Biodiversity > Context

Biodiversity and Development: Context

What is Biodiversity?

The term biodiversity (shorthand for biological diversity) refers to the full variety of life on earth-plants, animals and micro-organisms-including genes, species and entire ecosystems, and the vital services these ecosystems provide to society.

Biodiversity is considered to exist at three levels: ecosystems, species, and genes. An ecosystem is an array of living things and the physical and chemical environment with which they interact. The functioning of a given ecosystem is driven by its constituent organisms and is best understood as a cyclical flow of energy and materials. Depending on its environmental characteristics (area, latitude, diversity of terrain, etc.) an ecosystem may contain many millions of different species of organism or merely a handful.

The species is the yardstick by which the variety of life is traditionally measured. To date, around 1.7 million species have been discovered and described. This roster of known species is certain to be only a fraction of the total number. The gaps in our knowledge are easily seen. For example, a disproportionate number of named species (over two-thirds) are from the temperate world, for the simple reason that these regions have been home, over the centuries, to the majority of the planet's scientists. By contrast, fewer than half a million tropical species have been formally described. This is sure to be an inaccurate reflection of the true picture, since the tropics are plainly far more 'biodiverse' than the temperate regions. In fact, there are probably 15 to 20 unnamed tropical species for every named one.

For similar reasons, the catalogue of named species is artificially biased towards terrestrial organisms. Only around 275,000 marine species have been identified, compared to some 1.5 million terrestrial species. In reality, coral reef ecosystems alone are probably home to at least one million species, and as many as 10 million more may lurk in the deep ocean basins (only one-tenth of which have been systematically mapped). It is reasonably certain, then, that the greater part of species diversity remains to be discovered. Estimates of the total number of species on earth range from as 'few' as 3.6 million to as many as 100 million.

This magnificent variety of life is the result of billions of years of evolution: the cumulative, non-random selection of random genetic mutations. Evolution is also responsible for genetic diversity among individuals of the same species. The almost limitless variability of genes is thus the ultimate basis of biodiversity.

The Importance of Biodiversity

The extinction of a species or the degradation of an ecosystem leaves the world a poorer place, whether or not that species or ecosystem is of palpable use to humanity. But even if we leave aside such imponderables as life's intrinsic value or the question of a species' right to exist, the critical importance of biodiversity to humankind is clearly seen. In the guise of earth's ecosystems, for example, biodiversity provides the conditions and drives the processes that sustain our very survival. These 'ecosystem services' include:

Generation of soils and maintenance of soil quality
The activities of microbial and animal species, including bacteria, algae, fungi, crustacea, mites, millipedes and worms, condition soils, break down organic matter, and release essential nutrients to plants. These processes play a key role in the cycling of such crucial elements as nitrogen, carbon, sulphur and phosphorous between the living and non-living parts of the biosphere.

Maintenance of air quality
Photosynthetic species purify the air and regulate the composition of the atmosphere, recycling vital oxygen. Plant tissues capture and filter harmful particles resulting from industrial activities.

Maintenance of water quality
Wetland ecosystems (swamps, marshes, etc.) absorb and recycle essential nutrients, treat sewage, and cleanse industrial wastes. In estuaries, molluscs remove nutrients from the water, helping to prevent nutrient over-enrichment and its attendant problems. Trees and forest soils purify water as it flows through forest ecosystems. In preventing soils from being washed away, forests also prevent the harmful siltation of rivers and reservoirs.

Pest control
For all that an estimated 25 to 50 per cent of the world's crops are destroyed every year by pests (before or after harvesting), but for biodiversity, the situation could be a lot worse: around 99 per cent of potential crop pests are currently controlled by a variety of other organisms, including insects, birds and fungi. These natural pesticides are in many ways superior to their artificial equivalents, since pests can often develop resistance to chemical controls.

Detoxification and decomposition of wastes
Some 130 billion metric tons of organic waste is processed every year by earth's decomposing organisms. Many industrial wastes, including detergents, oils, acids and paper, are also detoxified and decomposed by the activities of living things. In soils, the end product of these processes - a range of simple inorganic chemicals - is returned to plants as nutrients. Higher (vascular) plants can themselves serve to remove harmful substances from groundwater.

Plant reproduction
Many flowering plants rely on the activities of various animal species - bees, butterflies, bats, birds, etc. - to help them reproduce through the transportation of pollen from one individual to another. More than one-third of humanity's food crops depend on this process of natural pollination. Many animal species have evolved to perform an additional function in plant reproduction through the dispersal of seeds.

Climate stabilization
Plant tissues and other organic materials within land ecosystems act as repositories of carbon, helping to slow the build-up of atmospheric carbon dioxide, and thus contributing to climate stabilization. Ecosystems also exert direct influences on regional and local weather patterns. Moisture released into the atmosphere by rainforest plants, for example, causes regular thunderstorms, limiting water loss from the region and helping to control the surface temperature. In cold climates, meanwhile, forests act as insulators and as windbreaks, helping to mitigate the impacts of freezing temperatures.

Prevention and mitigation of natural disasters
Forests and grasslands protect landscapes against erosion, nutrient loss, and landslides through the binding action of roots. Ecosystems bordering regularly flooding rivers (floodplain forests and wetlands) help to absorb excess water and thus reduce the damage caused by floods. Certain coastal ecosystems (salt marshes, mangrove forests, etc.) prevent the oceanic erosion of coastlines.

In addition to these services, biodiversity provides goods that are essential to human survival and development. These goods include the vast majority of our foodstuffs. Biodiversity also maintains food security, for when traditional food sources fail, a healthy, 'biodiverse' ecosystem can usually provide viable alternative supplies. Wild biodiversity guards against the failure of even the most advanced agricultural systems. For example, the productivity of many of the developed world's agricultural crops is maintained through the regular assimilation of new genes from wild relatives of these crops. These wild genes offer resistance to the pests and diseases that pose an ever-evolving threat to harvests. Genes drawn from wild populations of wheat and corn alone are worth over $2.7 billion per year to the food economy of the developed world.

In a more direct sense, wild (i.e. non-cultivated) ecosystems provide a wide variety of important edibles, including fruits, game meats, nuts, mushrooms, honey, spices and flavourings. Natural ecosystems also supply many of our most important building materials, fibres, and fuels, together with waxes, resins, aromatics, dyes, gums and pharmaceuticals.

Even in its wholly untapped state, biodiversity does great service to the global economy through 'ecotourism'. People taking nature-related holidays contribute at least $500 billion per year to the national incomes of the countries they visit. Florida 's coral reefs, for example, earn around $1.6 billion per year through tourism alone.

It's no wonder people are prepared to spend so much to experience wild biodiversity. The human species has evolved over millions of years to derive aesthetic and spiritual satisfaction from the natural world. Recent studies have begun to confirm what has always been known: our emotional wellbeing is enhanced by the proximity of nature. The umbilical bond between humanity and biodiversity is reflected in the art, religions and traditions of perhaps a majority of cultures: a spiritual heritage that will be rendered meaningless if its basis - nature itself - continues to be destroyed.

Biodiversity under Threat

The most obvious manifestation of biodiversity loss, and the only truly irreversible one, is the extinction of a species. This is a natural phenomenon: species have been going extinct since life began. Indeed, it is estimated that many more species have gone extinct than are currently in existence. For the greater part of life's history, during which environmental change has occurred on a geological timescale, the majority of extinctions have resulted from competition by newly evolved species with superior biological adaptations. The average lifespan of a species during these periods of relative stability has been estimated at around four million years - a rate of extinction that is more than equaled by the 'background' rate of species generation through evolution.

The fossil record suggests that this status quo has been punctuated on five or six occasions by brief periods of sudden and extensive species loss. The most recent such 'catastrophic extinction event' took place at the end of the Cretaceous period (some 65 million years ago). Around two-thirds of earth's species were wiped out, including, famously, the dinosaurs. The agent of disaster in this instance was most probably a massive asteroid impact. According to this theory, the extreme force generated by the collision threw a vast quantity of particulate matter into the atmosphere, severely restricting the amount of sunlight reaching the ground and thereby preventing photosynthesis in plants. The consequent destruction of plant life devastated plant-dependent species and ecosystems. As the dust clouds settled, evolution set about restoring earth's stricken biodiversity from a stock of around 500,000 surviving species, including birds (the direct descendants of the dinosaurs) and our own ancestors, the mammals.

This work of restoration is currently being undone, and at a rate not seen since the demise of the dinosaurs. Indeed, many have argued that the current spate of species loss should be viewed as a catastrophic extinction event in its own right. The present catastrophe differs from all such previous events in one important respect, however, for it is the result of the actions of a single species: Homo sapiens.

Since the total number of species on earth can only be guessed at, the exact rate of current species loss is difficult to gauge. The figure probably stands at between 50 and 150 extinctions per day. Working from the conservative estimate that earth is home to ten million species in all, this means that between 0.2 and 0.6 per cent of all species are being lost every year. This rate is at least 10,000 times greater than the 'background' or natural rate of species extinction, estimated (using the fossil record) at only 2.5 species per year.

The annual extinction rate is increasing still further. Over the next few decades, earth is on course to lose around 50,000 species per year. By 2100, according to current trends, fully two-thirds of species will have gone extinct.

The World Conservation Union (IUCN) has estimated that over 5,200 species of animals - including birds, mammals, reptiles, amphibians, fishes and invertebrates - are currently threatened with extinction, together with 34,000 species of higher plants.

Those considered vulnerable, threatened, or critically endangered include:

> Close to 1,100 species of mammals (about 24 per cent of the total number)

> Over 1,100 birds (around 12 per cent of known species)

> Over 2,000 species of freshwater fish (around 20 per cent of total number)

> Around 250 species of reptiles (20 per cent of total number surveyed)

> An estimated 125 species of amphibians (25 per cent of the total number surveyed)

The picture is no more encouraging from an ecosystem perspective:

> More than 50 per cent of the world's wetlands have been drained.

> Since 1950, some 3 billion hectares of forest cover - nearly half - has been lost. Each year, a further 16 million hectares of forest are destroyed.

> Between 50 and 80 per cent of mangrove ecosystems have been destroyed.

> Roughly one-third of the world's coral reef systems have been destroyed or highly degraded.

> One-fourth of the planet's topsoil has been lost.

> 69 per cent of the world's major fish stocks are either fully exploited, over-fished, depleted, or slowly recovering, and productivity has fallen in all but four of the 15 most important fishing regions.

> Nearly 2 billion hectares of crop and grazing land are suffering from moderate to severe soil degradation.

Genetic diversity within species is also being eroded. This trend is especially alarming from the perspective of humanity's agricultural systems. Since 1900, some three-quarters of the genetic diversity of cultivated crops have disappeared, together with nearly half of the gene pool of the wild relatives of domestic animals. The loss of genetic diversity matters because the world's agricultural systems depend on the regular assimilation of wild genes to stay one step ahead of the threat posed by pests and diseases.

The major causes of biodiversity loss include:

Habitat destruction
Ecologists have observed that an area of ten square miles contains twice as many species, on average, as an area of one square mile, suggesting that to reduce an area of ecosystem to a tenth of its original size will cause half its species to become extinct. Animals at the top of the food chain (lions, bears, etc.) require especially large habitats in order to maintain viable wild populations.

Invasive species
Ecosystems are fragile balancing acts, evolved over millions of years as an integrated whole. The sudden introduction to a given ecosystem of an alien species can severely disrupt its normal functioning - with disastrous consequences for native species. Such introductions are most often the result of human activities. The accidental introduction to the Black Sea of an Atlantic comb jellyfish species is a well-known example. These invaders have out-competed native fauna, and now comprise some 95 per cent of the Black Sea 's total biomass. In the US , meanwhile, the introduction of exotic species has been implicated in close to 70 per cent of the past century's freshwater fish extinctions.

Pollution
The chemical contamination of fresh water, seawater and soils can lead to the disappearance of populations and species. Acid rain, for example, can render lake habitats inhospitable to aquatic species.

Climate Change
Over the past century or so, global temperatures have risen by between 0.3 and 0.6°C (the largest increase in at least 1,000 years), due in large part to the increased presence in the atmosphere of 'greenhouse gases' from industrial processes. The effects of climate change have so far included a rise in sea levels of some 10-25 cm worldwide, a loss of glacier ice, changes in precipitation patterns, and an increased occurrence of extreme weather events. These fluctuations have disturbed seasonal cycles throughout the globe. It is feared that these changes are happening at too fast a rate for many species to adapt.

Over-harvesting
Many species have been harvested or hunted to rarity and beyond. Examples of such directly wrought extinctions include those of the passenger pigeon and the Carolina parakeet in the early part of the twentieth century. More recently, the Central African 'bushmeat' trade has placed mountain gorillas and chimpanzees under direct threat.

Biodiversity loss is not the inevitable result of social and economic development; environmental sustainability is possible. But there are a number of specific factors standing in the way of its widespread achievement. These factors originate in some of the most basic social, economic, political, cultural and historical features of society. They include:

Social, political and institutional weaknesses such as unsustainable production and consumption patterns, poverty, lack of clear land use rights, uneven distribution of land ownership, poor governance, fragmented decision making, lack of political will, political unrest and wars.

Market and economic policy failures such as inappropriate regulatory mechanisms, harmful subsidies and incentives, inadequate economic valuation of biodiversity, the absence of local and global markets for biodiversity goods and services and the lack of clear environmental and development policies.

Lack of knowledge of biodiversity's importance, particularly among those directly involved in the management of biodiversity and among economic and developmental decision-makers.

With these factors in mind, it is clear that just as humanity depends on biodiversity for its survival and development, the long-term survival of earth's biodiversity will necessitate the achievement of sustainable human development.

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