The dynamic evolution of ecological systems in which predators and preys compete for surviving has been investigated by applying suitable mathematical models. Dynamic systems theory provides a useful way to model interspecie competition and thus the evolution of predators and preys populations. This kind of mathematical framework has been shown to be well suited to describe evolution of economical systems as well, where instead of predators and preys there are consumers and resources.This paper suggests how dynamic systems could be usefully applied to maintenance context, namely to model the dynamic evolution of maintenance effort. When maintainers starts trying to recognize and correct code defects, while the number of residual defects decreases, the effort spent to find out any new defect has an initial increase, followed by a decline, in a similar way as preys and predators populations do.The feasibility of this approach is supported by the experimental data about a 67 months maintenance task of a software project and its successive releases.