North America is home to 91 species of oak trees. Astoundingly, the various species rarely, if ever, occur alone. Where one kind of oak is found, invariably at least one more will be found. How can nature support a setup like that when it operates on the principle that only the fittest survive in any one setting?
A study recently published in the American Journal of Botany has unearthed the secret: A unique evolutionary history that allows oak species to be different and similar at the same time — making them the most diverse and dominant trees species on the continent.
“We found the species that occurred together were distantly related but had similar functional characteristics, allowing them to occupy the same environment at the same time,” said Jeannine Cavender-Bares, professor of ecology in the College of Biological Sciences at the University of Minnesota and lead author of the paper.
"This study brings our work full circle to questions Cavender-Bares and colleagues started addressing over a decade ago," said co-author Andrew Hipp, a senior scientist with The Morton Arboretum near Chicago. "It illustrates how evolutionary biology can serve the interests of understanding and conserving plant communities."
When Cavender-Bares began studying the oddity of oak co-existence in Florida in the 1990s, she discovered that species that co-occurred were most often distant relatives that had evolved similar traits such as leaf shape and size. She speculated that evolution allowed multiple oak lineages to develop similar traits that made them a good fit for the setting at the same time they retained differences that gave each a special edge as well.