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Chapter9.docxMain content
Chapter Introduction
Endangered wild Siberian tiger
Tiago Jorge da Silva Estima/ Shutterstock.com
Core Case StudyWhere Have All the Honeybees Gone?
Learning Objective
· LO 9.1Explain how honeybees illustrate that the decline of a species can threaten vital ecosystem and economic services.
In meadows, forests, farm fields, and gardens around the world, industrious honeybees (Figure 9.1) flit from one flowering plant to another. They are collecting nectar and pollen that they take back to their hives. They feed young honeybees the protein-rich pollen, and the adults feed on the honey made from the collected nectar and stored in the hive.
Figure 9.1
European honeybee drawing nectar from a flower.
Darlyne A. Murawski/National Geographic Image Collection
Honeybees provide us one of nature’s most important ecosystem services: pollination. It involves a transfer of pollen stuck on their bodies from the male to female reproductive organs of the same flower or among different flowers. This fertilization enables the flower to produce seeds and fruit. Honeybees pollinate many plant species and some of our most important food crops, including many vegetables, fruits, and tree nuts such as almonds. European honeybees pollinate about 71% of vegetable and fruit crops that provide 90% of the world’s food and a third of the U.S. food supply.
Nature relies on the earth’s free pollination service provided by a diversity of bees and other wild pollinators. In contrast, farmers practicing industrialized agriculture on vast croplands and orchards rely mostly on this single honeybee species to pollinate their crops. Many U.S. growers rent European honeybees from commercial beekeepers that truck about 2.7 million hives to farms across the country to pollinate different crops.
However, European honeybee populations have been in decline since the 1980s because of a variety of factors including exposure to new parasites, viruses, fungal diseases, and pesticides. In 2006, a new threat emerged. Massive numbers of European bees in the United States and some European countries began disappearing from their colonies, especially during winter. Between 2006 and 2016, this phenomenon, named colony collapse disorder (CCD) , affected 23% to 33% of the European honeybee colonies in the United States. Since 2014, U.S. beekeepers have been losing 30% to 40% of their stock every season. Researchers are looking for the causes and for ways to reverse this decline of European honeybee populations.
Many farmers believe that we need the industrialized honeybee pollination system to grow enough food. However, many ecologists view heavy dependence on a single bee species as a potentially dangerous violation of the earth’s biodiversity principle of sustainability. They warn that this dependence could put food supplies at risk if the population of European honeybees continues to decline. If this occurs, food prices and hunger will rise. Ecologists call for more reliance on the free crop pollination services provided by variety of wild bee species and other pollinators as a way to implement the biodiversity sustainability principle.
The honeybee crisis is a classic case of how the decline of a species can threaten vital ecosystem and economic services. Scientists project that during this century, human activities, especially those that contribute to habitat loss and climate change, are likely to play a key role in the extinction of one-fifth to one-half of the world’s known plant and animal species. Many scientists view this threat as one of the most serious and long lasting environmental and economic problems we face. In this chapter, we discuss the causes of this problem and possible ways to deal with it.
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9.1Species Extinction
· LO 9.1ASummarize what scientists have learned about the number and extent of mass extinctions throughout the earth’s history.
· LO 9.1BState the scientifically estimated range of current extinction rates, in terms of species lost per year, along with the estimated background extinction rate.
· LO 9.1CList three causes of today’s higher extinction rate identified by biodiversity researchers.
· LO 9.1DList two reasons why researchers like Edward O. Wilson and Stuart Pimm argue that currently projected extinction rates might be too low.
· LO 9.1EExplain why some biologists argue we are creating a speciation crisis that will slow recovery from a possible sixth mass extinction.
· LO 9.1FExplain the difference between endangered species and threatened species.
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9.1aExtinctions Are Natural but Sometimes They Increase Sharply
The disappearance of all members of a species from the earth is called extinction . A species can become extinct when it cannot adapt and successfully reproduce under new environmental conditions, or when a catastrophic environmental event wipes out its members. Extinction is a natural process and has occurred at a low rate throughout most of the earth’s history. This natural rate is known as the background extinction rate. Scientists estimate that the background rate typically amounts to a loss of about 1 species per year for every 1 million species living on the earth. This amounts to 10 natural extinctions a year if the earth has 10 million species. Most species that have existed on the earth have gone extinct.
However, extinction does not always happen at a constant rate. The extinction of many species in a relatively short period of geologic time is called a mass extinction. Mass extinctions are global. Geologic, fossil, and other records indicate that the earth has experienced five mass extinctions, during which 50–90% of the species present at that time went extinct (see Figure 4.19) over thousands of years. The largest mass extinction took place some 250 million years ago and wiped about 90% of the world’s existing species.
The causes of past mass extinctions are poorly understood but probably involved global changes in environmental conditions. Examples are sustained and significant global warming or cooling, large changes in sea levels and ocean water acidity, and catastrophes such as multiple large-scale volcanic eruptions and large asteroids or comets hitting the planet.
Although mass extinctions devastate life on the earth, they also provide opportunities for new life forms to emerge, diversify, and fill empty ecological niches. Scientific evidence indicates that after each mass extinction the earth’s overall biodiversity returned to equal or higher levels (Figure 4.19). However, each recovery took 5-10 million years. The existence of millions of species today means speciation, on average, has kept ahead of extinction. It also demonstrates the biodiversity principle of sustainability as a factor in the long-term sustainability of life on the earth.
Scientific evidence indicates that extinction rates have increased as the human population has grown and spread over most of the globe, creating large and growing ecological footprints (see Figure 1.9). The extinction of one species can lead to the extinction of other species that depend on it for food or ecosystem services, and biodiversity researchers project that the rate of extinction will continue to increase. In the words of biodiversity expert Edward O. Wilson (see Individuals Matter 4.1), “The natural world is everywhere disappearing before our eyes—cut to pieces, mowed down, plowed under, gobbled up, replaced by human artifacts.”
Scientists estimate that the current annual extinction rate is 1,000 to 10,000 times the natural background extinction rate—mostly because of habitat loss and degradation, climate change, ocean acidification, and other environmentally harmful effects of human activities (Science Focus 9.1). Assuming there are 10 million species on the earth, this means that today we are losing an estimated 10,000 to 100,000 species per year, compared to the background extinction rate of 10 species per year. The higher of those estimates amounts to an average of about 274 species per day or about 11 every hour.
Science Focus 9.1
Estimating Extinction Rates
Scientists who try to catalog extinctions, estimate past extinction rates, and project future extinction rates face three problems. First, because the natural extinction of a species typically takes a long time, it is difficult to document. Second, we have identified only about 2 million of the world’s estimated 7 million to 10 million and perhaps as many as 100 million species. Third, scientists know little about the ecological roles of most of the species that have been identified.
One approach to estimating future extinction rates is to study records documenting past rates at which easily observable mammals and birds (Figure 9.A) have become extinct. Most of these extinctions have occurred since humans began to dominate the planet about 10,000 years ago. This information can be compared with fossil records of extinctions that occurred before that time.
Figure 9.A
Painting of the last pair of North American passenger pigeons, once the world’s most abundant bird species. They became extinct in the wild in 1912 mostly because of habitat loss and overhunting.
Louis Agassi Fuertes/National Geographic Image Collection
Another approach is to observe how reductions in habitat area affect extinction rates. The species–area relationship, studied by Edward O. Wilson (see Individuals Matter 4.1) and Robert MacArthur, suggests that, on average, a 90% loss of land habitat in a given area can cause the extinction of about 50% of the species living in that area. Thus, we can base extinction rate estimates on the rates of habitat destruction and degradation, which are increasing around the world.
Scientists also use mathematical models to estimate the risk of a particular species becoming endangered or extinct within a certain period and run them on computers. These models include factors such as trends in population size, past and projected changes in habitat availability, interactions with other species, and genetic factors.
Researchers are working hard to get more and better data and to improve the models they use in order to make better estimates of extinction rates and to project the effects of such extinctions on vital ecosystem services such as pollination (Core Case Study). These scientists contend that our need for better data and models should not delay our acting now to keep from hastening extinctions and the accompanying losses of ecosystem services through human activities.
Critical Thinking
1. Does the fact that extinction rates can only be estimated make them unreliable? Why or why not?
Biodiversity researchers project that these higher rates are mostly due to habitat loss and degradation, climate change, ocean acidification, and other environmentally harmful effects of human activities. By the end of this century, most of the big carnivorous cats, including cheetahs, tigers (see chapter-opening photo), and lions may exist only in zoos and small wildlife sanctuaries. Most elephants, rhinoceroses, gorillas, apes, chimpanzees, and orangutans will likely disappear from the wild.
Why does this matter? According to biodiversity researchers, including Edward O. Wilson and Stuart Pimm, an estimated 20% to 50% of the world’s 2 million identified animal and plant species could vanish from the wild by the end of this century because of climate change and various human activities. Many other species that have not been identified will also disappear. If these estimates are correct (see Science Focus 9.1), the earth is entering a sixth mass extinction caused primarily by human activities. Unlike previous mass extinctions, much of this mass extinction is projected to take place within a human lifetime instead of over many thousands of years, as past extinctions have done. As conservation ecologist Thomas E. Lovejoy (Individuals Matter 3.1) puts it: “The sixth great extinction has started and the issue is how far do we let it go.”
20–50%
Percentage of the earth’s known species that could disappear this century primarily because of human activities
A sixth mass extinction would likely impair some of the earth’s vital ecosystem services such as air and water purification, natural pest control, and pollination (Core Case Study). According to the Millennium Ecosystem Assessment, 15 of 24 of the earth’s major ecosystem services are already in decline. Conservation scientists view this potential massive loss of biodiversity and ecosystem services within the span of a human lifetime as one of the most important and long-lasting environmental and economic problems humanity faces. By saving as many species as possible from extinction—especially keystone species (see Chapter 4)—we could increase our beneficial environmental impact and help sustain and enrich our own lives and economies.
Wilson, Pimm, and other extinction experts consider a projected extinction rate of 10,000 times the background extinction rate to be low, for two reasons. First, both the rate of extinction and the resulting threats to ecosystem services are likely to increase sharply during the next 50–100 years because of the harmful environmental impacts of the rapidly growing human population and its growing per capita use of resources.
Biologists Philip Levin, Donald Levin, and others warn that, while our activities are likely to reduce the speciation rates and population sizes for some species, they could increase the speciation rates and population sizes for rapidly reproducing species such as weeds, rats, and species of insects such as cockroaches. Rapidly expanding populations of such species could reduce the populations of various other species, further accelerating their extinction and threatening key ecosystem services.
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9.1bEndangered and Threatened Species Are Ecological Smoke Alarms
Biologists classify species that are heading toward biological extinction as either endangered or threatened. An endangered species has so few individual survivors that the species could soon become extinct. A threatened species has enough remaining individuals to survive in the short term, but because of declining numbers, it is likely to become endangered in the near future. Some species have characteristics that increase their chances of becoming extinct (Figure 9.2). As biodiversity expert Edward O. Wilson puts it, “The first animal species to go are the big, the slow, the tasty, and those with valuable parts such as tusks and skins.” Figure 9.3 show four species that are listed as endangered under the U.S. Endangered Species Act.
Figure 9.2
Certain characteristics put a species in greater danger of becoming extinct.
Figure 9.3
Endangered natural capital: These four endangered species are threatened with extinction, largely because of human activities. The number below each photo indicates the estimated total number of individuals of that species remaining in the wild.
Geoffrey Kuchera/ Shutterstock.com; Ferenc Cegledi/ Shutterstock.com; Catcher of Light, Inc./ Shutterstock.com; Tiago Jorge da Silva Estima/ Shutterstock.com
Species can also become regionally extinct in the areas where they are normally found. A species can also become functionally extinct when its populations crash to the point where its interactions with other species are lost or greatly diminished. Important ecosystem services that depend on these interactions might also then be lost or diminished, and this is often difficult to detect until it is too late.
For example, the American alligator is a keystone species in its marsh and swamp habitats of the southeastern United States. (See Case Study, Chapter 4.) When its numbers dwindled in the 1960s, certain ecosystem services, such as the building of gator nests, diminished, and bird species that depended on these nesting sites declined. After the alligator was placed on the U.S. endangered species list, it made a strong comeback and its ecosystems recovered.
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9.2Why Should We Care about Species Extinction?
· LO 9.2AIdentify two reasons for the decline of the orangutans.
· LO 9.2BState four major reasons why biologists argue we should prevent our activities from causing or hastening the extinction of other species.
· LO 9.2CIdentify the ecosystem service provided by honeybees ( Core Case Study ) that makes them vital to our own survival.
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9.2aSpecies Are a Vital Part of the Earth’s Natural Capital
According to the World Wildlife Fund (WWF), about 119,000 orangutans (Figure 9.4) remain in the wild, down from 230,000 about a century ago. About 104,700 of them are in the tropical forests of Borneo, Asia’s largest island.
Figure 9.4
Natural capital degradation: These endangered orangutans depend on a rapidly disappearing tropical forest habitat in Borneo.
Critical Thinking:
1. What difference will it make if human activities hasten the extinction of the orangutan?
These highly intelligent animals are disappearing at an estimated rate of 1,000–2,000 per year. A key reason is that much of their tropical forest habitat is being cleared for plantations that grow oil palms, especially in Malaysia and Indonesia. They are a source of palm oil, a vegetable oil that is used in numerous products, including cookies, cosmetics, and biodiesel fuel for motor vehicles. Another reason for the orangutan’s decline is smuggling. An illegally smuggled, live orangutan sells for thousands of dollars on the black market. Because of their low birth rate, orangutans have a hard time increasing their numbers. Without urgent protective action, the endangered orangutan may disappear in the wild within the next two decades.
Orangutans are considered keystone species in the ecosystems they inhabit. The dispersal of fruit and plant seeds in their wastes throughout their tropical rain forest habitat is an important ecosystem service. If orangutans disappear, many rain forest plants and some of the animals that consume them may become threatened.
Does it matter that orangutans—or any species, for that matter—may disappear in the wild largely due to human activities? New species eventually evolve to take the places of species lost through background and mass extinctions, so why should we care if we greatly speed up the global extinction rate over the next 50–100 years? According to biologists, there are four major reasons why we should prevent our activities from causing or hastening the extinction of other species.
First, the world’s species provide vital ecosystem services (see Figure 1.3) that help to keep us alive and support our economies. For example, we depend on honeybees (Core Case Study) and other insects for pollination of many food crops. We also depend on certain species of birds, amphibians (see Chapter 4 Core Case Study), and spiders for natural control of insect pests. Aquatic species that live in streams can help purify flowing water. Trees produce oxygen that organisms need to survive. Earthworms aerate topsoil, which helps improve soil health. By eliminating a species or sharply reducing its population—especially a species such as the orangutan that plays a keystone role—we can speed up the extinction of other species. This can upset ecosystems and degrade their important ecosystem services.
Second, many species contribute to economic services that we depend on. Various plant species provide economic value as food crops, wood for fuel, lumber for construction, paper from trees, and substances for medicines. Bioprospectors search tropical forests and other ecosystems to find plants and animals, which scientists can use to make medicinal drugs (Figure 9.5)—an example of learning from nature. For example, aspirin, the widely used painkiller, was originally developed from the bark and leaves of the willow tree. Less than 0.5% of the world’s known plant species have been examined for their medicinal properties. GREEN CAREER: Bioprospecting.
Figure 9.5
Natural capital: These plant species are examples of nature’s pharmacy. Once the active ingredients in the plants have been identified, scientists can usually produce them synthetically. The active ingredients in 9 of the 10 leading prescription drugs originally came from wild organisms.
Learning from Nature
The wandering spider, a tropical species, has the ability to detect slight vibrations from several meters away. By studying its physiology, engineers have developed sensors that can detect human speech and a pulse. It could be used to make wearable electronics for health monitoring and other applications.
Another economic benefit from preserving species and their habitats is the revenues from ecotourism. This rapidly growing industry specializes in environmentally responsible travel to natural areas and generates more than $1 million per minute in tourist expenditures, worldwide. Conservation biologist Michael Soulé estimates that a male lion living to age 7 generates about $515,000 through ecotourism in Kenya but only about $10,000 if it is killed for its skin. Ecotourism promotes conservation, low environmental impact, respect for local cultures, and support for local economies. Travelers who sign up for ecotours have the chance to see endangered species such as orangutans and parrots (Figure 9.6) in the wild. Revenues from ecotourism generate more than $1 million per minute in tourist expenditures worldwide. GREEN CAREER: Ecotourism guide
Figure 9.6
Many species of wildlife such as this endangered hyacinth macaw in Brazil are sources of beauty and pleasure. Habitat loss and illegal capture in the wild by pet traders endanger this species.
Roy Toft/National Geographic Image Collection
A third reason for preventing a mass extinction is that it will take 5 million to 10 million years for natural speciation to replace the species we are likely to wipe out during this century (Figure 4.19).
Fourth, many people believe that wild species, such as orangutans, have a right to exist, regardless of their usefulness to us. This ethical viewpoint raises a number of challenging questions. Since we cannot save all species from the harmful consequences of our actions, we have to make choices about which ones to protect. Should we protect more animal species than plant species and, if so, which ones should we protect? Some people support protecting familiar and appealing species such as elephants, whales, tigers, giant pandas, and orangutans (Figure 9.4), but care much less about protecting plants that serve as the base of the food supply for other species (Core Case Study). Others might think little about getting rid of species that most people fear or dislike, such as mosquitoes, cockroaches, disease-causing bacteria, snakes, sharks, and bats.
In summary, a flourishing diversity of life on the earth is essential for sustaining the planetary life-support system on which the human species and other species depend, in keeping with the biodiversity principle of sustainability. To biologist Edward O. Wilson, carelessly and rapidly eliminating species that make up an essential part of the world’s biodiversity is like burning millions of books that we have never read.
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9.3Humans and Species Extinction
· LO 9.3AIdentify the four ecosystems most threatened by habitat destruction, degradation, and fragmentation, according to biodiversity researchers.
· LO 9.3BExplain how an invasive species can threaten habitats and other species using two of the following species as examples: the kudzu vine, wild boar, red fire ants, or the Burmese python.
· LO 9.3CList five steps you can take to prevent or slow the spread of invasive species.
· LO 9.3DExplain how a toxic chemical such as DDT can move through a food chain in a process called bioaccumulation.
· LO 9.3FDescribe five possible causes identified by scientists for the decline of honeybees.
· LO 9.3FDescribe five examples of how the illegal killing, capturing, and selling of wild animals is threatening some species.
· LO 9.3GUse the factors represented by the acronym HIPPCO to explain why many of the world’s bird species are declining.
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9.3aHabitat Destruction and Fragmentation: Remember HIPPCO
Biodiversity researchers summarize the most important direct causes of species extinction and threats to ecosystem services using the acronym HIPPCO : Habitat destruction, degradation, and fragmentation; Invasive (nonnative) species; Population growth and increasing use of resources; Pollution; Climate change; and Overexploitation.
According to biodiversity researchers, the greatest threat to wild species is habitat destruction (Figure 9.7), degradation, and fragmentation. Specifically, deforestation in tropical areas (see Figure 3.1) is the greatest threat to species and to the ecosystem services they provide. The next largest threat is the destruction and degradation of coastal wetlands and coral reefs (see Chapter 8 Core Case Study), the plowing of grasslands for planting of crops (see Figure 7.17), and the pollution of streams, lakes, and oceans. In Brazil, 93% of its once diverse Atlantic Forest has been lost because of logging, mining, cattle ranching, and clearance for sugar cane plantations. According to a 2019 UN study by 450 experts in 50 countries, there has been a 30% reduction in global habitat since 1970 and about 1 million plant and animal species are at risk of becoming extinct over the next few decades.
Figure 9.7
Natural capital degradation: These maps reveal the reductions in the ranges of four wildlife species, mostly as the result of severe habitat loss and fragmentation and illegal hunting for some of their valuable body parts.
Critical Thinking:
1. Would you support expanding these ranges even though this would reduce the land available for human habitation and farming? Why or why not?
(Compiled by the authors using data from International Union for Conservation of Nature and World Wildlife Fund.)
Island species—many of them found nowhere else on earth—are especially vulnerable to extinction when their habitats are destroyed, degraded, or fragmented, because they have nowhere else to go. This is why the Hawaiian Islands are America’s “extinction capital”—with 63% of its species at risk.
Habitat fragmentation occurs when a large, intact area of habitat such as a forest or natural grassland is divided into smaller, isolated patches or habitat islands (Figure 9.8)—typically by roads, logging operations, crop fields, and urban development. Fragmentation can divide populations of a species into increasingly isolated small groups that are more vulnerable to predators, competitor species, diseases, and catastrophic events such as storms and fires. In addition, habitat fragmentation creates barriers that limit the abilities of some species to disperse and colonize areas, locate adequate food supplies, and find mates. Scientists are using drones with cameras to count and monitor populations of endangered and threatened species and degradation and fragmentation of their habitats.
Figure 9.8
The fragmentation of landscapes reduces biodiversity by eliminating or degrading grassland and forest wildlife habitats and degrading ecosystem services.
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9.3bBeneficial and Harmful Nonnative Species
After habitat loss and degradation, the spread of harmful invasive species is the second largest cause of extinctions and loss of the ecosystem services. The introduction of many nonnative species to the United States has been beneficial. According to a study by ecologist David Pimentel, nonnative species such as corn, wheat, rice, and other food crops, as well as some species of cattle, poultry, and other livestock, provide more than 98% of the U.S. food supply. Similarly, nonnative tree species are grown in about 85% of the world’s tree plantations. Other deliberately introduced species have helped control pests. In the 1600s, English settlers brought highly beneficial European honeybees (Core Case Study) to North America to provide honey. Today, they pollinate one-third of the crops grown in the United States.
A problem can occur when an introduced species does not face the natural predators, competitors, parasites, viruses, bacteria, or fungi that controlled its populations in its native habitat. This can allow some nonnative species to outcompete populations of many native species for food, disrupt ecosystem services, transmit new diseases, and lead to economic losses. Such nonnative species are viewed as harmful invasive species. The spread of such species into ecosystems is the second largest cause of extinctions and loss of ecosystem services. Invasive species rarely cause the global extinction of other species, but they can cause population declines and local and regional extinctions of some native species.
Connections
Giant Snails and Meningitis
In 1988, the giant East African land snail was imported to Brazil from East Africa as a cheap substitute for conventional escargot (snails), used as a source of food. It is the world’s largest land snail, growing to the size of a human fist, and can feed on at least 500 different types of plants. When export prices for escargot fell, breeders dumped the imported snails into forests and other natural systems. Since then, they have spread widely around the world, devouring many native plants and food crops such as lettuce. They also can carry rat lungworm, a parasite that burrows into the human brain and causes potentially lethal meningitis.
Figure 9.9 shows some of the 7,100 or more invasive species that, after being deliberately or accidentally introduced into the United States, have caused ecological and economic harm. According to the U.S. Fish and Wildlife Service (USFWS), about 42% of the species listed as endangered or threatened in the United States and 95% of those in the U.S. state of Hawaii are at risk mainly because of threats from invasive species.
Figure 9.9
Some of the estimated 7,100 harmful invasive species that have been deliberately or accidentally introduced into the United States.
$162 Million
Estimated hourly global cost of invasive species
According to Achim Steiner, head of the UN Environment Program (UNEP), and environmental scientist David Pimentel, invasive species cause $1.4 trillion a year in economic and ecological damages, globally—an average of $2.7 million a minute. Some species that became invasive species were deliberately introduced into ecosystems (see the two Case Studies that follow).
Case Study
The Kudzu Vine and Kudzu Bugs
Some invasive species, such as kudzu vine (Figure 9.9), have been deliberately introduced into ecosystems. In the 1930s, this plant was imported from Japan and planted in the southeastern United States in an effort to control soil erosion.
Kudzu does control erosion, but it grows so rapidly that it engulfs hillsides, gardens, trees, stream banks, cars, buildings (Figure 9.10), and anything else in its path. Dig it up or burn it, and it still keeps spreading. It can grow in sunlight or shade and is very difficult to kill, even with herbicides that can contaminate water supplies. Scientists have found a common fungus that can kill kudzu within a few hours, but they need to investigate any harmful side effects it may have.
Figure 9.10
Abandoned building covered with kudzu.
Luke ferguson/ Shutterstock.com
Nicknamed “the vine that ate the South,” kudzu has spread throughout much of the southeastern United States. As the climate gets warmer, it could spread to the north.
Kudzu is considered a menace in the United States. However, for thousands of years Asians have used a powdered form of kudzu in herbal remedies to treat a range of ailments such as fever, inflammation, flu, dysentery, hangovers, and the effects of insect and snakebites.
Almost every part of the kudzu plant is edible, making it an inexpensive and readily available source of nutrition. Because it can grow rapidly where other plants cannot and is drought tolerant, it has helped people survive droughts and famines and restore severely degraded land.
Because ingesting small amounts of kudzu powder can lessen one’s desire for alcohol, it can be used to reduce alcoholism and binge drinking. Although kudzu can engulf and kill trees, it might eventually help to save some of them. Researchers at the Georgia Institute of Technology have found that kudzu could replace trees as a source of fiber for making paper. It is also being evaluated as a raw material for producing biofuel.
The brown, pea-sized Kudzu bug is another invasive species that was imported into the United States from Japan. It breeds in and feeds on patches of kudzu, and it can help to reduce the spread of the vine. However, it spreads even more rapidly than the kudzu vine. It also feeds on soybeans and thus could pose a major threat to soy crops.
Some pesticides can kill this bug, but might end up boosting their numbers by promoting genetic resistance to the pesticides. Researchers hope to change this bug through genetic engineering in such a way that it will stop eating soybeans. They are also evaluating the use of a wasp whose larvae attack kudzu bug embryos. However, so far, scientists see no way to eradicate this rapidly spreading invader species.
Case Study
Wild Boar Invasions
The wild boar (Figure 9.11, also known as wild hog or feral pig) is widely distributed over the earth’s land surface. Humans have introduced different versions of this species to numerous countries so that they can be hunted for sport and as a source of game meat.
Figure 9.11
Wild boar.
In the early 1900s, the Eurasian wild boar was introduced to the U.S. states of New York and North Carolina and kept in privately owned fenced hunting reserves. Some escaped from the reserves and others were moved to new areas and released into the wild for hunting. Wild boars have multiplied rapidly and have established populations in at least 36 states. In order, the three states with the most wild boars are Texas (with an estimated 3 million), Florida, and California.
Wild boars have many of the ideal qualities for a successful and destructive invasive species. They are big, strong, fast, intelligent, hard to kill or trap, and vicious when trapped. As adults, they typically weigh around 90 kilograms (200 pounds), run up to 40 kilometers per hour (25 miles per hour), jump as high as 0.9 meters (3 feet), and climb out of traps with walls as high as 1.8 meters (6 feet). In 2004, a legendary wild boar known as Hogzilla was shot. It was about 2.4 meters (8 feet) long, weighed about 360 kilograms (800 pounds), and had sharp tusks nearly 46 centimeters (18 inches) long.
Wild boars prefer forests but can live almost anywhere. They prefer plants and roots but can eat pretty much anything, including quail, the eggs of endangered sea turtles, and baby lambs, goats, calves, and deer. They come out at night to forage for food.
They use their long, plow-like snouts and strong necks to dig up land to a depth of 0.9 meters (3 feet), upturning large rocks as they go. They devour crops and uproot pastures, lawns, and forest floors. This causes soil erosion that muddies streams and destroys habitats for many animals, including ground-nesting birds, voles, and salamanders. By destroying native vegetation, boars can alter forest food webs and open the door to invasive plant species.
Wild boars breed at a high rate and do not have enough natural predators to control their dispersed and rapidly growing populations. They are among the most destructive invasive species in the United States and each year cause about $1.5 billion in damages and control costs.
Efforts to control wild boar populations include shooting and trapping. Researchers are also trying to develop poisons and birth control chemicals to use on the boars. After several decades of such efforts, the boars have been eliminated from several small islands. However, eliminating them in the continental United States and on other continents seems to be impossible.
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9.3cSome Accidentally Introduced Species Can Disrupt Ecosystems
Many unwanted nonnative invaders arrive from other continents as stowaways on aircraft, in the ballast water of tankers and cargo ships, and as hitchhikers on imported products such as wooden packing crates. Cars and trucks can also spread the seeds of nonnative plant species embedded in their tire treads. Many tourists return home with living plants that can multiply and become invasive. Some of these plants might also contain insects that can invade new areas, multiply rapidly, and threaten crops.
In the 1930s, the extremely aggressive red fire ant (Figure 9.9) was accidentally introduced into the United States probably on shiploads of lumber or coffee imported from South America. These ants have no natural predators in the southern United States where they have spread rapidly by land and by water because they can float. They have also invaded other countries.
When these ants invade an area, they can displace up to 90% of native ant populations, which provide important ecosystem services such as enrichment of topsoil, dispersal of plant seeds, and control of pest species such as flies, bedbugs, and cockroaches. Step on a red fire ant mound and as many as 100,000 ants may swarm out of their nest to attack you with painful, burning stings. Fire ants have killed deer fawns, ground-nesting birds, baby sea turtles, newborn calves, pets, and at least 80 people who were allergic to their venom.
Widespread insecticide spraying in the 1950s and 1960s temporarily reduced red fire ant populations. However, the insecticides also reduced populations of many native ant species. Widespread insecticide use also promoted genetic resistance to the insecticides in red fire ants through natural selection. The introduction of a species of tiny parasitic fly has shown some success in controlling red fire ant populations, but more research is needed to understand the long-term impacts of this biological remedy.
Florida is the global capital for invasive species. Some of its many harmful invasive species include Burmese pythons, African pythons, and several species of boa constrictors, all of which have invaded the Florida Everglades. About 1 million of these snakes, imported from Africa and Asia, have been sold as pets.
The Burmese python (Figure 9.12) is an example of what can happen when nonnative species escape or are released into the wild and become invasive species. Large numbers of these snakes are imported from Asia for sale as pets. Some buyers, after learning that these reptiles do not make good pets, let them go in the wetlands of Florida’s Everglades.
Figure 9.12
Employees of the South Florida Water Management District hunted and captured this invasive Burmese python in the Florida Everglades.
Dan Callister/Alamy Stock photo
The Burmese python can live 20 to 25 years and grow as long as 5 meters (16 feet), weigh as much 77 kilograms (170 pounds), and be as big around as a telephone pole. They have huge appetites, seizing prey with their sharp teeth, wrapping around them, and squeezing them to death before feeding on them. They feed at night and eat a variety of birds and mammals such as rabbits, foxes, raccoons, and white-tailed deer. Occasionally the pythons eat other reptiles, including young American alligators—a keystone species in the Everglades ecosystem (see Chapter 4, Case Study). They have also been known to eat pet cats, dogs, small farm animals, and geese. Research indicates that predation by these snakes is altering the complex food webs and ecosystem services of the Everglades.
According to wildlife scientists, the Burmese python population in Florida’s wetlands cannot be controlled. They are hard to find and kill or capture and they reproduce rapidly. Trapping and moving the snakes from one area to another has not worked because they are able to return to the areas where they are captured. Another concern is that the Burmese python could spread to other swampy wetlands in the southern half of the United States.
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9.3dControlling Invasive Species
Invasive species are a serious ecological and economic threat, but the situation is not hopeless. A rule of thumb is that only 1 of every 100 species that invade an area is able to establish a self-sustaining population and reduce the biodiversity of the ecosystem it has invaded. In addition, scientists have found that some invaders end up increasing the biodiversity of the areas they have moved into by creating new habitats and niches for other species.
However, once a harmful nonnative species becomes established in an ecosystem, removing it is almost impossible. Americans pay more than $160 billion a year to eradicate or control an increasing number of invasive species—without much success. Thus, the best way to limit the harmful impacts of these organisms is to prevent them from being introduced into ecosystems.
Scientists suggest several ways to do this, including
· Greatly increasing research to identify the major characteristics of successful invaders, the types of ecosystems that are vulnerable to invaders, and the natural predators, parasites, bacteria, and viruses that could be used to control populations of established invaders.
· Increasing ground surveys and drone and satellite observations to track invasive plant and animal species, and developing better models for predicting how they spread and what harmful effects they could have.
· Identifying major harmful invader species and establishing international treaties banning their transfer from one country to another, as is now done for many endangered species, and increasing inspection of imported goods to enforce such bans.
· Educating the public about the effects of releasing exotic plants and pets into the environment near where they live.
Figure 9.13 shows some things you can do to help prevent or slow the spread of harmful invasive species.
Figure 9.13
Individuals matter: Some ways to prevent or slow the spread of harmful invasive species.
Critical Thinking:
1. Which two of these actions do you think are the most important ones to take? Why? Which of these actions do you plan to take?
$2.7 Million
Estimated global cost per minute of harm from invasive species.
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9.3ePopulation Growth, High Rates of Resource Use, Pollution, and Climate Change
Past and projected human population growth (see Figure 1.12) and rising rates of resource use per person have greatly expanded the human ecological footprint (see Figure 1.9). People have eliminated, degraded, and fragmented vast areas of wildlife habitat (Figures 9.7 and 9.8) as they have spread out over the planet, and they use resources at increasing rates. This has threatened and caused the extinction of many species.
Pollution of the air, water, and soil by human activities also threatens some species with extinction. According to the U.S. Fish and Wildlife Service (USFWS), each year pesticides kill about one-fifth of the European honeybee colonies that pollinate almost a third of all U.S. food crops (Core Case Study and Science Focus 9.2). The USFWS estimates that pesticides also kill more than 67 million birds and 6 to 14 million fish each year. They also threaten about 20% of the country’s endangered and threatened species.
Science Focus 9.2
Honeybee Losses: A Search for Causes
Over the past 50 years, the European honeybee population in the United States has been cut in half. Scientific research has found several possible reasons for this decline. They include parasites, viruses, pesticides, stress, and poor nutrition.
Parasites such as the varroa mite feed on the blood of adult honeybees and their larvae, weakening their immune systems and shortening their lives. Varroa mites that feed on bees’ body fluids have killed millions of honeybees since first appearing in the United States in 1987—probably among bees imported from South America.
Several viruses are known to affect the winter survival of European honeybees. One example is the tobacco ringspot virus, which can infect honeybees that feed on pollen containing the virus. The virus is thought to attack the bees’ nervous systems. The virus has also been detected in varroa mites, which may help spread the virus as they feed on honeybees.
As honeybees forage for nectar, they are exposed to a number of harmful insecticides sprayed on crops and can carry these chemicals back to the hives. Research, including a 2018 report from the European Food Safety Authority based on 588 recent studies, indicates that widely used insecticides called neonicotinoids may play a role in colony collapse disorder (CCD). Neonicotinoids can disrupt the nervous systems of bees and decrease their ability to find their way back to their hives. These chemicals can also disrupt the reproductive and immune systems of bees and make them vulnerable to the harmful effects of other threats. Makers of neonicotinoids dispute these findings.
A researcher at a U.S. Department of Agriculture (USDA) laboratory in North Carolina found more than 170 different pesticides in samples of bees, honeycomb wax, and stored pollen. Each pesticide exposes the bees to a harmless dose, but exposure to such a cocktail of pesticides can weaken bees’ immune systems and make them vulnerable to deadly parasites, viruses, and fungi.
Stress from being transported long distances around the United States (Figure 9.B) can also play a role. Overworking and overstressing honeybees by moving them around the country can weaken their immune systems and make them more vulnerable to death from parasites, viruses, fungi, and pesticides.
Figure 9.B
European honeybee hive boxes in an acacia orchard. Each year, commercial beekeepers rent and deliver several million hives by truck to farmers throughout the United States.
Another factor is diet. In natural ecosystems, honeybees gather nectar and pollen from a variety of flowering plants. However, industrial worker honeybees feed mostly on pollen or nectar from one crop or a small number of crops that may lack the nutrients they need. In winter, bees in hives where most of the honey has been removed for sale are often fed sugar or high fructose corn syrup that provide calories but not enough protein for good health. Recent research indicates that rising levels of in the atmosphere might play a role in declining honeybee populations by decreasing protein levels in pollinated plants. The bees then get lower levels of the protein from the plant nectar, which can reduce their reproductive success.
The growing consensus among bee researchers is that colony collapse disorder and the decline of bee populations occurs because of a combination of these factors. These annual bee deaths raise the costs for beekeepers and farmers who use their services and could put many of them out of business if the problem continues. This could lead to higher food prices.
Critical Thinking
1. Can you think of some ways in which commercial beekeepers could lessen one or more of the threats described here? Explain.
During the 1950s and 1960s, populations of fish-eating birds such as ospreys, brown pelicans, and bald eagles plummeted because of the widespread use of a pesticide called DDT. The concentration of a chemical derived from the DDT remained in the environment and built up in the fatty tissues of organisms—a process called bioaccumulation (Figure 9.14). Then, as the chemical moved up through food chains and webs, it became successively more concentrated in the fatty tissues of higher-level organisms—a process called biomagnification (Figure 8.12). In some top predator birds, this decreased their ability to produce calcium in the shells of the eggs they laid, which made the eggshells so thin that they cracked before hatching and reduced the ability of the species to reproduce successfully.
Figure 9.14
Bioaccumulation and biomagnification: DDT is a fat-soluble chemical that can accumulate in the fatty tissues of animals. In a food chain or food web, the accumulated DDT is biologically magnified in the bodies of animals at each higher trophic level, as it was in the case of a food chain in the U.S. state of New York, illustrated here.
Critical Thinking:
1. How does this effect demonstrate the value of pollution prevention?
Populations of other predatory birds also declined sharply. They included the prairie falcon, sparrow hawk, and peregrine falcon, which helped control populations of rabbits, ground squirrels, and other crop eaters. Since the U.S. ban of DDT in 1972, most of these bird species have made a comeback—an example of the effectiveness of pollution prevention. For example, the population of bald eagles in North America went from 500 in 1967 to 70,000 in 2018, and the bald eagle was removed from the endangered species list in 2007.
According Conservation International, habitat loss and disruption of food webs associated with projected climate change could drive one-fifth to one-half of all known land animals and plants to extinction by the end of this century and accelerate the human-caused sixth mass extinction with a major loss of biodiversity and ecosystem services.
For example, scientific studies indicate that the polar bear is threatened because higher temperatures are melting sea ice in its Arctic habitat. Shrinkage of this floating ice makes it harder for polar bears to find seals, their favorite prey (Figure 9.15).
Figure 9.15
On floating ice in the Arctic sea, this polar bear has killed a bearded seal, one of its major sources of food.
Critical Thinking:
1. Do you think it matters that the polar bear may become extinct in the wild during this century primarily because of human activities? Explain.
Vladimir Seliverstov/ Dreamstime.com
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9.3fKilling, Capturing, and Selling Wild Species
Some protected animals are illegally killed (poached) for their valuable parts or are captured and sold live to collectors. According to World Wildlife Fund (WWF), the global wildlife trade is worth an estimated $19 billion a year. Organized crime has moved into illegal smuggling of parts of wildlife species and live members of species because of the huge profits involved. Live animals and their parts can sell from tens of thousands of dollars to as much as $500,000 on the black market. At least two-thirds of all live animals illegally smuggled around the world die in transit. Few smugglers are caught or punished.
It is highly profitable for poachers and organized crime to capture and sell highly endangered eastern mountain gorillas (of which there are about 700 left in the wild) and threatened giant pandas (1,864 left in the wild in China as of 2017) for their valuable pelts.
Four of the five rhino species, including the northern white rhino, are critically endangered, mostly because so many have been illegally killed for their valuable horns (Figure 9.16). In Asia, a rhino horn is worth about $9,000 per pound. A rhino’s horn is composed of keratin, the same protein that makes up your fingernails. Powdered rhino horn has long been used in traditional medicines for a variety of ailments and as an alleged aphrodisiac in many Asian countries including China, India, and Vietnam even though there is no verifiable evidence for such claims.
Figure 9.16
A poacher in South Africa killed this critically endangered northern white rhinoceros for its two horns. This species is now extinct in the wild.
Question:
1. What would you say if you could talk to the poacher who killed this animal?
Avalon/Photoshot License/Alamy Stock Photo
The illegal killing of elephants, especially African savanna elephants (see Figure 7.1), for their valuable ivory tusks has increased in recent years, despite an international ban on the trade of ivory. An adult male elephant’s two tusks can be worth $375,000 on the black market in China, which has the largest market for illegal ivory, followed by the United States. Elephants are being killed at a rate of 30,000 a year, according to WildAid.
Connections
Drones, Elephants, and Poachers
Researchers are using small drones with cameras connected to smart phones to track and monitor wildlife species such as endangered elephants and rhinos in Africa, tigers in Nepal, and orangutans in Sumatra. Drones with infrared cameras can find illegal poachers at night, expose their locations to wildlife rangers, and deter them by using bright strobe lights.
Since 1900, the overall number of the world’s wild tigers (see chapter opening photo) has declined by 99%, mostly because of a 90% loss of habitat (Figure 9.7), caused primarily by rapid human population growth, and poaching. About 70% of the world’s remaining 3,890 wild tigers are in India, which is doing more than other countries to protect them by establishing tiger reserves and working hard to protect the tigers in such reserves from poaching (Figure 9.17).
Figure 9.17
India has done more than any country to protect its remaining highly endangered tiger population. These poachers were caught while trying to sell a tiger skin in Madhya Pradesh State, India.
Steve Winter/National Geographic Image Collection
The Indian, or Bengal, tiger is at risk because a coat made from its fur can sell for as much as $100,000 in Tokyo. The bones and penis of a single tiger can fetch tens of thousands of dollars in China, the world’s biggest market for such illegal items. According to the World Wildlife Fund (WWF), without emergency action to curtail poaching and preserve tiger habitat, few if any tigers, including the Sumatran tiger (Figure 9.3d), will be left in the wild within a few years. During the past 100 years, the number of cheetahs—the world’s fastest land animal—has dropped about 100,000 to 7,100 mainly because of habitat loss and poachers killing them for their coats.
In India, conservation scientist and National Geographic Explorer Krithi Karanth is studying conflicts between the rapidly growing number of humans and the declining populations of wildlife such as tigers and Asian elephants. As wildlife habitats shrink, animals often damage farmers’ livestock and crops while trying to find food. Karanth has visited more than 10,000 households across 3,000 villages in India, and has enlisted 500 “citizen scientists” to help her interview villagers and collect data. Her goals are to document the disappearance of wildlife and the conflicts between humans and wildlife, and to find effective ways to reduce such conflicts.
Critical Thinking
1. Would it matter to you if all of the world’s wild tigers were to disappear? Why or why not? List two steps you could take to help protect the world’s remaining wild tigers from extinction.
Around the globe, the legal and illegal trade in wild species for use as pets is a huge and very profitable business. However, many owners of exotic wild pets do not know that, for every live animal captured and sold in the legal and illegal pet market, many others are killed or die in transit. According to the International Union for Conservation of Nature (IUCN), more than 60 bird species, mostly parrots (Figure 9.6), are endangered or threatened because of the wild bird trade (see Case Study that follows and Individuals Matter 9.1). In response, the United States passed the Wild Bird Conservation Act in 1992, making it illegal to import parrots into the United States. Any parrot purchased today in the United States must be from a domestic breeder, but some parrots are still illegally smuggled and sold in the Unites States.
Case Study
A Disturbing Message from the Birds
Approximately 70% of the world’s 10,000 or more known bird species are declining in numbers, and much of this decline is related to human activities, summarized by HIPPCO. According to the IUCN Red List of Endangered Species, roughly one of every eight (13%) of all bird species is threatened with extinction, mostly by habitat loss, degradation, and fragmentation (the H in HIPPCO)—primarily in tropical forests.
According to a State of the Birds study, more than one-third (37%) of the 1,150 bird species in North America are endangered (Figure 9.3b and c), threatened, or in decline, mostly because of habitat loss and degradation and invasive species (Individuals Matter 9.1). About one-third of all endangered and threatened bird species in the United States live in Hawaii.
Sharp declines in bird populations have occurred among songbird species that migrate long distances. These birds nest deep in North American woods in the summer and spend their winters in Central or South America or on the Caribbean Islands. Research indicates that the primary causes of these population declines are habitat loss and fragmentation of the birds’ breeding habitats in North America and Central and South America.
Population growth, the first P in HIPPCO, also threatens some bird species, as more people spread out over the landscape each year and increase their use of timber, food, and other resources, which results in destruction or disturbance of bird habitats. According to bird expert Daniel Klem, Jr., about 600 million birds die each year from collisions with windows in the United States and Canada. Pollution, the second P in HIPPCO also threatens birds. Countless birds are exposed to oil spills, insecticides, and herbicides. Research led by Leanne M. Flair found that persistent chemicals known as polychlorinated biphenyls (PCBs) may be hindering the ability of some common migratory songbirds to migrate, thereby playing a role in their decline.
Learning from Nature
While millions of birds collide with glass windows, birds in flight avoid spider webs because the webs reflect ultraviolet (UV) light. One company used this knowledge to create window glass incorporating web-like strands that reflect UV light without affecting the clarity of the glass.
Another rapidly growing threat to birds is climate change, the C in HIPPCO. A study done for the World Wildlife Fund (WWF) found that the effects of climate change, such as heat waves and flooding, are causing declines of some bird populations in every part of the globe. Such losses are expected to increase sharply during this century.
Overexploitation (the O in HIPPCO) is also a major threat to bird populations. Fifty-two of the world’s 388 parrot species are threatened, partly because so many parrots are captured for sale as pets, often illegally and usually to buyers in Europe and the United States. Collectors of exotic birds will pay thousands of dollars for an endangered hyacinth macaw (Figure 9.6) smuggled out of Brazil. However, during its lifetime, a single hyacinth macaw left in the wild could attract an estimated $165,000 in ecotourism revenues.
Biodiversity scientists (Individuals Matter 9.2) view this decline of bird species with alarm. One reason is that birds are excellent indicator species because they live in every climate and biome, respond quickly to environmental changes in their habitats, and are relatively easy to track and count. To these scientists, the decline of many bird species indicates widespread environmental degradation.
Individuals Matter 9.1
Juliana Machado Ferreira: Conservation Biologist and National Geographic Explorer
REBECCA DROBIS/National Geographic Image Collection
Every year, poachers illegally remove many millions of wild animals from their natural habitats in Brazil. Some of these animals stay in Brazil and others end up in the United States, Europe, and other parts of the world. Juliana Machado Ferreira is a conservation biologist with a PhD in genetics who fights this illegal removal of wildlife in her native country of Brazil.
She founded Freeland Brasil to help combat this highly profitable illegal trade. Many people in Brazil keep parrots, macaws, songbirds, monkeys, and other wild animals in their homes as pets and believe that it is a harmless cultural tradition. Her organization educates the public about the harmful ecological effects of removing birds and other species from the wild for the amusement of people who take them.
Ferreira has used her knowledge of genetics to develop molecular markers that can help identify the origins of illegal birds seized by police so that the birds can be returned to the areas where they lived. Ferreira is also trying to get the Brazilian government to pass and enforce strict laws against illegal wildlife trafficking. One of Freeland Brasil’s key projects is to establish a Molecular Biology Laboratory to help law enforcement agencies fight wildlife trafficking by using DNA tests to identify animals illegally taken from the wild.
In 2014, she was selected as a National Geographic Explorer. When asked what people can do to help save wild species she says: “Do not regard wild animals as pets.”
Individuals Matter 9.2
Çağan Hakkı Sekercioğlu: Protector of Birds and National Geographic Explorer
Rebecca Hale/National Geographic Image Collection
Çağan Sekercioğlu, assistant professor in the University of Utah Department of Biology, is a bird expert, a tropical biologist, an accomplished wildlife photographer, and a National Geographic Explorer. He has seen over 64% of the planet’s known bird species in 75 countries, developed a global database on bird ecology, and become an expert on the causes and consequences of bird extinctions around the world.
Sekercioğlu founded KuzeyDoğa. It is an award-winning ecological research and community-based conservation organization devoted to conserving and protecting the wildlife of northeastern Turkey. He also developed Turkey’s first protected wildlife corridor, which would stretch across the eastern half of the country, according to his plan. In 2011, he was named Turkey’s Scientist of the Year.
Based on his extensive research Sekercioğlu estimates that the percentage of the world’s known bird species that are endangered could approximately double from 13% today to 25% by the end of this century. He says. “I don't see conservation as people versus nature, I see it as a collaboration.”
Buyers of wild animals might also be unaware that some imported exotic animals carry diseases such as Hantavirus, Ebola virus, Asian bird flu, herpes B virus (carried by most adult macaques), and salmonella (from pets such as hamsters, turtles, and iguanas). These diseases can spread from pets to their owners and then to other people.
Other wild species whose populations are depleted because of the pet and collector trade include many amphibians (see Chapter 4 Core Case Study), reptiles, exotic butterflies and other insects, and tropical fishes taken mostly from the coral reefs of Indonesia and the Philippines. Some divers catch tropical fish by using plastic squeeze bottles of poisonous cyanide to stun them. For each fish caught alive, many more die and the cyanide solution kills the polyps, the tiny animals that create coral reefs. Some exotic plants, especially orchids and cacti (see Figure 7.15, center), are endangered because they are removed, and sold, often illegally, to collectors for thousands of dollars to decorate houses, offices, and landscapes.
Connections
African Vultures and Poachers
Detritus feeders such as vultures circle above animals such as elephants and rhinos that have been killed by poachers for their valuable ivory tusks and horns. This can help wildlife protection rangers in Africa locate poachers. To prevent this, poachers in parts of Africa have been killing thousands of vultures by poisoning the carcasses of dead elephants and rhinos. This is endangering some vulture species and preventing them from playing their important role in the chemical cycling of nutrients needed by plants.
9.3gRising Demand for Bushmeat Threatens Some African Species
For centuries, indigenous people in much of West and Central Africa have sustainably hunted wildlife for bushmeat as a source of food. In the last four decades, bushmeat hunting in some areas has skyrocketed. Some hunters provide the bushmeat as a food source for rapidly growing populations. Others make a living by supplying restaurants in major cities with exotic meats from gorillas (Figure 9.18) and other species. Logging roads in once-inaccessible forests have made hunting these animals much easier. As a result, some forests in areas such as Africa’s Congo basin are being stripped of many of their antelopes (the most commonly hunted bushmeat animal), monkeys, apes, elephants, hippos, and other wild animals.
Figure 9.18
Bushmeat such as this severed head of an endangered lowland gorilla in the Congo is consumed as a source of protein by local people in parts of West and Central Africa. It is also sold in national and international marketplaces and served in some restaurants, where wealthy patrons regard gorilla meat as a source of status and power.
Critical Thinking:
1. How, if at all, is this different from killing a cow for food?
Avalon/Photoshot License/Alamy Stock Photo
Bushmeat hunting has driven at least one species—Miss Waldron’s red colobus monkey—to extinction. It is also a factor in the reduction of some populations of orangutans (Figure 9.4), gorillas, chimpanzees, elephants, and hippopotamuses. Another problem is that butchering and eating some forms of bushmeat has helped to spread fatal diseases such as HIV/AIDS and the Ebola virus from wild animals to humans.
The U.S. Agency for International Development (USAID) is trying to reduce unsustainable hunting for bushmeat in some areas of Africa by introducing alternative sources of food, including farmed fish. They are also showing villagers how to breed large rodents such as cane rats as a source of protein.
9.4Sustaining Wild Species and Ecosystem Services
· LO 9.4AExplain how the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) has helped reduce the international trade of many threatened species.
· LO 9.4BExplain why the Convention on Biological Diversity (CBD) is a landmark in international law.
· LO 9.4CList four reasons why most biologists view the Endangered Species Act (ESA) as one of the world’s most successful environmental laws.
· LO 9.4DDescribe an example of a wildlife refuge and how it has protected a species.
· LO 9.4EList four limitations of seed banks, botanical gardens, zoos, aquariums, and wildlife farms in terms of protecting wild species.
· LO 9.4FState the Precautionary Principle and explain how it applies to reducing species extinction and sustaining ecosystem services.
· LO 9.4GList five difficult issues involved in the protection of wild species.
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9.4aTreaties and Laws
Some governments are working to reduce species extinction and sustain ecosystem services (see the Case Study that follows) by establishing and enforcing international treaties and conventions, as well as national environmental laws.
Case Study
The U.S. Endangered Species Act
The United States enacted the Endangered Species Act (ESA) in 1973 and has amended it several times. The act is designed to identify and protect endangered species in the United States and abroad. The ESA creates recovery programs for the species it lists. The goal is to help the populations of protected species recover to levels where legal protection is no longer needed. When that happens, a species can be taken off the list, or delisted.
Under the ESA, the National Marine Fisheries Service (NMFS) is responsible for identifying and listing endangered and threatened ocean species, while the U.S. Fish and Wildlife Service (USFWS) identifies and lists all other endangered and threatened species. Any decision by either agency to list or delist a species must be based on biological factors alone, without consideration of economic or political factors, although there are continuing political efforts to do away with this requirement. However, the two agencies can use economic factors in deciding whether and how to protect endangered habitat and in developing recovery plans for listed species.
The ESA also forbids federal agencies (except the U.S. Department of Defense) to carry out, fund, or authorize projects that would jeopardize any endangered or threatened species or destroy or modify its critical habitat. The law also makes it illegal for Americans to sell or buy any product made from an endangered or threatened species or to hunt, kill, collect, or injure such species in the United States.
For offenses committed on private lands, fines as high as $100,000 and a year in prison can be imposed to ensure protection of the habitats of endangered species. Although this provision has rarely been used, it has been controversial because at least 90% of the listed species spend part of their life cycles on private lands. Since 1982, the ESA has been amended to give private landowners various economic incentives to save endangered species living on their lands.
Between 1973 and December 2018, the number of U.S. species on the official endangered and threatened species lists increased from 78 to 1,661, with 1,164 (70%) having active recovery plans. According to a study by the Nature Conservancy, 33% of the country’s species are at risk of extinction, and 15% of all species are at high risk—far more than the current number listed.
According to a study by the CBD, 90% of the ESA-protected species are recovering at the rate projected in their recovery plans and 99% of the listed species have been saved from extinction. In addition, since 2003, the cumulative area designated as critical habitats increased almost tenfold. Successful recovery plans include those for the American alligator (Chapter 4 Case Study), gray wolf, peregrine falcon, bald eagle (Figure 9.19), humpback whale, and brown pelican.
Figure 9.19
The American bald eagle has been removed from the U.S. endangered species list. This eagle is about to catch a fish with its powerful talons.
Since 1995, there have been numerous efforts to weaken the ESA and to reduce its meager annual budget. Opponents of the act contend that it puts the rights and welfare of endangered plants and animals above those of people. Some critics would do away with this act entirely. They call it an expensive failure because, by 2018, only 52 species had recovered enough to be removed from the endangered list.
Most biologists view the act as one of the world’s most successful environmental laws, for several reasons. First, species are listed only when they are in serious danger of extinction. ESA supporters argue that this is similar to a hospital emergency department set up to take only the most desperate cases, often with little hope for recovery. Such a facility could not be expected to save all or even most of its patients.
Second, according to federal data, the conditions of more than half of the listed species are stable or improving, 90% are recovering at rates specified by their recovery plans, and 99% of the protected species are still surviving. A hospital emergency department having similar results would be considered an astounding success story.
Third, it takes many decades for a species to reach the point where it is in danger of extinction. Thus, it takes many decades to bring a species back to the point where it can be removed from the endangered list.
Fourth, the small federal budget for protecting endangered species has been flat or declining in recent years. To ESA supporters, it is amazing that the federal agencies responsible for enforcing the act have managed to stabilize or improve the conditions of 99% of the listed species on such a small budget.
A national poll conducted by the CBD and Public Policy Polling found that two out of three Americans polled want the ESA strengthened or left alone. However, some members of Congress and the executive branches have worked to weaken the law, essentially since it was passed in 1973.
In 2018, the Interior Department–under pressure from oil and gas companies, ranchers in western states, farmers, landowners, and real estate developers—proposed several major changes in the ESA:
· Allow economic factors based on cost-benefit analysis (explained in Chapter 23) to be used in listing and delisting species.
· Downgrade protections for threatened species and judge each threatened species on a case-by-case basis.
· Make it harder for a species to be listed as threatened
· Decrease or eliminate the role that climate change can play in judging whether a species is in danger of extinction.
A U.S. National Academy of Sciences study recommended three major changes in the law to make it more scientifically sound and effective:
· Greatly increase funding for implementing the act.
· Develop recovery plans more quickly.
· When a species is first listed, establish the core of its habitat as critical for its survival and give that area maximum protection.
· Provide more technical and financial assistance to landowners who want to help protect endangered species on their property.
Most biologists and wildlife conservationists believe that the United States also needs a new law that emphasizes protecting and sustaining biological diversity and ecosystem services rather than focusing mostly on saving individual species. (We examine this idea further in Chapter 10.)
One of the most far reaching of international agreements is the 1975 Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). This treaty, signed by 183 countries, bans the hunting, capturing, and selling of threatened or endangered species. It lists 1,003 species that are in danger of extinction and that cannot be commercially traded as live specimens or for their parts or products. It restricts the international trade of roughly 5,800 animal species and 30,000 plant species that are at risk of becoming threatened.
CITES has helped reduce the international trade of many threatened animals, including elephants, crocodiles, cheetahs, and chimpanzees. The treaty has also raised public awareness about the illegal trade of wildlife and poaching.
However, CITES is limited because enforcement varies from country to country and convicted violators often pay only small fines. Member countries can also exempt themselves from protecting any listed species. In addition, much of the highly profitable illegal trade in wildlife and wildlife products goes on in countries that have not signed the treaty.
Another important treaty is the Convention on Biological Diversity (CBD), ratified or accepted by 196 countries. It legally commits participating governments to reducing the global rate of biodiversity loss and to sharing the benefits from use of the world’s genetic resources. It also aims to prevent or control the spread of harmful invasive species.
This convention is a landmark in international law because it focuses on ecosystems rather than on individual species. However, implementation has been slow because some key countries (including the United States, as of 2018) have not ratified it. The law also lacks severe penalties or other enforcement mechanisms.
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9.4bWildlife Refuges and Other Protected Areas
In 1903, President Theodore Roosevelt (Figure 1.17) established the first U.S. federal wildlife refuge at Pelican Island, Florida, to help protect the brown pelican and other birds from extinction (Figure 9.20). In 2009, the brown pelican was removed from the U.S. Endangered Species list, thanks to Roosevelt’s early protection. By 2018, there were 556 refuges in the National Wildlife Refuge System. Each year, more than 53 million Americans visit these refuges to hunt, fish, hike, and watch birds and other wildlife.
Figure 9.20
The Pelican Island National Wildlife Refuge in Florida was America’s first National Wildlife Refuge.
George Gentry/U.S. Fish and Wildlife Service; Inset: Chuck Wagner/ Shutterstock.com
More than three-fourths of the refuges serve as wetland sanctuaries that are vital for protecting migratory waterfowl. At least one-fourth of all U.S. endangered and threatened species have habitats in the refuge system, and some refuges have been set aside specifically for certain endangered species. Such areas have helped Florida’s key deer, the brown pelican, and the trumpeter swan to recover.
Despite their benefits, activities that are harmful to wildlife, such as mining, oil drilling, and use of off-road vehicles, take place in nearly 60% of the nation’s wildlife refuges, according to a General Accounting Office study. Biodiversity researchers urge the U.S. government to set aside more refuges and increase the long-underfunded budget for the refuge system.
Elsewhere in the world, reserves and refuges have also been successful, and public awareness has played a big role in their success. Dereck and Beverly Joubert are National Geographic Explorers and award-winning filmmakers who, for more than 30 years, have been studying, filming, and writing about threatened lions, leopards, cheetahs, and other big-cat predators in Africa. They hope to heighten public awareness of the plight of these animals. Their efforts have contributed to the establishment of protected reserves for big cats and other African wildlife in Botswana, Tanzania, and Kenya.
National Geographic is funding several other efforts to preserve wild species, including that of Maia Raymundo, who is studying a critically endangered species of fruit bat in the Philippines, threatened by hunting and high rates of deforestation. Conservation biologists are alarmed about the steep decline of many bat species, which provide vital pollination and insect control services. Some populations of these fruit bats have decreased by as much as 98% in large areas of their range. Raymundo’s goal is to identify and protect critical habitat areas for the endangered bats.
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9.4cSeed Banks and Botanical Gardens
Some species cannot be preserved in seed banks. Seed banks also vary in quality, are expensive to operate, and are difficult to protect against destruction by fire or other mishaps. The Svalbard Global Seed Vault, an underground facility on a remote island in the Arctic has the capacity for 4.5 million samples of the world’s plant species. It was designed to withstand natural and human-caused disasters. However, it is threatened by flooding that could occur because a warmer climate is thawing out the surrounding permafrost that keeps the facility cold.
The world’s 1,600 botanical gardens contain living plants that represent almost one-third of the world’s known plant species. However, they contain only about 3% of the world’s rare and threatened plant species and have limited space and funding to preserve most of those species. Similarly, an arboretum is land set aside for protecting, studying, and displaying various species of trees and shrubs. There are hundreds of arboreta around the world.
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9.4dZoos, Aquariums, and Wildlife Farms
Zoos, aquariums, game parks, and animal research centers preserve some individuals of critically endangered animal species. The long-term goal is to reintroduce the species into protected wild habitats.
Two techniques for preserving endangered terrestrial species are egg pulling and captive breeding. Egg pulling involves collecting wild eggs laid by critically endangered bird species and then hatching them in zoos or research centers. In captive breeding, some or all of the wild individuals of a critically endangered species are collected for breeding in captivity, with the aim of reintroducing the offspring into the wild. Captive breeding has been used to save the peregrine falcon and the California condor (Figure 9.3b).
Several other techniques are used to increase the populations of captive species. They include artificial insemination, insertion of semen into a female’s reproductive system, embryo transfer (the surgical implantation of eggs of one species into a surrogate mother of another species), and cross fostering (in which the young of a rare species are raised by parents of a similar species). Scientists also match individuals for mating by using DNA analysis along with computer databases that hold information on family lineages of endangered zoo animals—a computer dating service for zoo animals.
The ultimate goal of captive breeding programs is to build populations to a level where they can be reintroduced into the wild. Successes include the black-footed ferret, the golden lion tamarin (a highly endangered monkey species), the Arabian oryx, and the California condor (Figure 9.3b). However, most reintroductions fail because of a lack of suitable habitat, an inability of the individuals bred in captivity to survive in the wild, renewed overhunting or poaching, or pollution and other hazards in the environment.
One problem for captive breeding programs is that a captive population of an endangered species must typically number 100 to 500 individuals in order to avoid extinction resulting from accidents, diseases, or the loss of genetic diversity through inbreeding. Recent genetic research indicates that 10,000 or more individuals are needed for an endangered species to maintain its capacity for biological evolution. Zoos and research centers do not have the funding or space to house such large populations.
Public aquariums (Figure 9.21) that exhibit unusual and attractive species of fish and marine animals such as seals and dolphins help educate the public about the need to protect such species. Some carry out research on how to save endangered species. However, mostly because of limited funds, public aquariums have not served as effective gene banks for endangered marine species, especially marine mammals that need large volumes of water in which to live.
Figure 9.21
The Monterey Bay Aquarium in Monterey, California (USA) with visitors viewing a kelp forest community.
photocritical/ Shutterstock.com
We can take pressure off some endangered or threatened species by raising individuals of these species on farms for commercial sale. In Florida, American alligators are raised on farms for their meat and hides. Butterfly farms established to raise and protect endangered species flourish in Papua New Guinea, where many butterfly species are threatened by development activities. These farms are also used to educate visitors about the need to protect butterfly species.
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9.4eThe Precautionary Principle
Biodiversity scientists call for us to take precautionary action to avoid hastening species extinction and disrupting essential ecosystem services. This approach is based on the precautionary principle : When substantial preliminary evidence indicates that an activity can harm human health or the environment, we should take precautionary measures to prevent or reduce such harm even if some of the cause-and-effect relationships have not been fully established scientifically. It is based on the commonsense idea behind many adages, including “Better safe than sorry” and “Look before you leap.”
Scientists use the precautionary principle to argue for both the preservation of species and protection of entire ecosystems and their ecosystem services. Implementing this principle puts the emphasis on preventing species extinction instead of waiting until a species is nearly extinct before taking emergency action that can be too late.
The precautionary principle is also used as a strategy for dealing with other challenges such as preventing exposure to harmful chemicals in the air we breathe, the water we drink, and the food we eat. We discuss the pros and cons of using this principle to prevent pollution in Chapter 17.
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9.4fProtecting Species and Ecosystem Services Raises Difficult Questions
Efforts to prevent the extinction of wild species and the accompanying losses of ecosystem services require the use of financial and human resources that are limited. This raises some challenging questions:
· Should we focus on protecting species or should we focus more on protecting ecosystems and the ecosystem services they provide?
· How do we allocate limited resources between these two priorities?
· How do we decide which species should get the most attention in our efforts to protect as many species as possible? For example, should we focus on protecting the most threatened species or on protecting keystone species?
· Protecting species that are appealing to humans, such as the giant panda, orangutans (Figure 9.4), and tigers, can increase public awareness of the need for wildlife conservation. Is this more important than focusing on the ecological importance of species when deciding which ones to protect?
· How do we determine which habitat areas are the most critical to protect?
Conservation biologists continually struggle to deal with these questions. Because of limited funds, they must decide which species will get priority. Figure 9.22 lists some guidelines you can follow to help protect species and increase your beneficial environmental impact.
Figure 9.22
Individuals matter: Ways you can help prevent the extinction of species.
Critical Thinking:
1. Which two of these actions do you believe are the most important ones to take? Why?
Big Ideas
· We are hastening the extinction of wild species and degrading the ecosystem services they provide by destroying and degrading natural habitats, introducing harmful invasive species, and increasing human population growth, pollution, climate change, and overexploitation.
· We should avoid causing or hastening the extinction of wild species because of the ecosystem and economic services they provide and because their existence should not depend primarily on their usefulness to us.
· We can work to prevent the extinction of species and to protect overall biodiversity and ecosystem services by establishing and enforcing environmental laws and treaties and by creating and protecting wildlife sanctuaries.
Tying It All TogetherHoneybees and Sustainability
Malwina Szweda/ Shutterstock.com
In this chapter, we learned about the human activities that are hastening the extinction of many species and about how we might curtail those activities. We learned that as many as half of the world’s known wild species could go extinct during this century, largely because of human activities that threaten many species and some of the vital ecosystem services they provide. For example, populations of honeybees, vital for pollinating crops that supply much of our food, have been declining for a variety of reasons ( Core Case Study ), many of them related to human activities. One of the key reasons for such problems is that most people are unaware of the highly valuable ecosystem and economic services provided by the earth’s species.
Acting to prevent the extinction of species from human activities implements two of the three scientific principles of sustainability. It preserves not only the earth’s biodiversity, but also the vital ecosystem services that sustain us, including chemical cycling. It also implements the ethical principle of sustainability that call for us to leave the earth in a condition that is as good as or better than what we inherited (see Inside Back Cover).
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Chapter Review
Critical Thinking
1. What are three aspects of your lifestyle that might directly or indirectly contribute to declines in European honeybee populations and the endangerment of other pollinator species (Core Case Study)?
2. Give your response to the following statement: “Eventually, all species become extinct. So, it does not really matter that the world’s remaining tiger species or a tropical forest plants are endangered mostly because of human activities.” Be honest about your reaction, and give arguments to support your position.
3. Do you accept the ethical position that each species has the right to survive without human interference, regardless of whether it serves any useful purpose for humans? Why or why not? Would you extend this right to the Anopheles mosquito, which transmits malaria, and to harmful infectious bacteria? Explain. If your answer is no, where would you draw the line?
4. Wildlife ecologist and environmental philosopher Aldo Leopold wrote this with respect to preventing the extinction of wild species: “To keep every cog and wheel is the first precaution of intelligent tinkering.” Explain how this statement relates to the material in this chapter.
5. What would you do if wild boar (Figure 9.11) invaded and tore up your yard or garden? Explain your reasoning behind your course of action. How might your actions affect other species or the ecosystem you are dealing with?
6. How do you think your daily habits might contribute directly or indirectly to the extinction of some bird species? What are three things that you think should be done to reduce the rate of extinction of bird species?
7. Which of the following statements best describes your feelings toward wildlife?
1. As long as it stays in its space, wildlife is okay.
2. As long as I do not need its space, wildlife is okay.
3. I have the right to use wildlife habitat to meet my own needs.
4. When you have seen one redwood tree, elephant, or some other form of wildlife, you have seen them all, so preserve a few of each species in a zoo or wildlife park and do not worry about protecting the rest.
5. All wildlife species should be protected in their current ranges.
8. How might your life change if human activities contribute to the projected extinction of 20–50% of the world’s identified species during this century? How might this sixth mass extinction affect the lives of any children or grandchildren you eventually might have?
Chapter Review
Doing Environmental Science
1. Identify examples of habitat destruction or degradation in the area in which you live or go to school. Try to determine and record any harmful effects that these activities have had on the populations of one wild plant and one animal species. (Name each of these species and describe how they have been affected.) Do some research on the Internet and/or in a school library on wildlife management plans, and then develop a management plan for restoring the habitats and species you have studied. Try to determine whether trade-offs are necessary with regard to the human activities you have observed, and account for these trade-offs in your management plan. Compare your plan with those of your classmates.
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Chapter Review
Data Analysis
Examine the following data released by the World Resources Institute and answer these questions:
|
Country |
Total Land Area in Square Kilometers (Square Miles) |
Protected Area as Percent of Total Land Area (2003) |
Total Number of Known Breeding Bird Species (1992–2002) |
Number of Threatened Breeding Bird Species (2002) |
Threatened Breeding Bird Species as Percent of Total Number of Known Breeding Bird Species |
|
Afghanistan |
647,668 (250,000) |
0.3 |
181 |
11 |
|
|
Cambodia |
181,088 (69,900) |
23.7 |
183 |
19 |
|
|
China |
9,599,445 (3,705,386) |
7.8 |
218 |
74 |
|
|
Costa Rica |
51,114 (19,730) |
23.4 |
279 |
13 |
|
|
Haiti |
27,756 (10,714) |
0.3 |
62 |
14 |
|
|
India |
3,288,570 (1,269,388) |
5.2 |
458 |
72 |
|
|
Rwanda |
26,344 (10,169) |
7.7 |
200 |
9 |
|
|
United States |
9,633,915 (3,718,691) |
15.8 |
508 |
55 |
|
Compiled by the authors using data from World Resources Institute, Earth Trends, Biodiversity and Protected Areas, Country Profiles.
1. Complete the table by filling in the last column. For example, to calculate this value for Costa Rica, divide the number of threatened breeding bird species by the total number of known breeding bird species and multiply the answer by 100 to get the percentage.
2. Arrange the countries from largest to smallest according to total land area. Does there appear to be any correlation between the size of country and the percentage of threatened breeding bird species? Explain your reasoning.
