Ecology Regents Practice Exam

Primary succession refers to the process of ecological development in areas where no soil exists initially, such as after a volcanic eruption or glacial retreat. This sequence begins with the colonization of bare rock or land by pioneer species, such as lichens and mosses, which can survive in such harsh conditions. Over time, these organisms help to break down the rock and contribute organic matter as they die and decompose, gradually leading to the formation of soil. This soil then allows for the establishment of more complex plant communities, eventually leading to a mature ecosystem.

While natural recovery after disturbances like fires and gradual changes in species composition are important ecological processes, they are characteristic of different types of succession. In contrast, the replacement of one species by another in a habitat typically falls under secondary succession, which occurs in previously inhabited areas that have experienced a disturbance. Thus, the definition provided in the correct answer best encapsulates the unique circumstances of primary succession.