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Landscape dynamics are widely thought to govern the tempo and mode of continental radiations, yet the effects of river network rearrangements on dispersal and lineage diversification remain poorly understood. We integrated an unprecedented occurrence dataset of 4,967 species with a newly compiled, time-calibrated phylogeny of South American freshwater fishes—the most species-rich continental vertebrate fauna on Earth—to track the evolutionary processes associated with hydrogeographic events over 100 Ma. Net lineage diversification was heterogeneous through time, across space, and among clades. Five abrupt shifts in net diversification rates occurred during the Paleogene and Miocene (between 30 and 7 Ma) in association with major landscape evolution events. Net diversification accelerated from the Miocene to the Recent (c. 20 to 0 Ma), with Western Amazonia having the highest rates of in situ diversification, which led to it being an important source of species dispersing to other regions. All regional biotic interchanges were associated with documented hydrogeographic events and the formation of biogeographic corridors, including the Early Miocene (c. 23 to 16 Ma) uplift of the Serra do Mar and Serra da Mantiqueira and the Late Miocene (c. 10 Ma) uplift of the Northern Andes and associated formation of the modern transcontinental Amazon River. The combination of high diversification rates and extensive biotic interchange associated with Western Amazonia yielded its extraordinary contemporary richness and phylogenetic endemism. Our results support the hypothesis that landscape dynamics, which shaped the history of drainage basin connections, strongly affected the assembly and diversification of basin-wide fish faunas. [ABSTRACT FROM AUTHOR]

Prey fish species can respond to the presence of predators using a variety of antipredatory behaviors to reduce their risk of being consumed. As such behaviors may also imply fitness costs, the ability of prey to perceive and appropriately respond to the predation threat is crucial to determine the persistence of its populations. Little is known whether antipredatory behaviors adopted by prey fish species are predator-specific or a general strategy employed regardless of predator species. Here, we used two phylogenetically close piscivorous fish species (Hoplias sp. 2 and Hoplerythrinus unitaeniatus) with similar morphology and foraging strategy (ambushing) to test whether prey (Moenkhausia sanctaefilomenae and Astyanax lacustris) behavioral responses were related to predator species identity. We video recorded and evaluated prey refuge use, habitat segregation, shoal formation, and mobility in microcosms before and after the addition of each predator. We found that M. sanctaefilomenae responded to the addition of Hoplias sp. 2 by reducing its mobility and keeping as far as possible from the predator location in a vigilant state, while shoal formation was employed regardless of predator species. On the other hand, A. lacustris had a consistent response to the presence of predators with no adjustment for predator species. We conclude that antipredatory responses may vary according to predator characteristics not obviously related to their morphology and foraging behavior, such as predator activity level and habitat use. [ABSTRACT FROM AUTHOR]

Abstract: Flood pulses are the main force driving the dynamics of aquatic communities in floodplains. The responses of communities to environmental changes following flood pulses usually demand a time lag to appear and reach the climax. We assembled a data set of 16 years of fish samplings to assess the relationship between water level and four functional diversity measures, in the upper Paraná River floodplain. Specifically, we approached four aspects of each relationship between water level and functional diversity: nature (positive or negative), sensitivity (response intensity), responsiveness (response delay) and extent (response duration). The nature of the relationship between water level and functional diversity was positive in all cases. Functional richness (FRic) responded right after flood pulses, although with shorter extent. Abundance‐dependent functional measures (evenness—FEve; divergence—FDiv; and Rao's quadratic entropy—Rao's Q) presented delayed responses, reaching peaks more than 1.5 years after flood pulses. Significant effects of floods on fish functional diversity were observed for more than 3 years, although the highest functional diversity was observed with 1.8 years, on average. More importantly, flood pulses had no longer significant effects on functional diversity after 4 years. Regarding conservation strategies in regulated systems, flood events should occur every 2 or 3 years, with adequate timing (October‐November), intensity (up to 450 cm) and duration (at least 50 uninterrupted days). Intervals longer than 3 years or inadequate timing, intensity and duration could dramatically decrease functional diversity and compromise ecosystem services. [ABSTRACT FROM AUTHOR]

Abstract: The long‐term impact of river regulation on fish functional diversity by a dam immediately upstream from the upper Paraná River floodplain, Brazil, was evaluated. It was expected that the resulting alterations in natural flow, downstream from the dam, would negatively impact fish species, resulting in a functional simplification of the ichthyofauna. In addition, this effect was expected to be more pronounced in the directly affected main channel of the Paraná River than in its tributaries, the Baía and Ivinhema rivers. Fish were sampled before (pre) and after (post) dam closure (the intervention). The functional traits used were diet, habitat use, mouth position, migration, parental care, internal fertilisation and maximum total length. Differences in trait composition between periods (pre and post) were tested using a PERMANOVA main‐test. An indicator value analysis (IndVal) was applied to identify which traits significantly increased or decreased in abundance after the intervention. The indexes used were functional richness (FRic), Rao's quadratic entropy (FDQ) and functional redundancy (FRed). The intervention analysis based on linear models for time series was used to evaluate differences in these indexes over time. Traits most representative during pre‐intervention were large‐bodied species with long reproductive migrations, pelagic, with subterminal and superior mouths, and herbivorous. Traits most representative during the post‐intervention were omnivorous species, with parental care, benthopelagic and insectivorous, which typically characterise fishes that inhabit stable environments. FRic decreased in Paraná and Baía rivers after the construction of the dam. However, the Ivinhema River showed an increase in mean FRic in the post‐intervention period. FDQ decreased substantially in all three rivers, while FRed increased. The combined results of FRic, FDQ and FRed corroborate the functional simplification hypothesis expected from flow regulation by dams on functional diversity. As expected, the most pronounced simplification occurred in the Paraná River. Therefore, hydroelectric power plants can act as environmental filters strongly selecting functional traits of the downstream fish fauna, generating long‐lasting impacts on ecosystem functioning and services. [ABSTRACT FROM AUTHOR]