chapter 53 population ecology

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Chapter 53 Population Ecology. Population Ecology. Study of the factors that affect population size and composition. Individuals of a single species that occupy the same area. Population. Important Characteristics. 1. Density 2. Dispersion. Density. - PowerPoint PPT Presentation


  • Population EcologyStudy of the factors that affect population size and composition.

  • PopulationIndividuals of a single species that occupy the same area.

  • Important Characteristics1. Density2. Dispersion

  • DensityNumber of individuals per unit area or volume.Ex: Diatoms - 5 million/m3Trees - 5,000/km2Deer - 4/km2

  • DispersionPattern of spacing among individuals.Types:1. Clumped2. Uniform3. Random

  • Clumped DispersionMay result form a patchy environment.May increase chances for survival.Ex: Schooling behaviorFlocks of birds

  • Uniform DispersionOften the result of antagonistic interactions between individuals.Ex: TerritoriesSpacing between desert plants

  • Random Dispersion Often the result of the absence of strong attractions or repulsions between individuals.Not a common pattern.

  • DemographyThe study of the vital statistics that affect population size.Ex: Birth and Death rates

  • Demographic FactorsAge structure of the population.Birth and Death rates.Generation time.Sex ratio and reproductive behavior.

  • Life TablesMortality summary for a cohort of individuals.First developed from life insurance studies.

  • Life Tables ShowMortality rate per year.Life span of the organism.Fecundity (birth rate).

  • Survivorship CurvePlot of the numbers of a cohort still alive over time.Curve Types:Type IType IIType III

  • Type ILow early deaths.High late deaths.Ex: HumansOther large mammals

  • Type IIConstant death rate.Ex: Annual plantsMany invertebrates

  • Type IIIHigh early deaths.Low late deaths.Ex: TreesOysters

  • CommentCurve type may change between young and adults.Ex: Nestlings - Type III Adult Birds- Type II

  • Life History Strategies1. "r" or Opportunistic species2. "k" or Equilibrial species

  • "r" SpeciesIncrease fitness by producing as many offspring as possible.Do this by:Early maturationMany reproductive eventsMany offspring

  • ResultMaximize reproduction so that at least a few offspring survive to the next generation.Most offspring die (Type III curve).

  • "k" SpeciesIncrease fitness by having most offspring survive.Do this by:High parental careLate maturationFew reproduction eventsFew offspring.

  • ResultMaximize survivorship of each offspring.Few offspring, but most survive (Type I curve).

  • What is the strategyFor a weed?For an endangered species?For Garden Pests?

  • Population GrowthDN/Dt = b - dWhere:N= population sizet = timeb = birth rated = death rate

  • Rate of Increaser = difference between birth rate and death rate.r = b - d

  • Equation:DN/Dt = rNN = population sizet = timer = rate of increase

  • From CalculusThe equation DN/Dt = rN becomes:dN/dt = rmax Nrmax = intrinsic rate of increase

  • Exponential GrowthdN/dt = rmax NCharacteristic of "r" species.Produces a J-shaped growth curve.Only holds for ideal conditions and unlimited resources.

  • Logistic GrowthdN/dt = rmax N K-N KK = carrying capacity

  • ResultS-shaped growth curve.Characteristic of k" species.Common when resources are limited.

  • CommentK is not a constant value.Populations often oscillate around K as the environment changes.

  • Additional CommentsPopulations often overshoot K, then drop back to or below K.AP Exam rarely asks you to work the equations, but you should be able to give them.

  • Regulation of Population Size1. Density- Dependent Factors2. Density- Independent Factors

  • Density-DependentAffect is related to N.As N increases, mortality increases.Ex: Food, nesting space, disease

  • Density-IndependentAffect is not related to N.Mortality not related to population size.Ex: Weather and climate

  • Population CyclesCyclic changes in N over time.Often seen in predator/prey cycles.Ex: Snowshoe Hare - Lynx

  • CausesDensity dependent factors. Chemical cycles.Saturation strategy to confuse predators.

  • Age Structure DiagramsShow the percent of a population in different age categories .Method to get data similar to a Life Table, but at one point in time.

  • ImportancesCan be used to predict future population growth trends, especially for long lived species.

  • Exponential GrowthProduces age structures that are a triangle or pyramid shape.

  • Logistic GrowthProduces age structures that have even sizes between most age categories.

  • Declining PopulationsProduce age structures with a narrow base and wider middles.

  • SummaryKnow density and dispersion patterns.Know Life Tables and survivorship curves.Be able to contrast and compare r and k strategies.

  • SummaryKnow exponential and logistic growth curves and equations.Know density and density-independent growth factors.


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