BiodiversityI INTRODUCTIONBiodiversity or Biological Diversity, sum of all the different species of animals, plants, fungi, andmicrobial organisms living on Earth and the variety of habitats in which they live. Scientists estimatethat upwards of 10 million—and some suggest more than 100 million—different species inhabit theEarth. Each species is adapted to its unique niche in the environment, from the peaks of mountains tothe depths of deep-sea hydrothermal vents, and from polar ice caps to tropical rain forests.Biodiversity underlies everything from food production to medical research. Humans the world overuse at least 40,000 species of plants and animals on a daily basis. Many people around the world stilldepend on wild species for some or all of their food, shelter, and clothing. All of our domesticatedplants and animals came from wild-living ancestral species. Close to 40 percent of the pharmaceuticalsused in the United States are either based on or synthesized from natural compounds found in plants,animals, or microorganisms.The array of living organisms found in a particular environment together with the physical andenvironmental factors that affect them is called an ecosystem. Healthy ecosystems are vital to life:They regulate many of the chemical and climatic systems that make available clean air and water andplentiful oxygen. Forests, for example, regulate the amount of carbon dioxide in the air, produceoxygen as a byproduct of photosynthesis (the process by which plants convert energy from sunlightinto carbohydrate energy), and control rainfall and soil erosion. Ecosystems, in turn, depend on thecontinued health and vitality of the individual organisms that compose them. Removing just onespecies from an ecosystem can prevent the ecosystem from operating optimally. Biodiversity of Gilgit BaltistanPerhaps the greatest value of biodiversity is yet unknown. Scientists have discovered and named only1.75 million species—less than 20 percent of those estimated to exist. And of those identified, only afraction have been examined for potential medicinal, agricultural, or industrial value. Much of theEarth’s great biodiversity is rapidly disappearing, even before we know what is missing. Mostbiologists agree that life on Earth is now faced with the most severe extinction episode since the eventthat drove the dinosaurs to extinction 65 million years ago. Species of plants, animals, fungi, andmicroscopic organisms such as bacteria are being lost at alarming rates—so many, in fact, thatbiologists estimate that three species go extinct every hour. Scientists around the world are catalogingand studying global biodiversity in hopes that they might better understand it, or at least slow the rateof loss.II INTERCONNECTEDNESS OF THE LIVING WORLD
Everywhere there is life, there is more than one distinct type of organism. Even a drop of seawateroffers a multitude of different microscopic plants, animals, and less complex life forms. The richdiversity of the living world is connected in two distinct ways. First, different types of organisms liveside by side in complex ecological networks of interdependency, each relying on the others that shareits habitat for nutrients and energy. Second, all life on Earth is connected in an evolutionary tree oflife. At the bottom of the tree is the common ancestor from which all living things descended—asingle-celled microbe that lived more than 3.5 billion years ago—and in its uppermost branches aregorillas, chimpanzees, orangutans, and our own species, Homo sapiens.A Ecological DiversityEcological diversity is the intricate network of different species present in local ecosystems and thedynamic interplay between them. An ecosystem consists of organisms from many different speciesliving together in a region that are connected by the flow of energy, nutrients, and matter that occursas the organisms of different species interact with one another. The ultimate source of energy innearly all ecosystems is the Sun. The Sun’s radiant energy is converted to chemical energy by plants.This energy flows through the systems when animals eat the plants and then are eaten, in turn, byother animals. Fungi derive energy by decomposing organisms, releasing nutrients back into the soilas they do so. An ecosystem, then, is a collection of living components—microbes, plants, animals,and fungi—and nonliving components—climate and chemicals—that are connected by energy flow.Removing just one species from an ecosystem damages the flow of energy of that system. Forinstance, in the late 19th and early 20th centuries, sea otters were hunted to near extinction in manykelp forests off the coast of the Pacific Northwest of the United States and western Canada, causingthe entire ecosystem to suffer. Otters eat sea urchins, small, spiny organisms that share their habitat.When the otters disappeared, the sea urchin population exploded and started to destroy the vast bedsof kelp. Without the kelp, other species that lived in the ecosystem, including many species of fish andsnails and other invertebrates, began to decline in number. Efforts to restore sea otter populationsbrought the kelp communities back to near normal in the late 20th century. Biodiversity of Gilgit BaltistanMeasuring ecological diversity is difficult because each of the Earth’s ecosystems merges into theecosystems around it. A lake, for example, might have a distinct shoreline, but the plants fringing itsedges are quite different from the aquatic plants in the middle of the lake or the trees and shrubssurrounding the lake. Beavers may live in the lake, but they construct dams from trees that grow inadjacent ecosystems. Nutrients flow into the lake via streams and rivers beyond the lake’s ecosystem.B Evolutionary Diversity
Every species on Earth is related to every other species in a pattern every bit as complex as thepatterns of energy flow within an ecosystem. In evolutionary diversity, the connection is not energyflow, but rather genetic connections that unite species. The more closely related any two species are,the more genetic information they will share, and the more similar they will appear. An ever-wideningcircle of evolutionary relatedness embraces every species on Earth. Biodiversity of Gilgit BaltistanAn organism’s closest relatives are members of its own species—that is, other organisms with which ithas the potential to mate and produce offspring. Members of a species share genes, the bits ofbiochemical information that determine, in part, how the animals look, behave, and live. One easterngray squirrel, for example, shares the vast majority of its genes with other eastern gray squirrels,whether they live in the same area or are separated by thousands of miles. Members of a species alsoshare complex mating behaviors that enable them to recognize each other as potential mates. When afemale eastern gray squirrel is ready to mate, she exudes a scent that attracts male eastern graysquirrels. Mating and sharing a common supply of genes unite a species. Biodiversity of Gilgit BaltistanFor virtually every species there is a similar and closely related species in an adjacent habitat. West ofthe Rocky Mountains, one finds western gray squirrels instead of eastern gray squirrels. Althoughwestern gray squirrels are more similar to than different from their eastern counterparts, theseanimals do not share a common mating behavior with eastern gray squirrels. Even when brought intoclose proximity, eastern and western gray squirrels do not mate, and so constitute two distinctspecies.Each species has other, more remotely related species, which share a more general set ofcharacteristics. Gray squirrels, chipmunks, marmots, and prairie dogs all belong to the squirrel familybecause they share a number of features, such as tooth number and shape, and details of skull andmuscle anatomy. All of these animals are rodents, a large group of more distantly related animals whoshare similar chisel-like incisor teeth that grow continuously. All rodents are related to a broadergroup, mammals. Mammals have hair, raise their young on milk, and have three bones in the middleear. All mammals, in turn, are more distantly related to other animals with backbones, or vertebrates.All these organisms are animals but share a common cell structure with plants, fungi, and somemicrobes. Finally, all living organisms share a common molecule, ribonucleic acid (RNA), and mostalso have deoxyribonucleic acid (DNA). These molecules direct the production of proteins—moleculesresponsible for the structure and function of virtually all living cells. Biodiversity of Gilgit BaltistanThis is the evolutionary chain of life. All species are descended from a single common ancestor. Fromthat ancient single-celled microbe, all inherited RNA. As time goes by, species diverge and developtheir own peculiar attributes, thus making their own contribution to biodiversity ( see Evolution).
III GLOBAL BIODIVERSITY CRISISMost biologists accept the estimate of American evolutionary biologist Edward O. Wilson that the Earthis losing approximately 27,000 species per year. This estimate is based primarily on the rate ofdisappearance of ecosystems, especially tropical forests and grasslands, and our knowledge of thespecies that live in such systems. We can measure the rate of loss of tropical rain forests, forexample, by analyzing satellite photographs of continents from different periods that show rates andamounts of habitat destruction—and from these measurements calculate the approximate number ofspecies being lost each year.This extraordinary rate of extinction has occurred only five times before in the history of complex lifeon Earth. Mass extinctions of the geological past were caused by catastrophic physical disasters, suchas climate changes or meteorite impacts, which destroyed and disrupted ecosystems around theglobe. In the fifth mass extinction, which occurred more than 65 million years ago, the Earth wasshrouded in a cloud of atmospheric dust—the result of meteorite impact or widespread volcanicactivity. The resulting environmental disruption caused the demise of 76 percent of all species alive atthe time, including the dinosaurs. Today’s sixth extinction is likewise primarily caused by ecosystemdisturbance—but this time the destroying force is not the physical environment, but ratherhumankind. The human transformation of the Earths surface threatens to be every bit as destructiveas any of the past cataclysmic physical disasters.IV HUMAN IMPACTThe underlying cause of biodiversity loss is the explosion in human population, now at 6 billion, butexpected to double again by the year 2050. The human population already consumes nearly half of allthe food, crops, medicines, and other useful items produced by the Earth’s organisms, and more than1 billion people on Earth lack adequate supplies of fresh water ( see World Food Supply). But theproblem is not sheer numbers of people alone: The unequal distribution and consumption of resourcesand other forms of wealth on the planet must also be considered. According to some estimates, theaverage middle-class American consumes an amazing 30 times what a person living in a developingnation consumes. Thus the impact of the 270 million American people must be multiplied by 30 toderive an accurate comparative estimate of the impact such industrialized nations have on the worldsecosystems.The single greatest threat to global biodiversity is the human destruction of natural habitats. Since theinvention of agriculture about 10,000 years ago, the human population has increased fromapproximately 5 million to a full 6 billion people. During that time, but especially in the past severalcenturies, humans have radically transformed the face of planet Earth. The conversion of forests,grasslands, and wetlands for agricultural purposes, coupled with the multiplication and growth ofurban centers and the building of dams and canals, highways, and railways, has physically alteredecosystems to the point that extinction of species has reached its current alarming pace.
In addition, overexploitation of the worlds natural resources, such as fisheries and forests, has greatlyoutstripped the rate at which these systems can recover. For example, 12 of the 13 largest oceanicfisheries are severely depleted. Modern fishing techniques, such as using huge fishing nets and bottomvacuuming techniques, remove everything in their paths—including tons of fish and invertebrates ofno commercial use. These victims, as well as porpoises and seals that are also hauled in as accidentalcatches, are permanently removed from their populations, significantly altering the ecosystems inwhich they live.As human populations have grown, people have spread out to the four corners of the Earth. In theprocess, whether on purpose or by accident, they have introduced nonnative species that havecreated ecological nightmares, disrupting local ecosystems and, in many cases, directly driving nativespecies extinct. For example, the brown tree snake was introduced to the island of Guam, probably asa stowaway on visiting military cargo ships after World War II (1939-1945). The snake devastated thenative bird population, driving over half a dozen native species of birds to extinction—simply becausethe native birds had not been exposed to this type of predator and did not recognize the danger posedby these snakes.V PRESERVING BIODIVERSITYAs the scope and significance of biodiversity loss become better understood, positive steps to stem thetide of the sixth extinction have been proposed and, to some extent, adopted. Several nations haveenacted laws protecting endangered wildlife. An international treaty known as the Convention onInternational Trade in Endangered Species of Wild Fauna and Flora (CITES) went into effect in 1975 tooutlaw the trade of endangered animals and animal parts. In the United States, the EndangeredSpecies Act (ESA) was enacted in 1973 to protect endangered or threatened species and theirhabitats. The Convention on Biological Diversity, held in Rio de Janeiro, Brazil, in 1992 and ratified bymore than 160 countries, obligates governments to take action to protect plant and animal species.In the last three decades, focus has shifted away from the preservation of individual species to theprotection of large tracts of habitats linked by corridors that enable animals to move between thehabitats. Thus the movement to save, for example, the spotted owl of the Pacific Northwest, hasbecome an effort to protect vast tracts of old-growth timber (see National Parks and Preserves).Promising as these approaches may be, conservation efforts will never succeed in the long run if thelocal economic needs of people living in and near threatened ecosystems are not taken into account.This is particularly true in developing countries, where much of the world’s remaining undisturbed landis located. At the end of the 20th century, international organizations such as the World Bank and theWorld Wildlife Fund launched a movement for all countries in the developing world to set aside 10percent of their forests in protected areas. But many communities living near these protected areashave relied on the rain forest for food and firewood for thousands of years. Left with few economicalternatives, these communities may be left without enough food to eat.