chapter 53 population ecology
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DESCRIPTIONChapter 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.