Model of the "predator-prey" is an equation describing the real environmental situation. For example, the model can determine how the number of foxes and rabbits changes in the forest. Let's say that herbs that the rabbits eat becomes grows in the forest constantly. We can assume that such an outcome for rabbits is favorable because they will be well multiply and increase the their number.
The paradox of the ecological balance claims that it is not the case: first, the number of rabbits really grows, but the growth of the population of rabbits in a closed environment (forest) will lead to an increase in the population of the foxes. Finally, the number of predators will increase so much that they destroy all the prey first, and then die out themselves.
In practice, this paradox does not apply to most types of animals because they do not live in a closed environment.