Since early studies of purple starfish in the 1960s to the reintroduction of wolves to historic habitat, keystone species have captured the imagination of many looking to restore biodiversity after periods of decline.  Ecosystem collapse describes the end result of cascading effects from not just the absence of a key member of the interacting whole, but also the dynamic shifts in population, food webs, health and resilience for every cohort—plant, animal, fungi, microorganism, habitat feature, and more—who rely upon a system in balance.  Biodiversity and habitat features, as well as life stage, reproductive fitness, predator-prey and mutualistic relationships, disease and resilience . . all are important considerations in the sphere of endless interaction and cycling continuum of presence and absence in a given set of biophysical and geographical and community aspects.  Change is also a long-term and immediate feature of any system, with rates and scales influencing many outcomes.