Final answer:
A keystone species is crucial for the ecological balance of a community, significantly influencing biodiversity and community structure. Examples such as the intertidal sea star and the banded tetra demonstrate their vital role in ecosystems.
Step-by-step explanation:
A keystone species is an organism that plays an essential role in maintaining the structure, biodiversity, and balance of an ecological community. Noteworthy examples include the intertidal sea star, Pisaster ochraceus, and the banded tetra, which are crucial in their respective ecosystems. The removal of a keystone species, such as the sea star, leads to an increase in mussel populations, disrupting the community structure and reducing biodiversity. Similarly, if the banded tetra were to disappear, the aquatic community would experience dramatic changes due to the loss of phosphorus supplied by these fish.
Keystone species may not always be the most abundant in a community, but their impact is disproportionately large compared to their numbers. They maintain the ecological equilibrium and prevent other species from becoming dominant, which could have negative effects on biodiversity and ecosystem function.