Upsetting the biodiversity apple cart

Upsetting the biodiversity apple cart McGill University

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McGill Reporter
November 8, 2001 - Volume 34 Number 05
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Home > McGill Reporter > Volume 34: 2001-2002 > November 8, 2001 > Upsetting the biodiversity apple cart

Upsetting the biodiversity apple cart

Biology professor Graham Bell has a radical notion that might alter the way scientists view biodiversity. Trouble is, a biologist has come up with some convincing arguments that seem to point in an entirely different direction. His name? Graham Bell.

Photo Biology professor Graham Bell
PHOTO: Claudio Calligaris

Yes, it's the same guy.

Recently, Bell published a paper in the prestigious journal Science that made the case for what is called the neutral theory of biodiversity. The theory pretty much flies in the face of the way most scientists approach notions of biological diversity and it has two principal champions -- Bell and the Smithsonian Tropical Research Institute's Stephen Hubbell.

Biologists have typically dealt with biodiversity using complex theorems that they believed matched the complexity evidenced by the startling array of life forms on the planet. Organisms tend to be highly specialized in their ability to cope with the demands of their settings, it was widely believed. Each organism is uniquely suited to deal with its own environment.

Sophisticated mathematical approaches were required to properly figure this all out. The number crunching was intensive. Bell wondered if things were really as complicated as all that.

Obviously there is a great deal of diversity in nature -- polar bears and crocodiles are uniquely suited to their own environments and wouldn't fare very well if forced to swap habitats.

But Bell wasn't struck so much by the variety of life forms that are present in nature. What he puzzled over was why were so many species so biologically similar?

Why were there 30 species of ferns in the forest instead of just one or two? Other organisms dependent on ferns for food or other reasons presumably didn't care. An animal that feasts on small forest rodents needs enough of a supply to carry on eating and surviving. But it doesn't really matter if there are 17 different but similar types of small rodents or only two varieties -- as long as there are enough small rodents, period.

So, in an attempt to understand diversity, Bell decided to focus on sameness. Did organisms that seemed to be, for all intents and purposes, pretty much the same act the part? Or were there subtle differences between them that played an essential role in fostering biodiversity? Was there a point to having 30 different kinds of ferns that warranted all the complicated number crunching?

Bell decided to look at bird populations in Britain. "We've been tracking them for centuries so it's one of the species we know best." He lumped together birds that seemed to be more or less the same -- not birds that ate other birds, for instance. Could one make conclusions about distribution patterns regarding one type of bird by checking the data related to a similar type of bird?

"I couldn't believe my eyes," says Bell. "The distribution looked exactly the same. At that point I knew I was onto something."

Bell says that the theory he has developed posits that "far from being completely distinct, all species are exactly the same. Not that snails are the same as ferns, of course, they are different kinds of organisms. Rather, it is assumed that all ecologically similar organisms, such as species of ferns, are all the same in a very precise sense. Each individual has exactly the same demographic properties -- rate of birth, death and migration -- in all circumstances."

Given a big enough backyard, Bell even suggests that you could make a fairly accurate prediction about how widespread a species is in North America from the number of individuals you can spot from your back porch.

Bell's theory has other implications -- that individual components of an ecosystem are not quite as necessary to the continuing health of the whole ecosystem as some ecologists would argue. If you wiped out all ferns, it would likely have an impact. But if half the varieties of fern suddenly disappeared, the ecosystem as a whole shouldn't suffer much.

Does Bell worry that such a suggestion might give developers an edge over ecologists in battles over logging or oil development?

"What I'm really afraid of is that ecology as a profession could be discredited -- you have to get the facts right when you present your case."

Bell suspects that some biologists will challenge his theory. Last year, in a series of papers he published in Nature with McGill colleague Rees Kassen and a team of Oxford researchers, Bell himself supplied his potential critics with ample ammunition.

In a lab setting, the team examined pond-scum bacteria. The overall goal was to gain a better understanding of why there is more biodiversity in some places with certain kinds of conditions and less in other places with different environments. What were the factors at play?

The initial bacteria yielded different sorts of genotypes -- some settling in the water, others clinging to the glass on the test tubes. What the researchers noted, among other things, was that in a heterogeneous environment mimicking environmental diversity, the diversity of life forms existing there flourished. But in a homogenous environment, a single generalized type will eliminate all others.

In a polluted lake, for instance, certain types of species will emerge as the best equipped to consume the nutrients available and "will crowd out everything else." So under certain types of conditions, a super-fern might beat out all the other sorts of ferns. The thinking that biodiversity is a pretty complicated affair might be correct after all.

So which Bell study is right? According to Bell, they both are. The neutral theory of biodiversity works -- but only to a point.

"What isn't clear to me is at what point does it fail?" If you plant coconuts in a peat bog, they won't grow, notes Bell, any more than spruce trees would grow on a tropical beach. At some point, the importance of specific environments to specific species becomes vital. But when?

That's the next conundrum Bell wants to tackle, along with plant scientist Marcia Waterway and fellow biologist Martin Lechowicz. They've already done some field survey research on this at McGill's research station at Mont St. Hilaire. But it's a task that could take forever in a forest setting -- scrupulously dividing an enormous tract of land into metric squares and going on and on until an important change that demonstrated the limits of the neutral theory of biodiversity became apparent.

So the trio is making use of McGill's research station in Schefferville. "There are long tracts of undistinguished landscape that you can only find in the North," Bell says. The terrain is ideal to the cause because there isn't as much biodiversity to keep track of and what is there is easier to observe. "We'll see at what point the hypothesis fails."

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