Keystone Severity Formula

When sea otters vanished from Pacific kelp forests, ecologists could find substitutes for their role as urchin predators—sunflower sea stars kept urchin populations in check until a 2013 wasting disease devastated them. But when gray wolves disappeared from Yellowstone in the 1920s, no substitute existed for their combined effects on elk behavior, vegetation patterns, stream geomorphology, and beaver habitat. The ecosystem waited 70 years for deliberate reintroduction in 1995—and recovery is still ongoing. This asymmetry—some keystones have functional equivalents while others are truly irreplaceable—demands a more sophisticated risk assessment than simple impact measurement. The Keystone Severity Formula multiplies Keystone Index (impact relative to resource allocation) by Substitution Difficulty (how hard it is to replace the function). TSMC commands roughly 70% of the global semiconductor foundry market and dominates advanced chip manufacturing. Its Keystone Index is astronomical—removing it would disrupt global technology supply chains. But the Substitution Difficulty is what makes it existential: building equivalent capacity requires massive capital investment, tens of thousands of specialized engineers, and years of construction. That's a Severity score in the thousands. The formula transforms vague concerns about 'critical dependencies' into quantified priorities that drive resource allocation.