Amphipods On a Stoichiometric Knife Edge? Effects Of Low Food C:P Ratio On Growth & Survival In Hyalella Azteca
Engstrom, Melanie E.; Watts, James M.; and Elser, James J.
School of Life Sciences, Arizona State University
The theory of ecological stoichiometry predicts that consumer growth and survival increase as food C:P ratios decrease when dietary P-limitation is a factor. However, recent studies have shown that further decrease of food C:P ratios to very low levels can impair consumer growth and survivalCproducing a unimodal, “stoichiometric knife edge” response. This study evaluates the generality of the stoichiometric knife edge hypothesis by assessing the response of the amphipod Hyalella azteca fed the algae (Scenedesmus) manipulated to have six levels of biomass C:P ratio. Scenedesmus was fed to H. azteca (10 replicate animals per treatment) in 50-mL jars for a period of 28 days. Body size and survival for each animal was assessed every 3 days and amphipod %P was determined at the end. Consistent with a “stoichiometric knife edge,” H. azteca mortality increased with decreasing food C:P. However, growth rate did not show a consistent decrease with decreasing food C:P. Further work is required to identify the shape of H. azteca’s response to stoichiometric food quality effects.