Competition Between Paramecia Tutorial

Enter the data from Gause (1934 - Page 114, Table 3, means for mixed population, ignoring the first 2 records) for Paramecium aurelia and P. caudatum reared in culture into P1a and construct single-species models of both populations. Save the models to disk and then load P2a.

• Enter the names you gave to the Paramecium data files, identifying both species as carnivorous and each harming the other. This specifies the interaction as COMPETITION.
• Press [F10] to continue and examine the trajectories of the time series (see figure). Notice how the density of P. caudatum increases at first but then subsides to a low density, suggesting that P. aurelia is the superior competitor.
• Press [F10] again to examine the phase portrait, noting that the two populations seem to be approaching a stable equilibrium. Is this a case of competitive coexistence?
• Press [F10] and examine the P. aurelia regression analysis, noting that the LV model provides a slightly better fit to the data than the RD model (the parameters can be compared in the top-right window). Also note the strong intraspecific effect (self-regulation) and very weak interspecific effect of P. caudatum on P. aurelia. Press [L] to accept the LV model.
• Press [F10] to continue and notice that the LV model also provides a better description of the P. caudatum R-function than the RD model, and that this species is more dependent on the density of its competitor; i.e., the interspecific effect is much greater. Press [L] to accept the LV model.
• Press [F10] to continue and then accept the preliminary model by pressing [R] four times.
• Press [S] to simulate, defaulting all conditions and running the model deterministically. NOTE that the simulated trajectory equilibrates in the region where the data attain their apparent steady-state (see figure).
• Run some stochastic simulations noting, in particular, how some of them resemble the data (see figure).
• When you have finished simulating and are satisfied with the model press [Alt]+[X] to exit P2a, remembering to save the two-species model to disk.

Reference:

• Gause, G. F. 1934. The struggle for existence. Williams & Wilkins Co., Baltimore.