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Chapter 7

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Chapter 7

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  1. Chapter 7 Community Ecology

  2. 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

  3. 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.

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

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

  6. 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.

  7. Species Diversity and Niche • Species diversity: combination of: • species richness - the number of different species it contains • species evenness - abundance of individuals within each of those species

  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. Species Diversity on Islands • species equilibrium model • at some point the rates of immigration and extinction should reach an equilibrium based on: • Island size • Distance to nearest mainland

  10. TYPES OF SPECIES • Native • Nonnative • Indicator • Keystone • Foundation species Play different ecological roles in communities.

  11. TYPES OF SPECIES • Native: those that normally live and thrive in a particular community. • Nonnative species: those that migrate, deliberately or accidentally introduced into a community.

  12. Invasive species Nonnative(Introduced) • They displace native species • They lower biodiversity • The can adapt very quickly to local habitats • They contribute to habitat fragmentation • They can reproduce very quickly

  13. Importation of Species • Ex. The Chinese chestnut had a fungus that spread & virtually eliminated the American chestnut. • Kudzu

  14. 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

  15. 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.

  16. 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.

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

  18. 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

  19. 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.

  20. 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).

  21. 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

  22. The Fundamental Niche • The fundamental niche of an organism is described by the full range of environmental conditions (biological and physical) under which the organism can exist. • The realized niche of the organism is the niche that is actually occupied. It is narrower than the fundamental niche. • This contraction of the realized niche is a result of pressure from, and interactions with, other organisms.

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

  24. 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

  25. 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.

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

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

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

  29. Chemical warfare (c) Bombardier beetle Fig. 7-8c, p. 153

  30. Chemical warfare & warning coloration (d) Foul-tasting monarch butterfly Fig. 7-8d, p. 153

  31. Chemical warfare & warning coloration (e) Poison dart frog Fig. 7-8e, p. 153

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

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

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

  35. 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.

  36. 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)

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

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

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

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

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

  42. 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

  43. 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.

  44. Succession • The process where plants & animals of a particular area are replaced by other more complex species over time.

  45. Primary Succession: Starting from Scratch Primary succession begins with an essentially lifeless are where there is no soil (bare rock). Soil formation begins with lichens or moss.

  46. Primary Succession • Primary begins with a lifeless area where there is no soil (ex. bare rock). Soil formation begins with lichens or moss.

  47. Primary Succession • Primary succession refers to colonization of a region where there is no pre-existing community. Examples include: • Newly emerged coral atolls, volcanic islands • Newly formed glacial moraines • Islands where the previous community has been extinguished by a volcanic eruption Hawaii: Local plants are able to rapidly recolonize barren areas

  48. Primary Succession • A classical sequence of colonization begins with lichens, mosses, and liverworts, progresses to ferns, grasses, shrubs, and culminates in a climax community of mature forest. • In reality, this scenario is rare. Unless there is the formation of a new island or volcanic eruption. Mature, slow growing trees Shrubs and fast growing trees Grasses and herbaceous plants Mosses and liverworts Bare rock and lichens

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

  50. 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