Why is Biodiversity Important?
Utilitarian Values 4
Direct Use Values: Goods 5
Building Materials, Paper Products, and Fuel 6
Clothing and Other Textiles 6
Industrial Products 7
Indirect Use Values: Services 8
Global Processes: Atmosphere and Climate Regulation 10
Global Processes: Land Use Change and Climate Regulation 11
Soil and Water Conservation 12
Nutrient Cycling 12
A Genetic Library for Crop and Livestock Improvement 13
Pollination and Seed Dispersal 13
Natural Pest Control 15
Biodiversity as a Source of Inspiration 15
Tourism and Recreation 16
Kinship With Nature 16
Spiritual Beliefs 16
Cultural Value 17
Aesthetic Value 17
Ecological Value 18
Scientific and Educational Value 19
Non-use Values 20
Potential Value 20
Existence and Bequest Values 22
Strategic Value 22
Intrinsic Value 22
How Do We Define Intrinsic Value? 22
Why Do Values Matter? 23
Literature Cited: 25
Why is Biodiversity Important?
M. F. Laverty, E.J. Sterling, and E.A. Johnson
“The last word in ignorance is the man who says
of an animal or plant: “What good is it?”
(Aldo Leopold 1949)
Humans depend upon biodiversity in many ways, both to satisfy basic needs like food and medicine, and to enrich our lives culturally or spiritually. Yet in an increasingly modern, technological world, people often forget how fundamental biodiversity is to daily life and are unaware of the impact of its loss (see Threats to Biodiversity module).
Despite its importance, determining the value or worth of biodiversity is complex and often a cause for debate. This is largely due to that fact that the worth placed on biodiversity is a reflection of underlying human values, and these values vary dramatically both among societies and individuals (Perlman and Adelson 1997). The perspective of rural versus urban dwellers towards wildlife is one example. People who don’t live with elephants on a daily basis appreciate elephants for their sheer size, charisma, and intelligence. Those who live near elephants, however, tend to perceive them as a threat to people and their crops and property.
Values are also dynamic; they change over time and vary according to specific situations. Both the diversity of values towards a species and the changes in values over time can be examined in the case of the gray wolf in the United States. Once widespread throughout the North America, the grey wolf (Canis lupus) was deemed a threat to human livelihoods and was systematically hunted, beginning in the 1600s. By the late 1800s, it had been virtually exterminated from its former range. But in the late 1970s, in sharp contrast to earlier views of wolves, the U.S. government began programs to restore them to their former range. To some people, wolves have come to signify the wilderness and in some areas have become an important tourist attraction (such as Yellowstone National Park and in northern Minnesota). Others still view wolves as a threat. The debate over wolf restoration programs demonstrates not only the changes in values but also the multiplicity of values within any one society (Lynn 2002).
The value of biodiversity is often divided into two main categories:
Utilitarian (also known as instrumental, extrinsic, or use) value, and
Intrinsic (also know as inherent) value.
A living thing’s utilitarian value1 is determined by its use or function. Usually utilitarian value is measured in terms of its use for humans, such as for medicine or food. However, it can also represent the value of an organism to other living things or its ecological value; pollinators, such as bees, are essential to the reproduction of many plants. In contrast, intrinsic value2 describes the inherent worth of an organism, independent of its value to anyone or anything else. In other words, all living things have a right to exist – regardless of their utilitarian value.
Determining the value or worth of biodiversity is complex. Economists typically subdivide utilitarian or use values of biodiversity into direct use value3 for those goods that are consumed directly, such as food, and indirect use value4 for those services that support the items that are consumed, including ecosystem functions such as nutrient cycling.
There are several less tangible values that are sometimes called non-use or passive values5, for things that we don’t use but we would consider as a loss if they were to disappear; these include existence value6, the value of knowing something exists even if you will never use it or see it, and bequest value7, the value of knowing something will be there for future generations (Moran and Pearce 1994). Potential or Option value8 refers to the use that something may have in the future; sometimes this is included as a use value; we have chosen to include it within the passive values here based on its abstract nature. The components included within the category of “utilitarian” values vary somewhat in the literature. For example, some authors classify spiritual, cultural, and aesthetic values as indirect use values, whiles others consider them to be non-use values, differentiated from indirect use values – such as nutrient cycling – because spiritual, cultural, and aesthetic values for biodiversity are not essential to human survival. Still others consider these values as separate categories entirely. (See also, Callicott 1997, Hunter 2002, Moran and Pearce 1994, Perlman and Adelson 1997, Primack 2002, Van Dyke 2003). In this module, we include spiritual, cultural and aesthetic values as a subset of indirect values or services, as they provide a service by enriching our lives (Table 1).
Table 1. Categories of Utilitarian Values of Biodiversity.
Direct Use Value(Goods)
Indirect Use Value (Services)
Food, medicine, building material, fiber, fuel
Atmospheric and climate regulation, pollination, nutrient recycling; Cultural, Spiritual and Aesthetic*
Potential (or Option) Value1; Existence Value2; Bequest Value3
*Some authors choose to differentiate these values from those services that provide basic survival needs such as the air we breathe.
1 Potential Value - Future value either as a good or service
2 Existence Value - Value of knowing something exists
3 Bequest Value - Value of knowing that something will be there for future generations
Direct Use Values: Goods
The earth provides an abundance of goods essential to human life – so many, indeed, that it is difficult to create a comprehensive list of them. Some examples of these goods include food, shelter, timber, fuel, clothing, fiber, industrial products, and medicine.
Humans have spent most of their existence as hunter-gatherers dependent on wild plants and animals for survival. Around 10,000 years ago, the first plants were cultivated, marking a fundamental shift in human history. Biodiversity played a central role in the development of agriculture, providing the original source of all crops and domesticated animals. And today people still depend on biodiversity to maintain healthy, sustainable agricultural systems.
Though humans have used over 12,000 wild plants for food, only twenty species now support much of the world’s population (Burnett 1999). Of all the plants that we depend on, none are more important than the grass family, the Gramineae (Heiser 1990). The grass family includes the world's principal staples: wheat (Triticum aestivum), rice (Oryza sativa L.), and corn (maize) (Zea mays). Rice and corn formed the basis of civilizations in the Far East and the Americas, while wheat, together with barley, formed the basis of the civilizations in the Near East.
Though agriculture depends on relatively few plants and animals, genetic diversity is essential to improve the productivity of crops and livestock, and to create varieties and breeds that are resistant to pests or disease. [For details of the importance of genetic diversity, see also the section on ‘Genetic Library’ under ‘Services’ ].
Biodiversity acts as a form of insurance for agriculture by helping to ensure that crops can adapt to future environments. Changing climates may require drought-resistant or salt-tolerant crops, for instance. Sorghum, emmer, and spelt were once widely grown grains but have been largely replaced by wheat. However, because of their unique environmental adaptations – sorghum, for example, can be grown in drier climates that do not support wheat – these grasses may become more important in the future, should climatic conditions change.
Less-familiar wild plants may become important foods in the future. For example, Peach Palm (Guilielma gasipaes or Bactris gasipaes Kunth, Arecaceae), also know as Pejibaye, from Central America, produces one of the most balanced foods for human nutrition – an ideal mixture of carbohydrates, protein, fat, vitamins, and minerals. Currently Peach Palm is cultivated for the heart of palm and its fruits, especially in Costa Rica and Brazil. Peach Palm plantations produce more protein and carbohydrate per hectare than corn (Mora-Urpi 1994; Vietmeyer 1996).
For many rural peoples in developing countries, wild species are still an important source of food and income, including green leafy plants, fruits, fungi, nuts, and meat (Bennett and Robinson 2000; Roe et al. 2002; Newmark 2002). Furthermore, with the exception of only a few species, the world's marine fisheries are dominated by wild-caught fish, representing 85.8 percent of the 100.2 million tons produced in 2000, according to the Food and Agriculture Organization (FAO 2002).
Building Materials, Paper Products, and Fuel
Trees and several grasses, most notably bamboo and rattan, are basic commodities used worldwide for building materials, paper products, and fuel. The worldwide production of timber and related products – including homes, furniture, mulch, chipboard, paper and packaging – is a multi-billion dollar industry. Outside of large market economies, products from particular species of wild-growing woody plants are key sources of shelter (e.g., termite-resistant support poles), household items (furniture, utensils, baskets, etc.), long-burning fuels, and dyes (Newmark 2002).
The common name ‘bamboo’ is used to describe many different species and genera. All of these are part of the subfamily Bambusoidaeae (of the family Poaceae, or Gramineae), which comprises both woody and herbaceous bamboos and includes a total of about 1575 species (Ohrnberger 1999). According to the International Network of Bamboo and Rattan, over one million people use bamboo for housing. Rattan (the common name which describes 13 genera and about 700 species) is not as widely used as bamboo. Its primary use is for cane furniture, as well as for matting, basketry, and handicrafts.
One of the most important uses of wood is for fuel. According to the World Resources Institute (2000-2001), 53 percent of all harvested wood is used as fuel, burned either directly or after being converted to charcoal. Fuelwood, charcoal, and other fuel from wood is the major source of energy in low-income countries; the major consumers and producers of wood for fuel are Brazil, China, India, Indonesia, and Nigeria (Matthews et al. 2000).
Clothing and Other Textiles
Fibers extracted from plants and animals are used to produce textiles and cloth. While synthetic fibers, such as polyester, that are manufactured from petroleum products are becoming increasingly common, cotton (Gossypium sp.) is still the single most important textile fiber in the world, and accounts for over 40 percent of total world fiber production (USDA 2003). The earliest fabric known is linen, created from the flax plant (Linum usitatissimum); it has been used for centuries and is historically significant for its use to produce sails. Some other fibers from plants include jute (Corchorus spp.), hemp (Cannabis sativa), sisal (Agave sisalana), and ramie (Boehmeria nivea). Fabric manufacturers also harvest wood for its fiber, using wood cellulose to make Tencel® and rayon. Silk fibers are created from the cocoons of the larvae of several different species of silkworm moths. The domesticated Bombyx mori (Mulberry silkworm) is the most common; its primary food is the leaves of plants of the family Moraceae, particularly Morus alba (White mulberry). There are other less common varieties, commonly known as "wild silk." For example, Antherea assama westwood, endemic to the Brahmaputra valley of India, produces the fine muga silk renowned for its golden color.
Many industrial products are also extracted from plants and animals. Some of the most important of these are cork, rubber, latex, shellac, resins, perfumes, waxes, and oils. A list of a few of these products and their source is provided in Table 2.
Originating plant or animal
Cork oak (Quercus suber)
Pará rubber tree (Hevea brasiliensis)
Lac insect (Laccifer spp.)
Carnauba palm (Copernicia cerifera)
Wax plant (Euphorbia antisyphilitica)
Jojoba plant (Simmondsia chinensis)
Cochineal insect (Dactylopius coccus)
Table 2. A few of the industrial products extracted from plants and animals.
Note: *The only red dye approved by the US Food and Drug Administration for use in foods, drugs, and cosmetics.
Some 80 percent of people in the developing world population still use plants as a primary source of medicine (Farnsworth et al. 1985). For example, Newmark (2002) reports that Tanzania had 600 Western-trained doctors; its 30-40,000 traditional healers treat a vast majority of its population. These healers rely on plants and plant parts for their remedies.
Many Western medicines were developed from a plant or an animal source; 57 percent of the top 150 most-prescribed drugs in the United States originate from living organisms (Grifo et al. 1997). For example, the antibiotic penicillin is derived from an ordinary bread mold, Pencillium notatum. Other examples include aspirin and common acne medicines that are derived from salicylic acids, first taken from the bark of willow trees (Salix sp.). While many of these drugs are now more efficiently synthesized than extracted from material collected in the wild, we still depend on the chemical structures in nature to guide us in developing and synthesizing new drugs (Grifo et al. 1997).
Some drugs are still synthesized in whole or in part from wild sources. For example, TAXOL, a potent drug originally used to fight ovarian and breast cancers and now used to treat a number of other cancers, was first derived from the bark of the Pacific Yew (Taxus brevifolia) (Jennewein and Croteau 2001). In fact, to produce one kg of TAXOL required 6.7 tons of bark or approximately two to three thousand trees. Because removing the bark killed the trees, and the tree is very slow growing, researchers began investigating alternative sources to create the drug. Fortunately, researchers found that the leaves of the European Yew (Taxus baccata), a close relative of the Pacific Yew, produce a similar chemical substance that can be used to produce TAXOL more sustainably and less expensively. At this time the production of TAXOL remains partially dependent on needles from wild or cultivated sources of the European Yew (Taxus baccata) or the Himalayan Yew (Taxus yunnanensis).
Another example is the Indian snakeroot plant (Rauwolfia serpentina), which has been used for thousands of years by Hindu healers to treat nervous disorders and mental illnesses (Oldfield 1984). Scientists based in the Western world only came to recognize its potential as a medicine in the 1940s. The chemical compound extracted from the plant (an alkaloid called reserpine) is a key, active ingredient in drugs that treat hypertension, anxiety, and schizophrenia. Commercial synthesis of reserpine is complex and expensive; it can be extracted naturally for half the cost. Rauwolfia serpentina was in such high demand that it virtually disappeared in the wild in India and Indonesia in the 1960s. Related species from Africa and the Americas were found that could act as a substitute and the plant is now also cultivated.
While plants are still the primary source for medicine, the aquatic realm is currently leading the next wave of medical discoveries (CGER 1999). Marine organisms produce many novel compounds, including some of the most powerful toxins on earth. For example, the mollusks cone shells (Conus spp.) use a special harpoon loaded with a potent venom that paralyses their prey almost instantly (Hart 1997). Ziconotide™ (SNX-111) is a new painkiller that was created from a peptide in cone shell venom. Not only is Ziconotide™ hundreds of times more powerful than morphine, but it also uniquely targets pain receptors without causing numbness. Injected at the spinal cord, it blocks the channels where pain signals normally travel, basically blocking the pain without causing numbness. There are over 500 species of cone shell and each has 50 to 200 active peptides in its venom; each of these peptides holds the promise of providing the basis for a drug that have a highly specific target point with minimal side effects.
Indirect Use Values: Services
Ecosystems, and the plant and animal species that constitute them, provide a host of services to all living things (Daily 1997), including:
regulating global processes, the regulation of atmospheric gases that affect global and local climates and the air we breathe;
soil and water conservation, maintaining the hydrologic cycle and controlling erosion;
nutrient cycling, the control of nutrient and energy flow through the planet – for example, waste decomposition and detoxification, soil renewal, nitrogen fixation, and photosynthesis;
a genetic library which provides a source of information to create better agricultural crops or livestock;
maintenance of plant reproduction through pollination and seed dispersal, in those plants we rely on for food, clothing or shelter
control of agricultural pests and disease;
a source of inspiration to solve agricultural, medical, manufacturing problems; and
tourism and recreation opportunities.
Often the values of ecosystem services are not considered in commercial market analyses, despite their critical importance to human survival. How can we assign a value to the atmospheric regulation of oxygen? In some ways, its value is infinite since without it we could not survive. Also many ecosystem services cannot be replaced or if they can, it is only at considerable cost. An attempt to estimate the value of ecosystem services was made by Costanza and others (1997). According to the study, the earth provides a minimum of $16 to $54 trillion dollars worth of "services" to humans per year, based on the value of 15 ecosystem services and two goods in 16 biomes. Some scientists and social scientists have disputed the quantitative conclusions of this study (Garwin and Masood 1998; Hueting et al. 1998; Norgaard et al. 1998; Serafy 1998; Toman 1998; Turner et al. 1998); among the criticisms of the study is the difficulty of "scaling up" across ecosystems and types of services. Nevertheless, the study by Costanza and others (1997) is an important first effort to estimate the global economic contribution of ecosystem services.
Many services provided by biodiversity go beyond what is needed for our immediate survival, including the many cultural, spiritual, and aesthetic values people place on nature and natural areas. Some feel that people have an innate connection or kinship with nature. Nature also provides insight and understanding of our role in the world, and has value for education, as well as for scientific research. Furthermore, each species has an ecological value as part of an ecosystem, and species diversity contributes to ecosystem function and resilience. While species diversity is related to ecosystem function and resilience, there is not necessarily a one to one correspondence. In other words, a hypothetical ecosystem with 150 species is not necessarily twice as good at providing ecosystem services than one with 75 species. However, regardless of diversity levels the wholesale removal of species from ecosystems is likely to disrupt the ability of an ecosystem to provide these services.
Global Processes: Atmosphere and Climate Regulation
Life on earth plays a critical role in regulating the earth’s physical, chemical, and geological properties, from influencing the chemical composition of the atmosphere to modifying climate.
About 3.5 billion years ago, early life forms (principally cyanobacteria) helped to create an oxygenated atmosphere through photosynthesis, taking up carbon dioxide from the atmosphere and releasing oxygen (Schopf 1983; Van Valen 1971). Over time, these organisms altered the composition of the atmosphere, increasing oxygen levels, and paved the way for organisms that use oxygen as an energy source (aerobic respiration), forming an atmosphere similar to that existing today.
Carbon cycles on the planet between the land, atmosphere, and oceans through a combination of physical, chemical, geological, and biological processes (IPCC 2001). One key way biodiversity influences the composition of the earth’s atmosphere is through its role in carbon cycling in the oceans, the largest reservoir for carbon on the planet (Gruber and Sarmiento, in press). In turn, the atmospheric composition of carbon influences climate. Phytoplankton (microscopic marine plants) play a central role in regulating atmospheric chemistry by transforming carbon dioxide into organic matter during photosynthesis. This carbon-laden organic matter settles either directly or indirectly (after it has been consumed) in the deep ocean, where it stays for centuries, even for thousands of years, acting as the major reservoir for carbon on the planet. In addition, carbon also reaches the deep ocean through another biological process – the formation of calcium carbonate, the primary component of the shells in two groups of marine organisms coccolithophorids (a phytoplankton) and foraminifera (a single celled, shelled organism that is abundant in many marine environments). When these organisms die, their shells sink to the bottom or dissolve in the water column. This movement of carbon through the oceans removes excess carbon from the atmosphere and regulates the earth's climate.
Over the last century, humans have changed the atmosphere’s composition by releasing large amounts of carbon dioxide. This excess carbon dioxide, along with other ‘greenhouse’ gases, is believed to be heating up our atmosphere and changing the world’s climate, leading to ‘global warming’. There has been much debate about how natural processes, such as the cycling of carbon through phytoplankton in the oceans, will respond to these changes. Will phytoplankton productivity increase and thereby absorb the extra carbon from the atmosphere? Recent studies suggest that natural processes may slow the rate of increase of carbon dioxide in the atmosphere, but it is doubtful that either the earth’s oceans or its forests can absorb the entirety of the extra carbon released by human activity (Falkowski et al. 2000).
Global Processes: Land Use Change and Climate Regulation
The energy source that ultimately drives the earth’s climate is the sun. The amount of solar radiation absorbed by the earth depends primarily on the characteristics of the surface. Although the link between solar absorption, thermodynamics, and ultimately climate is very complex, newer studies indicate that vegetation cover and seasonal variation in vegetation cover affects climate on both global and local scales. New generations of atmospheric circulation models are increasingly able to incorporate more complex data related to these parameters (Sellers et al. 1997). Besides regulating the atmosphere’s composition, the extent and distribution of different types of vegetation over the globe modifies climate in three main ways:
affecting the reflectance of sunlight (radiation balance);
regulating the release of water vapor (evapotranspiration); and
changing wind patterns and moisture loss (surface roughness).
The amount of solar radiation reflected by a surface is known as its albedo9; surfaces with low albedo reflect a small amount of sunlight, those with high albedo reflect a large amount. Different types of vegetation have different albedos; forests typically have low albedo, whereas deserts have high albedo. Deciduous forests are a good example of the seasonal relationship between vegetation and radiation balance. In the summer, the leaves in deciduous forests absorb solar radiation through photosynthesis; in winter, after their leaves have fallen, deciduous forests tend to reflect more radiation. These seasonal changes in vegetation modify climate in complex ways, by changing evapotranspiration rates and albedo (IPCC 2001).
Vegetation absorbs water from the soil and releases it back into the atmosphere through evapotranspiration10, which is the major pathway by which water moves from the soil to the atmosphere. This release of water from vegetation cools the air temperature. In the Amazon region, vegetation and climate is tightly coupled; evapotranspiration of plants is believed to contribute an estimated fifty percent of the annual rainfall (Salati 1987). Deforestation in this region leads to a complex feedback mechanism, reducing evapotranspiration rates, which leads to decreased rainfall and increased vulnerability to fire (Laurance and Williamson 2001).
Deforestation also influences the climate of cloud forests. For instance, in Costa Rica’s Monteverde Cloud Forest harbors a rich diversity of organisms, many of which are found nowhere else in the world. However, deforestation in lower-lying lands, even regions over 50 kilometers away, is changing the local climate, leaving the “cloud” forest cloudless (Lawton et al. 2001). As winds pass over deforested lowlands, clouds are lifted higher, often above the mountaintops, reducing the ability for cloud forest formation. Removing the clouds from a cloud forest dries the forest, so it can no longer support the same vegetation or provide appropriate habitat for many of the species originally found there. Similar patterns may be occurring in other, less studied montane cloud forests around the world.
Different vegetation types and topographies have varying surface roughness 11, which changes the flow of winds in the lower atmosphere and in turn influences climate. Lower surface roughness also tends to reduce surface moisture and increase evaporation. Farmers apply this knowledge when they plant trees to create windbreaks (Johnson et al. 2003). Windbreaks increase surface roughness and thereby reduce wind speed, change the microclimate, reduce soil erosion, and modify temperature and humidity. For many field crops, windbreaks increase yields and production efficiency. They also minimize stress on livestock from cold winds.
Soil and Water Conservation
Biodiversity is also important for global soil and water protection. Terrestrial vegetation in forests and other upland habitats maintains water quality and quantity, and controls soil erosion.
In watersheds12 where vegetation has been removed, flooding prevails in the wet season and drought in the dry season. Soil erosion is also more intense and rapid, causing a double effect: removing nutrient-rich topsoil and leading to siltation in downstream riverine and ultimately, oceanic environments. This siltation harms riverine and coastal fisheries and damages coral reefs (Turner and Rabalais 1994; van Katwijk et al. 1993).
One of the most productive ecosystems on earth, wetlands13 have water present at or near the surface of the soil or within the root zone all year or for a period of time during the year, and the vegetation there is adapted to these conditions. Wetlands are instrumental for the maintenance of clean water and erosion control. Microbes and plants in wetlands absorb nutrients and in the process filter and purify water of pollutants before they enter other aquatic systems. Wetlands also reduce flood, wave, and wind damage. They retard the flow of floodwaters and accumulate sediments that would otherwise be carried downstream or into coastal areas. Wetlands also serve as breeding grounds and nurseries for fish and support thousands of bird and other animal species.
Nutrient cycling is yet another critical service provided by biodiversity – particularly by microorganisms. Fungi and other microorganisms in soil help break down dead plants and animals, eventually converting this organic matter into nutrients that enrich the soil (Pimentel et al. 1995).
Nitrogen is essential for plant growth, and an insufficient quantity of it limits plant production in both natural and agricultural ecosystems. While nitrogen is abundant in the atmosphere, only a few organisms (commonly known as nitrogen-fixing bacteria) can use it in this form. Nitrogen-fixing bacteria extract nitrogen from the air, and transform it into ammonia, then other bacteria further break down this ammonia into nitrogenous compounds that can be absorbed and used by most plants. In addition to their role in decomposition and hence nutrient cycling, microorganisms also help detoxify waste, changing waste products into forms less harmful to the environment.
A Genetic Library for Crop and Livestock Improvement
Humans only cultivate a small fraction of the plant and animal species on earth. To ensure that we can sustain existing agricultural systems, we depend on biodiversity, especially the wild counterparts of cultivated food and domesticated animals, as a genetic library that we can use to create new varieties or breeds that are more tolerant of pests or disease or more suited to certain environmental conditions.
In the late 1970s, teosinte (Zea diploperennis), the closest wild relative of corn, was discovered and found to be resistant to viral diseases that infect Z. mays. The new species has the same chromosome number as Z. mays and can therefore hybridize with it. When this occurs, some of the viral resistance is transferred to domestic corn. Four viral-resistant commercial strains have since been produced, highlighting the importance of wild counterparts to cultivated food crops.
There are other cases in history when a widely grown crop has failed due to disease, with devastating consequences. One famous example is the Irish potato famine, which led to the death of 1 million people. In the mid-19th century, a blight (or fungus-like pathogen) destroyed much of the crop. European potato crops were particularly susceptible to infection since they had originated from only a few sources and thus were genetically very similar. To combat this disease, a long search began to find a plant resistant to the blight. By the early 20th century, a related plant in Mexico provided the solution. Hybridizing this plant with potatoes produced a resistant strain. Unfortunately, this was not a permanent solution. Today, potato blight is once again a concern, and it is likely the solution lies in existing biodiversity. As the world’s crops become increasingly homogenized, it is important to remember the lessons of this event: agricultural systems with higher genetic diversity are often more resilient, and ultimately, biodiversity may solve these crises.
Pollination and Seed Dispersal
An estimated 90 percent of flowering plants depend on pollinators such as wasps, birds, bats, and bees, to reproduce. Plants and their pollinators are increasingly threatened around the world (Buchmann and Nabhan 1995; Kremen and Ricketts 2000). Pollination is critical to most major crops and virtually impossible to replace. For instance, imagine how costly fruit would be (and how little would be available) if natural pollinators no longer existed and each developing flower had to be fertilized by hand.
Many animal species are important dispersers of plant seeds. While scientists hypothesize that the loss of a specific seed disperser could cause a plant to become extinct, to date there is no definitive example where this has occurred. A famous example that has often been cited previously is the case of the dodo (Raphus cucullatus) and the tambalacoque (Sideroxylon grandiflorum). The dodo, a large flightless bird that inhabited the island of Mauritius in the Indian Ocean, became extinct due to overhunting in the late seventeenth century. It was once thought that the germination of the hard-cased seeds of the tambalacoque, which is now endangered, depended upon the seeds’ passing through a dodo’s gizzard (Temple 1977). In the 1970s, only 13 trees remained and it was thought the tree had not reproduced for 300 years. The seeds of the tree have a very hard coat. As an experiment they were fed to a turkey; after passing through its gizzard the seeds were viable and germinated. This experiment led scientists to believe that the extinction of the dodo was coupled to the tambalacoque’s inability to reproduce. However, this hypothesis has not stood up to further scrutiny, as there were several other species (including three now-extinct species – a large-billed parrot, a giant tortoise, and a giant lizard) that were also capable of cracking the seed coat (Witmar and Cheke 1991; Catling 2001). Thus, the loss of several species, including the dodo, could have contributed to the decline of the tambalacoque. [For further details of causes of extinction see module on Historical Perspectives on Extinction and the Current Biodiversity Crisis]. Unfortunately, declines and/or extinctions of species are often unobserved and thus it is difficult to tease out the cause of the end result, as multiple factors are often operating simultaneously. Similar problems exist today in understanding current population declines. For example, in a given species, population declines may be caused by loss of habitat, loss in prey species, or loss of predators, a combination of these factors, or possibly some other yet unidentified cause, such as disease.
In the pine forests of western North America, corvids (including jays, magpies, and crows), squirrels, and bears play a role in seed dispersal. The Clark’s nutcracker (Nucifraga columbiana) is particularly well adapted to dispersal of whitebark pine (Pinus albicaulis) seeds (Lanner 1996). The nutcracker removes the wingless seeds from the cones, which otherwise would not open on their own. Nutcrackers hide the seeds in clumps. When the uneaten seeds eventually grow, they are clustered, accounting for the typical distribution pattern of whitebark pine in the forest.
In tropical areas, large mammals and frugivorous birds play a key role in dispersing the seeds of trees and maintaining tree diversity over large areas. For example, three-wattled bellbirds (Procnias tricarunculata) are important dispersers of tree seeds of members of the Lauraceae family in Costa Rica. Because bellbirds return again and again to one or more favorite perches, they take the fruit and its seeds away from the parent tree, spreading Lauraceae trees throughout the forest (Wenny and Levy 1998).
Natural Pest Control
Agricultural pests (principally insects, plant pathogens, and weeds) destroy an estimated 37% of US crops (Pimentel et al. 1995). Destruction varies depending on the crop, where it is grown, and the type of pest. According to study by Oerke and others (1994), production losses due to pests, pathogens, and weeds amount to 15%, 14%, and 13% on average for the principal cereals and potatoes. Without natural predators that keep pests in control, these figures would be much higher. Natural pest control saves farmers billions each year (Naylor and Erlich 1997), and pesticides are no replacement for the services provided by these crop-friendly predators.
Biodiversity as a Source of Inspiration
We value biodiversity for its ability to inspire creativity and to help us solve problems. Biomimicry14 is a relatively new term that refers to the study of models in the natural world as an inspiration to solve problems in agriculture, medicine, manufacturing, and commerce. Humans have long drawn inspiration from the wild:
Velcro was patterned after cockleburs, a plant that has spiny seeds that attach to clothes as people walk through a meadow (Benyus 1997).
A closer look at hedgehog spines, whose supple, strong structure enables them to bend without breaking, led to the development of lightweight wheels in which the tires have been replaced with an array of spines that effectively absorb shock (Benyus 1997).
Millipedes, invertebrates with multiple pairs of legs fringing their long bodies, are being studied to help design robots to carry heavy weights in cramped conditions where significant twisting and turning is necessary (Beattie and Ehrlich 2001).
Scientists study primates such as baboons, chimpanzees, and howler monkeys in the wild to learn how they “self-medicate” against diseases and how they use compounds from plants to regulate processes such as reproduction. This information can help scientists in the search for new drugs for humans (Clayton and Wolfe 1995)
Studies of the structure and function of natural grasslands are revealing new methods for fertilizing crops and protecting them from pests (Benyus 1997).
Enzymes, that can withstand extremely high temperatures, were discovered in bacteria (Thermus aquaticus) in the hot springs of Yellowstone National Park. One of these enzymes, taq polymerase, is central to genetic research, and is used to catalyze the polymerase chain reaction (PCR), allowing DNA to be replicated and manipulated in large quantities over short periods of time. PCR has revolutionized genetic engineering, opening new possibilities for improved health, agriculture, and even criminology (Brock 1994).
Biodiversity also serves as a model for medical research that allows researchers to understand human physiology and disease. When bears hibernate during the winter, they stop most normal functions (such as eating, drinking, urinating, or defecating) for 150 days (Nelson 1987). But unlike some hibernating animals, bears only lower their temperature slightly to accomplish this feat. Researchers are trying to understand the physiological changes that allow them to survive. One discovery is a blood protein that slows organ metabolism and reduces blood coagulation. This protein could be given to trauma patients being rushed to the hospital after a severe accident to minimize blood loss. Bears also recycle urea when they hibernate. In humans a toxic buildup of urine is fatal in a matter of days but bears seem able to break down urea and reuse it to build tissue. Most animals that don’t exercise -- including people -- lose bone, but bears survive hibernation with little to no bone loss; rather than losing calcium they can extract and continue to maintain bone mass (Harlow et al. 2001). Understanding these mechanisms could lead to treatments for kidney disease or osteoporosis.
Tourism and Recreation
Natural areas such as forests, lakes, mountains, and beaches provide venues for commercially valuable outdoor activities such as eco-tourism, bird watching, sport fishing, hunting, and hiking. Costanza and others (1997) estimate that the total recreational value of the world’s resources could be as high as $800 billion annually. The growing ecotourism industry generates an enormous amount of money and is fast becoming a lucrative industry for some developing nations. For example, in Costa Rica, tourism has expanded rapidly since the mid-1980s and is now the leading source of foreign revenue, surpassing the banana industry. [See also the module on Ecotourism and Biodiversity Conservation.]
Kinship With Nature
One important concept that speaks to our deep connections to biodiversity is Biophilia15, which refers to the notion that the love of nature may have been ingrained into our genes by natural selection. Edward O. Wilson coined the term and argues that our very survival through human evolution depended on a detailed knowledge of natural history. This was vital for finding food, shelter, materials, and medicine. Those lacking the ability to develop an intimate knowledge of biodiversity were simply less successful at surviving and reproducing.
The idea of kinship between animals and people is common in many parts of the world. In the islands of the South Pacific, fishing families have a unique relationship with certain animals, usually turtles or sharks. For each family, these special species (or groups of species) are considered sacred and it is taboo to hunt them; this relationship is carried on through the generations.
The natural world has played a central role in the development of human spiritual traditions. Religions help define the relationships between humans and their environment. Many religious guidelines arose as a response to natural phenomena, particularly threatening ones. Rules to protect crops, sustain fisheries, or avoid danger developed from the natural world, punishment was meted out through crop failures or other threats to survival; the reward was a healthy life and continued survival.
Animist belief systems integrate a series of allowed and prohibited actions. Punishment for prohibited actions is usually grave and results in a series of taboos. These taboos often apply to vulnerable natural resources. One example comes from the Lowland Peruvian Amazon; local fishers avoid fishing in particular oxbow lakes and seasonal fishing areas, because of a belief that there are spirits that protect all fish, animals, and plants found there. The most common belief is that these areas have “mothers” (usually giant anacondas [Eunectes murinus], caiman [Caiman crocodilus], jaguars [Panthera onca], or various monkeys) who will kill anyone who tries to extract resources. Research has shown that these lakes are important breeding areas for the fish (Pinedo-Vasquez and Padoch 1993).
Nature is used in religious imagery, and many religious traditions view the contemplation of nature as an important spiritual value (Chevalier et al. 1997):
In Thailand, trees are marked with yellow cloth to denote their sacredness to the Buddhist faith. This practice has saved some sacred groves from illegal logging, since to destroy these trees is a severe crime.
In Japan, Shinto temples are often located in large groves of trees, where spiritual forces are believed to exist.
Human stewardship over plants and animals (God’s other creations less able to protect themselves) is a central tenet of Christian, Judaism, and Islam. For example, the Garden of Eden and Noah’s Ark are important symbols that define human responsibility for biodiversity.
The natural world also provides a rich source of material and symbols used in art and literature. Plants and animals are central to mythology, dance, song, poetry, rituals, festivals, and holidays around the world. The natural world also influences areas as diverse as housing styles, type of dress, and regional farming methods. Nature is incorporated into language and many metaphorical expressions use plants and animals, such as "happy as a clam" or "fat as a pig." In many Asian cultures, bamboo has a central role in arts and traditions and is common in proverbs, for example “Make sure your life is as pure as a bamboo flute.” What plants and animals represent varies from culture to culture. Rats are considered pests in much of Europe and North America, delicacies in many Asian countries, and sacred in some parts of India. Of course, within cultures individual attitudes also vary dramatically.
Many natural scenes from a stunning mountain landscape to a majestic lion evoke feelings of awe or even intense pleasure (Kellert 1996). In studies conducted in industrialized countries, when shown two landscapes, individuals invariably selected natural scenes as more beautiful than the urban ones (Ulrich 1983, Ulrich 1986). People also value species for their beauty, rarity, complexity, and variability (Rossow 1981 – reprinted in van DeVeer and Pierce 1998). People are frequently attracted to natural areas for recreation or relaxation, or as a source of inspiration. Many hobbies reflect people’s fascination with nature, such as bird watching, hiking, gardening, scuba diving, or even watching nature shows (Erlich and Erlich 1992).
Natural communities are dynamic systems, in which component species can have complex interrelationships. Species that have ecological roles that are greater than one would expect based on their abundance are called keystone species16. Removal of one or several keystone species may have ecosystem-wide consequences immediately, or decades or centuries later (Jackson et al. 2001). Ecosystems are complex and difficult to study, thus it is often difficult to predict a priori which species are keystone species. The impact of removing keystone species from kelp forests in the Pacific is examined in Box 2.
Species that are important due to their sheer numbers are often called dominant species17. These species make up the most biomass of an ecosystem.
For example, salt marshes that extend along the Atlantic and Gulf coasts of North America are dominated by several grass species, including spartina patens (saltmeadow cordgrass) and spartina alterniflora (smooth cordgrass) among other species.
The topic of species diversity and community stability and resilience18 is complex. It appears that in many cases species diversity increases an ecosystem’s stability and resilience (Tilman 1999). In other cases, this direct relationship cannot be demonstrated. This may be partially explained by the fact that many ecosystems have built-in redundancies so that two or more species’ functions overlap. Because of these redundancies, some changes in the number or type of species may have little impact on an ecosystem. On the other hand, if enough species are removed, there is a good chance of disrupting ecosystem function. In addition, it is extremely difficult to predict which species are redundant and what the effect of removing any one species would be on a system.
Text Box 2.0
Pacific Kelp Forests
Kelp forests, as their name suggests, are dominated by kelp, a brown seaweed of the family Laminariales. They are found in shallow, rocky marine habitats from temperate to subarctic regions, and are important ecosystems for many commercially valuable fish and invertebrates.
Vast forests of kelp and other marine plants existed in the northern Pacific Ocean prior to the 18th century. The kelp was eaten by herbivores such as sea urchins (Family Strongylocentrotidae), which in turn were preyed upon by predators such as sea otters (Enhydra lutris). Hunting during the 18th and 19th centuries brought sea otters to the brink of extinction. In the absence of sea otters, sea urchin populations burgeoned and grazed down the kelp forests, at the extreme creating “urchin barrens,” where the kelp was completely eradicated. Other species dependent on kelp (such as red abalone Haliotis rufescens) were affected too. Legal protection of sea otters in the 20th century led to partial recovery of the system.
More recently, sea otter populations in Alaska seem to be threatened by increased predation from killer whales (Orcinus orca) (Estes et al. 1998). It appears that whales may have shifted their diet to sea otters when populations of their preferred prey, Stellar sea lions (Arctocephalus townsendi) and Harbor seals (Phoca vitulina) declined. The exact reason for the decline in the sea lion and seal populations is still unclear, but appears to be due to declines in their prey in combination with increased fishing and higher ocean temperatures. As a result of the loss of sea otters, increased sea urchin populations are grazing down kelp beds again.
Interestingly, a similar scenario in kelp forests in Southern California did not show immediate effects after the disappearance of sea otters from the ecosystem. This is thought to be because the system was more diverse initially and thus perhaps more resilient. Other predators (California sheephead fish, Semicossyphus pulcher, and spiny lobsters, Panulirus interruptus) and competitors (abalone Haliotis spp) of the sea urchin helped maintain the system. However, when these predators and competitors were over-harvested as well in the 1950s, the kelp forests declined drastically as sea urchin populations boomed.
In the 1970s and 1980s, a sea urchin fishery developed that then enabled the kelp forest to recover. However, it left a system with little diversity. The interrelationships among these species and the changes that reverberate through systems as species are removed are mirrored in other ecosystems on the planet, both aquatic and terrestrial.
As this example illustrates, biodiversity is incredibly complex and conservation efforts cannot focus on just one species or even on events of the recent past.
Scientific and Educational Value
Biodiversity provides a way for us to understand the world. Darwin’s observations of the diversity of finches on the Galapagos led to the development of his theories of evolution and natural selection (Hunter 2002). Curiosity about the world around us is fundamental not only to scientific investigations, but also to education. The diverse species and ecosystems around us provide unique educational opportunities and models to explore and learn from (Hunter 2002).