  The complexity of an ecological community can be distilled into a network,
where diverse interactions connect species in a web of dependencies. Species
interact not only with each other but indirectly through environmental effects,
however the role of these ecosystem engineers has not yet been considered in
models of ecological networks. Here we explore the dynamics of ecosystem
assembly, where the colonization and extinction of species within a community
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 higher frequencies of
mutualisms. We find that ecosystem engineering has large and nonlinear effects
on extinction rates, facilitating robustness by creating niche space, but at
the same time increasing the magnitude of extinction cascades. We emphasize the
importance of redundancies in engineered effects and show that such redundancy
lowers the barriers to colonization, promoting community diversity. Together,
our results suggest that ecological engineers may enhance community diversity
while increasing persistence by facilitating colonization and limiting
competitive exclusion.
