Elizabeth Stacy (Life Sciences), in collaboration with Becky Ostertag at the University of Hawaii, published: "," in Functional Ecology.
They asked how eight races, varieties, and species of ʻŌhiʻa trees (Hawaiian Metrosideros) can co-exist in a predictable sequence along the many leeward ridges of Koʻolau Volcano, Oʻahu, with both hairy and hairless forms co-occurring across the full elevation gradient. They found fundamental differences between the groups in response to light and phosphorus that appear to descend from the early- and late-successional varieties, respectively, that likely gave rise to them. In spite of these differences, the two groups showed growth patterns that suggest that they have evolved similar responses to environmental conditions (through parallel evolution) across the elevation gradient. It appears that the retention of original traits inherited from their ancestors allowed these two very closely related groups of trees to use resources a bit differently and thus share the same space, setting the stage for parallel evolution across elevations. Both stabilizing and divergent processes may promote the accumulation of species by permitting the coexistence of forms at the early stages of diversification.
