About this experiment
Grow two competing populations in a shared virtual habitat. Prepare different starting abundances in the phase plane, change interaction strengths and compare coexistence, exclusion and dependence on initial conditions.
Learning goals
- Interpret carrying capacities and interspecific competition coefficients.
- Relate nullclines to zero per-capita growth.
- Distinguish a positive equilibrium from a stable coexistence outcome.
How to use it
- 1Run weak competition and compare the two population traces.
- 2Click the phase plane to prepare another pair of initial populations.
- 3Choose strong competition and repeat from opposing initial advantages.
- 4Set one initial population to zero and test whether it can appear without immigration.
The model
Assumptions
- Both populations are continuous abundances in a spatially unresolved Lotka-Volterra competition system. No births or deaths are randomly sampled.
- The solver uses a fixed 0.01-day fourth-order Runge-Kutta step over 50 days. Values are interpolated for playback.
- Carrying capacities and growth rates are fixed within a trial. A population initially at zero remains absent because there is no immigration.
- A positive nullcline intersection can be stable under weak competition or unstable under strong competition. Coordinates alone do not prove stable coexistence.
- Flower icons approximate abundance on a fixed scale of 1000 population units. They are not exact individuals or fractions normalized to a changing carrying capacity.
Try this in class
- Q1Why can strong competition make the winner depend on starting abundances?
- Q2Why does changing carrying capacity alter a nullcline even before a trial runs?
Frequently asked questions
Why is an interior equilibrium not always reached?
Under strong reciprocal competition it can be unstable, and a small starting advantage may lead to exclusion.
Do flowers count actual organisms?
No. They symbolize continuous population abundance from the differential equations.