Read the first 5 Pages: Chapt2Frst5Pages.pdf
If you have 3D-XplorMath and want to play with the Voltera-Lotka Predator-Prey Model launch the program , and use the ODE submenu of the Category menu to change to the ODE(2D)1stOrder category, and then choose Volterra-Lotka from the ODE(2D)1stOrder menu.
The the direction field and several orbits of the Volterra-Lotka system. 3D-XplorMath Java Applet