Bound together in the web of life

As the World Climate Change summit in Paris ends, a new book underlines the interdependence of all living organisms

Frans Lanting

Before the Fall? Tropical rain forests are the most complex and diverse ecosystems on earth, highly threatened by human activity

Before the Fall? Tropical rain forests are the most complex and diverse ecosystems on earth, highly threatened by human activity

RACHEL CARSON launched the modern environmental movement in 1962 with her scientifically accurate and beautifully written book Silent Spring.

Her book inspired the public, and drove politicians to act. Some dangerous pesticides such as DDT (dichlorodiphenyltrichloroethane) were eventually banned, and the use of others was better controlled. As a result, the disappearing populations of some of the most interesting North American birds, such as the bald eagle and peregrine falcon, began to rebound.

But the banning of DDT did not make it disappear entirely. It is with us today: traces are found in environments and organisms (including people) around the world.

The poison is still killing birds in St Louis, Michigan, the site of a Velsicol Corporation plant that manufactured the pesticide until 1963, and left behind a toxic stew containing DDT in soil and groundwater.

Most of the dangers confronting nature were not removed by the environmental laws, however; human impacts on the environment have turned out to be much more complex and far-reaching than we once thought.

The measures that Carson inspired have been more than countered by other factors in recent decades. The celebrations of the 1970s were premature; for the trends in North America and elsewhere point to an overall downward curve — not just for birds, but also for the populations of most other wild species.

 

SUCH downward trends will have repercussions for humanity in a multitude of ways. All animals, including birds and mammals, are intricately involved in the processes and interactions of other organisms in natural ecosystems.

For example, land animals pollinate flowers; disperse seeds; transmit disease-causing organisms; and consume the roots, stems, seeds, foliage, and flowers of plants. Many prey on other animals, including those that attack our crops.

Most of their interactions with human beings are positive. Besides the ethical tragedy of diminishing the stock of life on earth, the most serious consequences of the declines and disappearances of animal species are the losses of critical natural services that emerge from the global system — losses that have important economic, social, and political implications for humanity.

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Nature’s services (ecosystem services) are the benefits that we humans obtain free from the structure and functioning of ecosystems, which are essential for maintaining life on earth. Put simply, populations of wild species and their activities are vital for maintaining the entire global system on which humanity depends.

 

A RECENT dramatic event in India powerfully illustrates a connection between biodiversity loss and human welfare. Scavenging vultures have been serving as free janitors, very important ones, especially in developing countries with poor sanitation.

The vultures feed on dead and decaying animal carcasses, and, by so doing, assist in nutrient cycling and maintenance of the rich community of tiny animals, plants, fungi, and microbes that make soils productive.

In addition, vultures attract other scavenging animals to carcasses, and together they all prevent the spread of disease by disposing of rotting carcasses quickly.

Vultures locate carcasses by sight, often from miles away, and, in some species, by smell; they are thought to have the best sense of smell of any bird.

Because vultures feed on animals that may have died of disease or poisoning, they obviously must have potent immune systems. The strong acid in their digestive system is believed to kill pathogens that they may pick up from the carcasses.

Further, vultures urinate on their featherless legs; evaporation of the urine cools their bloodstream, and, it has been hypothesised, to kill germs picked up while feeding on carcasses.

Since the 1990s, there has been a more than 90-per-cent decline in vulture populations in India, and similar population collapses have been reported elsewhere in Asia and in Africa.

 

THE veterinary use of the anti-inflammatory drug diclofenac appears to be behind these declines, at least in Asia. Cattle are considered sacred in India; so, when the animals are old, often they are treated with diclofenac to help them cope with joints and muscle pain.

Vultures ingest the drug when they feed on carcasses of livestock that were treated with it. Diclofenac residues in vultures result in renal failure and visceral gout (a build-up of uric acid in internal organs).

Ornithologists have reported that breeding populations of the white-backed vulture have been obliterated from the Keoladeo National Park in India, possibly because of diclofenac-related effects. To reverse the decline of vultures, the Indian government banned diclofenac in 2006.

Pharmaceutical companies in the Indian subcontinent are now promoting a new drug that is considered safe for vultures — meloxicam — as an alternative to diclofenac. We hope, however, that any negative effects of this drug on biodiversity will be carefully evaluated before its use becomes widespread.

The decline of vultures appears to have resulted in population explosions of disease-carrying rats and feral dogs. India suffers one of the highest numbers of human deaths due to rabies.

Because feral dogs are replacing vultures as carcass disposers, there have been concerns in India about the recent rise in rabies. The increase in cases of rabies and other diseases has amplified the repercussions of declines in vultures on human health.

 

AN OUTBREAK of bubonic plague in India in 1994 is suspected to have been due to an increased population of rats infested with plague-carrying fleas.

The rat population may have risen with the numbers of undisposed carcasses. In addition to 54 human deaths, the plague cost the Indian economy an estimated $US2 billion for quarantine measures, human evacuations, and a loss of tourism dollars.

Pathogens such as those that cause rabies and canine distemper also can be transmitted by rats and feral dogs to a wide range of other potential host species, such as mongooses and jackals, populations of which may increase as vultures decline in African savannas, and as carcasses become more available to them.

Cattle carcasses left to rot, it is feared, could also spread anthrax to livestock. Scavengers that replace vultures at carcasses thus may spread diseases to wildlife, livestock, and human populations.

 

THE loss of vultures has other social and economic implications. For centuries, vultures have played an indispensable part in Parsee burial-ceremonies. Parsees originated as Zoroastrians in Iran, who migrated to India in the tenth century because of persecution by Muslims. The global population of Parsees is estimated at about 100,000.

Parsees believe that if they burn a dead body, they will dishonour fire. And, if they bury the dead, they will pollute the earth. Therefore, they use the Tower of Silence, on which dead bodies are exposed to the skies and to the vultures, which eat the remains.

Most Parsees in India are now concentrated in Mumbai (formerly known as Bombay). They have been taking their dead to a parkland hill on the outskirts of the city. This place was originally secluded, but, thanks to human population expansion, it is now surrounded by urban sprawl.

It contains a number of Towers of Silence. Until the 1990s, hundreds of vultures could be seen perching on the towers, and they competently disposed of the bodies.

The disappearance of vultures from Mumbai is now causing a spiritual crisis among the Parsees. To counter the loss of vultures as the principal agents for disposal of the bodies, the Parsees are currently using solar panels to concentrate heat on the dead bodies and speed the process of decomposition.

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Parsees remain divided, however, on whether their ancient burial ritual is outdated. Some argue that “sky burial” is archaic, and should be replaced by cremation, while others have proposed that vulture aviaries should be erected over some of the towers.

Finally, the decimation of vulture populations is also having an impact on some traditional occupations.

Vultures can clean a carcass quickly, leaving little more than bones, which are then gathered by bone collectors and sold to fertiliser, gelatin, and glue industries. But this is becoming almost impossible because of the lack of vultures; their decline thus has been jeopardising the livelihoods of already impoverished bone-collectors.

 

This is an edited extract, with illustrations, from The Annihilation of Nature: Human extinction of birds and mammals by Gerardo Ceballos, Anne H. Ehrlich, and Paul R. Ehrlich, published by John Hopkins University Press at £19.50 (Church Times Bookshop £17.55).

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