Consistent trophic patterns among fishes in lagoon and channel habitatsof a tropical floodplain river: Evidence from stable isotopes

摘要

The relationship between food web dynamics and hydrological connectivity in rivers should be stronglyinfluenced by annual flood pulses that affect primary production dynamics and movement of organicmatter and consumer taxa. We sampled basal production sources and fishes from connected lagoons andthe main channel of a low-gradient, floodplain river within the Orinoco River Basin in Venezuela. Stableisotope analysis was used to model the contribution of four basal production sources to fishes, and toexamine patterns of mean trophic position during the falling-water period of the annual flood cycle.IsoSource, a multi-source mixing model, indicated that proportional contributions from productionsources to fish assemblages were similar in lagoons and the main channel. Although distributionsdiffered, the means for trophic positions of fish assemblages as well as individual species were similarbetween the two habitats. These findings contradict recent food web studies conducted in temperatefloodplain rivers that described significant differences in trophic positions of fishes from slackwater andfloodplain versus main channel habitats. Low between-habitat trophic variation in this tropical riverprobably results from an extended annual flood pulse (ca. 5 mo.) that allows mixing of sestonic andallochthonous basal production sources and extensive lateral movements of fishes throughout theriverscape.