{"id":1178,"date":"2021-07-07T15:13:08","date_gmt":"2021-07-07T15:13:08","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/suny-binghamton-envi101&envi201\/chapter\/__unknown__-3\/"},"modified":"2021-08-01T19:04:28","modified_gmt":"2021-08-01T19:04:28","slug":"chapter-25","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/suny-binghamton-envi101&envi201\/chapter\/chapter-25\/","title":{"raw":"Chapter 14 ~ The Biodiversity Crisis","rendered":"Chapter 14 ~ The Biodiversity Crisis"},"content":{"raw":"
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Key Concepts<\/h2>\r\n

After completing this chapter, you will be able to<\/p>\r\n\r\n

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  1. Outline how humans are causing the modern crisis of extinction and endangerment.<\/li>\r\n \t
  2. Give examples of species that have been made extinct through human activities.<\/span><\/li>\r\n \t
  3. Explain how a system of protected areas is essential to the preservation of biodiversity.<\/span><\/li>\r\n \t
  4. Outline the roles of governments, non-governmental organizations, scientists, and citizens in conserving species and other elements of biodiversity.<\/span><\/li>\r\n<\/ol>\r\n

    Introduction<\/h1>\r\n

    Earlier, we defined biodiversity as the total richness of biological variation and examined reasons why it is important (see Chapter 6). In this chapter, we examine the many threats to biodiversity that are associated with the human economy. The emphasis is on severe damage that is being caused, especially that associated with losses of species and of natural ecosystems.<\/p>\r\n

    Extinction refers to the loss of a species or another named biological entity (referred to as a taxon) over all of its range on Earth. Extirpation is a more local disappearance, with the taxon surviving elsewhere. Extinction represents an irretrievable loss of a unique portion of the biological richness of Earth, whereas it may be possible to re-establish an extirpated taxon from a surviving population.<\/p>\r\n

    Extinctions have always occurred as a result of natural influences. These include random catastrophes as well as the longer-term effects of environmental change, such as in climate or in biological factors such as disease or predation. In modern times, however, and even for the past 10-thousand years or so, almost all extinctions have been caused by anthropogenic influences, particularly by over-harvesting and the destruction of natural habitats. In fact, an enormous increase in the rate of extinctions has been one of the most important consequences of humans becoming the dominant species on Earth. Species are now disappearing so quickly that we refer to the phenomenon as an extinction crisis (or a biodiversity crisis).<\/p>\r\n

    Every species is unique, a fact that gives them great intrinsic value \u2013 this is a central tenet of the biocentric world view (see Chapter 1). Therefore, from an ethical perspective, any irretrievable loss of biodiversity is a shameful consequence of the ways that people are using their power to exploit other species and ecosystems. This is also a foolish way for humans to administer their global empowerment, because unique species are disappearing before they have been investigated for their potential usefulness in medicine or agriculture, and before we understand their importance as components of ecosystems. Human actions that result in extinctions can only be regarded as ecologically dangerous behavior.<\/p>\r\n

    In this chapter, we examine the modern biodiversity crisis \u2013 the reasons why it is happening, ways of repairing at least some of the damage already caused, and how to prevent further losses.<\/p>\r\n\r\n

    Natural Extinctions<\/h1>\r\n

    Life has existed on Earth for about 3.5 billion years. Almost all of the species that have lived during that period of time are now extinct, having disappeared \u201cnaturally\u201d for some reason or other. (The survivors are referred to as extant, or still living today.) In many cases, the extinct species could not adapt to changes that occurred in their environment, such as shifts in climate or increases in disease, predation, or competition with other species. Many species, however, disappeared during brief episodes of mass extinction, which may have been caused by unpredictable catastrophes, such as a meteorite hitting Earth.<\/p>\r\n

    The geological record clearly shows that many species and groups of organisms (such as genera, families, and phyla) have appeared and disappeared over time (see Chapter 7). For example, many phyla of invertebrate animals evolved relatively quickly during an evolutionary proliferation that occurred around the beginning of the Cambrian era, about 570 million years ago. Subsequently, most of those phyla and their many species became extinct. About 20 extinct phyla from that period were discovered in a renowned fossil deposit known as the Burgess Shale, located in Yoho National Park in southeastern British Columbia. In an evolutionary sense, each of those extinct phyla represented a novel \u201cexperiment\u201d in the form and function of invertebrate animals. We only know that these ancient creatures existed because their fragile body structures became fossilized under extraordinary geological circumstances (Gould, 1989).<\/p>\r\n

    The fossil record is replete with many other examples of ancient extinctions. However, the rate of extinction, and of the subsequent evolutionary radiation of new species, has not been uniform over time. The geological record clearly shows that relatively low and uniform rates of extinction have typically persisted for extremely long periods of time, but those tranquil eras were punctuated by five catastrophic events of mass extinction (Figure 14.1).<\/p>\r\n

    \"\"<\/p>\r\nFigure 14.1. Largest Mass Extinctions in Earth\u2019s History. Source: \u201c\u2019Big Five\u2019 mass extinctions in Earth\u2019s history\u201d<\/a> by OurWorldinData.org is licensed under CC BY-SA 3.0<\/a>.\r\n

    The most intense event occurred at the end of the Permian era, about 245 million years ago. This natural catastrophe resulted in the loss of about 54% of the existing families of marine animals, including 84% of the genera and 96% of the species (Erwin, 1990). Another mass extinction occurred at the end of the Cretaceous period, about 65 million years ago. This famous event involved the last of the dinosaurs and pterosaurs (flying reptiles), along with many other taxa, totaling perhaps three-quarters of the species living at the time. Many scientists believe that this crisis of paleobiodiversity was caused by a meteorite hitting the Earth, likely in the vicinity of the Yucatan peninsula of Mexico. Such a catastrophe would have caused a deadly tsunami, while also ejecting enormous quantities of dust into the atmosphere, likely resulting in a cooling of the climate that most species were unable to tolerate.<\/p>\r\n

    During the past several centuries, Earth\u2019s existing heritage of biodiversity has been buffeted by another mass extinction. This is an ongoing catastrophe, and it will certainly intensify into the foreseeable future. This ecological calamity is not a natural phenomenon. Rather, it is being caused by the influences and economic activities of modern humans.<\/p>\r\n\r\n

    Extinctions Caused by Humans<\/h1>\r\n

    Many kinds of human activities are causing species to become endangered or extinct. (A species is considered endangered if, because of a small population or loss of habitat, it has a high risk of becoming extirpated or extinct.) The most important cause is the destruction of natural ecosystems and their conversion into habitats that are unsuitable for the original species, a problem that is especially acute in tropical countries. Excessive harvesting of some species is also significant, as is damage caused by introduced predators, diseases, and competitors. Any of these stressors can cause populations to become increasingly small and fragmented, a circumstance that results in much greater risks of extirpation or extinction (Figure 14.2).<\/p>\r\n

    \"image\"<\/p>\r\n

    Figure 14.2. The Extinction Vortex. Extinction can be caused by various influences and activities of humans, such as habitat loss, excessive harvesting, and the introduction of alien diseases, predators, and competitors. As a result of these stressors, large and continuously distributed populations may fragment into small isolated units that are highly vulnerable to the deleterious effects of inbreeding, population instability, and random catastrophes. These can cause endangered populations to decline further and may ultimately result in extirpation or extinction. Conservation biologists refer to this accelerating spiral of endangerment as the extinction vortex.<\/p>\r\n

    Because of these anthropogenic influences, the past several centuries have witnessed huge increases in the global rate of extinction and in the number of species that are threatened with this catastrophe. Not surprisingly, our knowledge of recently extinct and endangered species is relatively complete for large and conspicuous species such as vertebrate animals, especially those that live in temperate and higher-latitude countries, where most biologists also live.<\/p>\r\n

    In fact, there have been at least 900 known extinctions, including ~800 animals and ~100 plants (many of these are distinct subspecies and varieties; IUCN, 2014). The losses include 85 species of mammals, 159 birds, 30 reptiles, 35 amphibians, and 80 fishes (Figure 14.3). All of these extinctions were caused by human influences. Much larger numbers of species are at grave risk of suffering extinction (1,317 species of mammals are at risk, as are 1,481 birds, 1,449 reptiles, 2,390 amphibians, and 3,040 fishes; Figure 14.4).<\/p>\r\n

    \"image\"<\/p>\r\nFigure 14.3. Number of Species That Have Gone Extinct Since 1500. Due to human activity, the rate of species loss is much higher today compared to background rates and rates from previous mass extinctions. Source: \u201cNumber of species that have gone extinct since 1500\u201d<\/a> by OurWorldinData.org is licensed under CC BY-SA 3.0<\/a>.\r\n

    \"image\"<\/p>\r\nFigure 14.4. Number of Species Threatened with Extinction. Due to human activity, the rate of species loss is much higher today compared to background rates and rates from previous mass extinctions. Source: \u201cNumber of species threatened with extinction\u201d<\/a> by OurWorldinData.org is licensed under CC BY-SA 3.0<\/a>.\r\n

    Unfortunately, we know much less about extinctions among less conspicuous groups of organisms. This is particularly true of the enormous diversity of relatively small, poorly known species that live in tropical ecosystems, especially in old-growth rainforest. Undoubtedly, huge numbers of tropical species, particularly plants and invertebrates, have become extinct during the past several centuries as their natural forest habitat was converted into agricultural and other land-uses. We can refer to these losses as \u201chidden extinctions\u201d because so few of the lost species had been discovered and named by taxonomists. Moreover, these hidden extinctions continue to occur rapidly, in fact at an accelerating rate, because their poorly explored tropical habitats are being destroyed so quickly.<\/p>\r\n

    In the following sections we will examine selected case studies of species that have been rendered extinct by humans and their activities.<\/p>\r\n\r\n

    Prehistoric Extinctions<\/h2>\r\n

    Many species are useful as \u201cresources\u201d that humans can harvest and use as a source of food, medicine, timber, fuel, or some other purpose. In many cases, the exploitation of these potentially renewable resources has been so insatiable that their \u201cmining\u201d has culminated in extinction. These once-valuable species now occur nowhere on Earth (Freedman, 1995).<\/p>\r\n

    We previously examined extinctions that were caused by prehistoric hunters as they over-hunted populations of large, naive animals in newly discovered lands (see Global Focus 11.2). In North America, it appears that paleohunters exterminated many species of large mammals soon after people discovered the continent by migrating across a Beringean land bridge more than 12 millennia ago, at the end of the most recent ice age. Known extinctions occurring around that time include 77 species of mammals, such as 10 species of horse, a giant ground sloth, four kinds of camels, two bison, the mastodon, several mammoths, and the sabre-toothed tiger. Other large animals became extinct when South America was colonized somewhat later.<\/p>\r\n

    The colonization of \u201cnew\u201d land masses by humans also caused prehistoric mass extinctions in other places. Australia and New Guinea were discovered about 50-thousand years ago. Soon after, many species of marsupials, large flightless birds, and tortoises became extinct, likely because of over-hunting.<\/p>\r\n

    New Zealand was colonized less than one-thousand years ago. Within two centuries, 30 large birds were extinct, among them a goose, a swan, and 26 species of large flightless birds known as moas. The extinctions proceeded as an anthropogenic wave that began in northern North Island, which was the initial point of colonization, to southern South Island. Many of the moas were herded by the hunters and their dogs to convenient butchering sites, where the great piles of bones were later used by early European farmers as a source of phosphate fertilizer.<\/p>\r\n

    In a similar fashion, the human colonization of Madagascar, about 1,500 years ago, resulted in the extinction of 14 species of lemurs, 6-12 flightless elephant birds, and various other big and edible animals. Other well-known prehistoric mass extinctions occurred on Hawaii, New Caledonia, Fiji, and the West Indies. In fact, this phenomenon likely occurred whenever a previously inhabited island was discovered and colonized.<\/p>\r\n

    The endemic (local) species that existed only on small islands are particularly vulnerable to extinction. The key reasons for this were:<\/p>\r\n\r\n