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.
Figure 1: Randomly assembled Foodweb from the ENIGMA model. Species (circles) are color-coded by trophic level. Some species feed on a primary resource "sunlight" (white circle). The species compete against each other for food. Species that additionally require another environmental resource (black circles) are assumed to be stronger competitors for food but go extinct in the patch when the respective resource disappears. The resources themselves are produced by some species. Imagine for example that a species "tree" produces a resource "nesting space" to another species "bird". The species that have evolved to utilize "nesting space" are stronger competitors, but can't survive if "tree" goes extinct and hence "nesting space" is no longer provided.