Rock-Paper-Scissors Dynamics in a Digital Ecology

In this paper we present an Alife-platform named Urdar aimed at investigating dynamics of ecosystems where species engage in cross-feeding, i.e. where metabolites are passed from one species to the next in a process of sequential degradation. This type of interactions are commonly found in microbial ecosystems such as bacterial consortia degrading complex compounds. We have studied this phenomenon from an abstract point of view by considering artificial organisms which metabolise binary strings from a shared environment. The organisms are represented as simple cellular automaton rules and the analogue of energy in the system is an approximation of the Shannon entropy of the binary strings. Only organisms which increase the entropy of the transformed strings are allowed to replicate. We find that the system exhibits a large degree of biodiversity and a non-stationary species distribution, especially during low rates of energy inflow, and that the time spent in each species configuration exhibits a broad distribution. Investigating the interaction between different species in the system by invasion experiments we observe that co-existence is a common feature and that some triplets of species exhibit intransitive, i.e. rock-paper-scissors like, interactions.