The Big Picture

The world's food supply is one potential limiting factor to human population growth. Will the Earth's human population exceed the food production of the planet? We already know that per capita food production is dropping in some parts of the world and for the world as a whole. This means that there is less food per person than there was just a decade ago. Some countries have already experienced famine (China, Bangladesh, Ethiopia, and Somalia) and more will in the future (as of this writing, North Korea is on the brink of starvation, with an estimated one month of food remaining). Some of these famines and food shortages are caused in part by social and political upheaval, and if these problems could be resolved, food production could increase. However, a common problem remains that food is unevenly distributed worldwide. There are nations with food shortages and nations with food surpluses, but no economical and convenient way to distribute the food rapidly between these nations when a shortage develops. In this chapter, you will examine world food production from an ecological perspective. You should try to imagine that you are a visitor from another planet, an ecologist, and that you are attempting to describe to people on your planet what you observed about the food supply in relation to the human population growth while you were on Earth. In this chapter, the authors describe how agro-ecosystems differ from other natural ecosystems, how much land is devoted to agriculture, how water availability can limit food production, how much advances in modern agriculture can improve food production, and how the growth of the human population causes deterioration of the very agro-ecosystems that support that population.

Frequently Asked Questions

• Most human food comes from land-based agriculture and livestock production, although about 5 % comes from fisheries and aquaculture.
• Of the 250,000 species of plants on Earth, about 300 are agricultural crops, but only 100 are grown for food on a large scale.
• Only 20 species of plants comprise the bulk of human food: wheat, rice, corn, potatoes, barley, sweet potatoes, cassavas, soybeans, oats, sorghum, millet, sugarcane, sugar beets, rye, peanuts, field beans, chick-peas, pigeon peas, bananas, and coconuts (listed in order of importance).
• Humans also eat livestock and they feed their livestock alfalfa hay, sorghum, and other grasses, and fish meal.

• Humans currently produce 1,780,000,000 metric tons of grain per year.
• There are approximately 5,700,000,000 humans on Earth. This works out to 0.31228 metric tons/person/year or (1 metric ton = 1000 kg) 312.28 kg/person/year (or 688.5 lbs/person/year).

• In order to maintain a minimal level of activity, people need 200 kg/year; this is the borderline between undernourishment and healthy levels of food intake.
• Many people need more than this level to be active and perform work every day.
• Thus, on a worldwide average, there is more food produced each year (312 kg) than is needed per person (200 kg).

• Food is unevenly distributed worldwide. Some countries have a food surplus (like the USA), and other lack enough food or the infrastructure to distribute it.
• All countries except the USA, Canada, and Australia are net food importers. Many developing countries grow cash crops rather than food crops to gain money to purchase food; thus, they are not self-sufficient when it comes to food production.
• However, many countries and people within those countries do not have sufficient funds to purchase food on the world market. In addition, food distribution systems (boats, trains, trucks, and stores) do not approach the levels that most Americans experience.
• Therefore, an unequal distribution of food results in famine and hunger, even though there is theoretically enough food for all.

• The world's grain supply can be measured in terms of the number of days of grain supply on-hand.
• Since 1960, the number has fluctuated, reaching a low of a 56-day supply in 1973 to a high of a 104-day supply in 1987.
• The 1995 estimate was a 62-day supply.
• By this measure, the supply of grain has been declining.

• It appears that Malthus was correct in 1798 when he predicted that there would be a point when population growth would exceed food production.
• The per capita food production rate is currently declining, after nearly four decades of steady increases in this measure of food production. (see the Environmental Issue, "Was Malthus Right?" in Chapter 10)

• About 2600 kilocalories per day are required for a minimum of activity and for a person to perform work.
• A more reasonable estimate is 3000 kcal/d for the average person, however this is a function of body size. In some climates, more energy may be required to make up for heat loss (Eskimos may need 7000 kcal/d).

• Undernourishment means that insufficient energy is taken in each day to offset metabolic uses. Everyone has a baseline metabolic rate and cellular respiration which is always ongoing. This causes people to use energy even when sleeping.
• If people consume fewer than 2600 kilocalories per day, the baseline metabolic rate, then they are considered undernourished. Undernourished people have little ability to move or work. If they do not receive this baseline metabolic rate, eventually they will die.
• This is the condition that causes death during famines.

• People that are malnourished, in contrast, may have sufficient energy intake in terms of kilocalories, but they are missing specific dietary nutrients, such as a lack of vitamins, proteins or essential amino acids.
• Malnourishment leads to chronic medical conditions such as marasmus or kwashiorkor, which do not kill people outright, but make them very unproductive individuals in society.

• Marasmus (from the Greek marasmos, meaning "wasting away") is a progressive emaciation of the body caused by a lack of proteins and calories.
• Symptoms include a pronounced slowing of growth and extreme atrophy (wasting away) of muscles.
• Occurs most frequently in children.

• Kwashiorkor is a native word in Ghana, meaning "displaced child".
• In this condition, people simply do not get enough protein in their diet. They do receive sufficient calories, however. Because of the lack of protein, they develop neurological problems and learning disabilities.
• Symptoms include edema (swelling), especially near the abdomen; stunted growth; brittle, dry reddish hair; and apathy.
• Occurs most frequently in children.

• This is an ecosystem that has been manipulated by humans to create special conditions in which the crops they prefer to eat can be grown in great abundances.
• These systems are very different than natural ecosystems and require great inputs of energy to maintain in this altered state.

Agro-ecosystems have the following characteristics that distinguish them from other ecosystems:

• Early successional stages - The crops are planted in fields that have been plowed, which creates a disturbance event. The crops that are planted do well in this early successional state, but any colonizer plants that could compete with them are removed (humans call these weeds).
• Monocultures - This means that all the crops in a field are of one species or variety. Genetic and species diversity are low in agro-ecosystems. Soils become depleted of species-specific nutrients if one variety is grown in the same place repeatedly. Crop rotation and artificial fertilizers are used to restore soil fertility.
• Low habitat complexity - Agro-ecosystems are planted in rows, which facilitates harvest, but can also facilitate disease and pest infestations. In natural ecosystems, there is complexity in the distribution of the plant species, so that species-specific infestations cannot spread as easily.
• Simple food webs and food chains - In agro-ecosystems, the food web is early successional low diversity, so there are few top predators. Herbivorous insect species can easily become abundant without the top predators, and this leads to pest outbreaks. In natural ecosystems, there are many species in a web and the predators can hold the prey in check.
• Frequent soil disturbance - plowing the soil represents a regular soil disturbance unlike anything in a natural ecosystem. Plowing increases soil erosion and nutrient losses.

• Crops are planted in the same field but in a designed sequence over many years, so that the soil nutrients can be replaced or recover.
• For example, rather than planting corn in the same field year after year, if the fields are planted with soybeans in alternate years, the soil nitrate levels will be rebuilt. Soybeans are legumes that fix their own nitrogen.

• Also called swidden, milpa, fang, or bush fallow agriculture.
• This is planting a diversity of crops in a cleared forest patch. No plowing, no rows, no pesticides, fertilizers, etc.
• This approach is called polyculture rather than monoculture. Something will always be fruiting and ready to harvest.
• This is sustainable agriculture at low human population densities.

• When soils lack a specific nutrient required by a plant, so that the plant cannot grow without it, that nutrient is called a limiting factor.
• These nutrients could be macronutrients such as sulfur, phosphorous, magnesium, calcium, potassium, nitrogen, oxygen, carbon, and hydrogen.
• They could also be one of the micronutrients, or trace elements, which are typically metals like molybdenum, copper, zinc, manganese, iron, boron, and chlorine. This is true in Australia, which has trace-metal deficient soils.
• It is also possible for there to be too much of each of these nutrients, and if this occurs, the plant will not grow either.

• Justus von Liebig was a farmer and understood about limiting factors.
• He noticed that the abundance and distribution of a species of crop is limited by the single soil nutrient factor that is in shortest supply.
• His law has been extended beyond soil nutrients to many other factors and species, and is the basis for the science of ecophysiology.

• There are several ways in which agricultural production may be increased by humans:
• Increase the farmed land area - we can attempt to farm additional land, but most farmland is already being farmed in the USA. In other areas, there can only be marginal increases in the area of land farmed. Water limits the use of additional land for farming.
• Use drip irrigation, & hydroponics - by using water more efficiently, we may be able to extend the limited water supplied into areas that don't have sufficient water. Drip irrigation is a method of efficiently supplying just the water that is needed for a crop. Hydroponics is growing crops such as lettuce and tomatoes in a totally artificial nutrient medium. This can be done effectively, but it is costly.
• Eating lower on the food chain - Some people believe that it would be better to use rangeland for growing grains for human consumption rather than to feed the grain to cattle and other domestic animals and then eat the animals. The benefit would be that less food energy would be lost to entropy in the food chain, and thus more food would be available for people. There are complicating factors with this simple idea, because not all land that is suitable for grazing can be used for grain production. Some land is only good for rangeland, like on steep slopes or in areas with low rainfall. In addition, animals will always be required by people for dairy food and meat, because humans are simply not adapted to be herbivorous.
• Modification of food distribution - Using massive relief efforts, there is a way of making the food surpluses available where food is scarce. There are many problems to be overcome in this approach, not the least of which is the tremendous cost of transportation of food to where it is needed. Governments need to cooperate and continue to share food among the rich and poor nations, but this is not a long-term solution to world hunger. The solution is to increase local food production rather than to force people to rely on foreign assistance.

• You may wish to consume a vegetarian diet for many reasons, including moral reasons, religious reasons, or you simply wish to "eat low on the food chain".
• Here are some things to bear in mind when and if you become vegetarian.:
• Normally humans are omnivores, not herbivores (see Schneider et al. 1977). The fossil record indicates that our ancestors ate seeds and insects, not leaves. We have largely dropped insects from our diets (except in certain cultures), but we have replaced them with meat. We have evolved from a society that was composed of hunters of meat and gatherers of fruits and seeds. Our dentition and digestive physiology reflect this evolutionary pattern, and these are different from the ruminants, which can obtain energy from cellulose. Humans can get some energy from cellulose, but most of our energy intake is from less complex carbohydrates such as sugars and starches.
• As you can see from the discussion of malnourishment above, one special dietary nutrient to be concerned about is proteins, which are made of amino acids, and are required for a healthy diet. You must consume all the essential amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, typtophan, and valine) in order to make the proteins your body needs to function. These essential amino acids cannot be synthesized rapidly enough by your body, and thus they must be present in your diet. Vegetable proteins are often lacking in essential amino acids; animal diets are not.
• Vegetarian diets can be nutritionally adequate if the foods consumed are selected wisely, because one vegetable lacking in a specific amino acid can be complemented with another vegetable protein that has the missing nutrient. For example, grains and legumes should be consumed together to provide all essential amino acids. One problem for those that choose to consume no animal products (no eggs, cheese, dairy products, etc.) is the absence of vitamin B₁₂ in the diet, which is only found in animal food (insects are animals, so they are rich in B₁₂). "Vegans", people who eat no animal products, must take vitamin B₁₂ supplements to maintain good nutritional health. Also, they should take calcium supplements, because most calcium comes from dairy products. Vegetarians should eat foods in combination as shown in the following table. Always consume something from Columns I and II:

• The name Green Revolution is given to the suite of crop improvements that were developed after World War II, including the use of genetic strains that grew well under conditions of unlimited fertilizer and pesticide application.
• These high-yielding varieties have produced some tremendous crops in the past, but there may be a limit to the amount of increased productivity that can be obtained using these methods.
• Also, because of the exclusive use of these genetic superstrains, overall crop genetic diversity has declined.

• Only 11 % of the Earth's land surface is considered good for farming.
• In the USA, it is more like 25 %, but 80 % of that is already being farmed. In the USA, there are 190 million ha of farmland for crops, and another 300 million ha for pasture and grazing (Figure 10.11)

• There is a net loss of 500,000 ha/year. Actually, 1 million ha are lost to development for human housing each year, but there are an additional 500,000 ha that are added through wetland drainage and irrigation of dry lands.

What is aquaculture?

• Aquaculture is the production of food from aquatic habitats using controlled breeding and rearing environments. There are many species of fishes and invertebrates that can be grown in culture environments, as the Chinese have been doing with carp in rice ponds since 475 B.C.
• In this ancient Chinese practice of carp and silkworm culture, carp are grown in ponds with mulberry trees planted around the edge. Silkworms consume the mulberry leaves and their waste products stimulate pond phytoplankon, which are fed upon by the carp. The sediment from the pond is used for fertilizer, so all nutrients are recycled in this simple system.
• There is great potential for the world to obtain some of its animal protein by means of aquaculture in the future. However, except in a few situations with a few species like catfish and shrimp, this practice is too expensive or it takes too long to obtain a marketable crop. In addition, unless every waste product is recycled as in the carp aquaculture, there will be pollution problems with aquaculture.

• This is aquaculture in a marine environment.
• There are many examples of successful, small-scale mariculture projects, but only a very few are economically viable.
• Pen-raised salmon are perhaps the best example of a closed maricuture system in the sea, but these fish are a high-dollar crop that will do little to solve the world's food crisis.
• There is potential for species like tilapia, which unlike salmon is a herbivore that can be grown in salt-water pens or ponds.
• Shrimp farming is extremely profitable, and 22 % of the world's shrimp are farm-raised.
• It is unlikely that mariculture will be the answer to world food problems, because it is far cheaper and easier to capture naturally spawned wild fish and invertebrates.

Ecology In Your Backyard

• Where does your food come from?
• What are the most common grains in your diet?
• What percentage of your diet is animal and plant food?
• Are you a vegetarian or an omnivore in your food habits?
• How can you eat lower on the food chain?
• Please respond to these questions or send your thoughtful comments to:

Hardcopy Links In The Library

• Register, U.D., L. M. Sonnenberg. 1973. The vegetarian diet. Journal of the American Dietary Association 62: 253.
• Recommended Dietary Allowances. Washington, DC, National Academy of Sciences Press.
• Schneider, H. A., C. E. Anderson, and D. B. Coursin (eds.) 1977. Nutritional Support of Medical Practice. Medical Department, Harper & Row, Publishers, Hagerstown, MD.

Ecolinks On The Web

• http://www.usda.gov/ - The United States Department of Agriculture Website. At the following link, you may read about what the USDA thinks Americans should eat to stay healthy: http://www.usda.gov/fcs/library/0102-1.txt

• http://www.ars.usda.gov/is/np/siysc.htm - Science in your shopping cart. The USDA's home page about foods and what research projects they doing to improve food stocks.

• http://www.ioa.com/home/aquamag - Aquaculture Magazine an excellent source of information and new developments in growing foods in ponds and the seas.

• http://www.fao.org/ - The UN Food and Agriculture Organization - Check out this excellent website for great information on the state of the world's food supply and the potential for future fishery harvests.

• http://www.foodweb.com/ - Foodweb.com. This is a great website, but mostly for the recipes, including a list of good ones about vegetarian/vegan meals.

 

• Note: If any of these links are not working, please see if alternative links are available at the Ecolink Update Site.

Ecotest Online

 1.Which of the following must a vegetarian human consume to ensure that all the essential amino acids are available in their diets?

a. beans and milk

b. Legumes and cheeses

c. Grains and Legumes

d. nuts and grains

2. The most efficient way to water crops is to use ________ irrigation.

a. ditch

b. drip

c. canal

d. spray

3. Which of the following foods is of greatest importance (by biomass) in the diet of the human population?

a. hamburger meat

b. chicken

c. fish

d. wheat

e. none of theses are correct

4. Which is greater on an annual basis, the amount of food produced per person, or the amount of food needed per person to meet basic needs?

a. food produced per person

b. amount of food needed per person

c. the amounts are the same

5. What is the main cause of world hunger?

a. There is not sufficient food produced each year in the world.

b. Sufficient food is produced, but it is poorly distributed in the world.

c. There is sufficient food, but hungry people are too weak to feed themselves.

d. There is no world food problem.

6. _____________________ is caused by a diet of too few calories.

a. Marasmus
b. Kwashiorkor

c. Undernourishment

d. Malnourishment

7. Food production, measured in number of days of grain supply on-hand, has been

a. holding steady at 104-day supply since 1973

b. has been steadily declining since 1960's high of a 62-day supply

c. has been steadily increasing since the 1960 low of a 56-day supply

d. has fluctuated, but has declined since 1970's high of 104-day supply to the 1995 level of a 62-day supply

8. Agro-ecosystems differ from normal ecosystems in which of the following ways?

a. They are late-successional stages

b. The are polycultures of many crop species

c. They have high habitat complexity

d. They have simple food webs and food chains

e. They have infrequent soil disturbance

9. ____________________ agriculture is done on small patches of cleared forest land with many species of crops grown together, without any rows, pesticides, or fertilizers.

a. Swidden

b. Milpa

c. Fang

d. Bush fallow

e. All of these are correct.

10. One sustainable method of aquaculture that has produced food for humans for over 2000 years and that is becoming more common today is __________________________.

a. farming of salmon in pens

b. shrimp ponds

c. tilapia culture

d. carp culture

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