Succession that occurs on surfaces where no soil exists is called ...

• A. Primary succession
• B. Secondary succession
• C. Immigration
• D. Gene pool

Answer: (A)

Primary succession is the process that occurs on surfaces with no soil. In these environments, there is nothing but bare rock or mineral substrate, so the first colonizers are hardy organisms like lichens and some mosses that can live directly on the surface. Their growth and eventual decay begin to build up a thin layer of organic material, gradually creating soil. With this new soil, other plants can establish, and the community changes over time from simple pioneers to more complex organisms. Secondary succession, by contrast, happens where soil already exists after a disturbance. Immigration refers to the arrival of species from elsewhere, and the gene pool is the collection of alleles in a population; neither describes the process of establishing life on bare surfaces.