Answer :
Final answer:
A keystone species is essential for maintaining the structure and biodiversity of its ecosystem, and its removal can cause significant changes in the ecosystem's balance, as illustrated by the intertidal sea star and the banded tetra fish.
Explanation:
A keystone species is one whose presence is key to maintaining biodiversity within an ecosystem and to upholding an ecological community's structure. The concept indicates that the removal or addition of a single species within an ecosystem can have a significant ripple effect on the balance of organisms. For example, the intertidal sea star, Pisaster ochraceus, is a keystone species in the northwestern United States.
When this sea star is removed from its habitat, mussel populations increase dramatically, which in turn causes a decrease in algal populations, and ultimately reduces the overall biodiversity. Similarly, the banded tetra fish plays an essential role by supplying nearly all the phosphorus within tropical streams. This inorganic nutrient is crucial for other species, meaning that a significant change in the population of banded tetras can affect the entire community structure.
