In a Prairie Ecosystem, Mycorrhizal Fungi Form Associations with the Roots

In a prairie ecosystem, mycorrhizal fungi form associations with the roots of prairie grasses, such as big bluestem. When the mycorrhizae are removed, the performance of big bluestem decreases, while the performance of other prairie grasses and wildflowers increases. This effect most clearly shows the influence of mutualisms on

A) species abundance.
B) species distribution.
C) ecosystem structure.
D) ecosystem diversity.