Easter Island is an extremely isolated island in the Pacific, about 3,500 km from South America. Although there are no forests on the island now, archeological studies, fossil pollen, and other data show that Easter Island was once home to forests containing giant palms and other trees. Some scientists think that the removal of the giant palms caused the forest ecosystem to collapse. Which of the following factors might have caused this collapse?
a. Shade-tolerant species increased in diversity in the absence of the palm.
b. Soil erosion decreased in the absence of the palm.
c. The absence of the palm trees may have reduced habitat quality for many other species.
d. Productivity increased, thereby increasing competition, in the palms' absence.