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...r Masson SAS. All rights reserved. 1. Introduction Studies using stable isotope analysis increasingly have stressed the importance of algal carbon in supporting river food webs (Hamilton et al.,1992; =-=Forsberg et al., 1993-=-; Thorp and Delong,1994, 2002; Douglas et al., 2005; Winemiller, 2005), but recent research indicates that sources of organic matter supporting consumers vary spatially and temporally (e.g., Herwig et...

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...ther isotopic studies in the Orinoco River Basin have concluded that phytoplankton and benthic algae are the primary energy sources supporting consumer biomass (Lewis, 1988; Lewis et al., 1990, 2001; =-=Hamilton et al., 1992-=-; Forsberg et al., 1993). In the Cinaruco River, a study measuring net ecosystem production (NEP) within the water column and benthic 1st – percentile contributions 99th – percentile contributionssTer...

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...he main channel for Hydrolycus armatus, Metynnis hypsauchen, and Piaractus brachypomus. K.A. Roach et al. / Acta Oecologica 35 (2009) 513–522 517 Author's personal copy been found at the reach scale (=-=Finlay et al., 1999-=-, 2002; Walters et al., 2007), the segment scale (Zeug and Winemiller, 2008; Roach et al., 2009), and the drainage network scale (Fry, 2002; Hoeinghaus et al., 2007), suggesting that exchange of produ...

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...d lateral migrations of fishes. In floodplain rivers of South America, seasonal changes in water levels are associated with shifts in algal biomass and assemblage structure (Hamilton and Lewis, 1987; =-=Forsberg et al., 1988-=-; Montoya et al., 2006). Low-water conditions in floodplain lagoons result in higher densities of phytoplankton (Rai and Hill, 1984; Putz and Junk, 1997) and benthic algae (Montoya et al., 2006). Diff...

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...m January to April, the aquatic habitat is greatly reduced. More than 280 fish species have been documented in the river, and this assemblage encompasses a great diversity of ecological niches (e.g., =-=Jepsen and Winemiller, 2002-=-). A previous analysis of stable isotope ratios in fish tissues in the Cinaruco River concluded that fishes are mostly dependent upon autochthonous primary production from benthic algae and phytoplank...

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...ycle. Ecological dynamics are strongly influenced by the highly predictable annual flow regime of the Cinaruco River, and this interannual consistency justifies pooling seasonal samples across years (=-=Layman et al., 2005b-=-; Arrington and Winemiller, 2006; Cotner et al., 2006; Montoya et al., 2006; Winemiller et al., 2006). Additionally, among-year variation in stable isotope signatures was low for the majority of speci...

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...tudies using stable isotope analysis increasingly have stressed the importance of algal carbon in supporting river food webs (Hamilton et al.,1992; Forsberg et al., 1993; Thorp and Delong,1994, 2002; =-=Douglas et al., 2005-=-; Winemiller, 2005), but recent research indicates that sources of organic matter supporting consumers vary spatially and temporally (e.g., Herwig et al., 2004; Zeug and Winemiller, 2008). In some tem...

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...rs, environmental conditions related to seasonal changes in hydrological connectivity affect the availability of alternative basal production sources for secondary consumers (Fisher and Willis, 2000; =-=Fisher et al., 2001-=-; Herwig et al., 2004). Such seasonal and temporal changes in hydrological connectivity can contribute to significant variation in the trophic position of secondary consumers (Zeug and Winemiller, 200...

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... River concluded that fishes are mostly dependent upon autochthonous primary production from benthic algae and phytoplankton, and that little carbon is assimilated from C3 macrophytes and C4 grasses (=-=Jepsen and Winemiller, 2007-=-). 2.2. Sample collections Samples of fishes and basal sources for organic matter were collected from lagoons and the main channel during the fallingwater period of the dry season (November–April) fro...

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...etynnis hypsauchen (Characiformes: Characidae) which integrates allochthonous C3 plants, and Semaprochilodus kneri (Characiformes: Prochilodontidae) which integrates autochthonous algae and detritus (=-=Layman et al., 2005a-=-,b). The mean trophic position of M. hypsauchen calculated using basal production sources was not significantly different between the two habitats (Student’s t-test, t 1.09, df 51, P 0.28, Fig. ...

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...hor's personal copy been found at the reach scale (Finlay et al., 1999, 2002; Walters et al., 2007), the segment scale (Zeug and Winemiller, 2008; Roach et al., 2009), and the drainage network scale (=-=Fry, 2002-=-; Hoeinghaus et al., 2007), suggesting that exchange of production sources and movements of consumer taxa between these habitats are relatively low. In Neotropical floodplain rivers, a few studies hav...

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...e local assemblages of fishes and other aquatic organisms across heterogeneous riverscapes, which may result in significant lateral and longitudinal transport of organic matter (Lowe-McConnell, 1964; =-=Lagler et al., 1971-=-; Welcomme, 1985; Fernandez, 1997; Winemiller and Jepsen, 1998). In the present study, we used stable isotope analysis (d13C and d15N) to examine foodweb patterns during the descending phase of the an...

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...temperate floodplain rivers, environmental conditions related to seasonal changes in hydrological connectivity affect the availability of alternative basal production sources for secondary consumers (=-=Fisher and Willis, 2000-=-; Fisher et al., 2001; Herwig et al., 2004). Such seasonal and temporal changes in hydrological connectivity can contribute to significant variation in the trophic position of secondary consumers (Zeu...

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...ue from each individual was removed from the dorso-lateral region using a scalpel, and then rinsed and preserved in salt. This preservation technique causes minimal isotopic shifts in tissue samples (=-=Arrington and Winemiller, 2002-=-). In order to account for ontogenetic shifts in diet, only tissues from adult consumers were sampled. All samples were transported to the laboratory at Texas Fig. 1. Map of the Cinaruco River in the ...

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...ics are strongly influenced by the highly predictable annual flow regime of the Cinaruco River, and this interannual consistency justifies pooling seasonal samples across years (Layman et al., 2005b; =-=Arrington and Winemiller, 2006-=-; Cotner et al., 2006; Montoya et al., 2006; Winemiller et al., 2006). Additionally, among-year variation in stable isotope signatures was low for the majority of species (Table 1). The Cinaruco River...

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...he highly predictable annual flow regime of the Cinaruco River, and this interannual consistency justifies pooling seasonal samples across years (Layman et al., 2005b; Arrington and Winemiller, 2006; =-=Cotner et al., 2006-=-; Montoya et al., 2006; Winemiller et al., 2006). Additionally, among-year variation in stable isotope signatures was low for the majority of species (Table 1). The Cinaruco River supports little aqua...

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...tritivorous fishes (S. kneri) that enter the Cinaruco from the Orinoco River and disperse upstream (Winemiller and Jepsen, 2004). During the lowwater period, some fish species enter lagoons to spawn (=-=Hoeinghaus et al., 2003-=-). However, because of the relatively long turnover times of tissues from secondary consumers, (i.e., weeks to months; McIntyre and Flecker, 2006), stable isotope signatures during the falling-water p...

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...er aquatic organisms across heterogeneous riverscapes, which may result in significant lateral and longitudinal transport of organic matter (Lowe-McConnell, 1964; Lagler et al., 1971; Welcomme, 1985; =-=Fernandez, 1997-=-; Winemiller and Jepsen, 1998). In the present study, we used stable isotope analysis (d13C and d15N) to examine foodweb patterns during the descending phase of the annual hydrological cycle in connec...

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...al., 1993; Thorp and Delong,1994, 2002; Douglas et al., 2005; Winemiller, 2005), but recent research indicates that sources of organic matter supporting consumers vary spatially and temporally (e.g., =-=Herwig et al., 2004-=-; Zeug and Winemiller, 2008). In some temperate floodplain rivers, environmental conditions related to seasonal changes in hydrological connectivity affect the availability of alternative basal produc...

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...nal copy been found at the reach scale (Finlay et al., 1999, 2002; Walters et al., 2007), the segment scale (Zeug and Winemiller, 2008; Roach et al., 2009), and the drainage network scale (Fry, 2002; =-=Hoeinghaus et al., 2007-=-), suggesting that exchange of production sources and movements of consumer taxa between these habitats are relatively low. In Neotropical floodplain rivers, a few studies have suggested a significant...

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... 2005), which in turn are affected by components of the flow regime. Tropical floodplain rivers experience predictable annual flood pulses that have been hypothesized to mix production sources (e.g., =-=Junk et al., 1989-=-); however, a synthesis of research conducted on the Orinoco River floodplain in South America concluded that export of organic carbon sources to themain channel is low due to restricted net lateral m...