Answer
d.
Work Step by Step
Option a. is incorrect. A keystone species is one on which many of the organisms in an ecosystem depends.
Option b. is incorrect. A climax species is plant life that remains unchanged in an ecosystem unless that ecosystem is disturbed.
Option c. is incorrect. Primary producers are organisms that take inorganic material and transform it into organic matter.
Option d. is correct. A pioneer species is the first species to colonize an area during the process of succession. Lichen and moss are normal pioneer species in ecosystems.
