R scripts for the analysis of a predatory fish invasion on a riverine food web

Catfishes are opportunistic feeders that are among the world's worst invasive species. Flathead catfish Pylodictus olivaris -- a large predatory catfish -- were first detected in the Susquehanna River, Pennsylvania, USA in 2002. Since then, they established a viable and rapidly growing population that is expanding its range throughout the river system. Although the predatory effects of invasive catfishes on native fish communities have been documented, the effects of invasion on riverine food webs is poorly understood. The goal of this study was to quantify the effects of invasive flathead catfish on the trophic position and isotopic niche space of components of the Susquehanna River food web by comparing invaded and non-invaded sites within the system.