Competition Between Paramecia Tutorial

Load P2b, then press [E] and load the two Paramecium models.

• Examine the isocline configuration (see figure) noting that a community equilibrium occurs at high P. aurelia density and low P. caudatum density.
• Plot the data with [F3] and notice how they approach then oscillate around the community equilibrium (see figure).
• Press [F8] and run a deterministic simulation, noting how the simulated trajectory curves in to the community equilibrium point (see figure).
• Examine the correspondence between the simulated deterministic trajectories and the data on arithmetic and logarithmic time series plots.
• Run several stochastic simulations and compare the simulated trajectories to the original data (see figure).

Conclusions

In this experiment, the two species of Paramecium were able to coexist near a stable community equilibrium. However, competition between the two species was asymmetrical, with P. aurelia obtaining a higher equilibrium density due to its greater maximum per-capita rate of increase (A1 = 0.89 versus A2 = 0.73) rather than its competitive ability (C12 = -0.0025 versus C21 = -0.0015). In other words P. aurelia had a growth rate advantage and P. caudatum a competitive advantage, and this enabled them to coexist.