Presentation on theme: "POPULATION DISTRIBUTION AND ABUNDANCE"— Presentation transcript:
1POPULATION DISTRIBUTION AND ABUNDANCE Chapter 9Molles: Ecology 2nd Ed.
2Physical environment limits geographic distribution of species Chapter ConceptsPhysical environment limits geographic distribution of speciesOn small scales, individuals within pops. are distributed in random, regular, or clumped patterns; on larger scales, individuals within pop. are clumpedPopulation density declines with increasing organism sizeRarity influenced by geographic range, habitat tolerance, pop. size; rare species vulnerable to extinctionMolles: Ecology 2nd Ed.
3PopulationsEcologists define a population as group of individuals of single species inhabiting specific area.Molles: Ecology 2nd Ed.
4HabitatPhysical environmental conditions that allow individuals of species to survive AND reproduceMolles: Ecology 2nd Ed.
5Ability of environmental conditions to support repro and survival Habitat qualityAbility of environmental conditions to support repro and survivalHabitat area/volumeResource concentrationTimeHigh habitat quality = organisms acquire many resources; high survival + repro = large pop.Molles: Ecology 2nd Ed.
6Population numbers vary with habitat quality Molles: Ecology 2nd Ed.
7Physical environment limits geographic distribution of species Distribution LimitsPhysical environment limits geographic distribution of speciesOrganisms can only compensate so much for environmental variationMolles: Ecology 2nd Ed.
8Geographical rangeGeographic 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 rangedue to variation in habitat qualityMolles: Ecology 2nd Ed.
10Kangaroo Distributions and Climate Caughley - relationship between climate + distribution of three largest kangaroos in AustraliaMolles: Ecology 2nd Ed.
14Distributions largely based on climate Fig 9.2Distributions largely based on climateMolles: Ecology 2nd Ed.
15Kangaroo Distributions and Climate Limited distributions may not be directly determined by climate.Climate often influences species distributions via:food productionwater supplyhabitatincidence of parasites, pathogens and competitorsMolles: Ecology 2nd Ed.
16Tiger Beetle of Cold Climates Tiger beetle (Cicindela longilabris) - higher latitudes + elevations than other NA speciesSchultz found metabolic rates of C. longilabris are higher and preferred temps. lower than other speciesPhysical env. limits species distributionsMolles: Ecology 2nd Ed.
17Adapted to cool climates Fig 9.3Metabolic rates of C. longilabris higher; preferred temps lower than other beetle speciesAdapted to cool climatesMolles: Ecology 2nd Ed.
18Distributions of Plants Along a Moisture-Temperature Gradient Encelia spp. distributions + variations in temp and precipitationFig 9.7Molles: Ecology 2nd Ed.
20Distributions of Barnacles - Intertidal Gradient Organisms in intertidal zone have evolved different degrees of resistance to dryingBarnacles - distinctive patterns of zonation within intertidal zoneMolles: Ecology 2nd Ed.
21Connell found pattern in barnacles: Chthamalus stellatus restricted to upper levels; Balanus balanoides limited to middle and lower levelsMolles: Ecology 2nd Ed.
22Distributions of Barnacles Along an Intertidal Gradient Balanus - more vulnerable to desiccation, excluded from upper intertidal zoneChthamalus adults excluded from lower areas by competition with BalanusMolles: Ecology 2nd Ed.
23Competition? How do we know that Balanus outcompetes Chthamalus? Molles: Ecology 2nd Ed.
25Distribution of Individuals on Small Scales Three basic patterns:Random: equal chance of being anywhereRegular: uniformly spacedExclusive use of areasIndividuals avoid one anotherClumped: unequal chance of being anywhereMutual attraction between individualsPatchy resource distributionMolles: Ecology 2nd Ed.
27Importance of scale in determining distribution patterns: At one scale pattern may be random, at another scale, might be uniform:Molles: Ecology 2nd Ed.
28Distribution of Tropical Bee Colonies Hubbell and Johnson predicted aggressive bee colonies have regular distributions;Predicted non-aggressive species have random or clumped distributionsMolles: Ecology 2nd Ed.
29Hubbell and Johnson results: 4 species with regular distributions were highly aggressiveFifth non-aggressive and randomly distributedMolles: Ecology 2nd Ed.
33Distributions of Desert Shrubs Traditional theory suggests desert shrubs are regularly spaced due to competitionPhillips and MacMahon - distribution of desert shrubs changes from clumped to regular patterns as they growMolles: Ecology 2nd Ed.
34Young shrubs clumped for (3) reasons: Seeds germinate at safe sites Hypothesis:Young shrubs clumped for (3) reasons:Seeds germinate at safe sitesSeeds not dispersed from parent areasAsexual reproductionMolles: Ecology 2nd Ed.
35Distributions of Desert Shrubs Phillips and MacMahon proposed as plants grow, some individuals in clumps die = reducing clumpingCompetition among remaining plants produces higher mortalityEventually creates regular distributionsMolles: Ecology 2nd Ed.
37Dug up roots, map distribution of 32 bushes Brisson and ReynoldsDug up roots, map distribution of 32 bushesfound competitive interactions with neighboring shrubs influences distribution of creosote rootsMolles: Ecology 2nd Ed.
38Creosote bush roots do not overlap with nearby plant roots So what?Creosote bush roots do not overlap with nearby plant rootsOnly 4% overlap between bushesFig 9.14Molles: Ecology 2nd Ed.
39Distributions of Individuals on Large Scales Bird Pops North AmericaRoot - at continental scale, bird pops have clumped distributions (Christmas Bird Counts)Clumped patterns in species with widespread distributionsMolles: Ecology 2nd Ed.Fig 9.14
40Similar distribution pattern for species with small range: few “hot spots” Fish crow Fig 9.14Molles: Ecology 2nd Ed.
41clumped only during breeding season? 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 9.16Molles: Ecology 2nd Ed.
42Density = number individuals per unit area/volume Sedentary organisms: plot approachMoving/secretive organisms: mark/recaptureRelative abundance = percent cover, CPUEMolles: Ecology 2nd Ed.
43Sedentary animals and plants Plot methods Area of known size Estimating densitySedentary animals and plantsPlot methodsArea of known sizeRandomly located plotsCount individuals in plotsAverage / plotDensity = average no. / plot areaMolles: Ecology 2nd Ed.
44Mobile or secretive animals: mark/recapture 1. Sample animals and mark Estimating densityMobile or secretive animals: mark/recapture1. Sample animals and mark2. Release (M out of N in pop marked)3. Wait for mixing4. Sample (n), count how many marked (m)5. Compute estimate of pop size:N = M (n + 1)(m + 1)Molles: Ecology 2nd Ed.
45Example: Estimating Population Size from Mark-Recapture Number of animals marked in 1st sample = 100Total number of animals in 2nd sample = 150Number of marked animals in 2nd sample = 11Population = M (n + 1) = 100 (151) = 1258Size (N) (m + 1)Molles: Ecology 2nd Ed.
46Sample M = 38 squirrels, marked, released Another ExampleSample M = 38 squirrels, marked, releasedAfter 2 weeks, resample, n = 120m = 12 of 120 markedEstimate of pop. size:N = M (n + 1) / (m + 1)= 38 ( ) / (12 + 1) = 353.7~ 354Molles: Ecology 2nd Ed.
4720 randomly located plots, 10 x 10 m squares (area = 100 m2) Example: maple trees20 randomly located plots, 10 x 10 m squares (area = 100 m2)Average sugar maple stems per plot = 4.5Unit area for trees = hectare (10,000 m2)Density = 4.5 maples per plot / 0.01 hectare plots = 450 maples / haMolles: Ecology 2nd Ed.
48Example: zooplankters 35 lake water samples, 50 ml eachAverage copepods per sample = 78Unit volume for zooplankton = litersSample volume = 0.05 lDensity = 78 copepods per sample / 0.05 l samples= 1560 copepods / lMolles: Ecology 2nd Ed.
49Organism Size and Population Density Population density decreases with larger organism sizeWhy?Bigger organisms need more space and resourcesBigger organisms have lower repro ratesMolles: Ecology 2nd Ed.
50Damuth (1981)Pop density of 307 spp. of herbivorous mammals decreased with increased body sizeFig 9.19Molles: Ecology 2nd Ed.
51Peters 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 9.20Molles: Ecology 2nd Ed.
52Plant Size and Population Density Plant population density decreases with increasing plant sizeUnderlying details different from animalsMolles: Ecology 2nd Ed.
53White (1985)Tree seedlings can live at high densities, but as trees grow, density declines until mature trees are at low densitiesMolles: Ecology 2nd Ed.
54Rabinowitz - 7 forms of rarity Rarity and ExtinctionRabinowitz - 7 forms of raritycommonness classification based on (3) factors:Geographic Range of SpeciesHabitat ToleranceLocal Population SizeMolles: Ecology 2nd Ed.
55All seven other other combinations create some kind of rarity Non-rare populations have large geographic ranges, broad habitat tolerances, some large local populationsAll seven other other combinations create some kind of rarity= risk of extinctionMolles: Ecology 2nd Ed.
56Large Range: Broad Habitat Tolerance: Small Local Pops RarityRarity ILarge Range: Broad Habitat Tolerance: Small Local PopsPeregrine FalconsMolles: Ecology 2nd Ed.
57Large Range: Narrow Habitat Tolerance: Small Local Pops Rarity IILarge Range: Narrow Habitat Tolerance: Small Local PopsPassenger PigeonsMolles: Ecology 2nd Ed.
62Highestvulnerability toextinctionOther Example ?
63White sucker - large range Broad habitat requirements Large body size Example: NA suckersWhite sucker - large rangeBroad habitat requirementsLarge body sizeMolles: Ecology 2nd Ed.
64Yacqui sucker - small range Narrow habitat requirements Small body sizeMolles: Ecology 2nd Ed.
65Physical environment limits geographic distribution of species SummaryPhysical environment limits geographic distribution of speciesOn small scales, individuals w/in pops. are distributed in random, regular, or clumped patterns; on larger scales, individuals w/in pop. are clumpedPopulation density declines with increasing body sizeRarity influenced by geographic range, habitat tolerance, pop size; rare species vulnerable to extinctionMolles: Ecology 2nd Ed.