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Human-mediated biological invasions can greatly reduce native species diversity. More than 138 nonnative fishes have been introduced to the United States. Many of these nonnative species can alter ecosystem dynamics and compete with native species. The planktivorous Silver Carp (Hypophthalmichthys molitrix Valenciennes in Cuvier and Valenciennes, 1844) is a nonnative species of concern that is currently expanding its range across the Greater Mississippi River Basin in the Midwestern United States. The objective of our study was to determine the degree of potential competition among invasive Silver Carp and the native planktivores, Gizzard Shad (Dorosoma cepedianum Lesueur, 1818) and Threadfin Shad (Dorosoma petenense Günther, 1867), in Kentucky Lake, a large reservoir located in western Kentucky and Tennessee. We used data derived from N and C isotopes to model isotopic niches, calculate quantitative metrics to describe variability within and among isotopic niches and trophic positions, and qualitatively assess seasonal shifts in trophic positions. Our results suggest that in the spring, older (≥1 y old) Silver Carp share resources with older and young-of-year (YOY; <1 y old) Gizzard Shad, whereas YOY Silver Carp only share resources with YOY Gizzard Shad. Additionally, our analyses showed that older Silver Carp and older Gizzard Shad share resources in the summer. In contrast, we found no overlap in resource use between YOY Threadfin Shad and YOY or older Silver Carp. Furthermore, we provide evidence of intraspecific ontogenetic shifts in isotopic niche area and overlap between invasive and native fishes (measured by sample-size corrected standard ellipse area). If resources become limiting, invasive Silver Carp may compete with multiple life stages of Gizzard Shad in Kentucky Lake and alter foodweb dynamics. [ABSTRACT FROM AUTHOR]

The ability of organisms to survive ingestion and digestion by their predators, or endozoochory, is a fascinating ecological phenomenon that can facilitate predator-mediated dispersal of prey and alter interaction strengths within ecological networks. However, the role of endozoochory in the context of invasive species is considered less often. Throughout the United States, Silver Carp (Hypophthalmichthys molitrix) are prolific invaders that often alter food web structure of recipient ecosystems through the consumption of basal resources. Despite the biogeochemical and food web effects of Silver Carp, there is limited understanding of plankton prey survival after Silver Carp consumption and digestion, and even less known about the ecological effects of selective diets and potential survival. In this study, we quantify hindgut contents of Silver Carp collected from Kentucky Lake, Kentucky, Tennessee River Valley, United States. We found the majority (83%) of phytoplankters within hindguts of Silver Carp showed little digestion prior to egestion. Our study suggests digestion limitations of Silver Carp may have important ecological implications for invaded environments. These results may be applicable in understanding how this rapidly spreading invasive fish can influence food web dynamics and biogeochemical cycles pertinent to toxic algal blooms within recently invaded ecosystems, and forecasting invasion in the near future. [ABSTRACT FROM AUTHOR]