Final answer:
Pioneer species are the first organisms to colonize a barren area. They help break down rock into soil, allowing other species to grow and replace them in a process called succession.
Step-by-step explanation:
Pioneer species are the first organisms to colonize a barren or disturbed area, such as bare rock. They play a crucial role in the process of succession, which is the gradual change in the composition of species in an ecosystem over time. Pioneer species, like lichens and some plants, help break down the rock into soil, making it suitable for other, less hardy but more competitive species like grasses, shrubs, and trees to grow and replace the pioneer species. Over time, an area reaches an equilibrium state with a set of organisms different from the pioneer species.