Food Web

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Food Web




Parts of an Ecosystem

This diagram presents a simplified community of interacting organisms, known as an ecosystem. Decomposers, producers, and consumers are connected to one another according to the food they provide or the food they eat. Click on the labels to learn about the parts of an ecosystem.

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Food Web, set of interconnected food chains by which energy and materials circulate within an ecosystem (see Ecology). The food web is divided into two broad categories: the grazing web, which typically begins with green plants, algae, or photosynthesizing plankton, and the detrital web, which begins with organic debris. These webs are made up of individual food chains. In a grazing web, materials typically pass from plants to plant eaters (herbivores) to flesh eaters (carnivores). In a detrital web, materials pass from plant and animal matter to bacteria and fungi (decomposers), then to detrital feeders (detritivores), and then to their predators (carnivores).

Generally, many interconnections exist within food webs. For example, the fungi that decompose matter in a detrital web may sprout mushrooms that are consumed by squirrels, mice, and deer in a grazing web. Robins are omnivores, that is, consumers of both plants and animals, and thus are in both detrital and grazing webs. Robins typically feed on earthworms, which are detritivores that feed upon decaying leaves.




Marine Food Pyramid

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The food web can be viewed not only as a network of chains but also as a series of trophic (nutritional) levels. Green plants, the primary producers of food in most terrestrial food webs, belong to the first trophic level. Herbivores, consumers of green plants, belong to the second trophic level. Carnivores, predators feeding upon the herbivores, belong to the third. Omnivores, consumers of both plants and animals, belong to the second and third. Secondary carnivores, which are predators that feed on predators, belong to the fourth trophic level. As the trophic levels rise, the predators become fewer, larger, fiercer, and more agile. At the second and higher levels, decomposers of the available materials function as herbivores or carnivores depending on whether their food is plant or animal material.




Through these series of steps of eating and being eaten, energy flows from one trophic level to another. Green plants or other photosynthesizing organisms use light energy from the sun to manufacture carbohydrates for their own needs. Most of this chemical energy is processed in metabolism and dissipated as heat in respiration. Plants convert the remaining energy to biomass, both above ground as woody and herbaceous tissue and below ground as roots. Ultimately, this material, which is stored energy, is transferred to the second trophic level, which comprises grazing herbivores, decomposers, and detrital feeders. Most of the energy assimilated at the second trophic level is again lost as heat in respiration; a fraction becomes new biomass. Organisms in each trophic level pass on as biomass much less energy than they receive. Thus, the more steps between producer and final consumer, the less energy remains available. Seldom are there more than four links, or five levels, in a food web. Eventually, all energy flowing through the trophic levels is dissipated as heat. The process whereby energy loses its capacity to do work is called entropy.

Contributed By:
Robert Leo Smith

Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.










Preliterate Societies

Trepanned Skull

Trepanning, the procedure of cutting a hole in the skull, is the earliest known medical operation. Some anthropologists believe that trepanning was performed on people with mental illnesses to drive out evil spirits from their heads. This skull dates from the Inca civilization.

Daniele Pellegrini/Photo Researchers, Inc.

Evidence for trepanning, the surgical procedure of cutting a hole in the skull, dates back 4,000 to 5,000 years. Some anthropologists speculate that Stone Age societies performed trepanning on people with mental illnesses to release evil spirits or demons from their heads. In the absence of written records, however, it is impossible to know why the operation was performed.



Ancient Societies


The Greek physician Hippocrates was one of the first scholars to challenge the notion that disease was punishment sent from the gods. He believed that all illnesses, including mental illnesses, had natural origins.

Culver Pictures

The literature of ancient Greece and Rome contains evidence of the belief that spirits or demons cause mental illness. In the 5th century bc the Greek historian Herodotus wrote an account of a king who was driven mad by evil spirits. The legend of Hercules describes how, driven insane by a curse, he killed his own children. The Roman poets Virgil and Ovid repeated these themes in their works. The early Babylonian, Chinese, and Egyptian civilizations also viewed mental illness as possession, and used exorcism—which sometimes involved beatings, restraint, and starvation—to drive the evil spirits from their victim.

Not all ancient scholars agreed with this theory of mental illness. The Greek physician Hippocrates believed that all illnesses, including mental illnesses, had natural origins. For example, he rejected the prevailing notion that epilepsy had its origins in the divine or sacred, viewing it as a disease of the brain. Hippocrates classified mental illnesses into categories that included mania, melancholia (depression), and phrenitis (brain fever), and he advocated humane treatment that included rest, bathing, exercise, and dieting. The Greek philosopher Plato, although adhering to a somewhat supernatural view of mental illness, believed that childhood experiences shaped adult behaviors, anticipating modern psychodynamic theories by more than 2000 years.



The Middle Ages

The Middle Ages in Europe, from the fall of the Roman empire in the 5th century ad to about the 15th century, was a period in which religious beliefs, specifically Christianity, dominated concepts of mental illness. Much of society believed that mentally ill people were possessed by the devil or demons, or accused them of being witches and infecting others with madness (see Witchcraft). Thus, instead of receiving care from physicians, the mentally ill became objects of religious inquisition and barbaric treatment. On the other hand, some historians of medicine cite evidence that even in the Middle Ages, many people believed mental illness to have its basis in physical and psychological disturbances, such as imbalances in the four bodily humors (blood, black bile, yellow bile, and phlegm), poor diet, and grief.

The Islamic world of North Africa, Spain, and the Middle East generally held far more humane attitudes toward people with mental illnesses. Following the belief that God loved insane people, communities began establishing asylums beginning in the 8th century ad, first in Baghdād and later in Cairo, Damascus, and Fez. The asylums offered patients special diets, baths, drugs, music, and pleasant surroundings.



The Renaissance

The Renaissance, which began in Italy in the 14th century and spread throughout Europe in the 16th and 17th centuries, brought both deterioration and progress in perceptions of mental illness. On the one hand, witch-hunts and executions escalated throughout Europe, and the mentally ill were among those persecuted. The infamous Malleus Maleficarum,which served as a handbook for inquisitors, claimed that witches could be identified by delusions, hallucinations, or other peculiar behavior. To make matters worse, many of the most eminent physicians of the time fervently advocated these beliefs.

On the other hand, some scholars vigorously protested these supernatural views and called renewed attention to more rational explanations of behavior. In the early 16th century, for example, the Swiss physician Paracelsus returned to the views of Hippocrates, asserting that mental illnesses were due to natural causes. Later in the century, German physician Johann Weyer argued that witches were actually mentally disturbed people in need of humane medical treatment.



The Age of Enlightenment

Pinel Frees the Insane

French physician Philippe Pinel supervises the unchaining of mentally ill patients in 1794 at La Salpêtrière, a large hospital in Paris. Pinel believed in treating mentally ill people with compassion and patience, rather than with cruelty and violence. This painting, Pinel Frees the Insane from Their Chains, was completed by French artist Tony Robert-Fleury in 1876.

Belzeaux/Photo Researchers, Inc.

During the Age of Enlightenment, in the 18th and early 19th centuries, people with mental illnesses continued to suffer from poor treatment. For the most part, they were left to wander the countryside or committed to institutions. In either case, conditions were generally wretched. One mental hospital, the Hospital of Saint Mary of Bethlehem in London, England, became notorious for its noisy, chaotic conditions and cruel treatment of patients (see Bedlam).


The Hospital of Saint Mary of Bethlehem, a London mental hospital commonly known as Bedlam, sold admission tickets to the public in the 18th century, becoming a popular tourist attraction. In this engraving by English artist William Hogarth, part of his series A Rake’s Progress (1735), two women (seen in the background) tour the hospital, watching the mentally ill patients for their amusement. The hospital became notorious for its miserable conditions and cruel treatment of patients.

Art Resource, NY

Yet as the public’s awareness of such conditions grew, improvements in care and treatment began to appear. In 1789 Vincenzo Chiarugi, superintendent of a mental hospital in Florence, Italy, introduced hospital regulations that provided patients with high standards of hygiene, recreation and work opportunities, and minimal restraint. At nearly the same time, Jean-Baptiste Pussin, superintendent of a ward for “incurable” mental patients at La Bicêtre hospital in Paris, France, forbade staff to beat patients and released patients from shackles. Philippe Pinel continued these reforms upon becoming chief physician of La Bicêtre’s ward for the mentally ill in 1793. Pinel began to keep case histories of patients and developed the concept of “moral treatment,” which involved treating patients with kindness and sensitivity, and without cruelty or violence. In 1796 a Quaker named William Tuke established the York Retreat in rural England, which became a model of compassionate care. The retreat enabled people with mental illnesses to rest peacefully, talk about their problems, and work. Eventually these humane techniques became widespread in Europe.



Reform in the United States

Clifford Beers

In 1908, after his release from a mental asylum, Clifford Whittingham Beers wrote A Mind That Found Itself, which exposed the poor conditions he had suffered while confined. He went on to establish several organizations dedicated to the promotion of mental health reforms in the United States.

Library of Congress

People living in the colonies of North America in the 17th and 18th centuries generally explained bizarre or deviant behavior as God’s will or the work of the devil. Some people with mental illnesses received care from their families, but most were jailed or confined in almshouses with the poor and infirm. By the mid-18th century, however, American physicians came to view mental illnesses as diseases of the brain, and advocated specialized facilities to treat the mentally ill. The Pennsylvania Hospital in Philadelphia, which opened in 1752, became the first hospital in the American colonies to admit people with mental illnesses, housing them in a separate ward. However, in the hospital’s early years, mentally ill patients were chained to the walls of dark, cold cells.

In the 1780s American physician Benjamin Rush instituted changes at the Pennsylvania Hospital that greatly improved conditions for mentally ill patients. Although he endorsed the continued use of restraints, punishment, and bleeding, he also arranged for heat and better ventilation in the wards, separation of violent patients from other patients, and programs that offered work, exercise, and recreation to patients. Between 1817 and 1828, following the examples of Tuke and Pinel, a number of institutions opened that devoted themselves exclusively to the care of mentally ill people. The first private mental hospital in the United States was the Asylum for the Relief of Persons Deprived of the Use of Their Reason (now Friends Hospital), opened by Quakers in 1817 in what is now Philadelphia. Other privately established institutions soon followed, and state-sponsored hospitals—in Kentucky, New York, Virginia, and South Carolina—-opened beginning in 1824.

Dorothea Dix

American reformer Dorothea Dix championed the causes of prison inmates, the mentally ill, and the destitute. Horrified by the conditions provided for the mentally ill in Massachusetts, Dix successfully petitioned the state government for improvements in 1843. She was directly responsible for building or enlarging 32 mental hospitals in North America, Europe, and Japan.


Nevertheless, circumstances for most mentally ill people in the United States, especially those who were poor, remained dreadful. In 1841 Dorothea Dix, a Boston schoolteacher, began a campaign to make the public aware of the plight of mentally ill people. By 1880, as a direct result of her efforts, 32 psychiatric hospitals for the poor had opened. Increasingly, society viewed psychiatric institutions as the most appropriate form of care for people with mental illnesses. However, by the late 19th century, conditions in these institutions had deteriorated. Overcrowded and understaffed, psychiatric hospitals had shifted their treatment approach from moral therapy to warehousing and punishment. In 1908 Clifford Whittingham Beers aroused new concern for mentally ill individuals with the publication of A Mind That Found Itself, an account of his experiences as a mental patient. In 1909 Beers founded the National Committee for Mental Hygiene, which worked to prevent mental illness and ensure humane treatment of the mentally ill.



Deinstitutionalization Movement

Following World War II (1939-1945), a movement emerged in the United States to reform the system of psychiatric hospitals, in which hundreds of thousands of mentally ill persons lived in isolation for years or decades. Many mental health professionals—seeing that large state institutions caused as much, if not more, harm to patients than mental illnesses themselves—came to believe that only patients with severe symptoms should be hospitalized. In addition, the development in the 1950s of antipsychotic drugs, which helped to control bizarre and violent behavior, allowed more patients to be treated in the community. In combination, these factors led to the deinstitutionalization movement: the release, over the next four decades, of hundreds of thousands of patients from state mental hospitals. In 1950, 513,000 patients resided in these institutions. By 1965 there were 475,000, and by 1990 state mental hospitals housed only 92,000 patients on any given night. Many patients who were released returned to their families, although many were transferred to questionable conditions in nursing homes or board-and-care homes. Many patients had no place to go and began to live on the streets.

The National Mental Health Act of 1946 created the National Institute of Mental Health as a center for research and funding of research on mental illness. In 1955 Congress created a commission to investigate the state of mental health care, treatment, and prevention. In 1963, as a result of the commission’s findings, Congress passed the Community Mental Health Centers Act, which authorized the construction of community mental health centers throughout the country. Implementation of these centers was not as extensive as originally planned, and many people with severe mental illnesses failed to receive care of any kind.



Recent Developments

One of the most important developments in the field of mental health in the United States has been the establishment of advocacy and support groups. The National Alliance for the Mentally Ill (NAMI), one of the most influential of these groups, was founded in 1972. NAMI’s goal is to improve the lives of people with severe mental illnesses and their families by eliminating discrimination in housing and employment and by improving access to essential treatments and programs.

During the 1980s, all levels of government in the United States cut back on funding for social services. For example, the Social Security Administration discontinued benefits for approximately 300,000 people between 1981 and 1983. Of these, an estimated 100,000 were people with mental illnesses. Although the government eventually restored Social Security benefits to many of these people, the interruption of services caused widespread hardship.

The emergence of managed care in the 1990s as a way to contain health care costs had a tremendous impact on mental health care in the United States. Health insurance companies and health maintenance organizations increasingly scrutinized the effectiveness of various psychotherapies and drug treatments and put stricter limits on mental health care. In response to these restrictions, Congress passed the Mental Health Parity Act of 1996. This law required private medical plans that offer mental health coverage to set equal yearly and lifetime payment limits for coverage of both mental and physical illnesses.

In 1997 the U.S. Equal Employment Opportunity Commission issued new guidelines intended to prevent discrimination against people with mental illnesses in the workplace. The rules, based on the Americans with Disabilities Act of 1990, prohibit employers from asking job applicants if they have a history of mental illness and require employers to provide reasonable accommodations to workers with mental illnesses.

In recent years international agencies, led by the World Health Organization (WHO) of the United Nations (UN) have developed mental health policies that seek to reduce the huge burden of mental illness worldwide. These agencies are working to improve the quality of mental health services in Africa, Asia, Latin America, the Middle East, and elsewhere by educating governments on prevention and treatment of mental illness and on the rights of the mentally ill.

Contributed By:
Alex Cohen
Arthur M. Kleinman

Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.