PARENT SESSION
Oral Session #77: Aquatic Ecology: Food webs, invertebrates. Presiding: R.A. Washington-Allen.
Friday, August 10, 2001. 8:00 AM to 12:00 PM. Hall of Ideas H.
The trophic cascade in ponds.
BELL, THOMAS1, NEILL, WILLIAM1, SCHLUTER, DOLPH1, 1
ABSTRACT- The trophic cascade is the mechanism by which the top trophic level causes patterns of higher biomass at alternate trophic levels. Although there have been more than 60 experimental studies of trophic cascades in aquatic systems with replicated zooplanktivorous fish present/absent treatments, only a couple have extended for longer than a year. It is therefore unclear as to whether the trophic cascade is stable over time scales longer than one generation of the top predator. We performed a 4-year trophic cascade experiment in ponds to see whether the trophic cascade predictions were upheld. We also analyzed data in the literature to compare the results of trophic cascade experiments of varying duration in different systems and with different depths. Although the results were in qualitative agreement with the predictions of the trophic cascade hypothesis, a smaller difference in zooplankton and phytoplankton biomass between control and fish ponds in the final year of the study raises some doubt as to whether trophic cascades are stable over longer time scales. In the literature analysis, we found that there was no relationship between zooplankton and phytoplankton effect sizes, but that zooplankton were much less affected in whole-lake manipulations compared to mesocosm and enclosure studies. We also show that the duration of the experiment and the depth of the system in which the experiment is performed might affect the strength of trophic cascades. Although we cannot conclude that trophic cascades are transient, we raise the possibility that the strength of trophic cascades dissipates with time.
KEY WORDS: biomanipulation, long-term experiment, compensation, meta-analysis