Landforms as combined expressions of multiple reciprocally interacting species: Refining the ecosystem engineering concept

Ecosystem engineering deals with how one species affects another (or others) via modifying habitat conditions and resource availability. Through the application of this concept, many Earth scientists have assessed the roles of focal species in modulating landscape formation and dynamics. No species, however, lives or evolves in isolation; moreover, few species exist without any engineering effects on their ambient environment. Based on these basic premises, it appears unlikely that any landform on Earth (except, for example, hyperarid desert dunes, recent lava flows, and glacial grooves) exclusively represents the engineering impact of a single species. Thus, surface topography, to some degree, can generally be a combined expression of ≥ two species that mutually interact with each other through their own engineering activities. The purpose of the present research was to review, refine, and expand upon the original ecosystem engineering concept to make it more inclusive and comprehensive. Accordingly, a new concept has been proposed here, the windows of combined ecosystem engineering (WoCEE), to indicate the range within which the relative importance of engineering effects for ≥ two species changes along a gradient, as defined by various abiotic and biotic factors. In support of this novel idea, real-world examples are presented, including ecological succession in terrestrial and coastal dune ecosystems, crab–plant interactions on tidal wetlands, pocket gopher–plant relationships in the grasslands, and biological invasions by exotic mollusks and macrophytes. Notably, there are likely various other examples in nature, provided the spatiotemporal scales at which multiple species play their bioengineering roles correspond to those at which landforms are shaped. This framework represents an important step forward in the realization of true ecosystem engineering and will potentially serve as a unifying theme of biogeomorphology.