Agriculture as an ecosystem

Great diversity in Natural habitats

Crops – low species diversity low genetic diversity

Green revolution

Machine Crops

Machine Crops _genetically uniform

Machine Crops– dwarf, responsive to fertilizer, fast growing…... E.g. Miracle rice

Chief beneficiaries

Machine Crops_require large amount of chemical fertilizer

Irrigation Machine Crops_large scale irrigation

Machine Crops_require pesticides

Impact of Agriculture: Soil degraded_Dust bowl

Impact of Agriculture: Land clearing for farming

Impact of Agriculture: Soil erosion

Impact of Agriculture: Salinization

Impact of Agriculture: Overgrazing

Impact of Agriculture: Ecological disruption

Impact of Agriculture: create weeds and pests

Weeds – competitors of crops

Factors contributing to pest problem

Pests and Pest control

Insect pests

Chemical control

Domestic crops were selected for maximum productivity and had little natural pest resistance

Blight hits potatoes, 1845 Based on: Population Reports, May 1992 Potato famine of Ireland was caused by genetically uniform crops and lack of pesticides to protect them

Pests attack and eat our food crops This problem is due, in part, to not selecting for pest resistance during domestication Today’s Pests Based on: National Geographic, February 1980

DDT was invented in the 1940’s and viewed as: - miracle for farmers - and safe

Arial crop sprayers were used to spray tons of DDT on crops across the U.S. Photo courtesy of Texas Parks and Wildlife Department

Pests became resistant to DDT Based on: National Geographic

Pesticide Resistance In the beginning, most pests were sensitive to DDT but a few were resistant The resistant forms survived and reproduced In the end, most pests were resistant to DDT Based on: National Geographic, February 1980

Bio-magnification The concentration of pesticides in higher levels of food chains

Most food chains consist of four trophic levels Based on: Mader, S., Inquiry Into Life, McGraw-Hill Trophic Levels

Energy Available to Consumers at Next Trophic Level Energy Lost by Respiration Energy Lost by Death and Decay Energy Lost by Excretion Energy Lost by Egestion of Feces Energy Ingested

DDT is concentrated as it moved up food chain This is because energy is lost (from respiration) as go up food chain but DDT is not DDT in Food Chain

Pests, DDT and biomagnification DDT, eagles and falcons Species endangered Organic foods Overview of Lesson

Bald Eagle Once was widelyOnce was widely distributed over U.S. distributed over U.S. As a top carnivore it feeds on fishAs a top carnivore it feeds on fish Swoops down and captures fish off the surface of the waterSwoops down and captures fish off the surface of the water Photo courtesy of Texas Parks and Wildlife Department

Scientists discovered that DDT wasScientists discovered that DDT was concentrated in the bald eagle concentrated in the bald eagle DDT affected the eagle’s ability to reproduceDDT affected the eagle’s ability to reproduce Photos courtesy of Texas Parks and Wildlife Department

Scientists found that the eagle eggs had thin egg shells and broke easily Nests contained broken, rotten eggs The number of young produced per breeding pair was reduced

Population of adult eagles declined to 4,000 and the eagle was listed as “Endangered” Photo courtesy of Texas Parks and Wildlife Department

The Environmental Protection Agency (EPA) banned DDT in 1972 (USA) Photo courtesy of Texas Parks and Wildlife Department

Eagle reproduction before and after DDT ban Based on: Grier, J., Science, 1982

Eagle populations increased rapidly and the eagle is now listed as “Threatened” From: Time, July 11, 1994

Peregrine Falcon Occurred naturallyOccurred naturally over most of continental U.S. over most of continental U.S. Nests on cliffsNests on cliffs Keen eyesightKeen eyesight (if human, could read newspaper print at 110 yards) Feeds on other birds, knocking them out of the sky at 200 m.p.h.Feeds on other birds, knocking them out of the sky at 200 m.p.h. Photo courtesy of Texas Parks and Wildlife Department

After DDT was introducedAfter DDT was introduced in 1940s, DDT weakened in 1940s, DDT weakened the birds’ egg shells, the birds’ egg shells, devastating the population devastating the population By early 1970s, the entireBy early 1970s, the entire U.S. population was down U.S. population was down to 12 breeding pairs to 12 breeding pairs Peregrines were declaredPeregrines were declared federally endangered and federally endangered and DDT banned DDT banned Peregrines were bred inPeregrines were bred in captivity and reintroduced captivity and reintroduced successfully in cities successfully in cities DDT & Peregrine Photos courtesy of Texas Parks and Wildlife Department

poisoning

Good insects

Red Fire ant

Red fire ant

Prickly pear Prickly pears were imported into Australia in the 19th century for use as a natural agricultural fence, but quickly became a widespread weed, rendering 40,000 km² of farming land unproductive. The Cactoblastis moth, a South American moth whose larvae eat prickly pear, was introduced in 1925 and almost wiped out the infestation. This case is often cited as a "textbook" example of successful biological pest control. The same moth, introduced accidentally further north of its native range into southern North America, is causing serious damage to some native species in that area.Australiaweed CactoblastismothSouth Americanbiological pest controlNorth America