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

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Presentation on theme: "Molles: Ecology 2 nd Ed. POPULATION DISTRIBUTION AND ABUNDANCE Chapter 9."— Presentation transcript:

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

2 Molles: Ecology 2 nd Ed. 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

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

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

5 Molles: Ecology 2 nd Ed. 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.

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

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

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

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

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

11 Molles: Ecology 2 nd Ed. Macropus giganteus – eastern grey Eastern 1/3 of continent temperate forest, tropical forest

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

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

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

15 Molles: Ecology 2 nd Ed. 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

16 Molles: Ecology 2 nd Ed. Tiger Beetle of Cold Climates Tiger beetle (Cicindela longilabris) - higher latitudes + elevations than other NA species 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

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

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

19 Molles: Ecology 2 nd Ed. Fig 9.5

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

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

22 Molles: Ecology 2 nd Ed. 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

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

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

25 Molles: Ecology 2 nd Ed. 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

26 Molles: Ecology 2 nd Ed. Fig 9.10

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

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

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

30 Molles: Ecology 2 nd Ed. Fig 9.11

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

32 Molles: Ecology 2 nd Ed. Fig 9.10

33 Molles: Ecology 2 nd Ed. 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

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

35 Molles: Ecology 2 nd Ed. 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

36 Molles: Ecology 2 nd Ed. Fig their hypothesis

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

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

39 Molles: Ecology 2 nd Ed. 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 Fig 9.14

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

41 Molles: Ecology 2 nd Ed. 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

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

43 Molles: Ecology 2 nd Ed. 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

44 Molles: Ecology 2 nd Ed. 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) (m + 1)

45 Molles: Ecology 2 nd Ed. 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 Example: Estimating Population Size from Mark-Recapture

46 Molles: Ecology 2 nd Ed. 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 ( ) / (12 + 1) =  ~ 354

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

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

49 Molles: Ecology 2 nd Ed. 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

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

51 Molles: Ecology 2 nd Ed. Peters and Wassenberg (1983) Aquatic invertebrates had higher pop densities than terrestrial invertebrates of similar size;  mammals have higher pop densities than birds of similar size Fig 9.20

52 Molles: Ecology 2 nd Ed. Plant Size and Population Density Plant population density decreases with increasing plant size  Underlying details different from animals

53 Molles: Ecology 2 nd Ed. White (1985) Tree seedlings can live at high densities, but as trees grow, density declines until mature trees are at low densities

54 Molles: Ecology 2 nd Ed. Rarity and Extinction Rabinowitz - 7 forms of rarity commonness classification based on (3) factors:  Geographic Range of Species  Habitat Tolerance  Local Population Size

55 Molles: Ecology 2 nd Ed. Rarity Non-rare populations have large geographic ranges, broad habitat tolerances, some large local populations All seven other other combinations create some kind of rarity = risk of extinction

56 Molles: Ecology 2 nd Ed. Rarity Rarity I  Large Range: Broad Habitat Tolerance: Small Local Pops  Peregrine Falcons

57 Molles: Ecology 2 nd Ed. Rarity II  Large Range: Narrow Habitat Tolerance: Small Local Pops  Passenger Pigeons

58 Molles: Ecology 2 nd Ed. Rarity Rarity III  Small Range: Narrow Habitat Tolerance: Small Pops  Mountain Gorilla

59 Increasing vulnerability to extinctionIncreasingRarity Least vulnerable to extinction

60 Moderate vulnerability to extinction

61 High extinction

62 Highest extinction Other Example ?

63 Molles: Ecology 2 nd Ed. Example: NA suckers White sucker - large range White sucker - large range Broad habitat requirements Broad habitat requirements Large body size Large body size

64 Molles: Ecology 2 nd Ed. Yacqui sucker - small range Yacqui sucker - small range Narrow habitat requirements Narrow habitat requirements Small body size Small body size

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

66 Molles: Ecology 2 nd Ed.


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