Microbial Predation

Food chains are now more commonly called food webs. At the bottom are the plants that use sunlight to photosynthesize food resources. These are consumed by organisms that do not carry out photosynthesis. Along the way up the chain or through the web, there is combat for survival. An organism plays many roles. It may eat some, for example, while others are trying to eat it. Predation is the name for one organism browsing to feed on another. In continuous culture it is easy to see what happens in predation. The first analysis was by Lotka and Volterra who worked independently of each other.

Collisions kill V and result in growth of P. The K's are different rate constants. We neglect death by old age for both V and P because we can choose a high dilution rate where most will wash out before growing old.

For the prey or victim, Organism V, its change in concentration is
dV/dt = µa V - D V - K1 V P
which says that it reproduces at a rate proportional to its concentration, washes out at a rate determined by the dilution rate, D, and is killed by collisions with the predator organism P.

The equation for predators, P, is
dP/dt = K2 V P - D P .

Things to look for in the following Applet are magnitudes and frequencies. Try to look back at the equations to seek explanations of what you observe.

  • Previous page: Terminology for interactions
  • Previous page: Competition
  • NEXT: Mutualism
  • Commensalism
  • Comments about ecosystems and some terminology
  • Computerized analysis of an ecosystem
  • DONE

    while on sabbatical leave in Porto, Sept. 96