SS3.10 Ecological Implications of Terrestrial Inputs into Lakes and Ponds
Date: Tuesday, June 11, 2002
Time: 11:45:00 AM
Location: Esquimalt
 
GeddesP, University of Chicago, Chicago, USA, pgeddes@uchicago.edu
 
COLORED DOM (CDOM) SUBSIDIES INTO POND PLANKTONIC COMMUNITIES: STABILITY AND SPECIES IDENTITY
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Subsidies are donor-controlled flows of energy, organic matter, and nutrients across systems. Studies document how subsidies affect communities, often involving substantial increases in biomass/abundance of recipient species, yet no experimental studies have assessed their stabilizing role as predicted by theory. I conducted a mesocosm experiment to evaluate the effects of humic substances on zooplankton biomass and stability. Humic substances significantly increased zooplankton biomass and, contrary to theoretical predictions, enhanced zooplankton variability relative to controls. A possible explanation for the mismatch between theory and experiments is that predictions might change if there are more than one species per trophic level. If individual species respond differently to subsidies, species identity and abundance might dictate how the whole trophic level behaves. I conducted a laboratory experiment in 20-L buckets to address how species of zooplankton responded to varying concentrations of carbon subsidies (leaf-leachate) and phytoplankton. Results from this experiment indicated that there was heterogeneity in the way species responded to treatments. Ignoring trophic level heterogeneity and species identity might lead to inaccurate predictions regarding the dynamic behavior of subsidized food webs.