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POPULATION DISTRIBUTION AND ABUNDANCE

POPULATION DISTRIBUTION AND ABUNDANCE. Chapter 9. Chapter Concepts. Physical environment limits geographic distribution of species On small scales, individuals within pops. are distributed in random, regular, or clumped patterns; on larger scales, individuals within pop. are clumped

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POPULATION DISTRIBUTION AND ABUNDANCE

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  1. POPULATION DISTRIBUTION AND ABUNDANCE Chapter 9 Molles: Ecology 2nd Ed.

  2. Chapter Concepts • Physical environment limits geographic distribution of species • On small scales, individuals within pops. are distributed in random, regular, or clumped patterns; on larger scales, individuals within pop. are clumped • Population density declines with increasing organism size • Rarity influenced by geographic range, habitat tolerance, pop. size; rare species vulnerable to extinction Molles: Ecology 2nd Ed.

  3. Populations • Ecologists define a population as group of individuals of single species inhabiting specific area. Molles: Ecology 2nd Ed.

  4. Habitat • Physical environmental conditions that allow individuals of species to survive AND reproduce Molles: Ecology 2nd Ed.

  5. Habitat quality • Ability of environmental conditions to support repro and survival • Habitat area/volume • Resource concentration • Time • High habitat quality = organisms acquire many resources; high survival + repro = large pop. Molles: Ecology 2nd Ed.

  6. Population numbers vary with habitat quality Molles: Ecology 2nd Ed.

  7. Distribution Limits • Physical environment limits geographic distribution of species • Organisms can only compensate so much for environmental variation Molles: Ecology 2nd Ed.

  8. Geographical range • Geographic area where species is found (based on macroclimate, salinity, nutrients, oxygen, light, etc.) Molles: Ecology 2nd Ed.

  9. “Large-scale” patterns of distribution: • Refer to variation in species abundance w/in range • due to variation in habitat quality Molles: Ecology 2nd Ed.

  10. Kangaroo Distributions and Climate • Caughley - relationship between climate + distribution of three largest kangaroos in Australia Molles: Ecology 2nd Ed.

  11. Macropus giganteus – eastern greyEastern 1/3 of continenttemperate forest, tropical forest Molles: Ecology 2nd Ed.

  12. Macropus fuliginosus – western grey southern and western regionstemperate woodlands and shrubs Molles: Ecology 2nd Ed.

  13. Macropus rufus – redarid / semiarid interior Molles: Ecology 2nd Ed.

  14. Fig 9.2 Distributions largely based on climate Molles: Ecology 2nd Ed.

  15. Kangaroo Distributions and Climate • Limited distributions may not be directly determined by climate. • Climate often influences species distributions via: • food production • water supply • habitat • incidence of parasites, pathogens and competitors Molles: Ecology 2nd Ed.

  16. Tiger Beetle of Cold Climates • Tiger beetle (Cicindela longilabris) - higher latitudes + elevations than other NA species • Schultz found metabolic rates of C. longilabris are higher and preferred temps. lower than other species • Physical env. limits species distributions Molles: Ecology 2nd Ed.

  17. Fig 9.3 Metabolic rates of C. longilabris higher; preferred temps lower than other beetle species Adapted to cool climates Molles: Ecology 2nd Ed.

  18. Distributions of Plants Along a Moisture-Temperature Gradient • Encelia spp. distributions + variations in temp and precipitation Fig 9.7 Molles: Ecology 2nd Ed.

  19. Fig 9.5 Molles: Ecology 2nd Ed.

  20. Distributions of Barnacles - Intertidal Gradient • Organisms in intertidal zone have evolved different degrees of resistance to drying • Barnacles - distinctive patterns of zonation within intertidal zone Molles: Ecology 2nd Ed.

  21. Connell found pattern in barnacles: • Chthamalus stellatus restricted to upper levels; Balanus balanoides limited to middle and lower levels Molles: Ecology 2nd Ed.

  22. Distributions of Barnacles Along an Intertidal Gradient • Balanus - more vulnerable to desiccation, excluded from upper intertidal zone • Chthamalus adults excluded from lower areas by competition with Balanus Molles: Ecology 2nd Ed.

  23. Competition? How do we know that Balanus outcompetes Chthamalus? Molles: Ecology 2nd Ed.

  24. Fig 9.8 Fig 9.9 Molles: Ecology 2nd Ed.

  25. Distribution of Individuals on Small Scales • Three basic patterns: • Random: equal chance of being anywhere • Regular: uniformly spaced • Exclusive use of areas • Individuals avoid one another • Clumped: unequal chance of being anywhere • Mutual attraction between individuals • Patchy resource distribution Molles: Ecology 2nd Ed.

  26. Fig 9.10 Molles: Ecology 2nd Ed.

  27. Importance of scale in determining distribution patterns: • At one scale pattern may be random, at another scale, might be uniform: Molles: Ecology 2nd Ed.

  28. Distribution of Tropical Bee Colonies • Hubbell and Johnson predicted aggressive bee colonies have regular distributions; • Predicted non-aggressive species have random or clumped distributions Molles: Ecology 2nd Ed.

  29. Hubbell and Johnson results: • 4 species with regular distributions were highly aggressive • Fifth non-aggressive and randomly distributed Molles: Ecology 2nd Ed.

  30. Fig 9.11 Molles: Ecology 2nd Ed.

  31. What causes overall pattern? • Behavior! • Aggressive bees were uniformly spaced due largely to their interactions. • Non-aggressive species were random - did not interact. Molles: Ecology 2nd Ed.

  32. Fig 9.10 Molles: Ecology 2nd Ed.

  33. Distributions of Desert Shrubs • Traditional theory suggests desert shrubs are regularly spaced due to competition • Phillips and MacMahon - distribution of desert shrubs changes from clumped to regular patterns as they grow Molles: Ecology 2nd Ed.

  34. Hypothesis: • Young shrubs clumped for (3) reasons: • Seeds germinate at safe sites • Seeds not dispersed from parent areas • Asexual reproduction Molles: Ecology 2nd Ed.

  35. Distributions of Desert Shrubs • Phillips and MacMahon proposed as plants grow, some individuals in clumps die = reducing clumping • Competition among remaining plants produces higher mortality • Eventually creates regular distributions Molles: Ecology 2nd Ed.

  36. Fig 9.13 - their hypothesis Molles: Ecology 2nd Ed.

  37. Brisson and Reynolds • Dug up roots, map distribution of 32 bushes • found competitive interactions with neighboring shrubs influences distribution of creosote roots Molles: Ecology 2nd Ed.

  38. So what? • Creosote bush roots do not overlap with nearby plant roots • Only 4% overlap between bushes Fig 9.14 Molles: Ecology 2nd Ed.

  39. Distributions of Individuals on Large Scales • Bird Pops North America • Root - at continental scale, bird pops have clumped distributions (Christmas Bird Counts) • Clumped patterns in species with widespread distributions Molles: Ecology 2nd Ed. Fig 9.14

  40. Similar distribution pattern for species with small range: few “hot spots”Fish crow Fig 9.14 Molles: Ecology 2nd Ed.

  41. Brown et al. (1995) • Relatively few study sites gave most records for each bird species in Breeding Bird Survey (June): • clumped only during breeding season? Fig 9.16 Molles: Ecology 2nd Ed.

  42. Density = number individuals per unit area/volume • Sedentary organisms: plot approach • Moving/secretive organisms: mark/recapture • Relative abundance = percent cover, CPUE Molles: Ecology 2nd Ed.

  43. Estimating density • Sedentary animals and plants • Plot methods • Area of known size • Randomly located plots • Count individuals in plots • Average / plot • Density = average no. / plot area Molles: Ecology 2nd Ed.

  44. (m + 1) Estimating density • Mobile or secretive animals: mark/recapture • 1. Sample animals and mark • 2. Release (M out of N in pop marked) • 3. Wait for mixing • 4. Sample (n), count how many marked (m) • 5. Compute estimate of pop size: • N = M (n + 1) Molles: Ecology 2nd Ed.

  45. Example: Estimating Population Size from Mark-Recapture • Number of animals marked in 1st sample = 100 • Total number of animals in 2nd sample = 150 • Number of marked animals in 2nd sample = 11 Population = M (n + 1) = 100 (151) = 1258 Size (N) (m + 1) 12 Molles: Ecology 2nd Ed.

  46. Another Example • Sample M = 38 squirrels, marked, released • After 2 weeks, resample, n = 120 • m = 12 of 120 marked • Estimate of pop. size: • N = M (n + 1) / (m + 1) • = 38 (120 + 1) / (12 + 1) = 353.7 • ~ 354 Molles: Ecology 2nd Ed.

  47. Example: maple trees • 20 randomly located plots, 10 x 10 m squares (area = 100 m2) • Average sugar maple stems per plot = 4.5 • Unit area for trees = hectare (10,000 m2) • Density = 4.5 maples per plot / 0.01 hectare plots = 450 maples / ha Molles: Ecology 2nd Ed.

  48. Example: zooplankters • 35 lake water samples, 50 ml each • Average copepods per sample = 78 • Unit volume for zooplankton = liters • Sample volume = 0.05 l • Density = 78 copepods per sample / 0.05 l samples • = 1560 copepods / l Molles: Ecology 2nd Ed.

  49. Organism Size and Population Density • Population density decreases with larger organism size • Why? • Bigger organisms need more space and resources • Bigger organisms have lower repro rates Molles: Ecology 2nd Ed.

  50. Damuth (1981) • Pop density of 307 spp. of herbivorous mammals decreased with increased body size Fig 9.19 Molles: Ecology 2nd Ed.

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