Final answer:
Keystone species are critical for controlling prey populations and maintaining biodiversity, as well as providing essential nutrients for other species within their ecological communities.
Step-by-step explanation:
Roles of Keystone Species in Community Structure
Keystone species play critical roles in maintaining the structure and biodiversity of ecological communities. One role is regulating prey populations to prevent any one species from becoming dominant. For instance, the intertidal sea star, Piaster ochraceous, is a keystone species in marine environments. By preying on mussels, they prevent mussels from overcrowding the environment, which preserves the biodiversity of the community. Another significant role of keystone species is nutrient provision. The banded tetra, a tropical fish, significantly contributes phosphorus, a vital nutrient, to the aquatic ecosystem, influencing the growth and health of other species within the community.