Using Ecosystem Models to Quantify Individual and Synergistic Effects of Invaders

Though often assumed undesirable, the effects of single introductions are frequently unclear, and the interactive effects of multiple, sequential invasions are even less understood. Reservoirs are particularly susceptible to invasion and often contain several introduced fish species, making them optimal systems in which to quantify the ways that invaders alter community structure and trophic dynamics.  Lake Norman, North Carolina,  has been subjected to multiple species introductions since its impoundment in 1963, and negative effects of four specific species (flathead catfish, alewife, spotted bass, and white perch) on established populations and trophic dynamics in the system have been implied (e.g., declines in sportfish) but not directly quantified.  We used an Ecopath with Ecosim modeling approach to help understand the effects of these introductions and to provide insight into potential management strategies.  We parameterized an Ecopath model with eighteen functional groups using data collected from 2007-2010.  Because synergies among multiple invaders may produce effects greater than the sum of their parts, we ran Ecosim to investigate the effects of each introduced species individually and combinations of species simultaneously.   This investigation provides a rare opportunity to quantify the ways in which multiple introduced species impact an established reservoir ecosystem.