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Chapter 22 : Ecology and Evolution in Agriculture

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Ecology and Evolution in Agriculture, Page 1 of 2

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Abstract:

This chapter discusses plant agriculture with respect to ecology and evolution, and provides an opportunity to know more about ecological interactions and evolutionary adaptations using row crop agriculture as the hook. It attempts to lessen the information gap that exists between farmers and citizens in the industrialized world. The chapter provides information on the: evolution of crop plants from wild relatives, conflicts between plant adaptations for increased fitness and human requirements for food crops, developments in agriculture that have allowed crop productivity to keep pace with the exponential growth of the human population, and ecological problems caused by agricultural activities. Farmers use preplant herbicides to rid their fields of weeds without fear of harming their crops because the herbicides become inactivated very soon after application. By allowing no-till or minimum-till agriculture, the preplant herbicides prevent soil erosion caused by plowing and conserve soil moisture, lessening the need for irrigation. Flowers and fruits are tactics for meeting a plant’s primary objective: reproduction. To encourage cross-pollination in order to create genetic diversity, many plants have evolved mechanisms to prevent or minimize self-fertilization. Many flowering plants depend on animals for pollination and seed dispersal and reward them for their services. Basing agriculture on annual plants necessitates annual habitat disturbance. This leads to soil erosion, agriculture's most significant negative impact on both the environment and the long-term sustainability of agricultural ecosystems.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22

Key Concept Ranking

Flowering Plants
0.56247556
Fruits and Vegetables
0.45780435
Natural Selection
0.4104446
Nitrogen-Fixing Bacteria
0.40809917
Vitamin C
0.40809917
Nitrogen-Fixing Bacteria
0.40809917
0.56247556
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Figures

Image of Figure 22.1
Figure 22.1

Changes in the U.S. agricultural workforce. As modern technologies replaced manual laborers, people left farming and joined the nonagricultural workforce. Technological improvements allowed one farmer to feed more and more people. The blue bars in the histogram represent the percentage of people directly involved in agriculture, and the yellow bars represent the number of people in the United States who are fed by one American farmer.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.2
Figure 22.2

Wild grasses. All major cereal staples, such as corn, wheat, rice, oats, and barley, belong to the plant family commonly referred to as the grass family (Poaceae). Approximately 40 of the 200 weeds listed in the U.S. Department of Agriculture (USDA) are in this plant family. The traits that make many grasses weeds also made them good crops for the first agriculturists. Wild grasses, such as this relative of wheat, , are prodigious seed producers that rapidly infest disturbed areas. (Photograph by Phil Westra, Colorado State University, courtesy of http://www.forestry.com.)

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.3
Figure 22.3

Global crop production. The cereal crops, such as corn, rice, and wheat, are by far the most important food source for most of the human population.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.4
Figure 22.4

Plant reproduction. In the flowering plants (angiosperms), flowers and fruits are reproductive organs.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.5
Figure 22.5

Hermaphroditic plants. Most flowers have both male and female reproductive organs. In this flower, , the white female stigma is surrounded by male anthers, which appear blue. Even though this flower is self-compatible, self-fertilization rarely occurs because the female stigma becomes receptive and pushes through the anther tube only after the pollen is no longer fertile. Squash plants are also hermaphroditic, but male (right) and female(left) reproductive structures occur in different flowers on the same plant. (Photograph in panel B courtesy of Purdue University Cooperative Extension Service.)

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.6
Figure 22.6

Avoiding self-pollination. When a passion flower first opens, the male anthers are positioned well below the female stigma. The flower's nectar is in a donut-shaped trough at the base of the reproductive organs. Pollinators, such as this bee, run around the trough, and pollen is deposited on their backs . A few hours later, the female stigma bends down and is at a perfect level to receive pollen from bees that have visited other flowers .

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.7
Figure 22.7

Seed dispersal. Wind-dispersed seeds, such as those from dandelions and maple trees , have structural adaptations that keep them airborne for a long time.This decreases competition among offspring and between the parent plant and its offspring.(Photographs by Kenneth Gale [A] and Dave Powell [B], courtesy of http://www.forestryimages.org).

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.8
Figure 22.8

Rewarding pollinators. Nectar, which is sugar water, and high-protein pollen are rewards that pollinators receive for helping plants reproduce. There is a downside to rewarding pollinators with pollen, because the plant's primary objective, reproduction, depends on the pollinator transferring pollen and not eating it. This plant, , solves that conflict by producing infertile (false) pollen on the brightly colored structures on one part of the flower and fertile pollen on the small, unobtrusive structures surrounding the female stigma.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.9
Figure 22.9

Seed dispersal. In tropical forests, bats play important roles in both pollination and seed dispersal. This plant ( sp.) relies on bats for seed dispersal. Ripened fruits are so easy to remove from the plant that bats fly through the rainforest and grab mouthfuls of piper fruits without stopping. This ensures that the piper plant's offspring are carried to a different part of the forest.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.10
Figure 22.10

Domestication and seed size. Seeds from domestic crops (inner circle) are usually larger, lighter in color, and more uniform than their wild relatives. Clockwise from top: peanuts, corn, rice, coffee, soybean, hops, pistachio, and sorghum. (Photograph by Stephen Ausmus, courtesy of Agricultural Research Service, USDA.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.11
Figure 22.11

Tomato domestication. Genetic modification through artificial selection and plant breeding has made the tomato an excellent food for people, but it has made the domesticated tomato completely dependent on humans for its survival. In addition to increasing the amount of pulp at the expense of seeds (offspring), the genetic changes significantly increased the amounts of vitamin A and vitamin C in tomatoes and decreased the amounts of naturally occurring tomato toxins.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.12
Figure 22.12

Domestication and seed dispersal. Wild grasses, such as this wild relative of barley, have structural adaptations for seed dispersal. Those same structures made it difficult for early farmers to get to the seed, so they genetically modified wild barley by artificial selection to create domesticated barley, which lacks these structures. (Photographs by Dave Powell, courtesy of http://www.forestry.org [A], and Robert Sonerg, courtesy of the Smithsonian Institution [B].)

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.13
Figure 22.13

Mechanical defense mechanisms. Many plants protect themselves with thorns, spines, and sticky glandular secretions, which have been removed or minimized in crop plants.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.14
Figure 22.14

Chemical defense. In Tanzanian grasslands in the dry season, there is little, if any, vegetation for primary consumers. Even so, the fruits of this tomato relative remain untouched. The tomato family (Solanaceae), which is commonly known as the nightshade family, is infamous for containing high levels of many toxins.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.15
Figure 22.15

Seedling emerging. (Photograph courtesy of the National Park Service.)

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.16
Figure 22.16

Soil erosion. Runoff from a heavy rain carries topsoil from an unprotected, highly erodable field in Iowa. (Photograph by Lynn Betts, courtesy of Natural Resources Conservation Service, USDA.)

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.17
Figure 22.17

Crop infestations. Large blocks of genetically identical organisms encourage pest outbreaks. In this example, a healthy tobacco crop (left) became infested with a viral pathogen, the yellow dwarf gemini virus (right). (Photograph by Gary Baxter, Department of Primary Industries, courtesy of http://www. forestryimages.org.)

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.18
Figure 22.18

Steam plow. In the 1800s, farmers replaced animals with mechanical power, such as this steam-powered plow. (Photograph courtesy of USDA.)

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.19
Figure 22.19

Wind erosion. Poor land management practices combined with four severe droughts in 10 years (1930 to 1940) created the Midwest Dust Bowl that led to massive migration and the creation of migrant camps from Missouri to California. (Map courtesy of U.S. Geological Survey Drought Mitigation Service, 1930–1940. Photographs by Arthur Rothstein [right] and Dorthea Lange [left], courtesy of Library of Congress.)

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.20
Figure 22.20

No-till agriculture. Preplant herbicides allow farmers to plant crop seeds without tilling the soil to plow weeds under. Not only does no-till agriculture reduce soil erosion, but the dead plants conserve moisture and nourish the crop. (Photograph by Linda Betts, courtesy of Natural Resources Conservation Service, USDA.)

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.21
Figure 22.21

U.S. corn production.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.22
Figure 22.22

Productivity gains in developing countries. Between the late 1950s and the early 1970s, agricultural production increased in many developing countries. Unfortunately, the population size of the developing world increased even more rapidly.

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.23
Figure 22.23

Preserving genetic diversity. The USDA's National Seed Storage Laboratory preserves more than 1 million samples of plant germplasm in an 18°C storage vault. Containers of seeds, cryopreserved in vats of liquid nitrogen, can remain viable for thousands of years. Each vat contains approximately 10,000 seeds. (Photographs by Scott Bauer, courtesy of Agricultural Research Service, USDA.)

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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Image of Figure 22.24
Figure 22.24

Crop genetic diversity. When combined, the genetic diversity of different cultivars of the same species, such as Phaseolus vigna, is significant, even though the gene pool has been depleted by centuries of breeding. Conserving wild relatives of crops greatly expands the available gene pool. (Photograph by Keith Weller, courtesy of Agricultural Research Service, USDA.)

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
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References

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Tables

Generic image for table
Table 22.1

Domestication changes versus plant needs

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
Generic image for table
Table 22.2

The Green Revolution and wheat production

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22
Generic image for table
Table 22.3

Number of collections worldwide and approximate number of germ plasm samples (accessions) for major crops

Citation: Kreuzer H, Massey A. 2005. Ecology and Evolution in Agriculture, p 569-590. In Biology and Biotechnology. ASM Press, Washington, DC. doi: 10.1128/9781555816094.ch22

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