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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. 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

  4. 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.

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

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

  7. 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: the number of different species it contains (species richness) combined with the abundance of individuals within each of those species (species evenness).

  8. Species Diversity and Niche Structure • Niche structure: how many potential ecological niches occur, how they resemble or differ, and 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.

  9. 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.

  10. 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

  11. 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.

  12. Keystone Species: Major Players • Keystone species help determine the types and numbers of other species in a community thereby helping to sustain it. Figures 7-4 and 7-5

  13. 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.

  14. 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

  15. 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

  16. Case Study: Why are Amphibians Vanishing? • Habitat loss and fragmentation. • Prolonged drought. • Pollution. • Increases in ultraviolet radiation. • Parasites. • Viral and Fungal diseases. • Overhunting. • Natural immigration or deliberate introduction of nonnative predators and competitors.

  17. How Would You Vote? • 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.

  18. 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).

  19. Animation: How Species Interact PLAY ANIMATION

  20. 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

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

  22. 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

  23. 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.

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

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

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

  27. (c) Bombardier beetle Fig. 7-8c, p. 153

  28. (d) Foul-tasting monarch butterfly Fig. 7-8d, p. 153

  29. (e) Poison dart frog Fig. 7-8e, p. 153

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

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

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

  33. 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.

  34. 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)

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

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

  37. (b) Clownfish and sea anemone Fig. 7-9b, p. 154

  38. (c) Mycorrhizal fungi on juniper seedlings in normal soil Fig. 7-9c, p. 154

  39. (d) Lack of mycorrhizal fungi on juniper seedlings in sterilized soil Fig. 7-9d, p. 154

  40. Video: Clownfish with Anemone PLAY VIDEO

  41. Commensalism: Using without Harming • Some species interact in a way that helps one species but has little or no effect on the other. Figure 7-10

  42. ECOLOGICAL SUCCESSION: COMMUNITIES IN TRANSITION • New environmental conditions allow one group of species in a community to replace other groups. • Ecological succession: the gradual change in species composition of a given area • Primary succession: the gradual establishment of biotic communities in lifeless areas where there is no soil or sediment. • Secondary succession: series of communities develop in places containing soil or sediment.

  43. Primary Succession: Starting from Scratch • Primary succession begins with an essentially lifeless area where there is no soil in a terrestrial ecosystem Figure 7-11

  44. Lichens and mosses Exposed rocks Balsam fir, paper birch, and white spruce forest community Jack pine, black spruce, and aspen Heath mat Small herbs and shrubs Time Fig. 7-11, p. 156

  45. Secondary Succession: Starting Over with Some Help • Secondary succession begins in an area where the natural community has been disturbed. Figure 7-12

  46. Mature oak-hickory forest Young pine forest with developing understory of oak and hickory trees Shrubs and pine seedlings Perennial weeds and grasses Annual weeds Time Fig. 7-12, p. 157

  47. Can We Predict the Path of Succession, and is Nature in Balance? • The course of succession cannot be precisely predicted. • Previously thought that a stable climax community will always be achieved. • Succession involves species competing for enough light, nutrients and space which will influence it’s trajectory.

  48. ECOLOGICAL STABILITY AND SUSTAINABILITY • Living systems maintain some degree of stability through constant change in response to environmental conditions through: • Inertia (persistence): the ability of a living system to resist being disturbed or altered. • Constancy: the ability of a living system to keep its numbers within the limits imposed by available resources. • Resilience: the ability of a living system to bounce back and repair damage after (a not too drastic) disturbance.

  49. ECOLOGICAL STABILITY AND SUSTAINABILITY • Having many different species appears to increase the sustainability of many communities. • Human activities are disrupting ecosystem services that support and sustain all life and all economies.

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