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ABSTRACT Fishes use a variety of physical and biological resources that shift ontogenetically, seasonally and spatially. Quantifying what resources such as prey are required for persistence can improve understanding of ecological needs of fishes and riverine macrosystem functioning. Bowfin (Amia ocellicauda) and largemouth bass (Micropterus nigricans) cohabitate in their native range and potentially compete with one another. Yet, there have been no direct comparisons of their diets across spatial gradients to assess whether they partition resources or shift in prey use. We used multiple univariate and multivariate analyses to compare diet composition, diet overlap, feeding strategy, prey importance and diet partitioning between largemouth bass and bowfin across three reaches of the Upper Mississippi River. Largemouth bass ontogenetically shifted their diet from aquatic invertebrates to fishes and a more diverse assemblage of aquatic invertebrates. Bowfin and adult largemouth bass were top predators which consumed mostly crayfish and fish and overlapped in their diets. Despite overlapping diets, predators partitioned resources by consuming different lengths and abundances of prey, and largemouth bass had greater trophic plasticity. Within a predator group, few differences in diets existed spatially, underscoring the relative homogeneity in resource use potentially from similarities in the river's physical structure. Combined, prey use likely differed sufficiently to reduce potential competition between largemouth bass and bowfin, allowing long‐term coexistence in this system. Our results also highlighted the importance of crayfishes to riverine food webs and underscored the use of multiple prey and habitat types that sustain these predators. [ABSTRACT FROM AUTHOR]

Effective management and conservation of fishes requires understanding habitat use across multiple life stages while ensuring necessary habitats are both available and accessible. Tributary habitats may play an important role in recruitment and dispersal of fishes in anthropogenically modified rivers such as the Mississippi and Illinois Rivers of the Midwest U.S.A. Identifying source locations that contribute to recruitment of fish populations can determine the importance of connectivity within river networks and pinpoint critical habitats that sustain fish populations. In the Upper Mississippi River System (UMRS), the environments that fish use in early life stages (i.e., natal origin) can be identified using otolith trace element analysis due to stability and distinctness in water chemistry (strontium: calcium [Sr:Ca]) among water bodies that is reflected in otoliths.Here, we used trace element analysis to determine natal origin of six small‐bodied fishes including bullhead minnow (Pimephales vigilax), emerald shiner (Notropis atherinoides), gizzard shad (Dorosoma cepedianum), bluegill (Lepomis macrochirus), orangespotted sunfish (Lepomis humilis), and yellow perch (Perca flavescens) across six reaches of the UMRS (Pools 4, 8, 13, 26, the Open River of the Middle Mississippi River, and the La Grange Pool of the Illinois River). Otolith core Sr:Ca for fishes was quantified using laser ablation inductively coupled plasma mass spectrometry. Using the resulting Sr:Ca chemical signatures of otolith cores, natal origin (tributary, immigrant, or potential resident) was determined for individual fish based on family‐specific relationships between otolith and water chemistries.We found that all species originated from tributaries and other reaches (i.e., were immigrants) to varying extents, which acted as evidence for network connectivity. Specifically, tributaries contributed up to 48% of individuals at a given reach. In certain reaches, Pool 26 and the Open River reach, up to 80% of individuals in a species immigrated from another mainstem river reach. Network connectivity was also important in both upstream and downstream directions. Contributions from network connectivity varied among species: bullhead minnow used less whereas orangespotted sunfish used more network connectivity than when all species were combined. Further, the use of network connectivity varied spatially where individuals captured in Pool 8 and the La Grange Pool less often and those from Pool 26 and the Open River more often originated from network connectivity compared to the whole assemblage across reaches.These results indicate that species' life history traits probably interacted with the physical environment, which differs spatially, to yield observed recruitment source patterns. Our results show that network connectivity contributes to established assemblages of native small‐bodied fishes throughout the UMRS and underscore the role of interjurisdictional management in maintaining network connectivity to sustain fish populations. [ABSTRACT FROM AUTHOR]