Stoichiometric food quality and herbivore dynamics
Muller, E.B., Nisbet, R.M., Kooijman, S.A.L.M., Elser, J.J. and
McCauley, E. 2001. Stoichiometric food quality and herbivore
dynamics. Ecological Letters, 4: 519 - 529.
Herbivores may grow with nutrient or energy limitation, depending on
food abundance and the chemical composition of their food. We present
a model that describes herbivore growth as a continuous function of
two limiting factors. This function uses the synthesizing unit
concept, has the hyperbolic Monod model as a limiting case, and has
the same number of parameters as the Monod model coupled to Liebig's
discontinuous minimum rule. We use the model to explore
nutrient-limited herbivore growth in a closed system with algae,
Daphnia and phosphorus as the limiting nutrient.
Phosphorus in algae may substantially influence Daphnia
growth. This influence changes over time and is most pronounced when
algae and Daphnia populations fluctuate strongly. Relative to classic
models that only consider food quantity as a determinant of Daphnia
growth, our model shows richer dynamical behaviour. In addition to the
standard positive equilibrium, which may be stable or unstable
depending on nutrient availability, a new positive equilibrium may
arise in our model when mortality rates are relatively high. This
equilibrium is unstable and reduces the likelihood of long-term
persistence of Daphnia in the system.