concept

Functional extinction

When a species is still biologically alive but has stopped performing its ecological role. The classic case is the American chestnut: a blight arriving in 1904 killed three to four billion trees, yet the species is not extinct — its root systems persist and keep sending up shoots, and the fungus kills those shoots before they can mature and reproduce. The species survives as tissue and is gone as an ecological participant. A useful reminder that "not extinct" and "still doing its job" are entirely different statements.