Agriculture as an ecosystem

Great diversity Great diversity in Natural habitatsin Natural habitats

Crops – low species diversitylow 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

IrrigationMachine Crops_large scale irri

gation

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: 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 Factors contributing to pest problempest problem

Pests and Pest control

Insect pests

Chemical control

Domestic crops were Domestic crops were selected for maximum selected for maximum

productivity and had productivity and had little little natural pest resistancenatural 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 Pests attack and eat our food cropseat our food crops

This problem is This problem is due, in part, to not due, in part, to not selecting for pest selecting for pest resistance during resistance during domesticationdomestication

Today’s PestsToday’s Pests

Based on: National Geographic, February 1980

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

Arial crop sprayers Arial crop sprayers were used to spray were used to spray tons of DDT on tons of DDT on crops across the crops across the U.S.U.S.

Photo courtesy of Texas Parks and Wildlife DepartmentPhoto courtesy of Texas Parks and Wildlife Department

Pests became resistant to DDTPests became resistant to DDT

Based on: National Geographic

Pesticide ResistancePesticide Resistance

In the beginning, most In the beginning, most pests were sensitive to pests were sensitive to DDT but a few were DDT but a few were resistantresistant

The resistant forms The resistant forms survived and reproducedsurvived and reproduced

In the end, most pests In the end, most pests were resistant to DDTwere resistant to DDT

Based on: National Geographic, February 1980

Bio-magnificationBio-magnification

The concentration of The concentration of pesticides in higher levels of pesticides in higher levels of

food chainsfood 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 Ne

xt 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 DDT is concentrated as it moved up food chainit moved up food chain

This is because energy This is because energy is lost (from respiration) is lost (from respiration) as go up food chain but as go up food chain but DDT is notDDT is not

DDT in Food Chain

•Pests, DDT and biomagnification•DDT, eagles and falcons•Species endangered•Organic foods

Overview of Lesson

Bald EagleBald Eagle

•Once was widelyOnce was widely distributed over U.S.distributed over U.S.

•As a top carnivore it As a top carnivore it feeds on fishfeeds on fish

•Swoops down and Swoops down and captures fish off the captures fish off the surface of the watersurface of the water

Photo courtesy of Texas Parks and Wildlife Photo courtesy of Texas Parks and Wildlife DepartmentDepartment

•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 DepartmentPhotos courtesy of Texas Parks and Wildlife Department

Scientists found thaScientists found that the eagle eggs had t the eagle eggs had thin egg shells and thin egg shells and broke easilybroke easily

Nests contained broNests contained broken, rotten eggsken, rotten eggs

The number of younThe number of young produced per breg produced per breedingedingpair was reducedpair was reduced

Population of adult Population of adult eagles declined to 4,000 eagles declined to 4,000 and the eagle was listed and the eagle was listed as “Endangered”as “Endangered”

Photo courtesy of Texas Parks and Wildlife DepartmentPhoto courtesy of Texas Parks and Wildlife Department

The Environmental Protection Agency (EPA) The Environmental Protection Agency (EPA) banned DDT in 1972 (USA)banned DDT in 1972 (USA)

Photo courtesy of Texas Parks and Wildlife DepartmentPhoto courtesy of Texas Parks and Wildlife Department

Eagle reproduction before and after DDT ban Eagle reproduction before and after DDT ban

Based on: Grier, J., Science, 1982

Eagle populations increased rapidly and Eagle populations increased rapidly and the eagle is now listed as “Threatened”the eagle is now listed as “Threatened”

From: Time, July 11, 1994

Peregrine FalconPeregrine Falcon •Occurred naturallyOccurred naturally over most of continentover most of continental U.S.al U.S.

•Nests on cliffsNests on cliffs

•Keen eyesight Keen eyesight (if human, could read newspap(if human, could read newspaper print at 110 yards)er print at 110 yards)

•Feeds on other birds, kFeeds on other birds, knocking them out of the nocking them out of the sky at 200 m.p.h.sky at 200 m.p.h.

Photo courtesy of Texas Parks and Wildlife DepartmentPhoto courtesy of Texas Parks and Wildlife Department

•After DDT was introducedAfter DDT was introduced in 1940s, DDT weakenedin 1940s, DDT weakened the birds’ egg shells,the birds’ egg shells, devastating the populationdevastating the population

•By early 1970s, the entireBy early 1970s, the entire U.S. population was downU.S. population was down to 12 breeding pairsto 12 breeding pairs

•Peregrines were declaredPeregrines were declared federally endangered andfederally endangered and DDT bannedDDT banned

•Peregrines were bred inPeregrines were bred in captivity and reintroducedcaptivity and reintroduced successfully in citiessuccessfully in cities

DDT & PeregrineDDT & Peregrine

Photos courtesy of Texas Parks and Wildlife DepartmentPhotos courtesy of Texas Parks and Wildlife Department

poisoning

Good insects

Red Fire ant

Red fire ant

Prickly pearPrickly 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.