When implementing the Lotka-Volterra model using one Compartment block (one for both the predator and prey), the compartment needs to be vectorized. I.e. the rabbit and fox species needs to be added as modelled materials. Then either one can use the same approach as in the two Compartment solution, using Source/Sink and Transfer blocks as means to model the dynamic behaviour or just explicitly define the differential equation inside the Compartment.
Figure 1 Ecolego matrix of one Compartment approach
Solution to the excersise