Chapter 5.1Human Population Expansion and its Cause

rapid human population expansion is a recent event, occurring mainly over the last 100 years until the 1800s, population growth was slow periodic setbacks kept the population

relatively small

human population totals

1830—1 billion 1930—2 billion 1960—3 billion 1975—4 billion 1987—5 billion 1999—6 billion

reasons for patterns of growth

before 1800s, fatal illnesses such as smallpox, diphtheria, measles, and scarlet fever combined to limit population growth

cholera and epidemics such as the black plague eliminated large numbers of adults

high reproductive rates were balanced by high mortality, especially in children

breakthroughs

late 1800s, Louis Pasteur and others discovered that diseases were caused by infectious agents organisms were transmitted via water, food, insects, and

rodents vaccinations were developed against many viruses communities began treating their sewage and

drinking water penicillin was the first antibiotic discovered in 1930 improvements in nutrition

declines

world population growth rate peaked at 2.1% per year in the 1960s after rising steadily for decades

by the 1980s, the number of humans added per year peaked at 87 million

declines are a result of a decrease in total fertility rates

total fertility rate was an average of 5.0 children in the 1960s; it is now 2.7 children per woman

Chapter 5.2Rich Nations, Poor Nations

World Bank divides countries into three main economic categories: 1. high income, highly developed, industrialized

countries Ex. USA, Canada, Australia, western Europe

2. middle-income, moderately developed countries Ex. Mexico, South Africa, eastern Europe

3. low-income, developing countries central African countries, central Asian countries

human poverty index

long and healthy life: probability at birth of not surviving to age 40

knowledge: adult literacy rate decent standard of living:

percentage of population not using improved water sources

percentage of children under 5 who are underweight 10-15% of people in developed countries are

unable to afford adequate food, shelter, or clothing (compare to 45% in developing countries)

population growth in rich and poor nations

developed world (estimated population = 1.2 billion) is growing at rate of 0.1% per year…adds less than 1 million people per year

remaining countries (population = 5.4 billion) are increasing at a rate of 1.5%per year…adds more than 75 million people per year

fertility

population growth occurs when births outnumber deaths

with lower mortality, major determining factor for population growth is births, measured by the total fertility rate

fertility rates greater than 2.0 lead to a growing population

replacement-level fertility accounts for childhood mortality (fertility rate that will replace population of parents is 2.1 in developed countries)

Chapter 5.3Consequences of Population Growth and Affluence

developing countries before the Industrial Revolution, most of the

human population survived through subsistence agriculture

families lived on the land, raised livestock, and produced enough crops for their own consumption and perhaps some extra for selling and trading

impacts of rapid growth on a population that is farming-based:

2. INTENSIFY CULTIVATION introduction of more highly productive

varieties of basic food crops puts more stress on land and soil (no crop

rotation or seasons off for fields) stress can lead to erosion and desertification

impacts of rapid growth on a population that is farming-based:

3. OPEN NEW LAND TO FARM most good agricultural land is already in production opening new land means disrupting natural

ecosystems, most likely including deforestation 4. ILLICIT ACTIVITIES

shortage of jobs outside of agriculture often drives individuals into theft, corruption, drug-related crop growth, and poaching wildlife

impacts of rapid growth on a population that is farming-based:

5. EMIGRATION AND IMMIGRATION countless number leave poorer countries in

hopes of a better life in a more affluent country

related issues: prejudice, disease and hunger in refugee camps, struggles to find work

6. MIGRATION TO CITIES urban population will likely pass rural

population by 2020

challenges in rapidly growing cities

cities struggle to provide basic services, such as road maintenance, sanitation, utilities, and law enforcement

many are forced to live in shantytowns and slums where diseases like malaria, malnutrition, and HIV are rampant

jobs that people came to the cities for are in short supply

challenges in affluent countries

U.S. leads the world in consumption of many resources

despite adverse effects, increasing average wealth can have a positive affect on the environment—clean water, pollution controls, habitat protection

U.S. still leads the world in the production of many pollutants

Ex. with 5% of the world’s population, the U.S. produces 24% of the carbon dioxide

Chapter 5.4Dynamics of Population Growth

demography: field of collecting, compiling, and presenting information about populations

age structure: proportion of people in each age group at a given date can be used as planning tool for future needs

(elementary schools, retirement homes, etc.) Social Security

future populations

population projections are based on three variables: births, deaths, and migration

graying populations: indicates proportion of elderly people is increasing in population

population momentum: refers to effect of current age structures on future populations

demographic transition

gradual shift in birth and death rates from the primitive to the modern condition crude birth rate: number of births / 1000 / yr crude death rate: number of deaths / 1000 / yr

CBR – CDR = natural change 10 = % change in population in populatio

70 doubling time = -----------------

% change in population

epidemiologic transition

throughout most of human history, crude death rates were high (~ 40 / 1000/ yr)

by middle of 19th C., fewer epidemics and improvements in social conditions led to a gradual decrease in CDR (~ 10 / 1000/ yr)

cancer and cardiovascular disease are the main causes of mortality today, meaning many more individuals survive to old age

fertility transition

in developed countries, crude birth rates have decreased from 40-50 / 1000 / yr to 9-12 / 1000 / yr

followed epidemiologic transition

phases of demographic transition

phase I: high CBR, high CDR phase II: high CBR, decreasing CDR

epidemiologic transition phase III: decreasing CBR, low CDR

fertility transition phase IV: low CBR, low CDR

demographic dividend

as birthrates decline in developing countries, with working-age population increases relative to the younger and older members of the population

dependency ratio: ratio of the nonworking population (under 15 and over 65) to the working-age population

for a time, society can spend less on schools and nursing homes, allowing in investments to alleviate poverty and generate economic growth

countries such as Brazil, Mexico, and South Korea have taken advantage of this window

large families or small

fertility transition is the most vital element in the demographic transition

socio-cultural factors cause the poor in developing countries to make different choices regarding large families:

(1.) security in old age no safety net, such as pension or Social

Security, in developing countries

large families or small

(2.) infant and childhood mortality frequency of childhood death (Ex. in Nigeria, 100 infants

out of every 1000 do not survive) causes parents to have more children

(3.) helping hands in subsistence-agriculture societies, women do most of the

work relating to child care; children are a productive asset (4.) importance of education

in subsistence-agriculture societies, education seems unnecessary, especially for women; children who attend school are an economic liability

large families or small

(5.) status of women traditional social structure of many developing

countries still discourages women from obtaining education, owning land, and pursuing many careers

(6.) availability of contraceptives poor women often lack access to reproductive

health information

conclusions

industrialization and development is usually accompanied by factors leading to smaller families relatively high cost of raising children existence of pensions and Social Security opportunities for women to join the workforce access to contraceptives and health care older age at marrying

vicious cycle

unfortunately, poverty, environmental degradation, and high fertility drive one another in a vicious cycle increasing population density leads to

depletion of community resources; couples have more children to help gather resources; search for scarcer resources leads to environmental damage…

Fertility rates decline as development provides: (1.) security in old age (2.) lower infant and childhood mortality (3.) universal education for children (4.) opportunities for education and careers

for women (5.) unrestricted access to contraceptives and

health care services

efforts on behalf of the poor are needed:

1. improving education (especially literacy and education for women)

2. improving health (with a focus on infant mortality)

3. making family planning accessible (available and affordable)

4. enhancing income through employment opportunities

5. improving resource management

improving education

basic literacy—reading, writing, and basic math—is what’s needed

literacy rates among women in developing countries ranges from 30-50%

ability to read empowers people with information on countless topics

Ex. Pakistan vs. South Korea both had similar growth rates and incomes in 1960 however, 30% of children were enrolled in schools in

Pakistan compared to 94% in South Korea now, South Korea has 3x greater economic growth

improving health

health care needed by most developing countries is not high-tech

basic nutrition and hygiene will slow the spread of disease

prenatal, postnatal, and child care must be emphasized boiling water properly treating infections

reproductive health

focuses on women and infants: prenatal care safe childbirth and postnatal care information and services related to contraception prevention and treatment of STDs abortion services (where legal) and care afterwards prevention and treatment of infertility elimination of violence against women (rape, sexual

trafficking)

family planning

agencies enable people to plan their own family size, allowing them to have children only if and when they want them

services include: counseling and education regarding human

reproduction, the hazards of STDs, and the benefits and risks associated with various methods of contraception

counseling and education on achieving the best prenatal and postnatal health for mother and child

counseling and education to avoid high-risk pregnancy providing contraceptive materials

employment and income

Grameen Bank established in 1976 to engage in microlending to the poor microloans average about $67 and are usually short-term

(4-6 months) loans provide basic things such as

seed and fertilizer for a peasant farmer to start growing tomatoes pans for a baker yarn for a weaver tools for an auto mechanic

loans are secured by having the recipients form credit associations

microlending

greatest impact is on women “when women borrow, the beneficiaries are

the children and the household” World Bank recently increased support of

microfinancing, investing $1 billion to support institutions that provide microloans

Chapter 23.1Urban Sprawl

sprawl’s signature is a wide urban-suburban network of low-density residential areas, shopping malls, industrial parks, and other facilities connected by multilane highways

“sprawl” is used because boundaries of cities have been extended outward into the countryside, one development after the next

farms and other natural areas are taken over by new developments

highways

influx of commuters created need for new and larger roads Congress passed Highway Revenue Act of 1956, which

created Highway Trust Fund and took advantage of a gasoline tax to build new roads

ironically, new highways alleviate existing congestion, but spur further development

average commuting distance has doubled since 1960, but average commuting time has remained about the same

increase in commuting distance has provided more revenue for the Highway Trust Fund

impacts of urban sprawl

environmental impacts depletion of energy resources

from 1950 to 2005, U.S. oil consumption doubled air pollution

despite improvements in pollution control, many cities still fail to meet standards

water pollution paved areas associated with sprawl lead to substantial increase in runoff,

leading to flooding and erosion increase in runoff also leads to more fertilizer, pesticides, and waste

entering the water loss of agricultural land

due to losses in local land, estimates suggest that food now travels an average of 1000 miles from where it is produced

loss of landscapes and wildlife

principles of smart growth

create range of housing opportunities create walkable neighborhoods encourage collaboration among citizens,

businesses, and municipal leaders foster distinctive, attractive communities mix land uses preserve open space, farmland, natural beauty, and

critical habitat provide variety of transportation choices strengthen development in existing communities take advantage of compact building designs

Chapter 23.2Urban Blight

exurban migration is the major factor underlying urban decay, or blight

moving to suburbs requires some degree of affluence, which has excluded the poor, elderly, and handicapped

due to a history of racial discrimination in the U.S., the poor are mostly minorities

historically, discrimination has prevented equal access to education, jobs, and home loans

vicious cycle of urban blight

migration to suburbs by more affluent citizens sets into motion a vicious cycle

points to consider: 1. local governments are responsible for services 2. source of revenue for local governments is based on

property taxes 3. as home values decrease, property values decrease 4. central city usually has a government separate from the

surrounding suburbs

with an increasing tax base, suburbs can improve services and attract more residents

urban decay in developing countries

more than half of the 3 million residents of Nairobi live in slums consisting of flimsy shacks made of scrap wood, metal, and plastic

burning trash and charcoal fires cloud the air people get their water from an array of sources crime and disease are endemic, and AIDS and

tuberculosis spread throughout the slums despite these conditions, cities like these in

developing countries are expected to continue growing

What makes cities livable? common features of “livable” cities:

(1) high population density (2) heterogeneous mix of residences, businesses, stores, and

shops (3) layout has human dimension so people can meet, conduct

business, or stroll in open areas world’s most livable cities are not those with perfect access

for cars cities have taken measures to reduce sprawl, decrease auto

traffic, and improve access by foot, bicycle, and public transportation

examples: Geneva, Switzerland prohibits auto parking in its city center Copenhagen bans all on-street parking in its core Paris has removed 200,000 parking spaces in its downtown

Chapter 8.1Soil and Plants

soil characteristics soil texture

parent material is mineral base for soil made of rock or deposited sediments regardless of origin, parent material is eventually broken

down by weathering as rock weathers, it breaks down into smaller and

smaller fragments fragments of soil

sand: particles from 2.0 to 0.02 mm in size silt: particles from 0.02 to 0.0002 mm in size clay: anything finer than 0.0002 mm

proportions

soil texture refers to the relative proportions of each type of particle in a given soil if one type of particle predominates, soil is

said to be sandy, silty, or clayey a common proportion, known as loam, is 40%

sand, 40% silt, and 20% clay

properties

three basic considerations determine how several important properties of soil are influenced by its texture: 1. larger particles have larger spaces separating them

than smaller particles 2. smaller particles have more surface area relative to

their volume than larger particles 3. nutrient ions and water molecules tend to cling to

surfaces soil texture also affects workability—the ease

with which a soil can be cultivated

soil profiles

processes of soil formation create a vertical gradient of layers that are often quite distinct

horizontal layers are known as horizons vertical slice through different horizons is

known as soil profile

soil profiles

O horizon: topmost layer; consists of dead organic matter (detritus) deposited by plants (leaves, stems, seeds, etc.) high in organic content primary source of energy for soil community decomposition is ongoing in lower portions of O horizon,

producing rich, dark material known as humus A horizon: mixture of mineral soil from below and

humus from above; also called topsoil usually dark due to humus filled with fine roots; thickness varies

soil profiles

E horizon: E stands for eluviation—process of leaching (dissolving away) of many minerals due to downward movement of water

B horizon: characterized by deposition of minerals that have leached from the A and E horizons referred to as subsoil; often is high in clay and is

yellowish or reddish in color often high in Fe, Al, and Ca

C horizon: parent mineral material that originally occupied the site

for best growth, plants need root environment that supplies conditions: proper amounts of mineral nutrients, water,

and air pH and salinity are also important

soil fertility—soil’s ability to support plant growth

fertilizer

in agriculture, there is an unavoidable removal of nutrients by crops

fertilizer replenishes the soil organic fertilizer includes plant or animal

wastes inorganic fertilizers are chemical formulations

of required nutrients much more prone to leaching

water and water-holding capacity

water is constantly being absorbed by the roots of plants

however, water is continuously exiting as vapor through small pores in the leaves called stomata

inadequate water leads plants to wilt, which conserves water by closing the stomata, wilting also shuts off

photosynthesis

water and water-holding capacity

three properties of soil regulate a plant’s water supply: 1. infiltration: soil’s ability to let water soak in 2. water-holding capacity: ability to hold water like a

sponge, providing a reservoir for plants to draw from between rains

sandy soils have poor water-holding capacity, while clayey soils are good at holding water

3. evaporative water loss: water returns to the atmosphere before serving the needs of plants (a well-developed O horizon helps retain water)

aeration

land plants depend on the soil being loose and porous enough to allow the diffusion of oxygen into the soil and carbon dioxide out of the soil

compaction closes the spaces between soil particles, preventing adequate aeration also reduces infiltration and increases runoff

other properties

relative acidity different plants are adapted to different pH levels most plants do best with a pH near 7

salt and water uptake buildup of salts in the soil makes it impossible for

roots of a plant to take in water only plants with special adaptations can survive saline

soils (and none of these are crop plants)

soil community

to supply good growing conditions for a crop, the soil must 1. have a good supply of nutrients and good nutrient-

holding capacity 2. allow infiltration, have a good water-holding

capacity, and resist evaporative water loss 3. have a porous structure that permits good aeration 4. have a pH near 7 5. have a low salt content

detritus, soil organisms, humus

detritus in soil supports a complex food web most numerous and important organisms are bacteria

humus—residue of partly decomposed organic matter found in the bottom of the O horizon

composting fosters the decay of organic waste under somewhat controlled conditions

soil structure—refers to the arrangement of soil particles loose soil structure is ideal for infiltration, aeration, and

workability humus has extraordinary ability to hold water and nutrients

interactions

mycorrhizae—symbiotic relationship between the roots of some plants and certain fungi drawing some nourishment from the roots,

mycorrhizae penetrate the detritus, absorb nutrients, and transfer them directly to plants

prevents loss of nutrients from leaching

Chapter 8.2Soil Degradation

erosion—process of soil and humus particles being carried away by water or wind occurs any time soil is bared and exposed to the

elements may be slow and subtle, like soil blown gradually by wind may be dramatic, as when gullies are washed out in a single

storm in ecosystems other than deserts, vegetation protects

against erosion grass is particularly good for erosion control with increased runoff volume and velocity, grass lies down to

form a smooth mat over which the water can flow without disturbing the soil

1. overcultivation

although plowing helps remove weeds and loosens the soil to improve infiltration, it also exposes the soil to wind and water erosion

soil may remain bare ad time passes before crops are planted

runoff and erosion are especially bad on slopes despite harmful impacts of cultivation, rotating

crops (corn hay clover) has been proven to be sustainable clover fixes nitrogen and adds organic matter to the soil

no-till

no-till agriculture allows continuous crops, yet minimizes soil erosion field is first sprayed with herbicide to kill weeds planting apparatus pulled behind tractor (a) cuts furrow

through dead weeds, (b) drops seed and fertilizer into the furrow, and (c) closes the furrow

at harvest, process is repeated, with the waste from the previous crop becoming detritus and mulch for the next crop

no-till farming is a variation in which only one pass is made with a tractor to plant wheat after a rice crop (previously, farmers would plow 6-12x)

fertilizer

optimal nutrients can be supplied by inorganic fertilizers

however, inorganic fertilizers do not supply organic matter to support soil organisms and build soil structure

in overcultivation, nutrients content may remain high thanks to fertilizer, but mineralization proceeds

with soil’s loss of nutrient-holding capacity, fertilizer leaches into waterways, causing pollution

US Natural Resource Conservation Service

established in response to Dust Bowl of 1930s

provides information to farmers regarding soil or water conservation practices Ex. contour strip cropping Ex. shelterbelts

2. overgrazing

grasslands that traditionally receive too little rain to support crops have traditionally been used for grazing livestock

too often, these lands are overgrazed overgrazing kills grass plants, causing erosion and

encroachment by desert plants such as sagebrush, mesquite, and juniper (which are not palatable to cattle)

besides damaging the land, overgrazing reduces biodiversity and alters feeding and breeding patterns of native species

3. deforestation

forest ecosystems are extremely efficient systems for holding and recycling nutrients and for absorbing and holding water maintain a very porous, humus-rich soil

when forests are cut and left exposed, topsoil becomes saturated with water and slides down slopes, leaving barren subsoil

problem is most acute in developing countries where tropical regions are cut thin layer of humus washes away very quickly, leaving

behind nutrient-poor clayey soil which is poor for agriculture

irrigation and salinization

irrigation—supplying water to croplands by artificial means traditionally, water has been diverted from rivers to

flood furrows in fields center-pivot irrigation has become much more

popular (gigantic sprinkler slowly pivots around well) salinization—accumulation of salts in and on

the soil to the point where plant growth is suppressed

Green Revolution

spread of technologies to the developing world that led to the agricultural revolution in industrialized countries

agriculture expert Norman Borlaug sent to Mexico to deliver agricultural technology bred dwarf hybrid wheat crop with a large head and

thick stalk (crop did well in warm weather when it was given water and fertilizer)

similar techniques were taken to other countries around the world, leading to tremendous increases in food production

Green Revolution

because technology raises yields without requiring new agricultural land, significant amounts of deforestation have been prevented

irrigation requirement for high-yield crops means that water shortages are becoming more common in dry regions

crops also require fertilizer, pesticides, and energy-intensive machines—all of which can be in short supply

subsistence agriculture

problems pressures of population and conversion of better land to

industrialized agriculture often leads to unsustainable practices

woodlands and forests removed for agriculture or firewood, leaving soil susceptible to erosion

lack of firewood leads residents to burn animal dung for cooking and heat, which diverts nutrients from the land

erosion-prone land is used to grow annual crops good agricultural land is used for multiple crops and never has a

chance to recover nutrients all of these factors tend to increase poverty, which then

puts more pressure on the land

animal farming

raising livestock (sheep, goats, cattle, buffalo, poultry) has many connections to raising crops Ex. 70% of U.S. grain crop goes to feed animals

As with crop farming, two general patterns: (1) in developed world, animals are raised in large

numbers, often under confinement (2) in developing world, livestock and poultry are

raised on family farms

factory animals

industrial-style animal farming can be damaging to the environment rangelands are susceptible to overgrazing animal manure is mismanaged according to EPA, animal-based agriculture is the most

widespread source of pollution in the U.S. rivers factory farms can also impact human health

crowded farms are perfect conditions for diseases to incubate and spread among animals

in Asia, more than 140 million birds have been killed as a result of avian flu

factory animals—other concerns

loss of rain forest in Latin America, over 58 million acres of tropical rain forest

have been converted to cattle pasture climate change

deforestation and other changes in land use in the tropics release 1.6 million tons of carbon into the atmosphere each year

cows and other ruminant animals release 100 million tons of methane through belching and flatulence

anaerobic decomposition of manure leads to another 30 million tons of methane (~3% of GHG)

groups such as Heifer International provide animals for rural families for sustainable development

prospects for increasing food production

currently, food production is keeping up with (and meat production is exceeding) population growth

concern is whether trend can continue in 2020, there will be 1.5 billion more people on Earth, and there

is already a significant portion that suffers from hunger or malnutrition

International Food Policy Research Institute expects demand for grain to remain constant, slightly ahead of population growth by 2020, meat consumption is likely to increase by 50%, with shift

from red meat to poultry outlook for developing countries attempting to keep pace is not

good (degrading land, limited water and resources)

prospects of increased food production

two main options: (1) continue to increase crop yields (2) grow food crops on land that is now used for feed

crops or cash crops

while yields have increased for many crops throughout the 20th C., much of the productivity of plants depends on the soil and water available possible impact of climate change on rainfall patterns is

difficult to predict

less meat?

70% of grain in U.S. goes to feed livestock, while only 2% is used in Sub-Saharan Africa and India feed grain can be seen as a buffer against world

hunger (people can eat lower on the food chain) current trend shows an increase in meat

consumption

Chapter 9.2Genetic Engineering

genetic engineering makes it possible to: crossbreed different plants incorporate desired traits into crops and animals

has potential to help developing world to make more food

most widely adopted genetically engineered products to this point: cotton plants with built-in insect resistance corn and soybean plants resistant to Roundup to

allow no-till farming techniques

new products of genetic engineering

sorghum (African crop) resistant to witchweed (parasitic plant)

corn and potatoes resistant to insects rice resistant to bacterial blight disease trees and salmon that grow rapidly

biotech crop research to benefit developing countries is proceeding at a rapid pace

researchers in China have sequenced the rice genome

other objectives: incorporate resistance to diseases and pests that

attack important tropical plants increase tolerance to environmental conditions, such

as drought and high salt levels improve the nutritional value of commonly eaten

crops produce pharmaceutical products in ordinary plants

Ex. bananas and tomatoes with antidiarrheal vaccine

environmental concerns related to genetic engineering

broad exposure to toxins such as pesticides can lead the pests to develop resistance, causing the transgenic crop to lose its advantage

pollen from pest-resistant crops may damage beneficial insects that carry pollen

pollen of transgenic species can spread to wild relatives, leading to “super” weeds

safety concerns related to genetic engineering

transgenic crops contain proteins from different organisms and might trigger an unexpected allergic response in people who consume the food

antibiotic-resistance genes are sometimes used to track cells that have been transformed product could then transfer antibiotic resistance to

humans plants could produce new toxins or allergens in their

tissues in response to the presence of foreign genes to date, no evidence of these concerns have

appeared in countries growing transgenic crops

policies

in the U.S., the EPA, USDA, and FDA have all had regulatory oversight of different aspects of biotechnology

Cartagena Protocol U.N. Convention on Biodiversity sponsored conference in

2000 to deal with trade of genetically modified organisms puts right to deny entry of any of transgenic organism in

the hands of the importing country however, decision must be based on sound science

(involving an assessment of the risks involved) and a broad sharing of information about the products

policies

Cartagena Protocol is based on the precautionary principal where there are threats of serious or irreversible damage, lack of

scientific certainty should not be used as a reason for failing to take measures to prevent potential damage

according to agreement, shipments containing food made with genetically modified organisms must be labeled to indicate that they may contain bioengineered products

the European Union has lifted a ban on genetically modified foods, but is requiring labels on any food that contains more than 0.9% of genetically modified ingredients

terms

hunger: lack of basic food required for energy and meeting nutritional needs, resulting in an inability to lead a normal, healthy life

malnutrition: lack of essential nutrients (amino acid, vitamin, mineral)

undernourishment: lack of adequate food energy (usually measured in calories)

extent of hunger

almost 2/3 o f the worlds undernourished (519 million) live in Asia and the Pacific (China, Bangladesh, Pakistan, and India are most seriously affected)

sub-Saharan Africa has the highest percentage of undernourished people, where 1/3 of the population (204 million) do not get enough food

famine

famine: severe shortage of food accompanied by a significant increase in the death rate usually a sign that a society is either unable

or unwilling to distribute food to all segments of its population

drought and conflict are the two prominent causes of recent famines

Chapter 16.1The Need for Pest Control

pest: any organism that is noxious, destructive, or troublesome includes pathogens, nuisance wild animals, annoying

insects, molds agricultural pest: organism that feeds on

ornamental plants or agricultural crops or animals includes insects, fungi, viruses, worms, snails, slugs,

rats, mice, birds weeds: compete with agricultural crops, forests,

and grasses for lights and nutrients

pest management

efforts to control pests in the U.S. in 2001 involved 888 million pounds of: herbicides—chemicals that kill plants pesticides—chemicals that kill animals and

insects many of the changes to agriculture, such as

monocultures and the use of genetically identical crops, have increased the portion of crops lost to pests

different philosophies of pest control

1. chemical treatment like antibiotics in medicine, seeks “magic

bullet” to eradicate or greatly decrease pest numbers

method is very successful, but success is often short-lived

chemicals may have damaging side-effects

different philosophies of pest control

2. ecological control similar to stimulating the body’s immune system attempts long-lasting protection by developing

controls based on the pest’s life cycle and ecological relationships

may be organisms or chemicals work in one of two ways:

highly specific for best that is being fought manipulate one or more aspects of the ecosystem

different philosophies of pest control

chemical treatment and ecological control are combined in approach called integrated pest management (IRM) approach to controlling pest populations using

all suitable methods—chemical and ecological—to bring about long-term management of pest populations with minimal environmental impact

problems with chemical pesticides

problems fit into three categories: 1. development of resistance 2. resurgences and secondary pest

outbreaks 3. adverse effects

human health environment

1. development of resistance

over the years, farmers have to use larger and larger quantities, try new and more potent pesticides, or both

resistance builds up because pesticides destroy the sensitive individuals in a population few that are left behind already have some

resistance resistance spreads rapidly due to insects’ ability

to reproduce quickly

2. resurgences and secondary outbreaks

resurgence: after a pest has been eliminated by a pesticide, the pest population generally recovers and explodes to higher and more severe levels

secondary outbreak: explosion of insect populations that were small before the application of the pesticide

in a recent study of 25 major pest outbreaks (each caused more than $1 million worth of damage) in California showed, all but one were followed by a resurgence or secondary outbreak

3a. human health effects

pesticides can be responsible for both acute and chronic effects

acute cases are most often farm workers or employees poisoned by direct contact with the chemicals

chronic effects are likely to be seen in consumers exposed to residues on food or farmers exposed to subacute levels

3a. human health effects

one likely chronic outcome is cancer at least 20 pesticides have some carcinogenic

properties other chronic effects include dermatitis, neurological

disorders, birth defects, and infertility studies have linked pesticide exposure to

suppression of the immune and endocrine systems, as well as Parkinson’s disease

evidence of some pesticides interfering with reproductive hormones

3b. environmental effects

impact of DDT ornithologists observed drastic declines in bird species at the top

of food chains during the 1950s and 1960s fish-eating birds such as eagles and osprey were on the brink of

extinction problem was reproductive failure—eggs were breaking in the nest

before hatching investigators found that the eggs contained high concentrations of

DDE, a compound that forms when DDT is partially broken down DDE interferes with calcium metabolism, leading to thin-shelled

eggs studies show that birds were acquiring high levels of DDT and DDE

through bioaccumulation and biomagnification

3b. environmental effects

bioaccumulation many synthetic organic compounds (man-made) are

soluble in lipids, but not in water as they pass through cell membranes, they leave the

water solution to become part of the lipid bilayer as a result, traces of synthetic organic compounds

become trapped in the body’s lipids because synthetics are unnatural compounds, the body

cannot fully metabolize them and has no mechanism to excrete them

over time, trace levels accumulate in the body and can build to toxic levels

4. environmental effects

biomagnification each individual organism accumulates contamination over time, the concentration of the contaminant becomes

much higher in the organism than in its food the next organism on the food chain then consumes food

that already has a high concentration of contaminant the contaminant eventually becomes concentrated into the

smaller biomass of the organisms at the top of the food chain

both bioaccumulation and biomagnification often go unrecognized until serious problems arise

four general categories of natural control:

1. cultural control 2. control by natural enemies 3. genetic control 4. natural chemical control

1. cultural control

nonchemical alteration of one or more environmental factors in a way that leads the pest to find the environment unsuitable human examples include brushing hair,

changing bed linens, disposing of garbage major disasters can compromise practices

of hygiene and sanitation

1. cultural control

Example 1: maintaining grass on lawn at a height of at least 3 inches keeps out most weeds

Example 2: marigolds and chrysanthemums act as insect repellants (while roses act as attractants)

Example 3: shelterbelts can provide refuge for natural enemies of pests (birds, amphibians, etc.)

Example 4: rotating crops eliminates pest that may only have a source of food every few years; likewise, a mixture of crops in an area can help prevent a pest outbreak

2. control by natural enemies

Example 1: gypsy moth controlled by imported parasitic wasp

Example 2: rabbits in Australia controlled by infectious virus

guidelines: protect native species

first step should be conservation of natural enemies avoid broad-spectrum pesticides

import aliens as last resort

3. genetic control

most plant-eating insects and plant pathogens attack only one species or a few closely related species

implies genetic incompatibility between pest and species that are not attacked

most genetic strategies are aimed at providing this incompatibility

3. genetic control

A. control with chemical barriers chemical barrier is chemical produced by plant

that is vulnerable to pest chemical is lethal, or at least repulsive to pests

B. control with physical barriers physical barriers are structural traits that impede

the attack of a pest Ex. hooked hairs on leaf surfaces trap leafhopper

insects that damage relatively smooth leaves

3. genetic control

C. control with sterile males involves flooding population with sterile males

that have been raised in laboratories Ex. screwworm fly has been controlled using this

method (aided by fact that females mate just once, lay their eggs, then die)

Ex. used to eradicate the tsetse fly from island of Zanzibar, eliminating sleeping sickness

3. genetic control

D. strategies using biotechnology one promising strategy is to incorporate the protein coat of a

plant virus into the plant when the plant expresses the viruses protein coat, the plant

becomes resistant to infection by the real virus many strategies involving biotechnology have the potential to

reduce the use of pesticides Bt = incorporation of important protein produced by Bacillus

thuringiensis widespread use of Bt crops means that resistance is likely to

develop EPA anticipated this problem and required seed companies to

verify that farmers planted at least 20% of their fields with non-Bt crops

4. natural chemical control

hormones: chemicals produced by animals to provide signals for the control of developmental processes and metabolic functions

pheromones: chemicals secreted by one individual that influence the behavior of another individual of the same species

both of these types of chemicals may be used to disrupt the life cycle of pests

advantages: nontoxic highly specific

4. natural chemical control

Ex. use of juvenile hormone to prevent pupation in caterpillars larvae continue to feed and grow until they become grossly

oversized and die Ex. synthetic version of ecdysone, the hormone that

controls molting in insects, prevents insects from completing molting process larva is trapped in its old skin and eventually starves to death

Ex. pheromones used in trapping technique lead pests to traps full of poison bait

Ex. pheromones used in confusion technique prevent males from finding mate