Perturbation and Resilience: A Long‐Term, Whole‐Lake Study of Predator Extinction and Reintroduction

Abstract

This paper presents the results of a long—term study of changing predator densities and cascading effects in a Michigan lake in which the top carnivore, the largemouth bass (Micropterus salmoides), was eliminated in 1978 and then reintroduced in 1986. The elimination of the bass was followed by a dramatic increase in the density of planktivorous fish, the disappearance of large zooplankton (e.g., two species of Daphnia that had historically dominated the zooplankton community), and the appearance of a suite of small—bodied cladoceran (zooplankton) species. The system remained in this state until bass were reintroduced. As the bass population increased, the system showed a steady and predictable return to its previous state; planktivore numbers declined by two orders of magnitude, large—bodied Daphnia reappeared and again dominated the zooplankton, and the suite of small—bodied cladocerans disappeared. Within each cladoceran species there was a steady increase in mean adult body size as planktivore numbers declined. Total zooplankton biomass increased ≈ 10—fold following the return of large—bodied Daphnia, and water clarity increased significantly with increases in Daphnia biomass and total cladoceran biomass. These changes in community structure and trophic—level biomasses demonstrate the strong impact of removing a single, keystone species, and the capacity of the community to return to its previous state after the species is reintroduced.