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Chapter 7

Chapter 7. Community Ecology. Chapter Overview Questions. What determines the number of species in a community? How can we classify species according to their roles in a community? How do species interact with one another? How do communities respond to changes in environmental conditions?

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Chapter 7

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  1. Chapter 7 Community Ecology

  2. Chapter Overview Questions • What determines the number of species in a community? • How can we classify species according to their roles in a community? • How do species interact with one another? • How do communities respond to changes in environmental conditions? • Does high species biodiversity increase the stability and sustainability of a community?

  3. Updates Online The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at www.thomsonedu.com to access InfoTrac articles. • InfoTrac: California's wild crusade. Virginia Morell. National Geographic, Feb 2006 v209 i2 p80(16). • InfoTrac: Traveling green. Carol Goodstein. Natural History, July-August 2006 v115 i6 p16(4) . • InfoTrac: Too hot to trot. Charlie Furness. Geographical, May 2006 v78 i5 p51(7). • The Nature Conservancy: Jaguar Habitat and Center of Maya Civilization Protected in Historic Land Deal • National Geographic News: Conservationists Name Nine New "Biodiversity Hotspots"

  4. Core Case Study:Why Should We Care about the American Alligator? • Hunters wiped out population to the point of near extinction. • Alligators have important ecological role. Figure 7-1

  5. Core Case Study:Why Should We Care about the American Alligator? • Dig deep depressions (gator holes). • Hold water during dry spells, serve as refuges for aquatic life. • Build nesting mounds. • provide nesting and feeding sites for birds. • Keeps areas of open water free of vegetation. • Alligators are a keystone species: • Help maintain the structure and function of the communities where it is found.

  6. Endangered Species • 1967 – American Alligator listed as endangered • By 1977 – reduced listing to threatened • Now there are farms that provide alligator meat and skin • There are invasive species that threaten the alligators: breeding populations of burmese pythons in Florida

  7. COMMUNITY STRUCTURE AND SPECIES DIVERSITY • Biological communities differ in their structure and physical appearance. Figure 7-2

  8. Desert scrub Tall-grass prairie Short-grass prairie Tropical rain forest Thorn scrub Thorn forest Coniferous forest Deciduous forest Fig. 7-2, p. 144

  9. Species Diversity and Niche Structure: Different Species Playing Different Roles • Biological communities differ in the types and numbers of species they contain and the ecological roles those species play. • Species diversity/ species richness • the number of different species it contains • species evenness • combined with the abundance of individuals within each of those species • Do you have equal numbers of different species?

  10. The Edges • Community structure varies around the edges • How? • Might be sunnier, warmer, drier than forest interior • Increasing edges with habitat fragmentation increases stress on organisms • How? • Species more vulnerable to predators and fire • Can create barriers to colonizing new areas, finding mates and food

  11. Species Diversity and Niche Structure • Niche structure: • how many potential ecological niches occur? • how they resemble or differ? • how the species occupying different niches interact? • Geographic location: • species diversity is highest in the tropics and declines as we move from the equator toward the poles.

  12. TROPIC • Consistent daily climate and reliable food sources results in specialists with narrow niches versus generalists • Species in higher latitudes with variable weather have adaptations that allow them to survive in a greater range of environments

  13. TYPES OF SPECIES • Native, nonnative, indicator, keystone, and foundation species play different ecological roles in communities. • Native: • those that normally live and thrive in a particular community. • Nonnative species: • those that migrate, deliberately or accidentally introduced into a community. • Also known as invasive

  14. Purposely introducing nonnatives • 1957 the African bee was introduced to increase the productivity of honey bees • This introduction created “The killler bees” • They have migrated North but are limited by cold weather. • Theses bees are overly aggressive compared with commercial honey bees

  15. CANE TOAD • We will watch a video that discusses the affects of the CANE TOAD introduced in Australia

  16. Case Study:Species Diversity on Islands • MacArthur and Wilson proposed the species equilibrium model or theory of island biogeography in the 1960’s. • Model projects that at some point the rates of immigration and extinction should reach an equilibrium based on: • Island size • Distance to nearest mainland

  17. Possible Author for Book • E. O. Wilson • Main works • The Theory of Island Biogeography, 1967, Princeton University Press (2001 reprint), ISBN 0-691-08836-5, with Robert H. MacArthur • The Insect Societies, 1971, Harvard University Press, ISBN 0-674-45490-1 • Sociobiology: The New Synthesis 1975, Harvard University Press, (Twenty-fifth Anniversary Edition, 2000ISBN 0-674-00089-7) • On Human Nature, 1979, Harvard University Press, ISBN 0-674-01638-6 • Genes, Mind and Culture: The coevolutionary process, 1981, Harvard University Press, ISBN 0-674-34475-8 • Promethean fire: reflections on the origin of mind, 1983, Harvard University Press, ISBN 0-674-71445-8 • Biophilia, 1984, Harvard University Press, ISBN 0-674-07441-6

  18. Success and Dominance in Ecosystems: The Case of the Social Insects, 1990, Inter-Research, ISSN 0932-2205 • The Ants, 1990, Harvard University Press, ISBN 0-674-04075-9, Winner of the Pulitzer Prize, with Bert Hölldobler • The Diversity of Life, 1992, Harvard University Press, ISBN 0-674-21298-3, The Diversity of Life: Special Edition, ISBN 0-674-21299-1 • The Biophilia Hypothesis, 1993, Shearwater Books, ISBN 1-55963-148-1, with Stephen R. Kellert • Journey to the Ants: A Story of Scientific Exploration, 1994, Harvard University Press, ISBN 0-674-48525-4, with Bert Hölldobler • Naturalist, 1994, Shearwater Books, ISBN 1-55963-288-7 • In Search of Nature, 1996, Shearwater Books, ISBN 1-55963-215-1, with Laura SimondsSouthworth • Consilience: The Unity of Knowledge, 1998, Knopf, ISBN 0-679-45077-7 • The Future of Life, 2002, Knopf, ISBN 0-679-45078-5 • Pheidole in the New World: A Dominant, Hyperdiverse Ant Genus, 2003, Harvard University Press, ISBN 0-674-00293-8 • From So Simple a Beginning: Darwin's Four Great Books. 2005, W. W. Norton. • The Creation: An Appeal to Save Life on Earth, September 2006, W. W. Norton & Company, Inc. ISBN 978-0393062175 • Nature Revealed: Selected Writings 1949-2006, Johns Hopkins University Press, Baltimore. ISBN 0-8018-8329-6 • The Superorganism: The Beauty, Elegance, and Strangeness of Insect Societies, 2009, W.W. Norton & Company, Inc. ISBN 978-0-393-06704-0, with Bert Hölldobler

  19. Indicator Species: Biological Smoke Alarms Species that serve as early warnings of damage to a community or an ecosystem. • Presence or absence of trout species because they are sensitive to temperature and oxygen levels. • Birds are affected quickly by change • Butterflies are associated with certain plants • Coal miners used to use canaries • If they stopped singing then its time to get out!!!

  20. Keystone Species: Major Players • Keystone species help determine the types and numbers of other species in a community thereby helping to sustain it. • How were Yellowstone wolves a keystone species? Figures 7-4 and 7-5

  21. Case Study: Why are Amphibians Vanishing? • Frogs serve as indicator species because different parts of their life cycles can be easily disturbed. Figure 7-3

  22. Adult frog(3 years) Young frog Sperm Tadpole develops into frog Sexual Reproduction Tadpole Eggs Fertilized egg development Egg hatches Organ formation Fig. 7-3, p. 147

  23. Case Study: Why are Amphibians Vanishing? • Frogs sensitive at various stage of life • Eggs absorb UV radiation or pollution • Tadpoles live in water and eat plants • As adults they eat insects (pesticide exposure) • Frogs have thin permeable skin • Easily absorb pollutants from water, air, soil • As of 2004 33% of populations threatened • 43% of populations declining

  24. Case Study: Why are Amphibians Vanishing? • See answers on next slide

  25. FROGS: No single cause has been indentified • Habitat loss and fragmentation • Draining and filling wetlands, deforestation, development • Prolonged drought: kills tadpoles • Pollution • Pesticides = sensitivity to bacterial, viral and fungal diseases and cause sexual abnormalities • Increases in ultraviolet radiation from ozone layer destruction • Harms embryos of amphibians in shallow ponds

  26. Frogs continued • Parasistes • Viral and Fungal diseases • Chytrid fungus attacks the skin • Climate Change: • Evaporated water increases cloud cover, lowers daytime temps and warms night = chytrid fungi • Overhunting (Frog leg delicacy in Asia and France) • Natural immigration or deliberate introduction of nonnative predators + competitors

  27. Why should we care if frogs die? • They signal degradation of habitat • They eat insects • They are genetic storehouse of pharmaceutical products waiting to be discovered • Painkillers, antibiotics, burns, heart disease, etc • They might not need us, but we need them

  28. Video: Frogs Galore PLAY VIDEO • From ABC News, Biology in the Headlines, 2005 DVD.

  29. Foundation Species: Other Major Players • Expansion of keystone species category. • Foundation species can create and enhance habitats that can benefit other species in a community. • Elephants push over, break, or uproot trees, creating forest openings promoting grass growth for other species to utilize. • Bats and birds regenerate deforested areas (how?) • Beavers create wetlands

  30. How Would You Vote? To conduct an instant in-class survey using a classroom response system, access “JoinIn Clicker Content” from the PowerLecture main menu for Living in the Environment. • Do we have an ethical obligation to protect shark species from premature extinction and treat them humanely? • a. No. It's impractical to force international laws on individual fishermen that are simply trying to feed their families with the fishing techniques that they have. • b. Yes. Sharks are an important part of marine ecosystems. They must be protected and, like all animals, they should be humanely treated.

  31. Sharks • Whale shark dorsal fin can = $10,000 • Bowl of soup can = $100 • Yet fins found to be high in MERCURY • Sharks killed because we fear them, yet only 7 people per year on average die from sharks • SHARKS are our key to cancer. • Sharks rarely get cancer and have effective immune systems • They grow slow, mature late = • SENSITIVE TO OVERFISHING

  32. SPECIES INTERACTIONS: COMPETITION AND PREDATION • Species can interact through competition, predation, parasitism, mutualism, and commensalism. • Some species evolve adaptations that allow them to reduce or avoid competition for resources with other species (resource partitioning).

  33. Resource Partitioning • Each species minimizes competition with the others for food by spending at least half its feeding time in a distinct portion of the spruce tree and by consuming somewhat different insect species. Figure 7-7

  34. Niche Specialization • Niches become separated to avoid competition for resources. Figure 7-6

  35. Number of individuals Species 2 Species 1 Region of niche overlap Resource use Number of individuals Species 1 Species 2 Resource use Fig. 7-6, p. 150

  36. Examples • The lion eats larger animals and leopards eat the smaller animals when both exist in the same habitat. • Hawks hunt by day and Owls hunt the same prey by night.

  37. SPECIES INTERACTIONS: COMPETITION AND PREDATION • Species called predators feed on other species called prey. • Organisms use their senses their senses to locate objects and prey and to attract pollinators and mates. • Some predators are fast enough to catch their prey, some hide and lie in wait, and some inject chemicals to paralyze their prey.

  38. PREDATION • Some prey escape their predators or have outer protection, some are camouflaged, and some use chemicals to repel predators. Figure 7-8

  39. Camouflage (a) Span worm Fig. 7-8a, p. 153

  40. Camouflage (b) Wandering leaf insect Fig. 7-8b, p. 153

  41. Chemical Warfare (c) Bombardier beetle Fig. 7-8c, p. 153

  42. Chemical Warfare Warning coloration (d) Foul-tasting monarch butterfly Fig. 7-8d, p. 153

  43. Chemical Warfare Warning coloration (e) Poison dart frog Fig. 7-8e, p. 153

  44. mimicry (f) Viceroy butterfly mimics monarch butterfly Fig. 7-8f, p. 153

  45. (g) Hind wings of Io moth resemble eyes of a much larger animal. Fig. 7-8g, p. 153

  46. Deceptive Behavior (h) When touched, snake caterpillar changes shape to look like head of snake. Fig. 7-8h, p. 153

  47. SPECIES INTERACTIONS: PARASITISM, MUTUALISM, AND COMMENSALIM • Parasitism occurs when one species feeds on part of another organism. • In mutualism, two species interact in a way that benefits both. • Commensalism is an interaction that benefits one species but has little, if any, effect on the other species.

  48. Parasites: Sponging Off of Others • Although parasites can harm their hosts, they can promote community biodiversity. • Some parasites live in host (micororganisms, tapeworms). • Some parasites live outside host (fleas, ticks, mistletoe plants, sea lampreys). • Some have little contact with host (dump-nesting birds like cowbirds, some duck species)

  49. Mutualism: Win-Win Relationship • Two species can interact in ways that benefit both of them. Figure 7-9

  50. (a) Oxpeckers and black rhinoceros Fig. 7-9a, p. 154

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