Ecological systems in which predators and prey compete for surviving were investigated by applying suitable mathematical models. An analogy can be drawn between biological prey and software defects, and between predators and programmers. In fact, when programmers start trying to recognize and correct code defects, while the number of residual defects decreases, the effort spent to find any new defect has an initial increase, followed by a decline, when almost all defects are removed, similar to prey and predator populations.
This paper proposes to describe the evolution of the maintenance and testing effort by means of the predator-prey dynamic model. The applicability of the model is supported by the experimental data about two real world projects. The fit of the model when parameters are estimated on all available data is high, and accurate predictions can be obtained when an initial segment of the available data is used for parameter estimation.