Seasonal variation in resource overlap of invasive and native fishes revealed by stable isotopes.
Species invasions may disrupt resource partitioning in aquatic ecosystems, potentially resulting in competitive exclusion, or shifts in resource use by native species. Diet overlap between invasive Silver Carp (Hypophthalmichthys molitrix) and native planktivores has been linked to declines in condition and abundance of native planktivores. However, there is little information on how such diet overlap varies temporally. We used stable-isotope ratios to examine seasonal resource overlap among Silver Carp and two native planktivores, Gizzard Shad (Dorosoma cepedianum) and Bigmouth Buffalo (Ictiobus cyprinellus). Resource overlap between Bigmouth Buffalo and Silver Carp was minimal (<1%) in all seasons, whereas overlap between Gizzard Shad and Silver Carp (7-36%) was larger and varied seasonally. The greatest resource overlap among species occurred in summer, while the smallest overlap occurred in spring. Resource use by Silver Carp appears to be highly specialized in the fall, as indicated by a narrow isotopic niche. Variation in niche size among seasons suggests that Silver Carp may be plastic in their resource use. Overall, the limited resource overlap among invasive and native species revealed in this study suggests potentially low invasive-native competition, although competition may have acted prior to our study to produce shifts in resource use by native fishes.