by DK
Ecologists have identified growing threats to biodiversity, many of them driven by human actions. The current rate of species extinction is thought to be up to 1,000 times greater than it was before 1800, when humans began to dominate the planet. The first use of the term “biodiversity,” in 1988, was by American biologist Edward O. Wilson, who became known as the “father of biodiversity.” He later highlighted five key threats to biodiversity using the acronym HIPPO: habitat destruction; invasive species; pollution; human population; and overharvesting by hunting and fishing.
The five human activities that most seriously affect biodiversity on Earth can be represented by HIPPO, the acronym devised by Edward Wilson, with the relative severity of each reflected in the order of the letters.
Habitat wreckers
The Red List of the International Union for Conservation of Nature (IUCN) includes more than 25,000 threatened species. Of these, 85 percent are endangered by the loss of habitats that once supported particular species. This destruction can occur as a result of natural causes, such as fire or flood, or, more commonly, through the expansion of agricultural land, timber harvesting, and overgrazing by livestock. Deforestation, in particular, has contributed hugely to habitat loss, with around half of the world’s original forests now cleared, mainly for agricultural use.
Some habitats are not destroyed but rather broken up or divided into more isolated units by human interventions, such as building dams or other water diversions. This habitat fragmentation is particularly dangerous for migratory animals because they may no longer be able to find places to feed or rest along their normal routes. Native species and ecosystems are also disrupted by the introduction, accidentally or deliberately, of new species. These invasive species. can threaten the food supply or other resources of native species, carry disease, and become a predatory threat. The brown tree snake, for example, was brought accidentally to the island of Guam on a cargo ship, and has caused the extirpation (the extinction of a species in a particular area) of 10 of the island’s 11 native bird species.
“It is that range of biodiversity that we must care for—the whole thing—rather than just one or two stars.”
David Attenborough
British broadcaster and naturalist
Air and water poisoning
Any kind of pollution threatens biodiversity, but air and water pollution are particularly harmful. Burning fossil fuels, for example, releases the waste gases sulfur dioxide and nitrogen oxide into the air; these return as acid rain, causing water and soil acidification and affecting ecosystem health and biodiversity. Ozone emissions at ground level can also damage cell membranes on plants, curbing their growth and development.
Water pollution is caused mainly by sewage or by chemicals absorbed into water as it flows off agricultural land. This pollution reduces oxygen levels in water, making survival more difficult for some species, particularly when combined with water temperatures that have risen due to climate change. Freshwater streams used by certain species of spawning fish, for example, can be made uninhabitable by pollution.
Some organisms can absorb a substance, such as an agricultural chemical, more quickly than they can excrete it, in a process known as bioaccumulation. Initial, low concentrations of chemicals may not be a problem. However, as those chemicals accumulate through the food chain—from phytoplankton to fish to mammal, for example—they can reach levels that cause birth defects and disrupt hormone levels and immune systems.
Rapid population growth has generated further damage to the environment. The world’s human population has risen from less than 1 billion in 1800 to more than 7 billion, and is expected to reach nearly 10 billion by 2050. As the population grows, so do other threats to biodiversity: increasing numbers of invasive species are spread through trade and travel; urban development and resource extraction destroy habitats; more pollution is created; and land is overharvested. The impacts of human population growth will be difficult to limit, as ever more people rely on food and shelter to survive, and demand ever more goods in an increasingly global consumer society.
“We should preserve every scrap of biodiversity as priceless while we learn to use it and come to understand what it means to humanity.”
Edward O. Wilson
EDWARD O. WILSON
Born in Alabama in 1929, Edward Osborne Wilson was left blind in one eye after a fishing accident aged seven, and switched interests from birdwatching to insects. He discovered the first colony of fire ants in the US when he was only 13, and later attended the University of Alabama and Harvard. Wilson’s work has focused primarily on ants but also extends to the study of isolated ecosystems, known as “island biogeography.” A leading environmentalist, he has spearheaded efforts to preserve biodiversity and educate people about it. He has been awarded over 150 prizes, including the National Medal for Science, the Cosmos Prize, and two Pulitzer Prizes for nonfiction, and was named one of the century’s leading environmentalists by Time and Audubon magazine.
Key works
1984 Biophilia
1998 Consilience: The Unity of Knowledge
2014 The Meaning of Human Existence
Upsetting the balance
Population growth also drives overharvesting, the final human-made threat to biodiversity in the HIPPO acronym. Found in forestry, livestock grazing, and commercial agriculture, overharvesting can also arise from targeted hunting, gathering, and fishing, as well as unintentional harvesting, such as fish discarded from catches. When the rate of harvest exceeds the rate of replenishment through either reproduction or human activities such as tree planting, the harvest is not sustainable, and without regulation could result in the extinction or extirpation of species.
A study of the IUCN’s Red List in 2016 showed that 72 per cent of species listed as threatened or near-threatened are harvested at a rate that means their numbers cannot be balanced by natural reproduction or regrowth. Some 62 per cent of species are at risk from agricultural activity alone, such as livestock farming, tree felling, and the production of crops for food, fuel, fibres, and animal fodder.
Poaching, forest clearance, and other human activities have largely contributed to the status of the African western lowland gorilla as a “critically endangered” species.
Protecting biodiversity
In reality, the five HIPPO threats identified by Wilson are interrelated, and there is generally no single reason why any particular species is endangered. Agricultural development, for example, can not only destroy a habitat, but can also releases greenhouse gases into the atmosphere, contributing to air pollution and climate change. More than 80 per cent of the species on the IUCN’s Red List are affected by more than one of the five major biodiversity threats.
Biodiversity maintains the health of the ecosystems of the planet. Ecosystems are a delicate balance of living creatures, both plant and animal, as well as the soil, air, and water in which they live. Healthy ecosystems provide resources that sustain human and all other life, improve resilience against natural disasters and human-made shocks, including climate change, and provide recreational, medicinal, and biological resources.
Although the threats to biodiversity from human activity are serious, ways to protect it are being developed. Foremost is a “sustainable” approach to harvesting and agriculture that allows species—such as fish, trees, or crops—to be maintained at a stable level and even increased over time. Official protected status for areas of land, water, and ice can help sustain threatened species, while national and international agreements and negotiations can mitigate the impact of both legal and illegal trade, such as poaching. Public education also helps people to better understand their potential impacts on biodiversity and how to protect it for future generations.
The building of railways across the US was accompanied by hunters hired to decimate the buffalo population that had sustained Native American tribes. By the end of the 19th century, only a small number of wild buffalo survived.
Anthropogenic biomes
/> The biosphere—all the areas of Earth and its atmosphere that contain living things—consists of biomes, which are large ecosystems based on a specific environment, such as desert or tropical rainforest. The impact of human actions on biodiversity and the consequent reshaping of much of the planet have led ecologists to reassess biomes and suggest that a designation of anthropogenic (manmade) biomes is now necessary. Anthropogenic biomes are grouped into six main categories: dense settlements; villages; croplands; rangeland; forested; and wildlands.
Unlike other biomes, which can range across continents, anthropogenic biomes are a mosaic of pockets over Earth’s surface. According to ecologists, more than 75 per cent of Earth’s ice-free land has been affected by at least some form of human activity, particularly in dense settlements (urban areas), which account for over half the world’s population, and villages (dense agricultural settlements).
See also: Biodiversity hotspots • Animal ecology • Island biogeography • Biodiversity and ecosystem function • Biomes • Mass extinctions • Deforestation • Overfishing
IN CONTEXT
KEY FIGURE
Norman Myers (1934–)
BEFORE
1950 Theodosius Dobzhansky studies plant diversity in the tropics.
AFTER
2000 Myers and collaborators reevaluate the list of hotspots and add several new ones, bringing the total to 25.
2003 An article in American Scientist criticizes the concentration of conservation effort on hotspots, saying that this neglects less species-rich but still important “coldspots”.
2011 A team of researchers confirm the forests of east Australia as the 35th hotspot.
2016 The North American coastal plain is recognized as meeting the criteria for a global biodiversity hotspot—and becomes the 36th.
A biodiversity hotspot is an area with an unusually high concentration of animal and plant species. The term was coined in 1988 by Norman Myers, a British conservationist, to describe areas that are both biologically rich and deeply threatened. Facing the huge and increasing challenge of mass extinctions of species caused by the destruction of premium habitats, Myers argued that priorities had to be set to establish where to concentrate resources to conserve as many lifeforms as possible.
The lush hillsides and forests of Arunachal Pradesh, India, are part of the Indo-Burma biodiversity hotspot. The area contains some 40 percent of India’s animal and plant species.
Defining hotspots
Initially, Myers identified ten hotspots crucial for conserving plant species that were endemic (did not grow anywhere else on Earth). By 2000, he had refined the concept to focus attention on regions that fulfilled two criteria: the area must contain at least 1,500 vascular plants (plants with roots, stems, and leaves) that were endemic, and it must have lost at least 70 percent of its primary vegetation (the plants that originally grew in the area). Conservation International, an environmental agency that uses Myers’ concept to guide its efforts, now lists 36 such regions. Although they represent only 2.3 percent of Earth’s land surface, they are home to nearly 60 percent of the planet’s plant, amphibian, reptile, mammal, and bird species—and a high proportion of these species live only in their respective hotspot.
Most hotspots lie in the tropics or subtropics. The one facing the highest threat level is the Indo-Burma area in Southeast Asia. Only 5 percent of the original habitat remains, but its rivers, wetlands, and forests are vital for the conservation of mammals, birds, freshwater turtles, and fish. Animals unique to this area include the saola, a forest-dwelling mammal that is related to cattle but looks like an antelope; it was seen for the first time in 1992, in the Annamite Mountains of Vietnam. The endangered Irrawaddy dolphin is found along the coastlines of Southeast Asia and the islands of Indonesia. Other rare animals include Eld’s deer, the fishing cat, and the giant ibis.
“Our welfare is intimately tied up with the welfare of wildlife … by saving the lives of wild species, we may be saving our own.”
Norman Myers
Protective measures
Conservation agencies agree on targets for every hotspot. They list species that are threatened and make plans to conserve and manage those areas with suitable habitat and viable populations of target plants and animals. Sites are ranked according to how vulnerable and irreplaceable they are.
Myers’ two criteria have been criticized by those who say they do not take account of changing land use in regions where less than 70 percent of good habitat has been destroyed. The Amazon rain forest, for example, is not within a hotspot but the forest is being cleared faster than anywhere else on Earth.
“We are into the opening stages of a human-caused biotic holocaust—a wholesale elimination of species—that could leave the planet impoverished for at least five million years.”
Norman Myers
NORMAN MYERS
Myers was born in 1934 and grew up in the north of England. He studied at the University of Oxford before moving to Kenya, where he worked as a government administrator and teacher. During the 1970s, Myers studied at the University of California, Berkeley, where his interest in the environment grew. He raised concerns about deforestation for cattle ranching, describing it as the “hamburger connection.”
Myers raised the concept of biodiversity hotspots in the article “Threatened Biotas: ‘Hotspots’ in Tropical Forests,” published in The Environmentalist in 1988. In his first book, Ultimate Security: The Environmental Basis of Political Stability, he argued that environmental problems lead to social and political crises. In 2007, Time magazine hailed Myers as a Hero of the Environment.
Key works
1988 “Threatened Biotas: Hotspots in Tropical Forests”
1993 Ultimate Security: The Environmental Basis of Political Stability
See also: Human activity and biodiversity • The ecosystem • Deforestation • Sustainable Biosphere Initiative
INTRODUCTION
Our understanding of the variety, behavior, and interaction of organisms has advanced considerably since Aristotle discovered that bee colonies have a queen and workers. Huge advances in technology, field observations, and laboratory experiments have increased our knowledge, and the modern study of animal behavior—ethology—continues to throw up surprises.
Life under the microscope
Until the microscope was invented, no one knew that bacteria even existed, let alone what they did. Bacteria were first observed by Dutch microscopist Antonie van Leeuwenhoek in 1676, using an instrument he had built himself. He called these tiny organisms “animalcules,” but little was known about them for many years. In the 1860s, French chemist Louis Pasteur and German microbiologist Robert Koch developed the germ theory of disease, highlighting the harmful role played by bacteria. Subsequent research has also highlighted their positive roles: facilitating digestion; inhibiting the growth of other, pathogenetic bacteria; “fixing” or converting nitrogen into molecules that aid plant growth; and breaking down dead organic material, which releases nutrients for the food web.
Another discovery made possible by microscopy was of the mutualistic relationship between fungi and trees, published by German plant pathologist Albert Frank in 1885. Studying what he first assumed was a pathological infection, Frank discovered that trees with the fungi attached to their roots were healthier than those without. The fine filaments, or hyphae, of the fungi make the roots more efficient at obtaining nitrate and phosphate nutrients from the soil. In return, the fungi get sugar and carbon from the tree.
Connected lives
No organism lives in isolation from the rest of its ecosystem. The behavioral interactions between them are complex and much is still being discovered about them. One of the greatest contributions in this field was made by British zoologist Charles Elton, whose 1927 classic Animal Ecology established many important principles of animal behavior, including food webs and food chains, prey size, and the concept of ecological niches.
Ethology, which looks at animal
behavior and its evolutionary basis and development, is a major component in the modern study of organisms. Back in 1837, British entomologist George Newport discovered that moths and bees could raise the temperature of their thorax by quivering their muscles. From the 1970s onward, German-American entomologist Bernd Heinrich and others uncovered more thermoregulatory adaptations that have helped insects thrive. As heterotherms, they are able to maintain different temperatures in different parts of the body.
Modern research now combines laboratory experiments, field observation, and new technology such as infrared thermography to understand insect behavior in ever more detail.
Field observations are a key tool in ethological research. In the 1940s, British ornithologist David Lack investigated the factors controlling the number of eggs birds laid (clutch size). His food limitation hypothesis states that the number of eggs laid by a species has evolved to match the food available. Evolutionary pressure has created a correlation between clutch size and food availability.
Austrian zoologist Konrad Lorenz and Dutch biologist Nikolaas Tinbergen also studied animals in the wild to help understand their behavior. Lorenz’s 1949 work Man Meets Dog explains the loyalty of a pet dog to its owner in terms of canines’ instinctive loyalty to their pack leader in the wild. Tinbergen’s field experiments showed how gull chicks, which tap a red spot on a parent’s beak when they want food, will tap colored marks painted on a model beak.