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"The large point is that this development is a sign of how desperate search for yield has become. In and of itself this "new" product appears not to be significant in aggregate terms, so in isolation it is not too alarming. But it is the sort of thing that can burn the unwary badly. If it becomes a meaningful-sized activty, the large-scale hazards go up too. Stay tuned."

The complexity of an ecological community can be distilled into a network, where diverse interactions connect species in a web of dependencies. Species interact directly with each other and indirectly through environmental effects, however to our knowledge the role of these ecosystem engineers has not been considered in ecological network models. Here we explore the dynamics of ecosystem assembly, where species colonization and extinction depends on the constraints imposed by trophic, service, and engineering dependencies. We show that our assembly model reproduces many key features of ecological systems, such as the role of generalists during assembly, realistic maximum trophic levels, and increased nestedness with mutualistic interactions. We find that ecosystem engineering has large and nonlinear effects on extinction rates. While small numbers of engineers reduce stability by increasing primary extinctions, larger numbers of engineers increase stability by reducing primary extinctions and extinction cascade magnitude. Our results suggest that ecological engineers may enhance community diversity while increasing persistence by facilitating colonization and limiting competitive exclusion.

The introduction of the Internet rapidly enabled unprecedented global connectivity. In about two decades, communication became instantaneous, affordable, and independent of physical barriers. People, however, do not seem to be communicating with each other homogeneously. Online communication networks appear to be polarized and echo-chambers are manifesting for political1-5 and non-political6-9 reasons. Understanding the emergent structure of information flows on the Internet and its implications for the complexity of society is a challenge for scientists and technology developers. Mapping the organization of social systems is crucial for effective policy making involving ethnic groups10 as well as economic growth.11