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Agriculture as an ecosystem. Great diversity in Natural habitats. Crops – low species diversity low genetic diversity. Green revolution. a large increase in crop production in developing countries achieved by the use of artificial fertilizers, pesticides, and high-yield crop varieties.
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Great diversity in Natural habitats
Green revolution a large increase in crop production in developing countries achieved by the use of artificial fertilizers, pesticides, and high-yield crop varieties.
Machine Crops Crops bred to have model characteristics that facilitate the use of machine. E.g. same size
Machine Crops dwarf / short, responsive to fertilizer, fast growing…... E.g. Miracle rice
Machine Crops -large scale irrigation Irrigation
Domestic crops were selected for maximum productivity and had little natural pest resistance
Potato famine of Ireland was caused by genetically uniform crops and lack of pesticides to protect them Blight hits potatoes, 1845 Based on: Population Reports, May 1992
The Great Famine (Irish) the Great Hunger was a period of mass starvation, disease, and emigration in Ireland between 1845 and 1849.
Today’s Pests Pests attack and eat our food crops This problem is due, in part, to not selecting for pest resistance during domestication 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
Pesticide Resurgence Pest resurgence is the rapid reappearance of a pest population, usually brought about after the application of a broad-spectrumpesticide has killed the natural enemies which normally keep a pest in check
Bio-magnificationThe concentration of pesticides in higher levels of food chains
Trophic Levels Based on: Mader, S., Inquiry Into Life, McGraw-Hill Most food chains consist of four trophic levels
Energy Available to Consumers at Next Trophic Level Energy Lost by Death and Decay Energy Lost by Respiration Energy Lost by Excretion Energy Lost by Egestion of Feces Energy Ingested
DDT in Food Chain 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
Bald Eagle • Once was widely • distributed over U.S. • As a top carnivore it feeds on fish • Swoops down and captures fish off the surface of the water Photo courtesy of Texas Parks and Wildlife Department
Scientists discovered that DDT was concentrated in the bald eagle DDT affected the eagle’s ability to reproduce
Scientists found that the eagle eggs had thin egg shells and broke easily
The use of DDT banned was 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
Biological control • a method of controlling pests using other organisms. • predation, parasitism, competition, or other natural mechanisms. • typically also involves an active human management role.
Biological control • Doesn’t aim at eliminating the pest completely but to • establish an equilibrium between crop, pest and their natural control agent
