Within One Cubic Foot
By Edward O. Wilson
Originally Published in February of
2010 in National Geographic Magazine
When you thrust a shovel into the soil or tear off a piece
of coral, you are, godlike, cutting through an entire world. You have crossed a
hidden frontier known to very few. Immediately close at hand, around and
beneath our feet, lies the least explored part of the planet's surface. It is
also the most vital place on Earth for human existence.
In
any habitat, on the ground, in the forest canopy, or in the water, your eye is
first caught by the big animals—birds, mammals, fish, butterflies. But
gradually the smaller inhabitants, far more numerous, begin to eclipse
them. There are the insect myriads creeping and buzzing among the weeds, the
worms and unnamable creatures that squirm or scuttle for cover when you turn
garden soil for planting. There are those annoying ants that swarm out when
their nest is accidentally cut open and the pesky beetle grubs exposed at
yellowed grass roots. When you flip a rock over, there are even more: You see
spiderlings and sundry pale unknowns of diverse form slinking through mats of
fungus strands. Tiny beetles hide from the sudden light, and pill bugs curl
their bodies into defensive balls. Centipedes and millipedes, the armored
snakes of their size class, squeeze into the nearest crevices and wormholes.
It may seem that the whole icky lot of them, and the
miniature realms they inhabit, are unrelated to human concerns. But scientists
have found the exact opposite to be true. Together with the bacteria and other
invisible microorganisms swimming and settled around the mineral grains of the
soil, the ground dwellers are the heart of life on Earth.
The terrain they inhabit is not just a matrix of dirt and
rubble. The entire ground habitat is
alive. Living forms create virtually all of the substances that flow around the
inert grains.
If all the organisms were to disappear from any one of the
cubic spaces depicted in these photographs, the environment in it would soon
shift to a radical new state. The molecules of the soil or streambed would
become smaller and simpler. The ratios of oxygen, carbon dioxide, and other gases
in the air would change. Altogether, a new physical equilibrium would be
approached, at which the cubic foot would resemble that on some distant,
sterile planet.
Earth is the only planet we know that has a biosphere. This
thin, membranous layer of life is our only home. It alone is able to maintain
the exact environment we ourselves need to stay alive.
Most of the organisms of the biosphere, and the vast number
of its species, can be found at the surface or just below it. Through their
bodies pass the cycles of chemical reactions upon which all of life depends.
With precision exceeding anything our technology can match, some of the species
break down the dead plant and animal material falling from above. Specialized
predators and parasites feed on these scavengers, and higher-level specialists
feed on them in turn. The whole, working together in a constant turnover of
birth and death, returns to the plants the nutrients needed to continue
photosynthesis. Without the smooth working of all this linkage, the biosphere
would cease to exist.
Thus, we need all of this biomass and biodiversity,
including all of the creepy-crawlies. Yet in spite of its vital role, life at
the ground level remains relatively unknown, even to scientists. About 60,000
species of fungi have been discovered and studied, for example, including
mushrooms, 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
roundworms. 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 bacteria,
representing several thousand 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-studied
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 species and is among the most abundant of
all the ants. At the end of my study, after 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
discovered, 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
creatures 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, bacteria, worms, ants, and all the
rest. The species of each group are strictly stratified 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
shifts 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.
The combination of these properties, down to a microscopic level, defines the
surface ecosystem. Each species is specialized to survive and reproduce best in
its particular niche.
Soil studies, and especially the biology of the ground
level, are growing rapidly into a major branch of science. Now bacteria and
other microscopic forms of life can be identified quickly by the decoding of
their DNA. The life cycles of increasing numbers of insects and other
invertebrate animals, many entirely unknown to science, are being explored in
the field and laboratory. Their physical and nutritional needs are coming
clear, species by species. The Encyclopedia of Life, available in a single
address (eol.org), is gathering all
known information on each species and making it available free throughout the
world.
A small world awaits exploration. As the floras 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 magnificent little ecosystems that have fallen
under our stewardship.