Document: GRE-3-56-14

Unraveling the bifurcation structure of a live predator-prey system.

FUSSMANN, G.F.* ¹, S.ELLNER ² and N.G.HAIRSTON JR. ¹

Cornell University, Ithaca, NY, 14853, USA ¹
North Carolina State University, Raleigh, NC, 27695, USA ²

Abstract:
Populations in the field are not usually at equilibrium. It has been a longstanding question whether intrinsic factors are likely to cause the fluctuations observed in natural communities. Our premise is that a combined empirical and theoretical approach to understanding simple laboratory communities should provide a valuable foundation for understanding organisms in the wild. Our experimental system consisted of single-stage chemostats culturing rotifers (Brachionus calyciflorus) and their algal prey (Chlorella vulgaris), with variable supply rate of the nutrient limiting algal growth (nitrogen). By altering the flow-through rate of the chemostat we established three principal dynamical states of the system: extinction of the predator, coexistence at an equilibrium, and predator-prey oscillations. More specifically, gradually increasing the flow-through rate transferred the system from a stable equilibrium to periodic oscillations, consistent with the occurrence of a Hopf bifurcation. A similar, but reverse bifurcation back to stable equilibrium occurred at very high flow-through rates. A realistic theoretical model can reproduce the bifurcation structure of this simple system. We conclude that mechanistic processes underlie the dynamics of simple multi-species communities.

Keywords: predator-prey interactions, bifurcation, chemostat

This abstract is being presented at: 4:00 PM in session:
Oral Session #11: Trophic Cascades.