Undeniable (12 page)

Exploring the deep ocean is difficult. It's cold, it's corrosive, and it's crushing (the sea's three Cs). Any equipment we send down has to be able to survive these rigors. On top (or bottom) of that, it's dark. The illumination from lights aboard deep-ocean submarines or submersibles is quickly absorbed as it passes through just a few meters of seawater, so the images we can return are just perhaps the size of a large living room. As we study the landscape of the deep-ocean floor, we see only the occasional sign of life—except at deep-ocean vents. In these extraordinary locations, geothermal heat provides the energy for ecosystems to thrive in the dark. There are enormous red-tipped tubeworms, strange fish, albino crabs, and clams the size of footballs. When brought to the surface and opened, they look like a steak but smell like a swamp.

The animals living around deep-sea vents are different than those near the surface. Their metabolism is based on chemical exchange with the hot, nutrient-rich seawater. We call the process chemosynthesis rather than green-plant photosynthesis. Clams down here need heat and hydrogen sulfide (poisonous to you and me), whereas clams near the sea surface depend on photosynthesis of plankton that they siphon through their digestive systems. As fascinating and just plain weird as the deep-sea geothermal vent ecosystems are, they have a great deal less diversity than we find in ecosystems that receive direct sunlight. At deep-sea vents we've counted about 1,300 species so far. In the Amazon rain forest, we can find 40,000 species of insects, just insects, in a typical square kilometer. Couple that with trees, monkeys, spiders, and snakes, and the rain forest has thousandfold the diversity. Why would that be?

Fundamentally, there is just less energy to be exploited in the very deep sea. Some of these hydrothermal vents run at 400° C, but that hot spot is concentrated in a small footprint—just a few hundred known locations along volcanically active strips on the ocean floor. (The water at this depth does not boil because it cannot form vapor bubbles under the pressure of the weight of the ocean above.) In contrast, solar energy falls on every part of the planet's surface, with an intensity of up to 1,000 watts per square meter.

I pursued this digression about the deep-ocean vents because it provides further insight into how evolution works. Fewer species per square meter in the deep ocean than in the brightly lit forest is exactly what we'd expect. Up here, where we live, there is more energy to drive more living things. They reproduce more quickly and we end up with more diversity. Deep in the cold ocean, life thrives only where there's enough energy to feed the system. There is not nearly as much energy down there to run the biodiversity machine.

In the 1990s when I was doing the
Bill Nye the Science Guy
show, we did a whole episode on biodiversity (show number 9). At that time, we were pretty sure that the most diverse ecosystems of all are not in the middle of one of the world's 292 major river systems. They are not in the shallow sea, at a coral reef, say. They are probably in between—in estuaries, where rivers meet the sea. Since then, it's been suggested that rain forests near the equator are the most diverse ecosystems. In either case, we find the greatest diversity where there is a great deal of freshwater.

When you look at a picture of Earth from space, the ocean is the biggest contiguous area you can see. So at first, you might assume that the ocean would be the place to find the most of everything, the most biodiversity. Furthermore since most of us, that is most living things, are full of liquid water, we can figure that life started in the ocean, and with all the extra time that ocean life has had to evolve, you'd expect results. You might think that any place in the sea where there's sunlight and enough mixing of deep-water nutrients would be the place of greatest diversity. But generally speaking, the ocean is not where we find the most diverse ecosystems.

To be sure, coral reefs carry enormous diversity. Having dived in coral reefs in Hawaii, the Pacific Northwest, and along the California coast, I can tell you that there are more different kinds of fish here than you can name in an hour. I often reflect on the species I can't see: the bacteria, viruses, transparent cnidarians (sea jellies, once commonly known as jellyfish), and rock-look-alike porifera (sponges). There are thousands upon thousands of species within just a few flipper strokes of anywhere you swim.

In the same way, when I went walking through the rain forests along the Sibun River in Belize, the Whirinaki River in New Zealand, and the Hoh River in the United States, I couldn't get over how much was going on all around me. When you walk in any of these places, you sense that there are countless species swarming, sprouting, hunting, and being hunted all around you. If you told me these are the most biodiverse places on Earth, I'd believe you.

From your own experience, you may know that you cannot drink salt water. It just makes you sick. You may also know that, except for a few remarkable species, you can't put a saltwater fish in freshwater or the other way around. The fish will die. You may have run a classic experiment in school demonstrating what chemists call osmosis. If you dissolve the shells off of uncooked eggs using vinegar, then place an intact exposed egg in distilled water and another in salt water, you'll observe the water molecules slowly passing through the membranes to the saltier environment. The egg in distilled water will swell. The egg in salt water will shrink. This same membrane chemistry would, one might think, keep the two types of ecosystems separate. To a degree, they do remain apart—except at the estuaries.

In estuaries, where river systems meet the sea, there's a mix of freshwater diversity with ocean-water diversity. Instead of either system winning out or cancelling the other type of system, they work together. The likely reason for this is that ecosystems with a lot of diversity can adjust as the environment changes around them. This is another testable evolutionary idea, and scientists have set out to see if it is true—if diverse ecosystems really are more robust overall.

It's possible to quantify the resilience of an ecosystem by measuring the number and mass of all the living things before and after a big change in environmental conditions. If there's a drought, or an unusual amount of rainfall, or sudden temperature swings to freezing or sweltering, the more diversity a system has, the better its species do at staying alive and reproducing. That's the hypothesis. There are at least two ways to investigate it. We can study systems where biodiversity has been reduced and where it has been increased, or we can make the same observations on ecosystems at each end of a spectrum. With either, the theory holds up. More diversity makes for a more robust ecosystem. That explains why the estuaries are so rich. Both the freshwater and saltwater ecosystems there are already full of species. The thick web of life helps saltwater organisms to adapt to some freshwater, and freshwater organisms to adapt to some salt water. Diversity begets more diversity.

The opposite also seems to be true: Places with low diversity are at a greater risk of losing even more. Finding places where the diversity has been decreased is nearly effortless, unfortunately. Humans have wrought havoc on so many environments worldwide that there is almost no such thing as an unspoiled natural area. I climbed mountains in the Pacific Northwest for many years and remember well reaching the summit of Mount St. Helens and looking north to the magnificent vista of Mount Rainier and seeing a distinct layer of smog. You didn't have to know anything about air pollution to conclude that the smog flowed in there from our beloved cities of Seattle and Portland. Sure enough, airborne insect populations are affected. The smog cuts into their numbers a little bit. In turn, the number of plants that can start growing in the volcanic soils below is reduced a little, because the insect carcasses provide less nitrogen for plants to take hold. The view is still gorgeous, but the scene is not quite pristine.

If you really want to get the creeps, visit a Confined Animal Feeding Operation (a CAFO). Wow. Livestock are kept confined and fed a diet to fatten them fast. Their hooves destroy any grazing area. Their excrement poisons everything it flows through and to. And of course, these cattle are fed a surfeit of antibiotics to suppress the diseases that can easily be communicated from one animal to the next, which in turn leads to the rapid evolution of those disease parasites, which in next turn renders those same antibiotics ineffective. And on it goes. While we're eating meat, we're producing new strains of diseases and destroying watersheds. I'm pretty sure that by understanding this process, we can do better. Here's hoping.

On modern large-scale farms, we see thousands of hectares or acres of a single crop. While this “monoculture” makes it easier for farmers and farm machinery to harvest the crop when it's ripe or ready, it also makes the crop more susceptible to attack by a single pest or parasite. If you are a corn-borer moth, you and your swarm can have a literal field day eating every cornstalk and ear of millions of corn plants across many thousands of acres. It's true for human-built farming systems, and it seems to be true in nature. When a monoculture gets established, it's vulnerable to problems.

Often forest ecosystems—especially temperate forest systems—look monocultural. From the air, western Canada looks like a limitless expanse of fir trees, for instance. But there is an important and not-so-subtle difference between a large natural stand of evergreens and a human-planted tree plantation: age. In natural stands there are trees of all ages. Old ones are tall; young ones are short. More important, the fallen trees provide nutrients for the next generation. There are microbial systems in the forest floor that support the root systems of living trees that are photosynthesizing and growing. There is a tremendous amount of invisible biodiversity in that seemingly unified evergreen forest.

In the Pacific Northwest in the springtime, the pollen falls so thickly that it looks like a yellow haze of fog. Even if you consider yourself allergy free, you can feel the pollen in your sinuses. It appears monocultural in species, but it is not so in age and stage of decay. It is hardly uncommon to hike through the Alpine Lakes Wilderness and see young tree after young tree literally growing right out of a fallen or felled old tree. By charming tradition the old dead tree's base is called a nurse stump. It's nurturing its progeny. In the cases where humans did the deadly sawing, “nurse stump” is an ironic turn of phrase.

Scientists have run remarkable tests showing the effect of biodiversity. In bare fields, researchers have planted essentially monocultures of grasses in one area and in another field an assortment of grasses tenfold more diverse in species. In the first few years, the monoculture field shows a lot of growth. It looks, at first, like the monoculture creates more plant matter, more so-called “biomass” than the diverse fields. But over the course of a few years, a decade or so, the field with the diversity of grass species wins out, producing more biomass and more healthy plants—and as a result a healthier group of animals that live off the grasses—than the monocultural cultivation.

This is apparently because diversity leads to an improved ability of an ecosystem to absorb changes in things like weather, climate, or the introduction of some new species. Try this as a simplified example. Let's say we have a monoculture meadow and a diverse meadow. In a diverse meadow, the different species of grasses and flowers produce pollen at slightly different times of the year, varying their seed and pollen production by a few weeks or even a few days. Pollinators like bats, birds, and bees can find steady work. They'll be there for each different pollen production cycle. On the other hand, in a meadow with a monoculture, where all the grass pollen is being produced at once, there is likely to be too few pollinators around. The bat, bee, and bird populations cannot sustain themselves between the cycles of abundance of the nectar and pollen. The grasses, the birds, the bees, and the bats all suffer a little. Without diversity, each of the species is less successful. Diversity leads to resilience.

You see the impact of humans on Earth's environment every day. We are trashing the place: There is plastic along our highways, the smell of a landfill, the carbonic acid (formed when carbon dioxide is dissolved in water) bleaching of coral reefs, the desertification of enormous areas of China and Africa (readily seen in satellite images), and a huge patch of plastic garbage in the Pacific Ocean. All of these are direct evidence of our effect on our world. We are killing off species at the rate of about one per day. It is estimated that humans are driving species to extinction at least a thousand times faster than the otherwise natural rate.

Many people naïvely (and some, perhaps, deceptively) argue that loss of species is not that important. After all, we can see in the fossil record that about 99 percent of all the different kinds of living things that have ever lived here are gone forever, and we're doing just fine today. What's the big deal if we, as part of the ecosystem, kill off a great many more species of living things? We'll just kill what we don't need or notice.

The problem with that idea is that although we can, in a sense, know what will become or what became of an individual species, we cannot be sure of what will happen to that species' native ecosystem. We cannot predict the behavior of the whole, complex, connected system. We cannot know what will go wrong or right. However, we can be absolutely certain that by reducing or destroying biodiversity, our world will be less able to adapt. Our farms will be less productive, our water less clean, and our landscape more barren. We will have fewer genetic resources to draw on for medicines, for industrial processes, for future crops.

Biodiversity is a result of the process of evolution, and it is also a safety net that helps keep that process going. In order to pass our own genes into the future and enable our offspring to live long and prosper, we must reverse the current trend and preserve as much biodiversity as possible. If we don't, we will sooner or later join the fossil record of extinction.