National Geographic : 2010 Feb
remains relatively unknown, even to scientists. About 60,000 species of fungi have been discov- ered and studied, for example, including mush- rooms, rusts, and molds, but specialists estimate that more than 1.5 million species actually exist on Earth. Along with them in the soil thrive some of the most abundant animals in the world, the nematodes, also known as round- worms. These include, among other forms, the barely visible white wigglers that can be found everywhere just underground. Tens of thousands of roundworm species are known, and the true number could be in the millions. Both fungi and roundworms are outdone dramatically in turn by still smaller organisms. In a pinch of garden soil, about a gram in weight, live millions of bacte- ria, representing several thou- sand species. Most of them are unknown to science. Ants, with more than 12,000 described species in the world (and the group on which I specialize as a naturalist), are among the better stud- ied insects. Yet it's a good guess that the actual number is double or even triple that. In 2003 I completed a study of the "big-headed ants" of the Western Hemisphere, a genus (Pheidole) that has the largest number of known spe- cies and is among the most abundant of all the ants. At the end of my study, a er 18 years of off-and-on effort, I had distinguished 624 species. A majority, 337, were new to science. Only a dozen or so of the species have been closely studied. One of the smallest, I discov- ered, feeds on oribatid mites, which are usually much smaller than the letter o on this page and resemble a cross between a spider and a turtle. Oribatids are among the most abundant crea- tures of their size in the soil. A cubic foot might contain thousands of individuals. Yet I found that their diversity and habits remain largely unknown, much more than in the case of ants. Life at the ground level is not just a random mix of species, not an interspersion of fungi, bac- teria, worms, ants, and all the rest. e species of each group are strictly strati ed by depth. In passing from just above the surface on down, the conditions of the microenvironment change gradually but dramatically. Inch by inch there are shi s in light and temperature, the size of the cavities, the chemistry of the air, soil, or water, the kind of food available, and the species of organisms. e combination of these properties, down to a microscopic level, de nes the surface ecosystem. Each spe- cies is specialized to survive and reproduce best in its par- ticular niche. Soil studies, and especially the biology of the ground level, is growing rapidly into a major branch of science. Now bacteria and other microscopic forms of life can be identi ed quickly by the decoding of their DNA. e life cycles of increas- ing numbers of insects and other invertebrate animals, many entirely unknown to science, are being explored in the field and laboratory. eir physical and nutritional needs are coming clear, species by species. e Encyclopedia of Life, available in a single address (eol.org), is gathering all known infor- mation on each species and making it available free throughout the world. A small world awaits exploration. As the o- ras and faunas of the surface are examined more closely, the interlocking mechanisms of life are emerging in ever greater and more surprising detail. In time we will come fully to appreciate the magni cent little ecosystems that have fallen under our stewardship. j sharpshOOter leafhOpper • PAROMENIA ISABELLINA, 0.5 IN LONG O What life lies below Central Park? See what crawled out of the leaves at ngm.com/cubicfoot.