chapter 53: population ecology

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Chapter 53: Population Ecology. Essential Knowledge . 2.a.1 – All living systems require constant input of free energy (53.3 & 53.4). - PowerPoint PPT Presentation


Population Ecology

Chapter 53: Population EcologyEssential Knowledge 2.a.1 All living systems require constant input of free energy (53.3 & 53.4).2.d.1 All biological systems from cells and organisms to populations, communities, and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy (53.1 53.5).4.a.5 Communities are composed of populations of organisms that interact in complex ways (53.1-53.3, 53.5 & 53.6).Population EcologyStudy of the factors that affect population size and composition.Population:Def: Individuals of a single species that occupy the same geographic areaEx: Humans living in Indianapolis, IN

Important Characteristics1. Density2. DispersionDensityNumber 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. Uniform/Even3. 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.Known as even or regular dispersionEx: 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 ratesFactors of Demography:Age structure of populationBirth and death ratesGeneration timeSex ratio and reproductive behaviorLife TablesMortality summary for a cohort of individuals.First developed from life insurance studies.What do they show us?Mortality rate per yearLife span of the organismFecundity (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 IILife 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 offspringResultMaximize 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 strategy?For a weed?For an endangered species?For Garden Pests?

Population GrowthDN/Dt = b - dWhere:N= population sizet = timeb = birth rated = death rateRate of Increaser = difference between birth rate and death rate.r = b - d

Equation with r:DN/Dt = rNN = population sizet = timer = rate of increaseFrom 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 capacityResult of logistic growth?S-shaped growth curveCharacteristic of k speciesCommon 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 FactorsDensity-DependentAffect is related to NAs N increases, mortality increasesEx: Food, nesting space, disease

Density-IndependentAffect is not related to NMortality not related to population sizeEx: Weather and climatePopulation CyclesCyclic changes in N over timeOften seen in predator/prey cyclesEx: Snowshoe Hare LynxCauses?Density dependent factorsChemical cyclesSaturation 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

ImportanceCan be used to predict future population growth trends, especially for long lived species.Exponential GrowthProduces age structures that are a triangle or pyramid shapeLogistic GrowthProduces age structures that have even sizes between most age categoriesDeclining PopulationsProduce age structures with a narrow base and wider middles

Summary Identify the difference between population density and dispersion.Recognize the types of dispersion patterns and the interactions that lead to them.Identify the types of survivorship curves.Recognize the characteristics of "r" and "k" life history strategies.Identify the types of population growth models.Identify factors that regulate population size.Recognize how age-structure diagrams relate to population growth.


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