This little book provides a compact introduction to fundamental concepts of ecology, the science that studies the marvelously complex interrelationships of life forms on planet Earth. These concepts are the foundation of the environmental movement, which aims to reduce or remedy damage caused to the natural order by humans and gives inspiration for changes in virtually every aspect of personal and family life, business management, and community or government policies. So the book also sketches how these ideas apply in practice.

Ecological ideas capture the ceaselessly changing, interconnected, incredibly intricate flow of life in Earth’s ecological systems—on which human...

Air seems so thin and insubstantial that we cannot intuitively grasp its role as a global circulator of the essential nutrients carbon, nitrogen, and sulfur as well as of that universal medium of life, water. How can something so light, invisible, even odorless, be so critical to life? We know that the air holds up birds and airplanes in flight. We can recall the delicious caress of a summer breeze on our skin, or the bite of subzero winter air in our noses. Yet, looking across a room, we’re conscious only of the people or objects in the room, not...

A few algae are very large, such as certain seaweeds, but most are tiny plants that float in streams, lakes, and oceans. (At sea they are called phytoplankton.) They grow by using carbon dioxide, along with sunlight and water, and form the base of the ocean food web as nourishment for larger organisms. Th ey lack the leaves, roots, and flowers of familiar plants, but oceanic algae produce about three-quarters or more of the planet’s oxygen. Algae grow considerably faster than land plants. Under some conditions they “bloom” in vast quantities, exuding toxins which can harm fish and infect oysters...

The entire living world depends on microbes — subvisible organisms (sometimes also called microorganisms) including bacteria, protists, and the smallest fungi. It’s utterly impossible to understand the ecology of larger living beings, including ourselves, without knowing about microbes.

If you take a drop of what appears to be clear water from a lake or puddle and put it under a strong microscope, you’ll see a lot of small beings, round, rod-shaped, or corkscrewlike. Some drift quietly, some move jerkily, some wriggle in a determined way. The smallest of these are bacteria. You’re likely also to see larger microbes—protists. Most greenish...

“Diversity” means variety, and much of the beauty of the world flows from the stupendous profusion of life. In a single forest landscape, we may see dozens of types of trees and even more types of bushes — a vast assortment of shapes and sizes. Supported by, and supporting, the vegetation is a rich, almost inconceivably varied community of mammals, birds, amphibians, reptiles, and insects, all of them with subtly varied ways of living and interacting. fungi and innumerable microbes with diverse metabolism and living both aboveground and underground are essential to a forest (or any other ecosystem) as they...

Living in a world of cars and highways, changing our residences frequently within and across state lines, most North Americans tend to be unconscious of geographic roots. Nonetheless, all living beings, including humans, have complex interconnections with the climate, altitude, soils, geology, and landforms of the places where they live. Thinking bioregionally makes us aware of these interconnections, and a movement called bioregionalism works to spread this consciousness widely.

A bioregion is a large geographic area where the native plants, animals, and microbes, along with their environment, are distinctively different from those in adjoining areas. If you drive across Tehachapi...

These two terms are virtually interchangeable.Biosphererefers to the global skin where life exists: animals, plants, fungi, and microbes, sometimes all together called the biota.Ecospherealso refers to all living beings on Earth but gives a stronger sense of their interconnections with their nonliving environment (soil, rocks, air, and water). For convenience, the biosphere/ecosphere can be divided into parts such as ecosystems, bioregions, or communities. But it is really one single, interconnected entity, and it is what makes our lives possible. No one can ever be independent, even for a short time, from the biosphere....

After the discovery of DNA, the genetic blueprint for life forms, and the invention of ways to transfer sections of it between organisms, manipulation of species in ways far more rapid and drastic than traditional breeding became possible. (To show how extraordinary such a process is, one artist and his scientist collaborators produced a live rabbit that glows fluorescent green under certain types of light.) Although the idea of single genes having single effects has been replaced by a more complex view of the intricate organization within cells and organisms, bacteria and yeasts have been successfully reprogrammed to produce medical...

Humans and other animals breathe in oxygen and breathe out carbon dioxide; plants (in daylight) do the reverse. This is a finely balanced system of coexistence, since the air contains only about one year’s reserve supply of carbon. Moreover, living organisms’ influence on the carbon cycle is one of the major factors regulating Earth’s temperature.

Life on Earth is sometimes called “carbon-based life” because the versatile element carbon forms compounds that are a universal fuel for the maintenance and energizing of living bodies. (Carbon, which can be seen in pure form in pencil lead and diamonds, makes up 18 percent...

The carrying capacity of a suitcase is the amount of clothing and other articles you can stuff into it. For any ecosystem — a vast forest, a continent-wide desert, or a miniature pond — carrying capacity is the maximum number of organisms it can support. Carrying capacity is determined by the resources that are available. A pond may support only a dozen frogs if it contains limited food resources for frogs, aquatic plants on which frogs lay eggs, and places to hide from predators. Populations tend to rise toward carrying capacity. A female frog produces tens of thousands of eggs,...

Communities in nature are convenient groupings of different organisms regularly found in the same place at the same time. These groupings are never absolutely fixed. In an Eastern mixed hardwood and conifer forest community, we expect to find maples, hickories, pines or hemlocks, oaks, bears, owls, woodpeckers, deer, and salamanders. We also know that under this forest’s soil there is a vast matching population of insects, worms, and bacterial and fungal decomposer species. In the piñon-juniper woodland community of the U.S. Southwest, we expect to find not only piñon and juniper trees but also antelope brush and scrub oak, together...

In America for at least ten millennia, the land was cared for by indigenous people. Using fire and selective harvesting, tribes “gardened” much of North America. Indian tribes sometimes fought over territories, but they did not believe that land could be owned by individuals. In Europe until about 400 years ago, most land and resources were sometimes preserved and sometimes abused by their owners — royal or noble families or the church.

By the time Europeans crossed the Atlantic, however, the old feudal pattern was breaking down, and it was never firmly established in the Americas. Instead, beginning in the...

For the past several centuries our industrial system has been taking massive quantities of resources and transforming them into salable products, most of which are soon disposed of as garbage — a one-way, one-time-use process. This is a shortterm strategy. It cannot continue indefinitely, as nature’s processes do. Life’s strategy, which has endured for billions of years, is to make repeated use of essential substances present on the planet only in fixed amounts, which go round and round again in cycles, closely coupled with the actions of living organisms. Humans cannot change the amount of these essential substances present on...

At first thought, it may seem sad that living beings die and decompose. But without death and decay, there could be no new life. If it were not for the breaking down of organisms into nitrogen, carbon, sulfur, and their other component substances, the planet would be littered with dead stalks, leaves, and carcasses. Your compost pile wouldn’t be able to turn kitchen scraps into rich garden humus. New growth would be impossible, and animals like ourselves would find nothing to eat. What we call the decomposition of formerly living things is in fact the beginning of new life, by...

Hardly a landscape exists that has not been ecologically shaped by human activities. Greek islands that are now semideserts with scattered olive and fruit trees were once thickly forested, but the ancient Greeks cut all their trees for cooking fuel, roof rafters, and ship planks. Eastern North America was once an endless, wildlife-rich forest. In our time, much of tropical Asia is being denuded of its lush rain forests by international timber companies seeking hardwoods for wallboard veneer or crating. In the United States, almost all the primeval forests in the Pacific Northwest states and Hawaii have been lumbered out....

Today, almost everyone has at least a vague idea of whatecologymeans — it has something to do with human impacts on nature. Actually, the science of ecology studies all interactions among living beings and their environment, whether we humans are involved or not. air and even some rocks that function as parts of life’s cycles are included, too. Ecology is a study of patterns, networks, balances, and cycles rather than the straightforward causes and effects studied in physics and chemistry. The goal of ecology is to understand the functioning of whole living systems, not simply to break them...

If you’ve taken a hike through a forest, you’ve been in a large ecosystem. However, within the forest we can mark off smaller ecosystems, like creeks or meadows, each with a characteristic set of species. Within an ecosystem, we always find organisms using photosynthesis (or, in a few cases, chemical synthesis) to grow and thus produce food for other organisms, together with decomposition organisms recycling the basic elements of life. An ecosystem is capable of the complete cycling of the basic elements carbon, nitrogen, oxygen, phosphorus, and sulfur. Within an ecosystem, nutrients are recycled from living organisms through organic wastes...

It feels good to turn your face to the sun. And no wonder. We and all other living beings are powered by energy captured from sunlight, which flows through humans and other organisms and then disperses out into space in the form of heat, never to come our way again. We and all other inhabitants of Earth live suspended in the great stream of solar energy. So ecology operates by the inescapable laws of energy.

Only two sources of energy power the metabolism of living cells: direct sunlight received by some bacteria, some protists, and most plants, and certain kinds...

We usually think of the environment as everything that surrounds us: sky, sea, mountains, forests, rivers, birds, animals. Whether we are shocked at the destruction of nature or inspired by visions of a healthier world, increasing numbers of people feel a responsibility for taking care of the environment. Environmental organizations, which have grown out of the conservation movement, deploy organizers, scientists, lawyers, and writers to propose changes in public or industry policies that would lessen our impacts on the environment or make it more habitable for us. Since protecting the purity of the air we breathe, reducing contamination of the...

In the early 1900s, the American environmental movement began among white, relatively privileged urban people who had the leisure and the money to go out and picnic or camp in remote, beautiful, unspoiled places. Th ey were the first to recognize the desirability of preserving virgin mountain ranges and redwood forests, and they formed the first organizations to work politically for these goals.

But in recent years, as the environmental movement has become more scientifically and socially sophisticated, ordinary people have grown aware that they face environmental problems unknown to the well-to-do, along with overwhelming problems of economic survival. Throughout...

Evolution, changes in existing species or the appearance of new ones, has been occurring since life began more than three billion years ago. It is not a kind of ladder that led “up” to human beings and then stopped, with us dominating nature at the summit. It will continue whether we are around or not. An immensely complex process of evolution has resulted in some 30 million species existing now, plus an immensely greater number now extinct. Many extinctions have been caused by human activity, directly or indirectly, and ecosystems are being reorganized. “Weedy” species thrive, and may even divide...

Now that we understand the role of DNA and the genetic code it embodies, we see extinction not only as the disappearance of all living tigers or spotted owls but also as the elimination forever of a unique configuration of DNA — coded messages responsible for producing tigers or spotted owls. An ecological understanding of extinction must also consider the ecosystem in which endangered organisms have been living. No species is an island, and the removal of one species aff ects all.

This is clear from examples both of extirpation (the wiping out of a species only in one region)...

We’re fascinated by fire, perhaps because it has been so useful to humans and prehumans for hundreds of thousands of years — to warm ourselves on winter nights, to roast meat, to scare away wild animals. If you go camping, you’ve probably experienced the feeling of comfort and safety that a nice fire provides. Both children and adults love to watch flames flicker and embers glow. But we also fear fire because it can kill us or destroy our homes and possessions.

Ecologically, fire is a special kind of rapid decomposition. Periodic fires are an essential part of the living...

A plant produces seeds. A mouse eats some of the seeds. A fox eats the mouse. An eagle eats the fox. This is the story of a food chain. But things are not this simple. Actually, relationships of eating and being eaten are almost infinitely complex.

Plants produce leaves, stems, and seeds. Butterfly caterpillars and many other herbivores eat the leaves. When leaves fall to the ground they’re consumed by insects and microbes, and from the wastes of these beings the nutrients in the wastes are made ready to be used by new plants. Birds eat the butterfly caterpillars, and...

When you eat mushrooms on pizza, you’re eating fungi—and bears and squirrels like them too. Fungi are a kingdom of organisms: molds, mushrooms, yeasts (one-celled fungi), puffballs, and many others. A few fungi are aquatic. The typical fungal growth pattern is a network of thin strands, all drawing nourishment from carbon compounds ultimately produced by photosynthesis or chemosynthesis. If you let a piece of bread get thoroughly moldy, you can see thin fungal strands stretching across it. If you turn over a log in the forest, you will see a gray, fuzzy mat of cobwebby growth—the mycelium from...

The Gaia theory, playfully named for a Greek goddess, suggests that Earth’s pleasant temperature, breathable air, and nonacidic waters are produced and regulated by the growth and metabolism of life. All life forms, according to Gaia theory, are physically connected through the air, oceans, fresh water, and other fluids of Earth

One perplexing question answered by Gaia theory is: Why does Earth have such an amazingly improbable balance of gases in its atmosphere? Th e atmospheres of our neighbor planets, Mars and Venus, are mostly carbon dioxide with only a little nitrogen. They seem to be products of purely chemical...

Earth’s atmospheric temperature, and the balance of very reactive gases in the atmosphere, have been maintained for at least a billion years by living organisms — bacteria, algae, and later plants. Th is vastly complex geophysiological process of regulation, known as gaia, relies on the biological production and removal of carbon dioxide in the air, together with water vapor, methane, and sulfur gases, that keep the planet comfortably warm through the greenhouse eff ect. Like glass in a greenhouse, these “greenhouse gases” limit incoming solar heat from bouncing back into space as it normally would, leaving the planet icy. In...

Plants, people and other animals, companies, and countries grow. In the ecological world, however, organisms only grow until reaching mature size—the size that enables them to successfully occupy their niches. Few individual beings expand in biomass indefinitely, although certain fungi, slime molds, and root-linked aspen trees grow until stopped. If an animal were larger, its bones might not be able to support its weight; it might have difficulty in moving effectively or taking in enough nutrients. (Imagine the problems if people grew a hundred feet tall!) And if an organism were smaller, it might not be able to catch...

An organism’s habitat is where it lives—in a sense, its address. (Its niche is how it lives — its lifestyle.) Every organism has its place, where conditions are right for its survival. This habitat provides enough water, sunlight, saltiness or its absence, the necessary temperature range, hiding and nesting places, food, and so on. Habitats are quite diff erent for different species. An oak forest with plenty of acorns is ideal for squirrels but of no use to ducks. In Yellowstone National Park, the boiling, bubbling muds where nothing else could survive are the habitat of colorful communities of...

You create an ecological (or environmental) impact when you turn on a light switch. The power plant that sends electricity to your dwelling must burn a little more fuel and thus create a little more air pollution. Or if your electricity comes from a dam, a little more water must be passed through the turbines, grinding up more fish and further disturbing the shallow waters below the dam where young fish and water insects live. Similarly, eating hamburgers has ecological impacts: beef cattle trample streamside vegetation and overgraze grasslands; producing hay or grain to feed cattle often requires irrigation and...

No humans or other living beings can survive without multiple interconnections with other organisms. You were totally dependent on your mother’s body before birth, and after birth you depended on parents and community. Throughout our lives, we depend on other humans for safety, food, shelter, comfort, love, hope, and joy. But we also depend on the whole biosphere for air to breathe, food to eat, materials for shelter, removal of waste, and all other necessities. This connection has always been recognized by indigenous peoples, who have lived by gathering food and hunting animals. It is just as true for urbanized...

As we search for interconnections between living beings, grouping them into categories helps us to understand their ways of living and evolutionary relationships. Kingdoms are the largest categories; taxonomy uses many subcategories. Everyday speech divides the living world into “animal” and “vegetable” kingdoms. To group life forms using their molecular, morphological, and developmental characteristics, however, we need five kingdoms. In the probable order of their appearance on Earth, they are:

Bacteria—microscopic beings, unicellular or multicellular microbes that lack cell nuclei but are extraordinarily varied in their chemistry and modes of survival. About 20,000 species are recognized, but since all...

You may have been horrified to look down into the utter desolation of a mile-wide pit mine or see a dry riverbed from which all the water has been diverted for irrigation. But the most universally devastating ecological impacts of human activities come from the seemingly innocent or sometimes even picturesque activities involved in our taking possession of almost all biologically productive land. We convert plains and prairies to farming and livestock raising, eliminating native grazing animals such as deer and antelope. We bring in foreign grasses and then overgraze them. We clear-cut forests and replace them with sterile single-species...

Microbes—bacteria, protists, and the smaller fungi (yeasts and molds)—are living beings so tiny that we need a microscope to see them. Humans are fairly large creatures, and other life forms that regularly engage our attention — pets, trees, cows — are large enough to be easily visible to us. So it’s hard to accept that most life on Earth is microscopic in size. Trillions upon trillions of organisms too small to see (except when they live in colonies, like the white stuff between your teeth if you don’t brush) vastly outnumber and outweigh all humans, other animals, and...

Life on planet Earth tends to be distributed in patches rather than uniformly spread: because species are sensitive to variable environmental factors, including temperature, humidity, acidity, and other chemical conditions, most living beings live within well-defined ranges. In the modern era, however, the Earth’s inhabitants, from the large to the tiny, are commingled because of human actions.

More than 250 million years ago, the continents were all jammed together, but the land masses gradually drifted into their present arrangement. Plants, mammals, and insects dependent on each other lived together with their ancestors and descendants in recognizable communities, themselves components of...

A niche is an organism’s lifestyle, the group of strategies it employs to obtain the food, water, shelter, mating spots, and other necessities that it must have to survive. Its habitat iswherea species lives; its niche ishowit lives, its job description. Plants occupy sunlit niches and themselves provide many niches for fungi, protists, and animals. Each type of animal has appropriate ways to find its food. Thus squirrels forage randomly and find nuts dropped from trees. In a given habitat, there are niches for large predators that rely on large prey and niches for small ones:...

Nitrogen, an element that in its gaseous form makes up 78 percent of the air, is essential to living organisms. All the large, complicated protein molecules in cell structures (including chlorophyll, essential for photosynthesis) contain nitrogen; the DNA molecules that the genes are made of also require nitrogen.

The cycle that transfers nitrogen from the air and soil to living beings and back again is complex but elegant. To grow, plants require nitrogen compounds, but they cannot absorb nitrogen directly from the air. In a step crucial to all life, gaseous nitrogen is fixed (turned into protein components that plants...

To a chemist, “organic” molecules are those that contain atoms of the element carbon as a kind of backbone surrounded by hydrogen atoms, making very complex structures possible. Most molecules involved in life processes—genes, proteins, and carbohydrates—contain carbon, as do oil, coal, and plastics. Ninety percent of the weight of living cells, aside from their water content, is made up of organic compounds. However, in recent years,organichas also become a familiar term for foods produced without the use of manufactured fertilizers, pesticides, herbicides, additives, or hormones. Growing numbers of people believe that organic food is not...

Phosphorus, the element that causes matches to light, is needed for all cell membranes, genes, teeth, bones, and many enzymes. Phosphorus is abundant on the planet. However, only compounds called phosphates, which are in limited supply, can be taken up by plants. This is a major restriction on life’s proliferation. Plants, aided by bacteria and especially by mycorrhizal fungi, bring us phosphorus. Phosphate reaches the decomposers either directly when bacteria, protists, fungi, or plants die or indirectly after plants are eaten by animals. Thus it is returned to the nutrient cycle through the soil. However, phosphorus-compound fertilizer is widely applied...

All life on Earth ultimately depends on light from the sun for energy and carbon from the air for food. But only specialized living beings—photosynthetic bacteria, protists, algae, and plants—can accept sunlight energy and use carbon to make food in the form of their bodies. These are the sole truly productive organisms on Earth, and all other forms of life in their vastly complex ecological interrelationships are utterly dependent on them. (Th is is true even of bacteria that live on the pitch-dark ocean floor and a few other types that live by reacting photosynthesis-derived oxygen with compounds...

To pollute water, air, or soil means to introduce materials that harm the health or survival of humans or other species. An upstream chemical company that pollutes a river by discharging wastes into it harms not only people downstream who drink river water but also the fish in the river, the birds who eat the fish, and thousands of other organisms who live in or near the river. People changing their own car oil cause pollution of nearby lakes, rivers, or bays when they dump used oil in storm drains.

We also pollute the air significantly, releasing toxics in gas...

You probably know the human population of your town or city, at least roughly. Ecologically speaking, a population is simply a collection of members of one species in the same place at the same time—people, other animals, plants, protists, fungi, or bacteria. Life is never lived as single individuals. Individuals always reproduce to form populations large or small.

In theory, within an ecosystem each species tends to increase its population until it is reaches the ecosystem’s carrying capacity. But in fact populations of most species usually neither rise above a level at which their habitats would be destroyed nor...

Predators are mobile bacteria, protists, and animals who live by eating other mobile forms of life. (Herbivores are moving beings that consume plants, algae, and bacteria that are stationary.) We humans eat grains and plants but also prey on domesticated animals—domestication is a way of making animals easy to catch and kill—and on farmed and commercially caught fish. However, about 50 million Americans occasionally hunt for and eat deer, elk, boar, rabbits, ducks, and pheasants. About 15 million catch fish—which they sometimes release rather than eat. Since many hunters and anglers are eager to preserve wild habitats...

Earth is aswarm with microbes called protists. These mostly unfamiliar beings are not bacteria because, like humans, their cells have nuclei. But they are not animals or plants because they do not develop from embryos. They are not fungi either, which develop from spores. Protists are the microscopic members of a kingdom containing 250,000 species today. Because protists have many larger relatives (including giant kelp), the awkward termprotoctistshas been devised for the kingdom they all make up. Perhaps, in time,macroprotistswill be adopted for the larger species, so that the whole kingdom could enjoy the simpler name...

Quarantines are sometimes used to stop the spread of contagious diseases: sick people are forbidden to travel or to leave their homes, and those who fall sick while away from home may be confined in a special facility. We also set up quarantine zones that we try to keep free of species that conflict with human purposes—for example, to prevent rabies or cattle diseases from crossing state or national borders. When Medflies, which damage orchard crops, appeared in California, the state government monitored the flies, kept infected fruit out of the state, quarantined large affected areas, and sprayed them...

If you cut yourself or break your arm, your body can heal the damage. Similarly, ecosystems have their own repair capabilities. They are able to maintain themselves against many natural disturbances—unlike machinery or buildings, which require constant human maintenance. But areas heavily affected by destructive human activities need human help in healing. Thus restoration of damaged ecosystems, like preservation of undamaged ones, is a major goal of the environmental movement. (Preservation is always cheaper, easier, and more successful than restoration.) Gradual or even violent change is normal for living systems. Since life began, it has been coping with stupendous...

Sex is fascinating to humans, and crucial to the survival of many other (though not all) species. Th rough sex, organisms pass from donor to recipient the genetic information embodied in DNA molecules—the “operating manual of life.” Scientifically, sex is the process of forming a new organism that combines genetic material from more than a single source.

The traditional belief is that sex produces the variation on which natural selection acts: by mixing up the genes of a species, sex produces a variety of traits in offspring, and some of these traits, better equipping individuals to survive changes in...

In the great drama of life, the acts of eating and avoiding being eaten, mating, and defense are negotiated by different modes of perception—by sight, sound, touch, and by sensitivities to chemical substances: taste and smell. In current research, the heretofore neglected sense of smell is also being revealed as an important part of how animals, including humans and insects, and even plants interrelate.

The smells we consciously notice seem a minor part of modern urban life. But smell is more important to us than we usually realize: a lot of our conscious or unconscious knowledge of what’s going...

People living in cities and suburbs have mostly lost the farmer’s appreciation for soil and tend to dismiss it as “dirt.” But almost all life exists at the interface of air with water or soil, and ancient thinkers sensing this considered “earth” one of the four elements from which everything was created. (The others were air, fire, and water—still fundamental terms for us, especially if we understand fire to include sunlight.) Along with climate, soil determines what can grow and live in an area. Astonishingly, there is a greater mass of life under the soil surface than above it....

When we talk about ecological interactions, we’re usually talking about relationships among members of different animal and plant species. A species is a clearly identifiable group of living beings: dogs, dandelions, white-tail deer. Among most mammals, only members of the same species can interbreed, producing offspring that survive and reproduce. Since collies can mate with retrievers and produce fertile pups, they’re not separate species, only different breeds of the dog species (whose scientific name isCanis familiaris).

Individual members of a species living in one place often look slightly different from individuals of the same species living elsewhere. When they...

The world of life changes constantly and without end. We humans seek to find patterns in these changes, and thus we have discovered regular patterns in how plants and other organisms take each other’s place—how they “succeed” each other. After a significant disturbance in an ecosystem, such as an avalanche, a major fire or hurricane, the clear-cutting of a forest, or the bulldozing of a meadow, a process of succession begins. Many of the original plants, along with the animals that depended on them, have vanished. So new species move in—although some disturbances like a lava flow from...

The sulfur cycle provides a mineral nutrient that is essential for forming proteins and many other cell parts. Sulfur is made available in usable forms by bacteria. It is taken up from the soil by fungi, bacteria, protists, and plants. From them, it is passed to animals. Unlike many other nutrients, sulfur is in short supply on land (though overabundant in the oceans).

Sulfur compounds are also important in regulating Earth’s temperature. Minute oceanic organisms produce sulfur compounds that rise into the air, where they are a major contributor to the formation of clouds. The whiteness of the resulting clouds...

From a human point of view, a sustainable society is one that satisfies its needs without diminishing the prospects of future generations. Th is ideal is the polar opposite to the ideal of unlimited material growth. It emphasizes durability and permanence, a reliable future for a reasonable number of human beings, rather than ever-growing consumption and population.

From a rigorous ecological point of view, an ecosystem operates sustainably if its inputs and outputs (of both energy and materials) are balanced; over time it is not losing substantial amounts of nutrients. Such a situation can be described as dynamic equilibrium or...

When members of at least two species live together in a prolonged and sometimes inherited physical association, we call it symbiosis. In a worldwide example of great ecological significance, reef-forming coral animals in nutrientpoor tropical seas provide protection for algae, which recycle the corals’ wastes and provide them with food and oxygen. Formerly considered a curiosity, symbiosis is in fact a key factor in evolution. populations of organisms live in communities with associated organisms, with whom they have coevolved.

Symbiotic relationships range from obligatory to loose and casual. In every case, however, a biological basis for the symbiosis can be...

Taxonomy is the naming, identifying, and classifying of organisms. Science early devised classifications for the marvelous variety of living beings, but without aid from the idea of evolution. Now the way in which we name hundreds of thousands of individual species is based on the idea of “descent with modification”—that life forms evolve in family trees. Grouping organisms makes it easier to think about their history and existence in a systematic way. We try to understand how they are related by studying their structure, appearance, and ecological role through evolution over time. Living organisms seem to be strikingly separated...

Human perception has evolved to focus our senses on sizes and speeds that matter in finding food or safety or mates. We notice the flick of a leaf or the crack of a twig, which might once have meant the presence of a hungry tiger. We’re continually if unconsciously aware of the positions, postures, and glances of other humans, and of both tame and wild animals we encounter. However, we cannot distinguish very rapid things, such as the beating of a hummingbird’s wings, and we manage to keep track of slow things, such as the turning of the years, only...

Now the sixth largest industry in the world, tourism has tremendous ecological impacts: carbon dioxide and pollutant emissions from the airplanes, cars, trucks, and buses that move tourists about and supply them; impacts on the natural landscape of massive tourist facility development; the relegation of host peoples to low-level service jobs; and the destruction of natural wonders through excessive visitation.

In response, alternatives calledecotourismhave evolved. But staying close to home is the least damaging thing you can do on vacations, and there are surely many extraordinarily interesting nearby destinations that can easily be reached by train, bus, or,...

If an organism eats, drinks, breathes, or absorbs something toxic, it may sicken or die. Toxics in low concentrations are widespread in nature. Many plants—even some we frequently eat—naturally produce toxics as a kind of chemical warfare against insects. (Snake and bee venom, and the products of some bacteria that can make us sick, are usually called toxins.) Humans have long used natural toxics for our own purposes. Rotenone, for instance, is an insecticide derived from tropical plant roots. A toxic substance generally aff ects many species; thus nicotine, sometimes used as an insecticide, also causes cancer and...

The ecology of cities is critically important because we inhabit an increasingly urban world. You probably live in a city or suburb, though some of your great-grandparents may well have lived on farms and produced much of their own food. In most countries today, economic pressures are forcing huge numbers of people off farms and into cities. In the United States, whose population was once mostly farmers, this process has gone on for the past century; we now have only two million farmers, many of them part-time. Numerous cities in Asia will soon reach huge populations of more than 20...

Values are basic ideas that guide us in how we should behave. We humans act on instinct most of the time, just like nonhuman animals. We seek food, protection, and sex without having to stop and think about these goals. If we lacked such instinctive strategies of action, surviving would require constant rethinking and decision making. But we are also capable, through language, of adopting rules about what we doand why we do it. Whether we recognize it or not, all individual humans and all human cultures possess such rules, or values. The Golden Rule, “Do unto others as you...

We usually think of viruses in the same way we think of harmful bacteria, as “germs.” Viruses, however, are not truly alive. They’re fragments of protein-encased genetic material that can only become active or replicate inside living cells. Many can be purified in inert crystal form, rather like salt. Nonetheless, they have coevolved with living organisms. A squirrel monkey virus, for example, doesn’t harm those monkeys but in fact aids them by killing rival kinds of monkeys who come into squirrel-monkey territory. Every species of animal seems to have at least one virus regularly associated with it (primates like ourselves...

Seen from space, the blue of Earth’s seas marks it as “the water planet.” Poets speak of the waters of life, and the water cycle is the most easily visualized of earthly cycles. As one of our most ancient texts says, “All the rivers run into the sea; yet the sea is not full; and unto the place from whence the rivers flow, thither they also return again.” Humans have a natural affinity for water, as if we instinctively realize that without it life cannot exist. We love water’s taste, its look in sunlight or running over rocks, and the...

Because we’re brought up in the midst of civilization—a human-dominated world—we tend to think that most of life is under human control. “Wild things” and wilderness must be somewhere off in the distance, probably in limited, protected parks. After all, people domesticate or control once-wild animals like cows and cats. Also, we have a strong sense that we are in command of our own bodies: we can run, jump, dance, chew, swallow, look here or there, speak, sing, swim. Controlling these complicated and marvelous abilities occupies most of our conscious time.

However, many other functions of our bodies,...

All over the world, landscape paintings traditionally depicted scenes containing lakes, streams, and seasides. Humans delight in well-watered places, and landscaped gardens have often featured fountains or fishponds. But in those large and expanding parts of the United States (and the rest of the planet) where desert or semidesert conditions prevail and water supplies are overstretched, we must now think in terms of xeriscapes—dry landscapes. In place of waterthirsty lawns, residents of Southwestern cities have begun to prefer native plants (including cacti and certain trees) that have evolved in the bioregion and are adapted to the skimpy rainfall of...

The concept of sustainable yield first arose in fisheries and forestry. Sustainable yield measures how many fish, trees, or animals we can “harvest” yearly without reducing the average number of fish, the total standing crop of timber, or the populations of animal species, and without reducing the underlying primary productivity that supports them.

Humans, as predators, can consume some of a wild species’ productivity sustainably because nature provides every species with a surplus of off spring. The young of fish, trees, or any other species suffer heavy reduction by disease and predators before they in turn can reproduce. A hundred...

Meeting animals on their own ground, in wild areas or in habitats we share with them, makes us tingle with excitement, whether they are large and potentially dangerous like deer or small and nonthreatening like squirrels. Zoo animals can be fascinating, too, in their strangeness, beauty, and variety. Visiting a zoo helps us to appreciate the grace of antelopes, the charming playfulness of monkeys and apes, and the dignity of bears and elephants. We may sometimes experience deep feelings of communion with these fellow living beings. In a zoo we make some contact with the vivid life of our animal...

Vocabularies—sets of terms such as those explained in this book—are never neutral. Things that are included in a vocabulary gain a familiar reality; things that are left out are ignored or even have their existence denied. Moreover, a vocabulary implies a story of how the world works and why. Such stories always serve the interests of established institutions or classes. In science, politics, or art, a new way of talking about the world threatens to displace established ideas and the groups that espouse them, so it encounters vigorous opposition.

Today, the struggle over the basic terms of public...