Alternative prey species lead to prey buffering not apparent competition

Background/Question/Methods

Ecosystem approaches to fisheries management require an understanding of community interactions, particularly competition and predation, which may change under different environmental conditions.  Introductions of additional prey species can have both positive and negative effects on simple predator-prey communities through prey buffering and apparent competition.  Functional response curves that incorporate prey switching may be useful to develop a mechanistic understanding of how predator-prey dynamics respond to changes in community structure.  Here, we use the long-term fisheries data set available for Oneida Lake, NY to explore how alternative prey species modify a simple predator-prey dynamic.  We updated functional response curves developed using data from the 1970’s with additional data from 1990’s and 2000’s to test whether the addition of alternative prey lead to prey buffering or apparent competition.  Across these time periods the diversity of the fish community shifted from one with a dominant predator, walleye (Sander vitruem), and primary prey, yellow perch (Perca flavescens), during the 1970’s, to one with multiple prey species during recent years.  Functional response curves are integrated with time series of walleye and yellow perch abundance to reconstruct walleye predation on yellow perch and identify thresholds that lead to prey switching and, ultimately, buffering from predation.

Results/Conclusions

Historically, walleye and yellow perch represented a tightly linked predator-prey dynamic, with walleye accounting for ~86% of juvenile yellow perch mortality.  In recent years, this linkage has weakened as juvenile perch mortality attributed to walleye predation dropped to ~50%.  This decoupling is likely driven by walleye switching prey and an increase in predation on yellow perch by other species in the lake.  These results suggest alternative prey species tend to have a positive effect on yellow perch through prey buffering and not apparent competition.  Timing of prey switching shifted across years and appears to be primarily driven by the relative biomass of yellow perch and alternative prey species, such as gizzard shad (Dorosoma cepedianum).  Prey switching occurred earliest in years with weak yellow perch year-classes, increasing prey buffering and providing a compensatory mechanism to explain relatively stable age-1 recruitment.  By developing functional response curves that incorporate information on the availability of multiple prey species, fisheries scientists can more accurately model predator-prey dynamics, and explore potential positive and negative direct and indirect effects within communities.