Here's a stochastic interpretation of the Lotka-Volterra equations:
V' = beta*V - S*P*V
P' = alpha*S*P*V - mu*P
(Mnemonics: P is predator; V is prey (victim); beta is the birth rate; mu is the death rate; S is the search rate; and alpha is how efficient predators are at turning prey into other predators.)
The sliders are parametrized in a sort of funny way; beta, mu and alpha vary between 0 and 1, whereas the maximum value of S is 0.001.
You can read details about the stochastic interpretation used here.