The continued health of human societies depends upon a natural environment that is productive and contains a wide diversity of plant, animal, and microbe species. Life on the earth comprises at least 10 million species of plants, animals, and microbes, while in the United States there are an estimated 750,000 species, of which small organisms such as anthropods and microbes comprise 95 percent.
The sustainability of the forest ecosystems and other natural ecosystems are in danger from the expanding world population, which now totals of more than 6 billion. With an estimated growth rate of 1.4 percent per year, it is projected to reach 12 billion by the year 2050. Further, due in large part to the growing human population and diverse human activities (supported in large part by fossil fuels), the current extinction rate of species ranges from approximately 1,000 to 10,000 times higher than natural extinction rates. This is alarming for several reasons. Foremost, biodiversity is essential for the sustainable functioning of agricultural, forest, and natural ecosystems upon which human survival and health depends. The loss of a key species (e.g., loss of a predator) creates an imbalance among the remaining species, and can sometimes rest in the collapse of the entire ecosystems. Altering a habitat may also improve the environment for an infectious disease, like dengue.
Species diversity affects the quantity and quality of human food supply. For example, conserving pollinations and natural enemies of pests is essential for successful grain, fruit, and vegetable production. Improving food production decreases malnutrition. Yet, at present, the rapidly expanding human population is intensifying the need for increased food supplies. In the year 2000, more than 3 billion people were suffering from malnutrition which is the largest number and proportion of people to date. Each year, between 6 million and 14 million people die from the effects of malnutrition.
In many parts of the world, especially in developing countries (e.g., in the Sahelian region of Africa), severe shortages of vitamin A are causing blindness and even death. Worldwide, approximately 250 million children are vitamin A deficient, and each year vitamin A deficiency causes approximately 2 million deaths and 3 million serious eye problems, including blindness.
Similarly, iron intake per person has been declining, especially in the Sub-Saharan Africa, South Asia, the People's Republic of China, and South America, because overall shortages of food result in inadequate nutrition. In 1998 more that 2 billion persons were sufficiently iron deficient to cause anaemia in 1.2 billion people. An estimated 20 percent of the malnutrition deaths are attributed to severe anaemia.
Malnutrition is also associated with parasitic infections that are found in areas where conditions of poverty and inadequate sanitation also exist. The health of malnourished individuals, especially children, is seriously affected by parasitic infections, because their presence reduces the availability of nutrients. Parasitic infections diminish appetites while increasing the loss of nutrients, by causing diarrhea and dysentery. Hookworms, for instance, can suck as much as 30 milliliters of blood from an infected individual each day, lowering his or her resistance to other diseases. Because an estimated 5 to 20 percent of an individual's daily food intake is used by the body to offset the effects of parasitic illnesses, the overall nutritional status of a parasite-infected person is greatly diminished over time.
As a human population continues to expand and biodiversity declines, waste grows and its disposal becomes a major environmental problem. Each year, the total quantity of waste produced by humans, livestock, and crops weighs about 38 billion tons worldwide. Numerous invertebrate animals and microbes function to degrade and recycle wastes. Their preservation in ecosystems is essential to maintain a healthy and productive environment.
Worldwide chemical waste and pollution are also major environmental problems. In the twenty-first century in the United States, 80,000 different chemicals are used and released into the soil, water, and air; worldwide, an estimated 100,000 chemicals are used. In the United States, more than 1,100 kilograms of chemicals per person are used each year; nearly 10 percent of these are known carcinogens. Each year nearly 3 billion kilograms of pesticides are applied worldwide. These toxic chemicals cause 26 million human poisonings annually, with about 220,000 deaths, and affect approximately 750,000 people with chronic diseases like cancer.
Approximately 75 percent by weight of the chemicals released into the environment can be degraded by biological organisms. Thus, species biodiversity helps provide continuos cleanup of contaminated sites (such as residue of pesticides in agriculture), and has a significant advantage over other techniques. Conserving beneficial natural enemies not only controls crop pests but also helps reduce the amount of pesticides applied.
In addition to degrading chemicals, some invertebrate and microbe species also degrade and recycle biological pollutants in water resources. Again, the biological pollution problem is particularly serious in developing nations. About 1.2 billion people in the world lack clean, safe water because most household and industrial wastes are dumped directly into rivers and lakes without treatment. this pollution contributes to the rapidly increasing incidence of diseases worldwide and 90 percent of all infectious diseases found in developing countries. A lack of sanitary conditions contributes to about 2 billion human infections of diarrhea, resulting in about 4 million deaths, per year, mostly among infants and young children.
Sometimes altering a natural habitat inadvertently leads to the spread of an infectious diseases. Diseases like schistosomiasis that are associated with contaminated fresh water are expanding worldwide. In 1999, it was estimated that schistosomiasis caused 1 million deaths per year. The escalation of the incidence of this disease followed an increase in suitable habitats for the snail that serves as the intermediate host of the causative agent, Schistosoma mansoni. Thus, construction in 1968 of the Aswan High Dam in Egypt and its related irrigation systems was followed by an explosion in the prevalence of Schistosoma mansoni, which increased in the human population from 5 percent in 1968 to 77 percent in 1993.
Considered together, the natural biodiversity of plants, animals, and microbes functions in many ways to enhance the health and quality of life enjoyed by human society. In view of the likely continued growth in human population, and the resultant alteration of the earth's fragile natural ecosystems, greater efforts must be made to conserve biodiversity as a natural and essential treasure.
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