Final answer:
Pioneer species are the initial colonizers in environments like fresh volcanic land, starting the process of primary succession and ultimately paving the way for more diverse communities.
Step-by-step explanation:
The correct answer to this question is d. pioneer species. Pioneer species are the first organisms to colonize barren environments, such as areas that have been covered by volcanic lava. This process, known as primary succession, starts with these hardy species altering the environment in ways that allow other, less hardy species to establish themselves later. Pioneer species typically include lichens and some plants that are able to grow on the newly formed rock and begin the process of soil formation. As these pioneer species live and die, they contribute organic material to the developing soil layer, which provides a basis for subsequent plant and animal life to thrive. Over time, a sequence of plant and animal communities will succeed each other until a stable, climax community is established, usually featuring a rich array of species vastly different from the original pioneer species.