POPULATION DISTRIBUTION AND ABUNDANCE

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POPULATION DISTRIBUTION AND ABUNDANCE

• Chapter 9

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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

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Populations

• Ecologists define a population as group of
  individuals of single species inhabiting specific
  area.

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Habitat

• Physical environmental conditions that allow
  individuals of species to survive AND reproduce

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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.

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Population numbers vary with habitat quality
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Distribution Limits

• Physical environment limits geographic
  distribution of species
• Organisms can only compensate so much for
  environmental variation

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Geographical range

• Geographic area where species is found (based on
  macroclimate, salinity, nutrients, oxygen, light,
  etc.)

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• Large-scale patterns of distribution
• Refer to variation in species abundance w/in
  range
• due to variation in habitat quality

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Kangaroo Distributions and Climate

• Caughley - relationship between climate
  distribution of three largest kangaroos in
  Australia

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Macropus giganteus eastern greyEastern 1/3 of
continenttemperate forest, tropical forest
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Macropus fuliginosus western grey southern and
western regionstemperate woodlands and shrubs
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Macropus rufus redarid / semiarid interior
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Fig 9.2
Distributions largely based on climate
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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

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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

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Fig 9.3
Metabolic rates of C. longilabris higher
preferred temps lower than other beetle species
Adapted to cool climates
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Distributions of Plants Along a
Moisture-Temperature Gradient

• Encelia spp. distributions variations in temp
  and precipitation

Fig 9.7
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Fig 9.5
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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

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Connell found pattern in barnacles

• Chthamalus stellatus restricted to upper levels
  Balanus balanoides limited to middle and lower
  levels

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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

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Competition? How do we know that Balanus
outcompetes Chthamalus?
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Fig 9.8
Fig 9.9
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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

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Fig 9.10
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Importance of scale in determining distribution
patterns

• At one scale pattern may be random, at another
  scale, might be uniform

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Distribution of Tropical Bee Colonies

• Hubbell and Johnson predicted aggressive bee
  colonies have regular distributions
• Predicted non-aggressive species have random or
  clumped distributions

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Hubbell and Johnson results

• 4 species with regular distributions were highly
  aggressive
• Fifth non-aggressive and randomly distributed

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Fig 9.11
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What causes overall pattern?

• Behavior!
• Aggressive bees were uniformly spaced due largely
  to their interactions.
• Non-aggressive species were random - did not
  interact.

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Fig 9.10
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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

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Hypothesis

• Young shrubs clumped for (3) reasons
• Seeds germinate at safe sites
• Seeds not dispersed from parent areas
• Asexual reproduction

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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

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Fig 9.13 - their hypothesis
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Brisson and Reynolds

• Dug up roots, map distribution of 32 bushes
• found competitive interactions with neighboring
  shrubs influences distribution of creosote roots

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So what?

• Creosote bush roots do not overlap with nearby
  plant roots
• Only 4 overlap between bushes

Fig 9.14
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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
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Similar distribution pattern for species with
small range few hot spotsFish crow
Fig 9.14
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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
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Density number individuals per unit area/volume

• Sedentary organisms plot approach
• Moving/secretive organisms mark/recapture
• Relative abundance percent cover, CPUE

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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

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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)

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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
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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

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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

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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

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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

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Damuth (1981)

• Pop density of 307 spp. of herbivorous mammals
  decreased with increased body size

Fig 9.19
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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
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Plant Size and Population Density

• Plant population density decreases with
  increasing plant size
• Underlying details different from animals

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White (1985)

• Tree seedlings can live at high densities, but as
  trees grow, density declines until mature trees
  are at low densities

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Rarity and Extinction

• Rabinowitz - 7 forms of rarity
• commonness classification based on (3) factors
• Geographic Range of Species
• Habitat Tolerance
• Local Population Size

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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

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Rarity

• Rarity I
• Large Range Broad Habitat Tolerance Small Local
  Pops
• Peregrine Falcons

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Rarity II

• Large Range Narrow Habitat Tolerance Small
  Local Pops
• Passenger Pigeons

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Rarity

• Rarity III
• Small Range Narrow Habitat Tolerance Small Pops
• Mountain Gorilla

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Least vulnerable to extinction
Increasing vulnerability to extinction
Increasing Rarity
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Moderate vulnerability to extinction
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High vulnerability to extinction
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Highest vulnerability to extinction
Other Example ?
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Example NA suckers

• White sucker - large range
• Broad habitat requirements
• Large body size

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• Yacqui sucker - small range
• Narrow habitat requirements
• Small body size

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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

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