Maintenance of Species Diversity by Predation in the Tierra System

One of the ecological theories has proposed that high species diversity can be maintained by predation, and several experimental studies showed that a few predator individuals with positive frequency-dependent behavior were able to maintain the coexistence of two prey types. However, in a natural environment, when a single predator species regulates the diversity of prey species, it is likely to be a full population of predators, not just a few individual predators. The role of a predator population in maintaining species diversity has not been carefully investigated in laboratory experiments but has been seriously questioned by computer simulations. In this paper, we introduce predation into the Tierra system and the dynamic relationship between prey and predator populations is examined. The robust appearance of the “Lotka-Volterra-like” cycle in Tierra suggests that the digital creatures may follow the same fundamental principles as their organic counterparts. Moreover, when each predator in a large predator population searches for prey in its neighboring area and performs positive frequency-dependent predation based on local prey abundance, a global pattern of coexistence of prey species emerges. This suggests that positive frequency-dependent predation may be a reasonable mechanism to maintain species diversity in nature.