Predicting Straw Decomposition by a Four-Species Fungal Community: A Cellular Automaton Model

1. We have developed a cellular automaton model based on the measured and inferred properties of the fungal saprophytes, Mucor hiemalis, Agrocybe gibberosa, Chaetomium globosum and Sphaerobolus stellatus. In this model, the fungal mycelia are represented by the players MH, AG, CG and SS, respectively. The model was used to investigate the rate of breakdown of litter, assumed to be made up of sugar and cellulose, and the associated persistence of the four model mycelia. We examined the persistence times of the fungi and the degree of breakdown of the resources. 2. This model reproduces most of the results of competition experiments on malt extract agar medium between different fungi. However, perfect reproduction of observations was not possible since real fungi showed a variety of responses under similar conditions. 3. The model predicts a number of phenomena seen in other experimental situations. The model expects coexistence between species to continue for longer when spatial effects are important. Persistence of each species is found to be greatest for some intermediate level of resource patchiness. 4. The model also exhibits the phenomenon of secondary colonization, obligate sugar users can re-colonize through the release of sugars from the breakdown of cellulose by other fungi. 5. The model predicts that, when the resources are patchy, decomposition will take much longer to complete. If the resources are sufficiently patchy, all species die before breakdown of resources is complete.