Assembly of complex ecological networks by species invasion

Background/Question/Methods

As Darwin theorized, evolution occurs within a dynamic interdependent network of interactions among communities containing many diverse species. Such communities evolve over time through both assembly involving invasion by already established species and by evolution involving speciation of new species as well as loss of species caused by invasion and speciation.  A key distinction between these two mechanisms concerns relative novelty.  Assembly can, but not necessarily, introduce highly novel species whose function is very different from species already in the community.  Speciation necessarily introduces organisms relatively similar to the parent species co-occurring in the same community.  We explore how this distinction plays out in complex ecological networks that model ecosystems invaded by both more and less novel species. 

Results/Conclusions

We find that speciation is typically more disruptive often leading to the extinction of the parent species or extinction of the novel variant of the parent species.  In contrast, assembly is less disruptive in that invading species more often successfully establish without extirpating species already in the community. The most extreme disruptions occur during speciation which occasionally extirpates most of species in the community. Given these results, we hypothesize that community-level effects can be distinguished by speciation leading to high sensitivity on average and invasion leading to low mean sensitivity.