Rats + Fire = Salvation of California Plant

That grabbed some headlines. But work recently undertaken by San Francisco State's Professor Tom Parker may change the way scientists think about evolution. Parker -- one of the aforementioned experts called in to verify the Franciscan Manzanita -- asserts that one of the key factors in manzanita survival is ... rats.

While supervising his students' field studies on seed predation -- in plain English, seeds being eaten by rats and other rodents -- Parker noticed something interesting about manzanita growth patters in fire zones. Emerging from the charred earth, the young plants came up in clusters of 10, 20, or even 30 plants packed together in a small space. It occurred to the professor that an odd, symbiotic relationship might be going on: Rats may be burying manzanita seeds deep enough that they survive fires and form the next generation.

It's a nifty idea. But to prove it, you need to follow around some rats. So Parker did. 

Parker put together some student teams and headed out to the wild. The researchers left out some delicious manzanita seeds, but in order to get to them, the rodents had to trod upon pans of ultraviolet fluorescent powder. Parker and his students then followed the tiny, glowing footprints to the rats' seed caches.

"We dug them up very carefully so we could see how deep they were," he says. "We were basically on our bellies, digging with a spoon."

Scientists have long known that manzanitas often require fire to successfully germinate (the seeds' hard exteriors crack open when exposed to chemicals present in smoke). But the rat connection may be a silver bullet. Now that Parker knows how deep the seeds are buried, he can run experiments to gauge the effect of fire on the rats' caches. But his preliminary observations definitely seem to point to the manzanitas' leaning heavily on rats for survival.

That's most obvious when he visited burn zones. The more heavily burned the area was, the higher the proportion of seedlings that sprouted from rodent caches. "At low-intensity areas, most seedlings come out of natural seed banks that rodents didn't bury," says Parker. "But as fire increases in intensity, the proportion of seedlings that comes out of rodent caches increases to nearly 100 percent."

It's an interesting and counter-intuitive notion -- especially as scientists will now struggle to save the rediscovered Franciscan Manzanita. Perhaps they won't be able to do it without fire -- and rats.