molles: ecology 2 nd ed. population distribution and abundance chapter 9
TRANSCRIPT
Molles: Ecology 2nd 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
Molles: Ecology 2nd Ed.
Populations
• Ecologists define a population as group of individuals of single species inhabiting specific area.
Molles: Ecology 2nd Ed.
Habitat
• Physical environmental conditions that allow individuals of species to survive AND reproduce
Molles: Ecology 2nd 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.
Molles: Ecology 2nd Ed.
Population numbers vary with habitat quality
Po
pula
tion
siz
e
Environmental gradient
Low Optimal High
GoodhabitatPoor
habitatPoorhabitat
Molles: Ecology 2nd Ed.
Distribution Limits
• Physical environment limits geographic distribution of species Organisms can only compensate so much
for environmental variation
Molles: Ecology 2nd Ed.
Geographical range
• Geographic area where species is found Geographic area where species is found (based on macroclimate, salinity, nutrients, (based on macroclimate, salinity, nutrients, oxygen, light, etc.)oxygen, light, etc.)
Molles: Ecology 2nd Ed.
• ““Large-scale” patterns of distribution:Large-scale” patterns of distribution:• Refer to variation in species abundance w/in Refer to variation in species abundance w/in
rangerange due to variation in habitat qualitydue to variation in habitat quality
Molles: Ecology 2nd Ed.
Kangaroo Distributions and Climate
• Caughley - relationship between climate + distribution of three largest kangaroos in Australia
Molles: Ecology 2nd Ed.
Macropus giganteus – eastern greyEastern 1/3 of continent
temperate forest, tropical forest
Molles: Ecology 2nd Ed.
Macropus fuliginosus – western grey southern and western regions
temperate woodlands and shrubs
Molles: Ecology 2nd 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
Molles: Ecology 2nd Ed.
Tiger Beetle of Cold Climates
• Tiger beetle (Tiger beetle (Cicindela longilabrisCicindela longilabris) - higher ) - higher latitudes + elevations than other NA specieslatitudes + elevations than other NA species SchultzSchultz found metabolic rates of found metabolic rates of C. C.
longilabrislongilabris are higher and preferred temps. are higher and preferred temps. lower than other specieslower than other species Physical env. limits species distributionsPhysical env. limits species distributions
Molles: Ecology 2nd Ed.
Fig 9.3
Metabolic rates of Metabolic rates of C. C. longilabrislongilabris higher; higher; preferred temps preferred temps lower than other lower than other beetle speciesbeetle species
Adapted to cool Adapted to cool climatesclimates
Molles: Ecology 2nd Ed.
Distributions of Plants Along a Moisture-Temperature Gradient
• Encelia spp. distributions + variations in temp and precipitation
Fig 9.7
Molles: Ecology 2nd Ed.
Distributions of Barnacles - Intertidal Gradient
• Organisms in intertidal zone have evolved Organisms in intertidal zone have evolved different degrees of resistance to dryingdifferent degrees of resistance to drying Barnacles - distinctive patterns of zonation Barnacles - distinctive patterns of zonation
within intertidal zonewithin intertidal zone
Molles: Ecology 2nd Ed.
ConnellConnell found pattern in barnacles: found pattern in barnacles:
• Chthamalus stellatusChthamalus stellatus restricted to upper restricted to upper levels; levels; Balanus balanoidesBalanus balanoides limited to middle limited to middle and lower levelsand lower levels
Molles: Ecology 2nd 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
Molles: Ecology 2nd 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
Molles: Ecology 2nd Ed.
Importance of scale in determining distribution patterns:
• At one scale pattern may be random, at another scale, might be uniform:
Molles: Ecology 2nd 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
Molles: Ecology 2nd Ed.
Hubbell and Johnson results:
• 4 species with regular distributions were highly aggressive
Fifth non-aggressive and randomly Fifth non-aggressive and randomly distributeddistributed
Molles: Ecology 2nd Ed.
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.
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.
Hypothesis:
Young shrubs clumped for (3) reasons: Seeds germinate at safe sites Seeds not dispersed from parent areas Asexual reproduction
Molles: Ecology 2nd 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
Molles: Ecology 2nd Ed.
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.
• Creosote bush roots do not overlap with nearby plant roots
• Only 4% overlap between bushes
Fig 9.14
So what?
Molles: Ecology 2nd 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
Molles: Ecology 2nd Ed.
Similar distribution pattern for species with small range: few “hot spots”
Fish crow
Fig 9.14
Molles: Ecology 2nd 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
Molles: Ecology 2nd Ed.
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.
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.
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)
Molles: Ecology 2nd 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
Molles: Ecology 2nd 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 (120 + 1) / (12 + 1) = 353.7 ~ 354
Molles: Ecology 2nd Ed.
Example: maple trees
• 20 randomly located plots, 10 x 10 m 20 randomly located plots, 10 x 10 m squares (area = 100 msquares (area = 100 m22))
• Average sugar maple stems per plot = 4.5Average sugar maple stems per plot = 4.5• Unit area for trees = hectare (10,000 mUnit area for trees = hectare (10,000 m22))• Density = 4.5 maples per plot / 0.01 hectare Density = 4.5 maples per plot / 0.01 hectare
plots = 450 maples / haplots = 450 maples / ha
Molles: Ecology 2nd Ed.
Example: zooplankters
• 35 lake water samples, 50 ml each35 lake water samples, 50 ml each• Average copepods per sample = 78Average copepods per sample = 78• Unit volume for zooplankton = litersUnit volume for zooplankton = liters• Sample volume = 0.05 lSample volume = 0.05 l• Density = 78 copepods per sample / 0.05 l Density = 78 copepods per sample / 0.05 l
samplessamples– = 1560 copepods / l= 1560 copepods / l
Molles: Ecology 2nd 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
Molles: Ecology 2nd Ed.
Damuth (1981)
• Pop density of 307 spp. of herbivorous mammals decreased with increased body size
Fig 9.19
Molles: Ecology 2nd 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 sizeFig 9.20
Molles: Ecology 2nd Ed.
Plant Size and Population Density
• Plant population density decreases with increasing plant size Underlying details different from animals
Molles: Ecology 2nd Ed.
White (1985)
• Tree seedlings can live at high densities, but as trees grow, density declines until mature trees are at low densities
Molles: Ecology 2nd Ed.
Rarity and Extinction
• Rabinowitz - 7 forms of rarity• commonness classification based on (3)
factors: Geographic Range of Species Habitat Tolerance Local Population Size
Molles: Ecology 2nd 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
Molles: Ecology 2nd Ed.
Rarity
• Rarity I Large Range: Broad Habitat Tolerance:
Small Local Pops Peregrine Falcons
Molles: Ecology 2nd Ed.
Rarity II
Large Range: Narrow Habitat Tolerance: Small Local Pops
Passenger Pigeons
Molles: Ecology 2nd Ed.
Rarity
• Rarity III Small Range: Narrow Habitat Tolerance:
Small Pops Mountain Gorilla
IncreasingIncreasingvulnerability tovulnerability to
extinctionextinction
IncreasingIncreasingRarityRarity
LeastLeastvulnerable tovulnerable to
extinctionextinction
Molles: Ecology 2nd Ed.
Example: NA suckersExample: NA suckers
• White sucker - large rangeWhite sucker - large range• Broad habitat requirementsBroad habitat requirements• Large body sizeLarge body size
Molles: Ecology 2nd Ed.
• Yacqui sucker - Yacqui sucker - small rangesmall range
• Narrow habitat Narrow habitat requirementsrequirements
• Small body sizeSmall body size
Molles: Ecology 2nd 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