Evolutionary dynamics of species diversity in an interaction web system

I used a computer simulation to investigate the effect of evolution of species characteristics on species diversity in an interaction web system. In the system, species interacted with other species neighboring on a hypothetical niche space. The system changed temporally via evolution of species. Species harming other species survived by killing their enemies. However, while the system was dominated by such species, the system was stable and maintained high species diversity. Species not harming other species survived by developing mutualism, as they could not eliminate their enemies. Because such species could attain larger growth rates than species that harmed others, evolution tended toward species that did not harm others. As a result of this evolution, a small group of species with highly developed mutualism filled the carrying capacity of the system. Consequently, the system became unstable, and the diversity in the system decreased suddenly. Mutualism among species did not increase species diversity in the interaction web system.