On Science: Learning what we have to lose
This article first appeared in the St. Louis Beacon, Sept. 1, 2009 - An image captured my eye three weeks ago. It was a photograph of a tiny deer with enormous ears huddled in underbrush, no doubt shivering as it peered up at one of the few scientists ever to see its species. Called a muntjac or leaf deer, it was discovered by modern science 10 years ago in the sparsely explored Himalayan mountain region of northern Myanmar. Just under 3 feet tall and weighing 24 pounds, it is the smallest deer species in the world.
It is impossible for me to look at this image and not wonder what else is out there that we scientists have never noticed. If our warnings of a biodiversity crisis have any substance, if we are really living in the midst of a great extinction unparalleled since the loss of the dinosaurs, then many species like this little leaf deer face an uncertain future.
In an attempt to come to grips with the size of the problem, The World Wildlife Fund has gathered information from a broad array of scientists and organizations carrying out biological research in the Eastern Himalayas, a vast region reaching from Butan and northeast India, across the far north of Myanmar where the leaf deer lives, to Nepal and Tibet.
Where the Indian subcontinent comes crashing into Asia, the Eastern Himalayas are one of the most bio-diverse (species rich) regions on earth. More than 10,000 plant species, 300 mammal species, 977 birds, 176 reptiles, 105 amphibians and 269 kinds of freshwater fish live there - at least, that's how many we had known about.
The WWF survey, released Aug. 11, adds 244 newly discovered species of plants, 60 new invertebrates, 16 amphibians, 16 reptiles, 14 fish, two birds and two mammals. One of the mammals, the Arunachal macaque, was first described in 2005 -- at the time, the first new monkey species identified anywhere in the world in over a century.
The point of all this, the reason we should look up and pay attention, is that every one of these new species is in danger of extinction. "This rugged and remarkable (Eastern Himalayan) landscape is already seeing direct, measurable impacts from climate change, and risks being lost forever," said Jon Miceler, director of the WWF program in the Aug. 11 press release.
So what does a threat to a leaf deer have to do with life on the Mississippi? Why should my readers in St. Louis and elsewhere care about the fate of Arunachal macaques? Other than a brief bow to "Do not ask for whom the bell tolls," is there any practical reason we should care?
I suspect any faithful reader of this column will know my feelings on the subject. I have written about it often, and will not retrace those steps today.
Instead, I want to address a far simpler subject, the very one addressed by the WWF report. To have any hope of coming to grips with the biodiversity crisis, it will be necessary for us to get a firm grasp on what it is we are in danger of losing. Just exactly how many species are going extinct? Where is this happening, and what kinds of animals and plants are we talking about?
Before we can make much progress exploring these numbers, we need a clear estimate of the most fundamental number of all: How many species are there in the world, right now? If we don't know where we are, it is difficult to estimate clearly how rapidly things are changing. Said more simply, if you don't know what you have, it's hard to know how much of it you are losing.
Counting species might at first seem a straightforward task, like counting items of fruit in a grocery store. It's not. Taxonomists (the scientists who assign names to new species) don't always agree when a slightly different specimen should be called a new species, or when the difference should be considered natural variation. Think of how different the breeds of dogs look, and yet they are all the some species.
Those who tend to consider each different kind of individual a new species are called "splitters," while those who tend to cluster similar individuals into one species are called "lumpers."
Plants -- 270,000
Fungi -- 70,000
Nematodes -- 15,000
Mollusks -- 70,000
Arthropods -- 915,000
Vertebrates -- 45,000
However, lumping and splitting tend to cancel out when considering the total number of species in the higher taxonomic categories. Against this background of uncertainty, prominent ecologist Robert May has estimated the numbers of described species living on Earth today.
You can see that there are far more arthropod species than any other kind of multicellular organism: 75,000 species of arachnids (spiders, scorpions and mites), 40,000 species of crustaceans (crabs, shrimps and lice), and an enormous 800,000 species of insects (120,000 are flies, 130,000 are ants and wasps, 150,000 are butterflies and moths, and a staggering 400,000 are beetles). When asked what was the most important thing he had learned after a lifetime of study, famed biologist J.B.S. Haldane said "God shows an inordinate fondness for beetles."
May's careful count indicates a total number of about 1.5 million described species. Other scientists' counts roughly agree. Are we done, then? Is this the number we need?
In a word, "No."
The problem is that we have scientifically described only a small fraction of life's diversity. Last month's WWF report describing new Himalayan species makes that point clearly. While people's fascination with watching birds has ensured that there are few undescribed species (only a few new members are added to the list of 10,000 species of bird each year) and any addition to the 5,000 species of mammals makes the world news, what about nematodes? There is no passionate interest in them, no affection that would lead to their species being counted by enthusiastic naturalists.
Clearly, far fewer numbers of nematode species are collected and described than birds or mammals. But how few? What is the number of undescribed species? he largest estimates reach 100 million!
How can we tell? How can we count what we have never seen? Even among experts, there are wide disagreements, as estimates in the absence of data are only guesses.
The biggest disagreement comes with the largest category, insects living in the most diverse and unstudied place on Earth, the canopy of tropical rain forests. While the forest floor is dark, the canopy of leafy vegetation 35 meters above is rich with insect life. And practically every tree in a square kilometer of tropical rain forest is a different species and will have insect species that live on no other species of tree.
How can one collect and study these insects? Climbing the trees can be done, but it is a challenge and dangerous. And how, once up there, grasping a branch, can a researcher hope to collect all the insects that live in that tree's canopy. Not going to happen.
Ecologist Terry Smith of the Smithsonian Institution has taken an extreme approach: He drapes large plastic sheets over the canopy of particular trees and performs "canopy knockdowns," squirting in clouds of potent insecticides that kill all the insects on the tree. They fall to the ground, where they can be collected and studied. As tropical biologists had predicted, the numbers are enormous. A single species of tropical rain forest tree yielded 1,200 species of canopy-dwelling beetles. Importantly, over 13 percent of them, 163 species, were found only on that tree species, and lived on no other (the other beetle species lived on more than one tree species).
Now comes the controversial part. There are about 50,000 species of trees in the tropics. If you multiply 163 unique species per tree by this number, you get more than 8 million species of canopy beetle alone. Forty percent of described insects are beetles, so the total number of canopy insect species could exceed 20 million! Careful studies suggest that there are four times as many insect and spider species on the ground as in the canopy, increasing the estimate to an astonishing 100 million species.
Can this be true? This estimate is a stepwise multiplication of several large and very uncertain numbers, and most experts favor a far smaller estimate, say 12 million total species. Clearly there is still great uncertainty -- which only serves to underline how little we know about what we are losing.
George B. Johnson's "On Science" column looks at scientific issues and explains them in an accessible manner.
Johnson, Ph.D., professor emeritus of Biology at Washington University, has taught biology and genetics to undergraduates for more than 30 years. Also professor of genetics at Washington University’s School of Medicine, Johnson is a student of population genetics and evolution, renowned for his pioneering studies of genetic variability. He has authored more than 50 scientific publications and seven texts.
As the founding director of The Living World, the education center at the St Louis Zoo, from 1987 to 1990, he was responsible for developing innovative high-tech exhibits and new educational programs.
Copyright George Johnson