ABSTRACT
The conversion efficiency of prey biomass into predator biomass (or plant-biomass into herbivore-biomass) at the individual level is not constant. Measured by the yield factor, this conversion appears to depend on size, energy reserves, and a few species-specific compound parameters involving a variety of elements from the dynamic energy budget. This efficiency is studied here on the basts of a continuous time model for the energy budget of an individual organism.
At the population level, the conversion of prey into predator biomass depends on harvesting processes. Included in harvesting is death by aging. In the absence of harvested individuals from a population of predators, a constant supply rate of prey results in a predator population of constant size. At equilibrium, this gives a conversion efficiency of zero. When the predator population is harvested, the conversion efficiency increases up to a maximum and then decreases to a threshold level, above which the population goes extinct. A practical implication is that it is possible that populations with substantial standing crops cannot stand sustained increased harvesting.
For a well tested model for energy budgets of individuals, the conversion efficiency of prey biomass into predator biomass has been compared for two modes of prey selection by the predator: random predation and fixed age predation. Both strategies gave almost identical biomass conversion efficiencies. Propagation through eggs has been found to be a bit less efficient that propagation through binary fission.
The way the efficiency depends on parameters of the individual energy budget is an important link between ecology and physiology, a fact which is highly relevant to areas of applied ecology, such as eco· toxicology. The study of this relation is complicated by population oscillations induced by the harvesting process, but computer simulations show that an analysis of the conversion efficiency on the basis of stable age distributions is still valid.
