The Ecology Book

by DK

  However, the impact of modern-day humans on the environment is unprecedented. In the past 200 years, the human population has exploded. This has fueled the rapid growth of cities, the development of large-scale industry based on the extraction of fossil fuels and raw materials, a growing agricultural demand to feed more people, and conflict and war. All these have taken their toll on the natural world.

  Yosemite National Park was created in 1890, thanks to the efforts of John Muir. The park is famed for its glaciers, waterfalls, and granite rock formations, such as the El Capitan monolith.

  Fragile ecoregions

  A concept that is now often used to identify the major habitat types on Earth is that of the ecoregion—smaller than a biome, with a more detailed gauge of biodiversity. Ecoregions are defined as large units of land or water containing a geographically distinct mix of species, natural communities, and environmental conditions. Some examples include deserts, tropical rain forests, temperate coniferous forests, lakes, mangrove swamps, and coral reefs. Of these, coral reefs and tropical rain forests are under particular threat from humankind.

  JOHN MUIR

  Born in Scotland in 1838, John Muir developed a passion for nature as a boy. He moved with his family to Wisconsin at the age of 11. In 1867, he had an accident in which he lost his sight temporarily, after which he “saw the world in a new light.” An accomplished botanist, geologist, and glaciologist, Muir visited the Yosemite Valley in California in 1868, and later determined to preserve it from the scourge of domestic sheep (which he called “hoofed locusts”). In 1903, Muir took President Theodore Roosevelt on a guided tour through the Yosemite Valley, and their three-day trip inspired Roosevelt to create the US Forestry Service and, in 1916, to form the National Conservation Commission. Until his death in 1914, Muir continued to advocate for the conservation of land such as Mount Rainier, which became a National Park in 1899.

  Key works

  1874 Studies in the Sierra

  1901 Our National Parks

  1911 My First Summer in the Sierra

  Rain forest clearance

  Despite covering only 6 percent of Earth’s land surface, tropical rain forests represent the greatest biomass of any terrestrial ecoregion, and are home to about 80 percent of land species. Every year, some 54,000 sq miles (140,000 sq km) of tropical rain forest is cleared—the equivalent of a soccer field every second. Logging is carried out for firewood and construction materials, and is also driven by the demand for roads, settlements, and agriculture.

  Globally, the rain forests that are under greatest threat are in West Africa, Central America, and Southeast Asia. Indeed, only about 30 percent of the lowland rain forest in Borneo now survives. In the Amazon Basin, home to nearly one-third of the world’s rain forest, much of the clearance is for agriculture, especially ranching.

  Once deforestation starts, the problem quickly gets worse. When rain falls on a forested slope, it is mostly absorbed by vegetation. But when the slope is cleared, the rainfall erodes the soil, making it useless for agriculture and impossible to replant. It produces silt runoff into rivers and lakes, killing fish, and increases the risk of flooding. The destruction of any forest reduces its capacity to absorb the greenhouse gas carbon dioxide, thereby contributing to the acceleration of climate change.

  Palm oil trees are being planted on a large scale in Indonesia and Malaysia, where this is one of the main drivers of deforestation. Orangutans are among the species endangered as a result.

  Loss of coral reefs

  Coral reefs are important ecoregions and yet are especially endangered. They support about 25 percent of the planet’s marine species, and are also nurseries for billions of fish. Two-thirds of the world’s reefs are under threat, and about a quarter of them are likely damaged beyond repair. Possibly the biggest threat to coral reefs is increased acidity caused by a greater uptake of CO2 from the atmosphere. This impedes the ability of many sea creatures to build their shells, and induces coral “bleaching,” which is a step on the way to the reef dying. In addition, coral reefs are being destroyed by overfishing, and by harmful practices such as cyanide and blast fishing, and bottom trawling. Sediment resulting from coastal development blocks the sunlight that reefs need. Chemical pollution, coral mining, and careless tourism all add to the burden on this highly sensitive habitat.

  Wide-ranging impacts

  All over the world, diverse natural habitats are critically threatened by human activity. Tropical deciduous dry forest is easier to clear than rain forest, and on Madagascar, where dry forest was widespread, less than 8 percent now remains. At one time, tallgrass prairie stretched across the US Midwest, but only 3 percent of it is left: the rest has been converted to farmland. Many wetlands have been drained for agriculture or urban development; others are irreversibly damaged by pollution. Nutrient runoff from agricultural fertilizers has spoiled many lakes and rivers. In many countries, intertidal zones have been destroyed by the building of ports. Coastal development has been largely responsible for the loss of 35 percent of mangrove swamps. In the tropics and subtropics, overgrazing by domestic animals such as goats has converted an estimated 3.5 million sq miles (9 million sq km) of seasonally dry grassland and scrub into desert.

  Wetlands and intertidal zones are important for marine invertebrates and migratory shorebirds, but in many parts of the world they have been drained for industry and ports.

  “In every walk with nature, one receives far more than he needs.”

  John Muir

  Halting the decline

  The destruction of these habitats is not only a loss in terms of natural beauty and biodiversity, but also creates serious problems for people: for example, poorer water quality, declining fish stocks, crashes in populations of pollinators, flooding from increased rainwater runoff, and faster buildup of greenhouse gases. Conservation is now paramount, and ecologists work to refine their understanding of the best ways to go about it.

  Appropriate measures depend on the situation, and range from the creation of protected reserves or “corridors,” to link areas that have become fragmented, to projects to recreate lost habitat. Sustainable sources of fuel and timber for those who are otherwise dependant on forest wood are also important, as is banning the trade in rain forest hardwood. Since the impact of habitat destruction is global, international agreements and cooperation are crucial.

  Protected areas

  Muskoxen are Arctic herd animals whose numbers were severely depleted in the 19th century by hunting. They now live on reserves in Alaska, Norway, and Siberia.

  National parks, wilderness areas, nature reserves, and sites of special scientific interest (SSSIs) are all types of protected habitats. Within these areas, interference with the natural environment is prohibited or limited by some kind of legal framework. They must cover a specified expanse of land or sea, but they vary greatly in size and in the level of protection given. Just over 10 percent of Earth’s land is protected, but only 1.7 percent of the oceans; though marine reserves are essential, they require local and national governments to agree on key issues such as fishing rights.

  Marae Moana, the largest protected area on Earth, is 772,000 sq miles (2 million sq km) around the Cook Islands in the Pacific Ocean. It is home to sea turtles, at least 136 species of corals, and 21 whales and dolphins. The biggest land reserve is the Northeast Greenland National Park, which covers almost 386,000 sq miles (1 million sq km) of ice sheet and tundra.

  See also: Human activity and biodiversity • Biodiversity hotspots • Biomes • Deforestation • Environmental ethics

  IN CONTEXT

  KEY FIGURE

  Charles Keeling (1928–2005)

  BEFORE

  1896 The Swedish chemist Svante Arrhenius is the first to estimate the extent to which atmospheric CO2 could increase Earth’s temperature.

  1938 Comparing historic temperature data and CO2 measurements, the British engineer and scientist Guy Stewart Callendar concludes that the increase in CO2 is
responsible for the warming of the atmosphere.

  AFTER

  2002 The European Space Agency’s ENVISAT satellite begins to produce up to 5,000 readings of greenhouse gases every day.

  2014 NASA’s Orbiting Carbon Observatory generates up to 100,000 high-precision measurements daily.

  The Keeling Curve, named after Charles Keeling, an American scientist, charts the daily record of atmospheric carbon dioxide (CO2), measured in parts per million by volume (ppmv), in a series dating back to 1958. It shows two things: the natural seasonal respiration of Earth and the year-on-year rise in atmospheric CO2. Atmospheric CO2 is significant because carbon dioxide is the most important of the greenhouse gases, which trap warmth in Earth’s atmosphere. More molecules of CO2 and other greenhouse gases cause more heat to be trapped, leading to an overall increase in temperature and global climate change.

  “We were witnessing for the first time nature’s withdrawing CO2 from the air for plant growth during summer and returning it each succeeding winter.”

  Charles Keeling

  Measuring CO2 levels

  Since the start of the Industrial Revolution in the late 1700s, human activity has produced increasing emissions of CO2. This is largely due to burning fossil fuels, while forest clearance for agriculture and development has resulted in less vegetation absorbing CO2 through photosynthesis. Many scientists once believed that excess CO2 would be absorbed by the oceans. Others disagreed, but there was little hard evidence either way.

  Charles Keeling was not the first to propose a link between atmospheric warming and CO2 emissions. Others had measured CO2 levels but had produced only “snapshots” in time rather than a long-term dataset. Keeling knew that a long study was needed to prove the link. In 1956, he took up a post at the Scripps Institution of Oceanography in San Diego, California, and obtained funds to establish CO2 monitoring stations at remote locations 9,843 ft (3,000 m) up on Mauna Loa, Hawaii, and at the South Pole. By 1960, Keeling was sure that he had a long-enough series of records to detect a year-on-year increase.

  Mauna Loa in Hawaii is an ideal site for an atmospheric research station. The high altitude and remote location of the volcano ensure that the air is largely unaffected by humans or vegetation.

  Seasonal changes

  Although South Pole funding ended in 1964, Mauna Loa has produced data from 1958 onward. Plotted on a graph, the measurements became known as the Keeling Curve. It is, in fact, a series of annual curves, reflecting seasonal changes. During spring and summer in the Northern Hemisphere, as new foliage takes more CO2 out of the atmosphere, the global concentration of the gas declines, reaching a low point in September. It increases again in the northern autumn as leaves fall and photosynthesis declines. Plant growth in the Southern Hemisphere later in the year does not make up for the loss, because most of Earth’s vegetative cover is in the north.

  Ancient air bubbles trapped in polar ice cores reveal that, over the past 11,000 years, average CO2 concentrations were 275–285 ppmv, but increased sharply from the mid-19th century. In 1958, the level was 316 ppmv. It rose steadily at a rate of 1.3–1.4 ppmv each year until the mid-1970s, then increased by about 2 ppmv each year. By spring 2018 it had hit 411 ppmv, almost 1.5 times higher than preindustrial levels.

  The Keeling Curve of steadily rising CO2 levels is clearly shown on a graph plotting results from the continuous monitoring of atmospheric carbon dioxide (CO2) at Mauna Loa, Hawaii.

  CO2 analysis in icecaps

  Bubbles in an ice core provide a sample of the atmosphere going back centuries. Scientists measure the CO2 in the trapped air bubbles.

  Scientists can measure past concentrations of carbon dioxide by analyzing bubbles of air trapped in Antarctic and Greenland ice sheets. This evidence indicates that there have been several cycles of variation over the past 400,000 years. These range from lower readings in the most severe glaciations—when glaciers actually formed—to higher readings during warmer, interglacial periods. The increase since the start of the Industrial Revolution has been matched by the average global temperature. This has risen by 0.13 °F (0.07 °C) per decade since 1880 and 0.31 °F (0.17 °C) per decade since 1970.

  The Intergovernmental Panel on Climate Change (IPCC) warns that unless the world's governments reduce greenhouse gas emissions dramatically, by the year 2100 average temperatures could be around 7.7 °F (4.3 °C) higher than they were before the Industrial Revolution. Such an increase would cause both a marked rise in sea levels and more extreme weather, which would result in people having to abandon some regions of the world entirely.

  See also: Global warming • The biosphere • Environmental feedback loops • Halting climate change

  IN CONTEXT

  KEY FIGURE

  Rachel Carson (1907–64)

  BEFORE

  1854 Henry David Thoreau’s book Walden describes a social experiment to live the simple life in tune with nature. It is seen as an inspiration for the environmentalist movement.

  1949 A Sand County Almanac by Aldo Leopold proposes a deep ecology of people living in harmony with the land.

  AFTER

  1970 The US establishes the Environmental Protection Agency (EPA).

  1989 Bill McKibben’s book The End of Nature highlights the dangers of global warming.

  2006 The documentary An Inconvenient Truth records former US vice president Al Gore’s efforts to educate the public about climate change.

  Arguably the most revered and influential book ever published on the subject of environmentalism, Silent Spring garnered a huge amount of publicity when it was released in 1962. It galvanized the fledgling conservation movement, forced legislative change, and, perhaps most significantly, championed the right of the public to question those in power and hold them to account.

  However, the author of this ground-breaking work was far from the typical “eco-warrior”—a term that was unheard of when the book was first published. On the contrary, Rachel Carson was a quiet, scholarly woman, with a masters degree in zoology and 20 years’ service as an aquatic biologist in the United States. Most of all, she was an exceptional writer, able to fuse scientific fact with compelling narrative.

  Spraying insecticide such as DDT whether indoors or outside, has been—and in some places still is—a common method of controlling the mosquitoes that transmit malaria.

  Dying wildlife

  Like many great and influential works, Silent Spring began in a very personal way. In January 1958, Carson’s friend Olga Huckins sent her a letter that she had originally tried to have published in the Boston Herald. It spoke about aerial spraying of a mixture of fuel oil and a chemical compound named DDT (dichloro-diphenyl-trichloroethane), in the vicinity of her small bird sanctuary in Michigan. The morning after the spraying, Huckins found several birds dead on her property and hoped that Carson might know someone in Washington who could stop further spraying. Carson was outraged and resolved to help. For more than a decade she had been aware of troubling incidents in which indiscriminate spraying of DDT had been killing wildlife. Carson swiftly approached the editor of the New Yorker, E.B. White, suggesting that the magazine run a piece about the growing concern around synthetic pesticides and their effect on nontarget organisms. The editor suggested that she write the article herself. Reluctantly, Carson began research on what she at first called “the poison book.” It went on to shake the world.

  RACHEL CARSON

  Born in 1907, Rachel Carson grew up on a farm in Pennsylvania, where she developed a love of nature. She won a scholarship to Pennsylvania College for Women and later gained a masters in zoology. Growing up in a land-locked state, Carson dreamed of the ocean; it became an enduring passion, and she went to work as an aquatic biologist with the US Fish and Wildlife Service (FWS).

  Carson wrote and published many educational brochures and eventually became the US Fish and Wildlife Service’s editor-in-chief. From 1941 onward, she wrote books about marine biology, most notably The Sea Around Us, which won t
he National Book Award, and was a national best seller. This success enabled Carson to write full time and she began work on Silent Spring in 1958. In 1960, Carson was diagnosed with breast cancer; she died in 1964.

  Key works

  1941 Under the Sea Wind

  1951 The Sea Around Us

  1955 The Edge of the Sea

  1962 Silent Spring

  The chemical future

  Silent Spring’s impact needs to be seen against the backdrop of the time in which it was published. Although academics and scientists had already voiced concerns about synthetic pesticides, the public was oblivious to this issue.

  Synthesized pesticides had been in use since the 1920s but had advanced significantly during World War II, powered by military-funded research. During the 1950s, the popular notion was that they could solve the world’s problems of famine and sickness by killing pests that destroyed crops and transmitted disease. Advertising campaigns of chemical giants such as Union Carbide, DuPont, Mobil, and Shell spread this message to a huge audience. Silent Spring aimed to challenge the received wisdom, arguing that the so-called scientific progress enjoyed in post-war America would come at a huge price for the environment.

  The most notorious of the pesticides, and the one most associated with Silent Spring, was DDT. It was first synthesized in the late 19th century, but in 1939, Swiss chemist Paul Hermann Müller realized that it could be used to kill a wide range of insects, due to its pervasive action as a nerve poison. It was used during World War II to control insects that destroyed vital food crops as well as those which transmitted malaria, typhus, and dengue fever to combat troops.