricultural expansion often elicits other human-induced disturbances, many of which are poorly addressed by existing environmental legislation and conservation programmes. This is particularly true for tropical freshwater systems, where there is considerable uncertainty about whether a legislative focus on protecting riparian vegetation is sufficient to conserve stream fauna. 2.To assess the extent to which stream fish are being effectively conserved in agricultural landscapes, we examined the spatial distribution of assemblages in river basins to identify the relative importance of human impacts at instream, riparian, and catchment scales, in shaping observed patterns. We used an extensive dataset on the ecological condition of 83 low-order streams distributed in three river basins in the eastern Brazilian Amazon. 3.We collected and identified 24,420 individual fish from 134 species. Multiplicative diversity partitioning revealed high levels of compositional dissimilarity (DS) among stream sites (DS = 0.74 to 0.83) and river basins (DS = 0.82), due mainly to turnover (77.8 to 81.8%) rather than nestedness. The highly heterogeneous fish faunas in small Amazonian streams underscore the vital importance of enacting measures to protect forests on private lands outside of public protected areas. 4.Instream habitat features explained more variability in fish assemblages (15-19%) than riparian (2-12%), catchment (4-13%) or natural covariates (4-11%). Although grouping species into functional guilds allowed us to explain up to 31% of their abundance (i.e. for nektonic herbivores), individual riparian- and catchment-scale predictor variables that are commonly a focus of environmental legislation explained very little of the observed variation (partial R2 values mostly < 5%). 5.Policy implications. Current rates of agricultural intensification and mechanisation in tropical landscapes are unprecedented, yet the existing legislative frameworks focusing on protecting riparian vegetation seem insufficient to conserve stream environments and their fish assemblages. To safeguard the species-rich freshwater biota of small Amazonian streams, conservation actions must shift towards managing whole basins and drainage networks, as well as agricultural practices in already-cleared land