Evolutionary assembly drives community complexity.

With a mixture of ecological (i.e. via invasion) and evolutionary (i.e. via speciation) assembly events, we investigate the effect of the combination of invasion and evolution on the process of community assembly. (A) The scenario of pure invasion (green) promotes the smallest values of richness while pure evolution (blue) promotes the highest values. Mixed scenarios, with 20%, 50%, and 80% of invasion, exhibit a generally proportional decrease in values of richness from pure evolution to pure invasion. Except that pure invasion and 80% invasion are closer together than expected in a proportional difference. (B) The proportions of mutualistic interactions follow a similar pattern. (C) A disproportional increase of connectance happens in the scenario of pure evolution, while all scenarios containing invasion promote values of connectance that are closer together. (D) As a result, pure evolution promotes a disproportional increase in complexity. A majority of evolution also exhibits a gap in complexity compared to the scenarios with 50% and 80% of invasions and the scenario of pure invasion. The plots show the average values of 15 samples for every 50 assembly events (dots) and the vertical lines show the standard errors, calculated as the standard deviation divided by the square root of the number of samples. Each sample is a simulation of the entire assembly process for a scenario. Parameter values: interaction strengths were drawn from a half-normal distribution of zero mean and a standard deviation of 0.2, and strength for consumers was made no larger than the strength for resources. Communities started with 5 non-interacting species. New species were given initial abundances equal to the extinction threshold . The connectance of invading species was drawn from a uniform distribution between 0.05 and 0.5. In speciation, offspring species had up to 5 interactions differing from the parent species, chosen randomly (, see Methods). Handling times for mutualism and consumer-resource were 0.1.