Standard BfStandard Bf

: The student will demonstrate an : The student will demonstrate an understanding of the understanding of the interrelationships among organisms interrelationships among organisms and the biotic and abiotic indicators and the biotic and abiotic indicators of their environments.of their environments.

Chapter 15Chapter 15PopulationsPopulations

Section 1Section 1

How Populations GrowHow Populations Grow

What is a Population?What is a Population? A A populationpopulation consists consists

of all the individuals of all the individuals of a species that live of a species that live together in one place together in one place at one time.at one time.

Demography – the Demography – the statistical study of all statistical study of all populationspopulations

Study the Study the composition of a composition of a population and try to population and try to predict how the size predict how the size of the population will of the population will changechange

Three Key Features of PopulationsThree Key Features of Populations Population sizePopulation size – –

most important most important feature –can affect feature –can affect the population’s the population’s ability to surviveability to survive

Population densityPopulation density – – the number of the number of individuals that live individuals that live in a defined spacein a defined space

#of individuals #of individuals = =

area(units)area(units)

population densitypopulation density

Dispersion – the Dispersion – the way the way the individuals of individuals of the population the population are arranged in are arranged in an area or a an area or a volumevolume

Population Population dispersion dispersion patterns patterns influence the influence the rate of gene rate of gene flow among and flow among and between between speciesspecies

Gene FlowGene Flow Migration-the Migration-the

movement of movement of individuals to or individuals to or from a population from a population (immigrants add (immigrants add alleles and alleles and emigrants emigrants subtract allelessubtract alleles

Gene flow the Gene flow the movement of movement of alleles into or out alleles into or out of a populationof a population

Three main patterns of Three main patterns of dispersion are possible dispersion are possible within a populationwithin a population

Randomly spaced – the Randomly spaced – the location of each location of each individual is self-individual is self-determined or determined or determined by chance determined by chance within an area or volumewithin an area or volume

Evenly spaced – they are Evenly spaced – they are located at regular located at regular intervals – territoriality intervals – territoriality and intraspecies and intraspecies competition for limited competition for limited resources lead to resources lead to individuals living at individuals living at specific distances from specific distances from one anotherone another

Clumped Clumped distribution – distribution – individuals are individuals are bunched together bunched together in clusters – may in clusters – may live close together live close together in groups in order in groups in order to facilitate mating, to facilitate mating, gain protection, or gain protection, or access foodaccess food

Each one reflects Each one reflects the interactions the interactions between the between the population & population & environmentenvironment

Plant dispersionPlant dispersion Plant also exhibit the Plant also exhibit the

same dispersion same dispersion pattern as those of pattern as those of animalsanimals

Most common is Most common is clumped dispersion clumped dispersion patternpattern

Plants close together Plants close together would compete – would compete – uniform dispersionuniform dispersion

Random – adapted to a Random – adapted to a variety of conditions variety of conditions and seeds windblownand seeds windblown

Survivorship curvesSurvivorship curves Is a generalized Is a generalized

diagram showing the diagram showing the number of surviving number of surviving members over time members over time from a measured set from a measured set of births of births

Give information Give information about the life history about the life history of a speciesof a species

Type I common Type I common among large among large mammals – behavior mammals – behavior common –parental common –parental care care

Type II – roughly Type II – roughly equal at all ages equal at all ages birds, small mammalsbirds, small mammals

Type III – high birth Type III – high birth

rate/ high infant rate/ high infant mortality ratemortality rate

Ex. Invertebrates, Ex. Invertebrates, fish, plantsfish, plants

Modeling Population GrowthModeling Population Growth Population model- a Population model- a

hypothetical hypothetical population that population that attempts to exhibit attempts to exhibit the key the key characteristics of a characteristics of a real populationreal population

Demographers can Demographers can predict what might predict what might occur occur

Three stages of Three stages of complexitycomplexity

Tagging MonarchTagging Monarch Monarch Watch was Monarch Watch was

formed in 1992formed in 1992

Essential Question:Essential Question:

What can we learn What can we learn about migrationabout migrationfrom tagged from tagged monarchs? monarchs?

Population grows when Population grows when birthrate is greater than birthrate is greater than death rate – P.G. death rate – P.G. difference between the difference between the birthrate & the death ratebirthrate & the death rate

Exponential growth curve Exponential growth curve – a curve in which the – a curve in which the rate of population growth rate of population growth stays the same – increase stays the same – increase steadilysteadily

To calculate the # of To calculate the # of individuals that will be individuals that will be added –multiply the size added –multiply the size of the current pop.(N) by of the current pop.(N) by the rate of growth (r)the rate of growth (r)

Carrying capacityCarrying capacity (K) (K) –the population size –the population size that an environment that an environment can sustaincan sustain

Carrying capacity can Carrying capacity can change when the change when the environment changesenvironment changes

Population crash is a Population crash is a dramatic decline in dramatic decline in the size of a the size of a population over a population over a short period of timeshort period of time

Limiting factor – has Limiting factor – has the greatest effect in the greatest effect in keeping down the keeping down the size of populationsize of population

Density-dependent Density-dependent factorsfactors –the effect of –the effect of limited resources will limited resources will affect the population affect the population density that uses themdensity that uses them

Competition, predation, Competition, predation, parasitism and disease parasitism and disease are limiting factorsare limiting factors

Logistic modelLogistic model – a – a population model in population model in which exponential which exponential growth is limited by a growth is limited by a density-dependent density-dependent factorfactor

Competition Competition for food, for food, shelter, shelter, mates, and mates, and limited limited resources resources tends to tends to increase as a increase as a population population approaches approaches its carrying its carrying capacitycapacity

Accumulation Accumulation of wastes also of wastes also increasesincreases

http://www.worldometers.info/

Growth Patterns in Real PopulationsGrowth Patterns in Real Populations Density-independent Density-independent

factors – growth limited factors – growth limited by environmental by environmental conditionsconditions

Weather & climate are Weather & climate are the most importantthe most important

Some organisms grow Some organisms grow exponential, while others exponential, while others grow logistic growth grow logistic growth model,model,

Some will use both at Some will use both at different times as the different times as the environment changesenvironment changes

Rapidly Growing PopulationsRapidly Growing Populations R-strategists – grow R-strategists – grow

exponentially when exponentially when environmental environmental conditions allow them conditions allow them to reproduceto reproduce

R-strategists have R-strategists have short-life span, short-life span, reproduce early, have reproduce early, have many offspring which many offspring which are small and mature are small and mature rapidly with little or rapidly with little or no parental careno parental care

Slowly Growing PopulationsSlowly Growing Populations K-strategists- K-strategists-

population density population density is usually near the is usually near the carrying capacity carrying capacity (K) of their (K) of their environmentenvironment

Long life span, slow Long life span, slow maturing process, maturing process, reproduction late in reproduction late in life, extensive care life, extensive care of their young, tend of their young, tend to live in stable to live in stable environmentsenvironments

Population PyramidsPopulation Pyramids

http://www.china-profile.com/data/ani_ceu_pop.htm

Homework Homework

P. 325 Section 1 review all P. 325 Section 1 review all questionsquestions

P. 335 Questions 1-3,6,10,13,16, 18P. 335 Questions 1-3,6,10,13,16, 18

How Populations EvolveHow Populations EvolveSection 2Section 2

Hardy-Weinberg Hardy-Weinberg principle –the principle –the frequencies of alleles frequencies of alleles in a population do not in a population do not change unless change unless evolutionary forces evolutionary forces act on the populationact on the population

Holds true if Holds true if population is big population is big enough that members enough that members will not mate with will not mate with relativesrelatives

Five principle Five principle evolutionary forces: evolutionary forces: mutation, gene flow, mutation, gene flow, nonrandom mating, nonrandom mating, genetic drift, genetic drift, andand natural selectionnatural selection

Can cause the ratios to Can cause the ratios to differ significantly from differ significantly from predicted by the predicted by the Hardy-Weinberg Hardy-Weinberg principleprinciple

MutationMutation Mutation rates in Mutation rates in

nature are very nature are very slowslow

Not all mutation Not all mutation result in result in phenotype phenotype changes changes

Several codons Several codons can code for the can code for the same amino acidsame amino acid

Mutation is a Mutation is a source of source of variationvariation

Gene FlowGene Flow Migration-the Migration-the

movement of movement of individuals to or individuals to or from a population from a population (immigrants add (immigrants add alleles and alleles and emigrants emigrants subtract allelessubtract alleles

Gene flow the Gene flow the movement of movement of alleles into or out alleles into or out of a populationof a population

Nonrandom MatingNonrandom Mating Prefer to mate with Prefer to mate with

others that live others that live nearby or are of their nearby or are of their own phenotypeown phenotype

Mating with relatives Mating with relatives (inbreeding) causes a (inbreeding) causes a lower frequency of lower frequency of heterozygotes than heterozygotes than predicted by Hardy-predicted by Hardy-Weinberg principleWeinberg principle

Also when organisms Also when organisms choose based on choose based on certain traitscertain traits

Genetic DriftGenetic Drift Genetic drift – the Genetic drift – the

random change in random change in allele frequency in a allele frequency in a populationpopulation

Changed by chance Changed by chance events causing events causing isolationisolation

Genetic uniformity Genetic uniformity can reduce disease can reduce disease resistanceresistance

Lack of genetic Lack of genetic diversity may hasten diversity may hasten extinctionextinction

Natural SelectionNatural Selection Causes deviations Causes deviations

from H-W proportions from H-W proportions by changing by changing frequencies of allelesfrequencies of alleles

Frequency will Frequency will increase or decrease, increase or decrease, depending on allele’s depending on allele’s effects on survival & effects on survival & reproductionreproduction

Sickle cell anemia in Sickle cell anemia in USUS

One of the most One of the most powerful agents of powerful agents of genetic changegenetic change

Genetic Genetic conditions conditions are not are not eliminated eliminated by natural by natural selection selection because because very few of very few of the the individuals individuals bearing the bearing the alleles alleles express the express the recessive recessive phenotypephenotype

Natural selection Natural selection enables individuals enables individuals who express who express favorable traits to favorable traits to reproduce & pass reproduce & pass those traits on – acts those traits on – acts on phenotypes not on phenotypes not genotypesgenotypes

Selection cannot Selection cannot operate against rare operate against rare recessive alleles recessive alleles unless heterozygous unless heterozygous individuals are individuals are common & produce common & produce homozygous offspringhomozygous offspring

Natural selection Natural selection shapes populations shapes populations affected by affected by phenotypes that are phenotypes that are controlled by one or controlled by one or by a large number of by a large number of genesgenes

Polygenic traitPolygenic trait – a – a trait that is influenced trait that is influenced by several genesby several genes

Normal distribution-a Normal distribution-a range of phenotypes range of phenotypes clustered around an clustered around an average valueaverage value

Directional SelectionDirectional Selection Eliminates one Eliminates one

extreme from a range extreme from a range of phenotypes, alleles of phenotypes, alleles for that trait become for that trait become less commonless common

Directional selection – Directional selection – the frequency of a the frequency of a particular trait moves particular trait moves in one direction in a in one direction in a rangerange

Has a role in the Has a role in the evolution of a single-evolution of a single-gene traitsgene traits

Stabilizing SelectionStabilizing Selection When selection When selection

reduces extremes, reduces extremes, the frequencies of the the frequencies of the intermediate intermediate phenotypes increasephenotypes increase

Distribution becomes Distribution becomes narrower tending narrower tending to”stabilize” the to”stabilize” the average by increasing average by increasing the proportion of the proportion of similar individualssimilar individuals

Very common in Very common in naturenature