Using Digital Evolution To Explore Effects Of Mass Extinction On Community Stability And Emergence Of Coordinated Stasis

The phenomenon of coordinated stasis is an extension of punctuated equilibria,it describes the long-term stability of multi-species communities.Coordinated stasis and community stability can be described by these indices:(1)Species composition and community organization keep stable during long periods of time.(2)The long-lasting morphological invariance of species.(3)High resistance of community to minor disturbances,external and internal invasion.(4)Good resilience of communities after disturbances.Despite considerable attention from paleobiologists,results of paleontological investigation remain inconclusive regarding coordinated stasis and the mechanisms behind it,and the authenticity of them is still in dispute at the same time.This work applied digital evolution as the main tool,to investigate coordinated stasis in a controlled experimental setting and assess the community stability at different levels.We created populations of self-replicating computer programs,digital organisms,that replicate,mutate,compete for space and resources,and evolve new genotypes and phenotypes.As the digital organisms consumed some resources and generated others that can be used by other organisms,simple but plausible ecosystems evolved over time.Then we examined coordinated stasis at ecological,morphological,phylogenetic levels,investigated whether and how often coordinated stasis emerges,and the range of its occurrences.We implemented mass extinction to examine the effects on community stability by external disturbances.We evaluated the authenticity and mechanisms of ecological stasis by using the unique advantages in data analyses and replicating experiment of digital evolution.The main results indicated:(1)Most of the control communities kept stable during long periods of time in species composition and community organization without disturbance.(2)Control communities always had pretty high stability at phylogenetic level,but it's more or less affected by internal interaction.(3)Community stability at different levels is related to extinction intensity,the stronger the extinction the lower the stability became.(4)The stability we found in performance with time shift invasion trials are different from the stability at other levels,it means "stasis" inferred from eco-phenotypic measures is largely illusory.(5)Results of the fitness change of community members supported fitness-deterioration interpretation of Red Queen:Any evolutionary advance in one member will entail a loss of fitness in others.(6)Stasis we observed from the results is largely uncoordinated,that is an intermediate state between coordinated stasis and full transitive evolution.This work is helpful for enhancing understanding of multi-agent evolutionary systems involving multiple biotic interactions among community members.Contrast to the traditional paleontological methods and numerical simulations,digital evolution can closely integrate ecological,phenotypic,and phylogenetic data in analyses,and conduct analyses at levels ranging from individual to community-wide across time.The results will help:(1)Highlight the relative roles of ecological and evolutionary dynamics in producing macroevolutionary patterns.(2)Enhance understanding of how ecologies assemble and persist.(3)Contribute to a closer unification of micro-and macroscale views of evolution.(4)Provide new ideas and directions for evolutionary and paleontological research in the future.