Practice question

Primary succession begins where a biological legacy and developed soil are absent, as on new lava, exposed bedrock, or recently deglaciated substrate. Colonists must initiate weathering and organic-matter accumulation before a deeper soil and more demanding vascular plants can become established. Successional trajectories emerge from dispersal, establishment, species interactions, and organism-driven environmental change. Priority effects can make arrival order important, while retained soil and propagules strongly accelerate recovery after disturbance. Facilitation, tolerance, and inhibition are alternative mechanisms rather than mandatory universal stages; more than one may operate at the same site or at different times. The eventual assemblage also depends on climate, substrate, disturbance frequency, and the regional species pool, so a climax is better viewed as dynamic persistence than permanent equilibrium. In this context, the keyed term, Occurs on bare rock or lifeless area, identifies the relevant mechanism or quantitative relationship and links the observed pattern to its underlying ecological cause.