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DO CHEMICAL COMPOUNDS EXPLAIN TREE DIVERSITY?

May 26, 2014

DO CHEMICAL COMPOUNDS EXPLAIN TREE DIVERSITY?

A mad scientist isn’t loose on Barro Colorado Island, no matter what a recent proliferation of bright pink flagging tape with the words “Psycho Sedio” may suggest

A mad scientist isn’t loose on Barro Colorado Island, no matter what a recent proliferation of bright pink flagging tape with the words “Psycho Sedio” may suggest. The tags mark Psychotria horizontalis, a small tree species that figures in postdoctoral researcher Brian Sedio’s ambitious two-year project. By collecting 8,000 leaf-eating insects from the 100 most abundant tree species on the island, Sedio hopes to better understand why so many tree species coexist in such close proximity in the tropics.

It’s a question that has stymied forest ecologists for more than four decades. Evidence shows tropical tree species need to be rare to successfully reproduce, a hypothesis called negative density dependence. No single tree species can take over the forest, because natural enemies, such as herbivorous insects and pathogenic fungi, attack their host species wherever it is abundant.

“The big mystery is all the agents thought to be responsible — fungal pathogens, insect herbivores, bacteria — as far as we know, are not that specialized,” said Sedio, from three closely related species from the Psychotria genus. “They attack a suite of species that are often closely related, particularly in the same genus. There is some sort of paradox here.”

Sedio, a Smithsonian postdoctoral fellow, will run specialized mass spectrometry tests on tree leaves and sequence plant DNA from material retrieved from the guts of the herbivores. “I think the paradox will be resolved if we take a closer look at the chemistry,” he said. “What is driving diversity is evolution with respect to their interactions; their chemical and defensive traits.”

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