Predator–prey cycles in an aquatic microcosm: testing hypotheses of mechanism


K. W. Shertzer, Center for Coastal Fisheries & Habitat Research, National Oceanic & Atmospheric Administration, 101 Pivers Island Road, Beaufort, NC 28516, USA. Tel. (252) 728 8607; Fax: (252) 728 8619; E-mail:


  • 1Fussmann et al. (2000 ) presented a simple mechanistic model to explore predator–prey dynamics of a rotifer species feeding on green algae. Predictions were tested against experimental data from a chemostat system housing the planktonic rotifer Brachionus calyciflorus and the green alga Chlorella vulgaris .
  • 2The model accurately predicted qualitative behaviour of the system (extinction, equilibria and limit cycles), but poorly described features of population cycles such as the period and predator–prey phase relationship. These discrepancies indicate that the model lacked some biological mechanism(s) crucial to population cycles.
  • 3Here candidate hypotheses for the ‘missing biology’ are quantified as modifications to the existing model and are evaluated for consistency with the chemostat data. The hypotheses are: (1) viability of eggs produced by rotifers increases with food concentration, (2) nutritional value of algae increases with nitrogen availability, (3) algal physiological state varies with the accumulation of toxins in the chemostat and (4) algae evolve in response to predation.
  • 4Only Hypothesis 4 is compatible with empirical observations and thus may provide important insight into how prey evolution affects predator–prey dynamics.