Chapter 14 : Ecological Interactions

Figure 14.1

Two ecosystems. (Photographs by Apollo 17 astronauts, courtesy of Johnson Space Center, National Aeronautics and Space Administration.)

Figure 14.2

Coral reef ecosystems. The species compositions of ecosystems from different geographic locations vary. Even though all of these photos are immediately identifiable as coral reefs, the species compositions are different. (A) Two fish species, an angelfish and a sergeant major, from a reef in south Florida. (B) Yellow and gray butterfly fish in the Pacific Ocean near Palau. (C) A two-banded clown fish hiding in a sea anemone on a coral reef in the Red Sea. (Photographs by Florida Keys National Marine Sanctuary staff [A], James McVey [B], and Mohammed Al Momany [C], courtesy of the U.S. National Oceanic and Atmospheric Administration.)

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(A) Three protozoans graze on phytoplankton. (Photograph courtesy of Hans Paerl, Institute of Marine Sciences, University of North Carolina.) (B) Phytoplankton eukaryotes. (Left) Diatoms. (Photograph courtesy of the U.S. National Oceanic and Atmospheric Administration. Photographer, Neil Sullivan.) (Right) Mat of unicellular green algae. (Photograph courtesy of Linda Fisher.) (C) Phytoplankton prokaryotes. (Left) Cyanobacteria, Anabaena. (Photograph courtesy of Hans Paerl, Institute of Marine Sciences, University of North Carolina.) (Middle) Cyanobacteria, Oscillatoria. (Photograph courtesy of Roger Burks.) (Right) Mats of Microcystis. (Photograph courtesy of Hans Paerl, Institute of Marine Sciences, University of North Carolina.) (D) Phytoplankton populations. (Left) The Grand Banks. (Right) Southeastern United States in January. (Photographs by Jeff Schmaltz [left] and Jacques Descloitres [right], courtesy of the MODIS Team, National Aeronautics and Space Administration.)

Figure 14.3

Ecosystem energetics. Energy enters an ecosystem primarily as light energy from the Sun. Some of that light energy is captured by photosynthetic organisms, the autotrophs, which convert it to chemical-bond energy stored in biological molecules. These primary producers use some of that energy to run their own metabolic processes, and the remainder is available to the other organisms in the ecosystem, the heterotrophs, that rely on the primary producers. Note that each time energy is transferred in an ecosystem, some is lost from the ecosystem as heat.

Figure 14.4

Trophic levels. Food chains quickly become food webs when all of the trophic interactions are included.

Figure 14.5

Fungi. All fungi are heterotrophs, and many are essential to life on Earth because they permit the recycling of molecular materials. (A) Multicellular fungi consist of an intricate mass of filaments known as a mycelium. (Photograph courtesy of the U.S. Forest Service. Photographer, Jim Trappe.) (B) The dark-blue threadlike structures in the micrograph are individual filaments, or hyphae. Decomposition occurs as the hyphae invade tissues and secrete digestive enzymes. (Photograph by Nick Hill, courtesy of the Agricultural Research Service, U.S. Department of Agriculture.)

Figure 14.6

Energy pyramid. In every ecosystem, a small portion of energy at one trophic level is transferred to the next trophic level. Some is used by organisms at each level for metabolism, and some is lost as heat.

Figure 14.7

The carbon cycle.

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Figure 14.8

Fossil fuels and the carbon cycle. Organisms that lived millions of years ago provide fossil fuels, such as coal and oil. (A) In 1907, Colorado coal miners extracted coal that contained a fossilized imprint of a palm leaf. (B) A leaf from a tropical plant was fossilized in the coal deposits of Antarctica. Both photographs also illustrate the tremendous shifts in species distribution that have occurred during the Earth's history. (Photographs by H. S. Gale [A] and D. L. Schmidt [B], courtesy of the U.S. Geological Survey.)

Figure 14.9

Deforestation. Every year, farmers in the developing world prepare to plant crops by clearing and burning millions of acres of vegetation, which releases large amounts of carbon dioxide. Shown are images of Brazil, taken in March and at the beginning of the growing season in September. The Xs mark the same location in the different types of images. (A) Created by NASA's MOPITT program, which measures levels of atmospheric pollution, these computer-generated images show the increase in carbon dioxide that occurs when Brazilian farmers clear land for planting crops in September. Blue indicates low levels of carbon dioxide; yellow and orange indicate intermediate levels; purple and black indicate the highest levels. (B) This increase in carbon dioxide is due primarily to biomass burning across Amazonia and not to industrial emissions. The red dots indicate fires. (Photographs by David Edwards and John Gille [A] and Jessie Allen, MODIS Team [B]; all images courtesy of the National Aeronautics and Space Administration.)

Figure 14.10

The nitrogen cycle.

Figure 14.11

Nitrogen-fixing bacteria. (A) Cross section (left) of a leaf stem from the tropical plant Gunnera (right), with arrows indicating the colonies of nitrogen-fixing cyanobacteria that reside there. (Photograph on left courtesy of David Dalton.) (B) Soybean root nodules. (Photograph courtesy of Manuel Becana.)

Figure 14.12

Low reproductive potential. During a reproductive life span that can last 40 years, a female Asian elephant produces approximately five or six offspring. Females mature at 12 years and give birth to a single offspring after a 22-month pregnancy. Their lactation period can last 2 years, though some mothers wean their offspring earlier. On average, females give birth every 5 years. (Photograph by Jessie Cohen, courtesy of the Smithsonian Institution National Zoological Park.)

Figure 14.13

Exponential growth curve. This type of growth is seen in populations when resources are abundant.

Figure 14.14

Opportunistic species. Small rodents and weedy plants are archetypal opportunistic species. (A) The house mouse is sexually mature at 1 month. After a 20-day gestation period, a female gives birth to five to seven blind, hairless offspring. Within hours after giving birth, she is impregnated again. Therefore, while she is lactating, another litter is developing in utero. (Left) House mouse adult female. (Right) Three-day-old house mice. (B) Weedy plants are designed to maximize their reproductive output after invading disturbed habitats, such as a roadside or a farmer's field. Each knapweed plant produces 25,000 seeds in one growing season and then dies. This leads to large infestations of a single species. (Photographs of knapweed by Norman Rees, Agricultural Research Service, U.S. Department of Agriculture; courtesy of http://www.forestryimages.org.)

Figure 14.15

Logistic growth curve.

Figure 14.16

Predators and their prey. (A) In nature, the predator-prey relationship encompasses interactions much broader than dramatic struggles between large, fierce carnivores and helpless prey, such as that depicted here. (B) Herbivory. Plant-eating insects are also predators. (C) Carnivorous plants. A number of plant species, such as this Venus flytrap, have turned the tables on herbivores or other small invertebrates. This one is making a meal of a spider. (Photograph by Barry Rice, courtesy of http://www.sarracenia.com.) (D) Predatory fungi. Hyphae from a filamentous fungus lasso a nematode. (Photograph courtesy of George Barron and Nancy Allin.)

Figure 14.17

Escaping predation. Selective pressures have led to a variety of self-defense strategies in animals. (A) Warning coloration. To escape predation, a number of animals synthesize noxious chemicals. They often advertise their distastefulness with bright colors. (Left) The poison arrow frog's skin secretions are so toxic that indigenous people place a few drops on their arrow tips to kill large mammals. (Right) The warning message is reinforced when the animals aggregate, especially when the noxious chemical is sprayed on predators, as these bugs do. (B) Mimicry. Some animals hide from predators by having structural adaptations that make them look like something the predator is not interested in eating, such as a leaf (left) or bird droppings (right). (C) Protective coloration. A certain pattern of coloration camouflages a Costa Rican ground-nesting bird, the paraque, which is similar to the North American whip-poor-will. The photographs on the left and right were taken from essentially the same spot. The photograph on the left shows two eggs in the paraque's nest; the female is sitting on the nest in the photograph on the right. Can you find her?

Figure 14.18

Sizes of predator and prey populations. The number of available prey affects the population size of the predators, which in turn affects the population size of the prey. In the classic example of snowshoe hare and lynx populations, an increase in the number of hares consistently led to a corresponding increase in the lynx populations. As the number of lynx increased, greater predation pressure caused a decline in the prey population, causing the lynx population to decrease as well.

Figure 14.19

Microbial growth curve. When resources are abundant, a population of bacteria exhibits the classic pattern of exponential growth until it reaches the carrying capacity defined by availability of nutrients, space, or both. During the stationary phase, the rate of reproduction equals the death rate. As bacterial waste products accumulate, deaths exceed births, rbecomes negative, and the population size decreases.

Figure 14.20

Carrying capacity and environmental degradation. In the schematic graph, which is not drawn to scale, lines B and C represent the initial carrying capacities for the deer and predator populations, respectively. Line A is the theoretical carrying capacity for the deer population, based on the number of deer the Kaibab Plateau vegetation could support. Predation pressure is responsible for the difference between the theoretical and actual numbers of deer. The removal of predators caused an exponential increase in the deer population, and the resulting damage inflicted on the island's vegetation caused the deer population to crash. The plant population could never recover to its pre-1907 levels, creating a significantly lower carrying capacity for deer.

Figure 14.21

Human population growth. Key dates in the graphs are 8000 BC, when people began domesticating plants and animals, and AD 1650 to 1750, when the scientific and industrial revolutions began. (A) A lag phase that lasted thousands of years gave way to an exponential growth rate that continues today. (B) The graph uses a logarithmic scale for population size instead of the absolute numbers of individuals. It provides information on changes in the rate of population growth in addition to changes in the number of people over time.

Figure 14.22

Modern day hunter-gatherers. In Africa and Australia, a small number of people continue to live as hunters and gatherers. (A) This group contained 12 adults and four children. Note the large bow on the left side of the photo. (B) The people hunt with primitive weapons, such as the bow and arrow this man is using to kill a young vervet monkey. (C) A group member retrieves the vervet monkey from the tree. (D) Another group member started a fire with the friction generated from rubbing two sticks together, and they cooked the monkey immediately after removing its intestines.

Figure 14.23

Causes of mortality. Immunization and antibiotics have led to significant shifts in the major causes of death in the United States and other industrialized countries in the past century. In the 1900s, infectious diseases (orange bars) were responsible for over 60% of deaths in the United States. Now, noninfectious diseases (blue bars), such as heart disease and cancer, are by far the leading causes of death.

Figure 14.24

Agricultural technology and r. (A) Pattern of population growth in industrialized countries. In those countries that began incorporating modern agricultural technologies into their farming operations, birth rates began decreasing steadily around 1850, paralleling the decreasing death rate brought on by medical advances. (B) Pattern of population growth in developing countries. Those countries that did not use modern agricultural technologies until recently showed no decrease in the birth rate as the death rate decreased. (C) Relative numbers of people in developing and industrialized regions. As a result, over the past two centuries, the population growth rate in developing countries has been significantly greater than that in industrialized countries.