Community‐wide transient dynamics of lake fish populations in response to two decades of suppressing an introduced predator

Abstract Understanding the full impacts of introduced and invasive species suppression on ecological communities requires long‐term suppression experiments where native species with different life histories can reach new population equilibria. Responses documented in shorter term studies are likely to be transient. This study evaluated the abundance and size structure of 11 species of littoral fishes across 20 years in response to annual, lake‐wide removal of smallmouth bass, a non‐native predator that competes with and consumes native species. Many changes in relative abundance of species were evident from comparing community composition before, immediately after, and 20 years into the invader suppression experiment. Long‐term dynamics were classified as showing abrupt change, gradual change, or no discernible change, based on a change point analysis. Relative abundance of most fish community members increased in the year following initiation of bass removal but became more varied thereafter. After initial increases, most species declined in abundance, with some declining to near or below their pre‐experiment levels and others remaining above pre‐removal levels. Many species showed an initial decrease in body size following bass removal, indicating increased abundance of young‐of‐year, but long‐term patterns varied among species. Ongoing fluctuations of populations throughout this study indicate that the direction, tempo, and stability of population responses to removing a dominant invader are often transient. Changes in population abundance and body size across our 20‐year experiment were not correlated across species, suggesting that fish communities require many generations to achieve a new stable state following the loss or suppression of a dominant predator. Synthesis and applications. Fish community restoration efforts are rarely followed by long‐term evaluations, hence current understanding of responses to removal of introduced and invasive species may be largely based on transient dynamics. Instead, both population abundance and size structure should be documented for at least a few generations of the longest‐lived species. Insights into management outcomes of suppressing or eliminating introduced and invasive predators require accounting for demographic time lags as species interactions become restructured over long periods of time.