Food Chains in the Biosphere
Sixty-seven million miles from the sun, a small planet moves silently through space in a path that takes it two hundred and twenty five days to go around the sun. Giant storm clouds of ammonia, sulfuric acid and carbon dioxide shroud this planet. The temperature is over nine hundred degrees, far too hot for any biosphere to exist on Venus.
One hundred and forty one million miles from the sun another small planet takes six hundred and eighty seven days to complete its trip around the sun. It has little atmosphere of any kind with dry ice caps of frozen carbon dioxide around its poles. There is no biosphere on Mars.
But in between, a reasonable ninety three million miles from the sun; taking a leisurely three hundred and sixty five and a quarter days to make a trip around the sun; having an atmosphere of one part oxygen to three parts nitrogen, with small but important amounts of water vapor and carbon dioxide; a comfortable range of temperatures between fifty below and one hundred and ten above zero; blessed with a good medium size for a ship in space, big enough to give a solid feel to objects on its surface, but not so big as to make them oppressively heavy; protected from deadly radiation by a cleverly designed invisible gaseous barrier of ozone gas and by an equally invisible barrier of charged particles and magnetic fields called the Van Allen radiation belts; cooled and cushioned with lots of water over three quarters of its surface; rotating fast enough on its axis, once around every twenty four hours, giving one side of the ship a chance to cool off while the other side works; spaceship earth does have a biosphere, a living sphere.
Imagine the excitement space travelers would feel if they had been traveling for years in the dark space between stars and suddenly they spied from afar this small blue spaceship, with the deep warm glow of life.
Unlike any other place we know of in our solar system, indeed in all the universe so far as we know today, matter and energy have joined together here and have come alive.
The biosphere, the living sphere, that surrounds planet earth is thin but tenacious. If you were to reduce everything to scale, the biosphere would be thinner than the thickness of the paint on a classroom globe. Inside this ever so thin shell, the only place in the universe that we know for sure, a staggering number of life forms live and die- passengers all on a well designed, well situated spaceship that has been self-sufficient for five to six billion years.
It has only been in recent spaceship earth years--the last fifty or sixty of those five to six billion years of earth history--that earth scientists have led the way to a more subtle understanding of the intimate inner workings--that is, understanding just how matter and energy did and do manage to join together to produce life.
Up until now these subtle dynamics have worked automatically-- without so far as we know, any conscious intelligent tinkering. In our day for the first time in the spaceship's history one particular life form, human beings, have begun to assume some conscious guidance of this biosphere, hoping to guide it to serve human ends. In order to do this it would be wise if we knew a little more about how the automatic systems have worked in the past are still working today.
Lesson One. The fundamental life cycling in the living biosphere seems to work something like this.
There are four main parts: producers, consumers, decomposers, abiotic chemicals.
Let's take the simplest of the four parts first, the abiotic. Things like air, earth and water. Chemicals in other words. To be more specific, chemicals like carbon dioxide, water, and simple mineral compounds containing nitrogen, sulfur, phosphorus, iron, magnesium and about fifteen to twenty more life needed elements. These abiotic chemicals are the most plentiful elements in the universe. Which is not so surprising when you come to think of it- that we should be made of the most common clay so to speak. Better stick with the ordinary and easy to come by, rather than bank on the exotic, foreign and hard-to-get items.
The producers are almost all green plants and green plants alone. These green plant producers have a remarkable molecule in their cells called chlorophyll. The chlorophyll is in tiny cell parts called chloroplasts which are usually in the leaf. With the aid of this molecule the plants can perform quite a trick. Taking carbon dioxide from the air and water from the soil, using radiant energy from sunlight as a power source, green leaves are able to tear apart and then weld back together the atoms from carbon dioxide and water so that they come out with a whole new much larger molecule called sugar!
C6H1206. That is, a chain containing six atoms of carbon, twelve atoms of hydrogen and six atoms of oxygen. Sugar. Packaged sunlight. The beginnings of Food.
This sugar, in addition to being an interesting chemical, a molecule, is also captured energy, stored now in a chemical form that will prove useful to all the living parts of the biosphere, providing the basic energy to convert other abiotic molecules into flowers and fruits and seeds, into teeth and claws and brains.
Once the green chlorophyll aided plant leaf has turned the trick of making sugar, it can now proceed to diversify its manufacture. Using the stored chemical energy of sugar as its source of fuel, the plant can manufacture all the other needed plant parts, such as proteins, enzymes, nucleic acids.
These chemicals, in turn, are the parts needed to build new leaves, bark, roots, flowers, fruits and seeds. In other words, the plants eat some of the food they themselves made. Fortunately they produce more than they use and animals take advantage of this surplus by eating it. Especially the most precious of the plant's storage bins, the fruits and seeds.
Some animals have taken a further step in this direction by not eating just plants, and plant parts, but by eating other animals. Or eating animals that have eaten animals. And so you get a whole pyramid of possible eats and be eatens. Note that in this pyramid at each step up there will of necessity be fewer living things, or at least less biomass.
If eagles eat big fish, and fig fish eat small fish, and small fish eat water bugs, and water bugs eat green algae, there has be quite a few more big fish than eagles, more small fish than fig fish, more water bugs than small fish and more algae than water bugs.
At least ten times as much with each step down the pyramid as a matter of fact. That is, each creature is at best ten percent efficient in converting the life he is eating into the life that is his own.
Of course there is a great variation and complication in these living food chains. In arctic oceans it might be a very short and simple food chain. The blue whale eats great quantities of small shrimp-like crustaceans, which in turn get their life energy from eating the microscopic plant plankton, which gets its life energy by making its own food through photosynthesis with the help of the sun.
In a tropical rain forest, on a Pacific island, or in a Wisconsin glacial lake when you put many food chains all in one diagram you get a food web that is more complicated.
Food chains also change over time. Sometimes quite rapidly. Lakes, for instance, are always changing. The Great Lakes of mid-America, for instance, were formed in that last ice age, about 12,000 years ago. When first formed there was a minimum of dissolved abiotic nutrients. Microscopic plants used these nutrients to create good for smaller microscopic animals. These in turn were food for insect larvae and small crustaceans, which in turn fed small fish, which in turn fed a few large fish like trout, whitefish and walleyes.
As the lakes begin to age, the food chains change. With more dissolved nutrients (especially in the shallower likes like Lake Erie) the abiotic base is richer in phosphates and nitrates. Different kinds of blue-green algae now become more plentiful and primary producers. These blue-green algae are poor food for crustaceans. Hence the insect larvae, small fish and big fish which depend on the insect larvae also decrease in size and numbers. We get a new simpler food chain now with blue green algae at the bottom, the insect larvae replaced by small alewives fish. These are eaten by larger alewives. And the few large trout and whitefish left then become easier prey to parasites like the imported lamprey eels.
In all of these cases -- food chains and food webs -- as one creature is eaten by another, which in turn is eaten by still another, you also get a surprising amount of selective concentration of certain kinds of atoms and molecules.
For instance. You catch a beautiful trout in a clear water lake and you find that it has a concentration of PCBs (polychlorinated biphenols) in its flesh ten thousand times as great as the waters of the lake in which it swims.
What has happened?
Each living step in the chain has selectively concentrated the PCBs, mistaking them for similar needed chemicals. By the time it gets through five or six steps in the chain, the concentration of the harmful chemical can be enormously larger than in its original abiotic environmental state.
However complicated the food chains become, it is all in the consumer part of our larger scale cycling diagram. To complete the cycle we must still somehow get back to the non-living abiotic chemical part. And we do this by way of the fourth main part, the decomposers.
Decomposers are mostly microscopically small living creatures, such as bacteria, molds and other fungi. Decomposers all gain their life energy and glean their life materials by breaking down the still energy-rich chemicals of dead plants and animals, decaying them back to the dust from which they came.
In the naturally and automatically working biosphere there is no such thing as waste or pollution. All parts are carefully picked apart and reused, recycled over and over and over again.
The parts, the chemicals that is, are only one half of the story. To change chemicals into life takes energy, which flows but does not recycle.
Here is a biosphere energy chart. Notice that it is a one-way flow. It starts as sunlight energy and ends up as random heat energy, warming the universe, but useless now for life.
The first critical step in the energy flow through the biosphere is the capturing of the sunlight energy by green plants in the process of photosynthesis, where carbon dioxide and water are changed into high energy sugar. The plant itself uses some of the energy of this sugar to provide the push for its own growth and metabolism and reproduction, for its own sedentary but elegantly beautiful lifestyle.
The consumer animals then use some of the stored plant energy and finally the decomposers use what is left of the plant and animal energy after the plants and animals die.
In all cases, in every use of this sun-stored energy, some of it gets lost. Some of the energy leaks away in the form of random heat, and this random heat drifts back into space to warm the universe. Incidentally, it is exactly the same amount that came in from the sun. But now the energy is deteriorated in quality, no longer intense concentrated, ready-to-power-life sunlight, but diffuse, random, spread much-too-thin heat waves.
In rough figures, as little as one hundredth of one percent of the annual sun received energy that makes it to earth actually gets trapped, and captured as sugar stored energy by the photosynthesis of green leaves. Then less than ten percent of that hundredth of one percent gets used constructively to build consumer life. And at each step up the food pyramid another ninety percent of what is left is lost. As you get ten percent of ten percent of ten percent of one hundredth of one percent, you end up with very small amounts of energy.
On the other hand, looking at it another way, when you see an eagle or a large salmon or a cat or dog or human you are looking at very concentrated energy!
So far we have looked only at existing food chains of today on this spaceship called earth. Matter cycles and recycles through the producer-consumer-decomposer-abiotic paths. Energy flows from sun to green plants to animals to random heat sent out to warm the universe.
What about the past of spaceship earth? These cycling food chains and energy flows have gone on for billions of years on earth. One important modern legacy of past food chains is the stored energy that now powers our industrial societies. That legacy is, of course, fossil fuels--coal, oil and gas.
In the Carboniferous Age, some 50 to 100 million years ago, ancient plants captured energy from sunlight just as plants do today. These prehistoric plants and animals used most of that sun-stored energy for their own life activities just as plants and animals (including humans) do today. Over that 50 million year time, however, some of these plants and animals died in ways and in places that prevented the decomposer organisms from completing their work. The plant and animal remains, in other words, were only partially decomposed. Instead of returning completely to the abiotic, they were buried under mineral and rock deposits and became coal veins, and oil and gas deposits.
That long-ago stored energy is now being used by modern power plants, automobiles, home and factories. That long ago stored energy is the very life-blood of our modern civilizations everywhere on earth.
One problem--this rich legacy will not last forever. Within the 21st century we will probably see a major portion of these stores of fossil fuels get used up and disappear.
A second problem is that while the energy they contained drifts off into space as random heat, the matter, the chemicals of the fossil fuels do not disappear. As we burn fossil fuels in our power plants, our automobiles our homes and factories these chemicals change partners and the carbon part of the fuels ends up combined with oxygen to make carbon dioxide. This carbon dioxide goes directly into the atmosphere and if it is not taken out by green plants (or somehow sequestered in other ways) it will lead to a gradual warming of the atmosphere. This global warming could bring drastic changes in rainfall patterns, rising levels of ocean water and serious disruptions in the life styles for all living creatures on this planet.
To cope with the first problem--the slow disappearance of fossil fuels--humans will have to find new ways to capture and store energy if industrial civilization itself is not to disappear.
One possible solution is to find new ways to capture more of the current sunlight energy. Green plants learned how to do this some billions of years ago by the invention of photosynthesis. Humans are now learning new ways to do it in the 21st century.
Solar voltaic cells like these on a new community project next to the post office in Madison, Wisconsin directly convert sunlight into electricity. This small solar array can do the electrical generating work of 12,000 tons of coal a year in a coal-fired power plant.
The sun heats some parts of the earth more than others and this creates winds. Windmills like these near Palm Springs, California tap this solar power and do the work of many more tons of coal, oil or gas in providing electricity to energy-hungry Los Angeles.
The sun lifts water up from the ocean. Dams like this one in Tennessee can harness the energy of this water as it flows back to the ocean, turning it into electricity.
Scientists and engineers are working today on other ways to create large amounts of energy that do not directly rely on the sun at all. These include geothermal power plants, nuclear fission power plants and nuclear fusion power plants.
Some day scientists and engineers may learn to duplicate the green plants trick. In other words learn how to use energy whether from the sun or from other sources to make food. How to start with carbon dioxide, water and common minerals and convert them in the laboratory first and then in a factory into sugar, starch, protein, vitamins, enzymes. Into food.
But until that day we are all of us dependent on our friends, the green plants and the sun. To make our food and to power and to protect our living space, our biosphere.
Operating rules for small spaceships:
#1. Be very careful to nurture and protect green things. At the moment, and for the foreseeable future we depend on them as our only means of effectively capturing the sun's energy and storing power for the life and health of all the passengers.
#2. While nurturing and protecting green plants, try to figure out other ways of capturing sunlight for the future health and safety of the spaceship. Better understanding of photosynthesis and better ways of directly converting sunlight into chemical or electrical energy seem the most promising at the moment.
#3. Don't rule out tapping the energy of atoms themselves, that is nuclear energy, the same energy the sun itself uses.
#4. Take time out occasionally to feel the sun's energy flow through you for in the long run, energy is eternal delight.