Stoichiometry and food chain dynamics
Kuijper, L. D. J., Kooi, B. W., Anderson, T. R. and Kooijman, S. A. L. M. 2004.
Stoichiometry and food chain dynamics. Theor. Pop. Biol. 66: 323--339.
Traditional models of chemostat systems looking at interactions
between predator, prey and nutrients have used only a single currency,
such as energy or nitrogen. In reality growth of autotrophs and
heterotrophs may be limited by various elements, e.g. carbon,
nitrogen, phosphorous or iron. In this study we develop a dynamic
energy budget (DEB) model chemostat which has both carbon and nitrogen
as currencies, and examine how the dual availibility of these elements
affects the growth of phytoplankton, trophic transfer to zooplankton,
and the resulting stability of the chemostat ecosystem. Mineral
nitrogen (DIN) and carbon (DIC) form the base of the food chain, and
they are supplied at a constant rate. In addition, the biota in the
chemostat recycle nutrients by means of respiration and excretion, and
organic detritus is recycled at a xed rate. We use numerical
bifurcation analysis to assess the model's dynamic behavior. The model
predicts that phytoplankton is nitrogen limited, and that nitrogen
enrichment can lead to oscillations and multiple stable
states. Moreover, we found that recycling has a destabilizing effect
on the food chain due to the increased repletion of mineral
nutrients. We found that both carbon and nitrogen enrichment stimulate
zooplankton growth. Therefore, we conclude that the concept of single
element limitation may not be applicable in an ecosystem context.