Conservation Biology and Global Change

honeyeater (Melipotes carolae), a species that had never been described before (Figure 56.1). In 2005, a team of American, Indonesian, and Australian biologists experienced many mo- 56 ments like this as they spent a month cataloging the living riches hidden in a remote mountain range in Indonesia. In addition to the honeyeater, they discovered dozens of new frog, butterfly, and plant species, including five new palms. Conservation To date, scientists have described and formally named about 1.8 million species of organisms. Some biologists think Biology and that about 10 million more species currently exist; others estimate the number to be as high as 100 million. Some of the Global Change greatest concentrations of species are found in the tropics. Unfortunately, tropical forests are being cleared at an alarm- ing rate to make room for and support a burgeoning human population. Rates of deforestation in Indonesia are among the highest in the world (Figure 56.2). What will become of the smoky honeyeater and other newly discovered species in Indonesia if such deforestation continues unchecked? Throughout the biosphere, human activities are altering trophic structures, energy flow, chemical cycling, and natural disturbance—ecosystem processes on which we and all other species depend (see Chapter 55). We have physically altered nearly half of Earth’s land surface, and we use over half of all accessible surface fresh water. In the oceans, stocks of most major fisheries are shrinking because of overharvesting. By some estimates, we may be pushing more species toward extinction than the large asteroid that triggered the mass ex- tinctions at the close of the Cretaceous period 65.5 million years ago (see Figure 25.16). Biology is the science of life. Thus, it is fitting that our final chapter focuses on a discipline that seeks to preserve life. Conservation biology integrates ecology, physiology, mo- ᭡ Figure 56.1 What will be the fate of this lecular biology, genetics, and evolutionary biology to conserve newly described bird species? KEY CONCEPTS 56.1 Human activities threaten Earth’s biodiversity 56.2 Population conservation focuses on population size, genetic diversity, and critical habitat 56.3 Landscape and regional conservation help sustain biodiversity 56.4 Earth is changing rapidly as a result of human actions 56.5 Sustainable development can improve human lives while conserving biodiversity OVERVIEW Striking Gold Tucking its wings, a bird lands on a branch deep inside a tropical jungle. Sensing the motion, a conservation biologist scans the branch through binoculars, a glimpse of golden or- ᭡ Figure 56.2 Tropical deforestation in West Kalimantan, ange stopping her short. Staring back is a wattled smoky an Indonesian province. 1238 UNIT EIGHT Ecology biological diversity at all levels. Efforts to sustain ecosystem processes and stem the loss of biodiversity also connect the life sciences with the social sciences, economics, and humanities. In this chapter, we will take a closer look at the biodiversity crisis and examine some of the conservation strategies being adopted to slow the rate of species loss. We will also examine how human activities are altering the environment through cli- mate change, ozone depletion, and other global processes, and we will consider how these alterations could affect life on Earth. Genetic diversity in a vole population CONCEPT 56.1 Human activities threaten Earth’s biodiversity Extinction is a natural phenomenon that has been occurring since life first evolved; it is the high rate of extinction that is re- sponsible for today’s biodiversity crisis (see Chapter 25). Be- cause we can only estimate the number of species currently existing, we cannot determine the exact rate of species loss. Species diversity in a coastal redwood ecosystem However, we do know that the extinction rate is high and that human activities threaten Earth’s biodiversity at all levels. Three Levels of Biodiversity Biodiversity—short for biological diversity—can be considered at three main levels: genetic diversity, species diversity, and ecosystem diversity (Figure 56.3). Genetic Diversity Genetic diversity comprises not only the individual genetic variation within a population, but also the genetic variation between populations that is often associated with adaptations to local conditions (see Chapter 23). If one population be- Community and ecosystem diversity comes extinct, then a species may have lost some of the ge- across the landscape of an entire region netic diversity that makes microevolution possible. This erosion of genetic diversity in turn reduces the adaptive po- ᭡ Figure 56.3 Three levels of biodiversity. The oversized tential of the species. chromosomes in the top diagram symbolize the genetic variation within the population. Species Diversity • A survey by the Center for Plant Conservation showed Public awareness of the biodiversity crisis centers on species that of the nearly 20,000 known plant species in the diversity—the variety of species in an ecosystem or across the United States, 200 have become extinct since such records biosphere (see Chapter 54). As more species are lost to extinc- have been kept, and 730 are endangered or threatened. tion, species diversity decreases. The U.S. Endangered Species • More than 30% of the known species of fishes in the Act (ESA) defines an endangered species as one that is “in world either have become extinct during historical times danger of extinction throughout all or a significant portion of or are seriously threatened. its range.” Threatened species are those that are considered • In North America, at least 123 freshwater animal species likely to become endangered in the near future. The following have become extinct since 1900, and hundreds more are just a few statistics that illustrate the problem of species loss: species are threatened. The extinction rate for North • According to the International Union for Conservation of American freshwater fauna is about five times as high as Nature and Natural Resources (IUCN), 12% of the 10,000 that for terrestrial animals. known species of birds and 21% of the 5,500 known species • According to a 2004 report in the journal Science that was of mammals are threatened. based on a global assessment of amphibians by more than CHAPTER 56 Conservation Biology and Global Change 1239 500 scientists, 32% of all known amphibian species are en- persers in the Pacific Islands, where they are increasingly dangered, with many species very near extinction. hunted as a luxury food (Figure 56.5). Conservation biologists fear that the extinction of flying foxes would also harm the na- Extinction of species may also be local; for example, a species tive plants of the Samoan Islands, where four-fifths of the tree may be lost in one river system but survive in an adjacent species depend on flying foxes for pollination or seed dispersal. one. Global extinction of a species means that it is lost from Some ecosystems have already been heavily affected by all the ecosystems in which it lived, leaving them perma- humans, and others are being altered at a rapid pace. Since nently impoverished (Figure 56.4). European colonization, more than half of the wetlands in the Ecosystem Diversity contiguous United States have been drained and converted to agricultural and other uses. In California, Arizona, and The variety of the biosphere’s ecosystems is a third level of bio- New Mexico, roughly 90% of native riparian (streamside) logical diversity. Because of the many interactions between communities have been affected by overgrazing, flood con- populations of different species in an ecosystem, the local ex- trol, water diversions, lowering of water tables, and invasion tinction of one species can have a negative impact on other by non-native plants. species in the ecosystem (see Figure 54.17). For instance, bats called “flying foxes” are important pollinators and seed dis- Biodiversity and Human Welfare Philippine eagle Why should we care about the loss of biodiversity? One reason is what the Harvard biologist E. O. Wilson calls biophilia, our sense of connection to nature and all life. The belief that other species are entitled to life is a pervasive theme of many religions and the basis of a moral argument that we should protect biodiversity. There is also a concern for future human Yangtze River generations. Paraphrasing an old proverb, G. H. Brundtland, dolphin a former prime minister of Norway, said: “We must consider our planet to be on loan from our children, rather than being a gift from our ancestors.” In addition to such philosophical and moral justifications, species and genetic diversity bring us many practical benefits. Benefits of Species and Genetic Diversity Many species that are threatened could potentially provide food, fibers, and medicines for human use, making biodiversity a crucial natural resource. If we lose wild populations of plants closely related to agricultural species, we lose genetic resources Javan rhinoceros ᭡ Figure 56.4 A hundred heartbeats from extinction. These are just three members of what E. O. Wilson calls the Hundred Heartbeat Club, species with fewer than 100 individuals remaining on Earth. The Yangtze River dolphin was even thought to be extinct, but a few individuals were reportedly sighted in 2007. To document that a species has actually become extinct, what spa- ᭡ Figure 56.5 The endangered Marianas “flying fox” bat ? tial and temporal factors would you need to consider? (Pteropus mariannus), an important pollinator. 1240 UNIT EIGHT Ecology that could be used to improve crop qualities, such as disease re- reason for preserving ecosystems. Humans evolved in Earth’s sistance. For instance, plant breeders responded to devastating ecosystems, and we rely on these systems and their inhabi- outbreaks of the grassy stunt virus in rice (Oryza sativa) by tants for our survival. Ecosystem services encompass all screening 7,000 populations of this species and its close rela- the processes through which natural ecosystems help sustain tives for resistance to the virus.

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