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PopulationsPopulations

Population GeneticsPopulation Genetics

Population GrowthPopulation Growth

Interactions Among PopulationsInteractions Among Populations

Ecological SuccessionEcological Succession


• A population is a group of individuals of the A population is a group of individuals of the same species occupying the same habitat at same species occupying the same habitat at the same timethe same time

• The gene pool of a population is all of the The gene pool of a population is all of the different genes that occur within the populationdifferent genes that occur within the population

• A deep gene pool results when there is great A deep gene pool results when there is great variation within a population within a population

• A shallow gene pool results when there is A shallow gene pool results when there is little diversity in a population in a population

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• For a given trait the For a given trait the frequency of each phenotype can be can be calculatedcalculated

• The frequency of each genotype can The frequency of each genotype can be estimatedbe estimated

• The frequency of each allele can be The frequency of each allele can be estimatedestimated

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• The Hardy-Weinberg equilibrium predicts The Hardy-Weinberg equilibrium predicts that allelic frequencies remain constant that allelic frequencies remain constant over time provided over time provided five conditions are met are met

• A population at equilibrium is not evolving A population at equilibrium is not evolving with respect to the traitwith respect to the trait

• A population that has its equilibrium A population that has its equilibrium disturbed is evolving with respect to the disturbed is evolving with respect to the traittrait

http://www.phschool.com/science/biology_place/labbench/lab8/concepts.html


• Microevolution is the directional change is the directional change in frequency of alleles over timein frequency of alleles over time

• Change in allele frequencies can occur Change in allele frequencies can occur due to:due to:

1. Genetic Drift: the reproductive success : the reproductive success or failure of an individual in a small or failure of an individual in a small populationpopulation

http://www.techapps.net/interactives/pepperMoths.swf

http://www.bio.georgiasouthern.edu/bio-home/harvey/lect/images/GeneticDrift.gif


2. Mutation: new mutations can add new : new mutations can add new alleles or change existing alleles that alleles or change existing alleles that could be advantageous or could be advantageous or disadvantageousdisadvantageous

3.3. Gene Flow (Migration): Disproportionate Gene Flow (Migration): Disproportionate movement of individuals into or out of a movement of individuals into or out of a populationpopulation

http://bcs.whfreeman.com/thelifewire/content/chp23/2302003.html

Population GeneticsPopulation Genetics4.4. Non random mating due to preferences Non random mating due to preferences

based on inheritable characteristicsbased on inheritable characteristics

5.5. The founder effect decreases diversity in the The founder effect decreases diversity in the population of descendents of a small population of descendents of a small founding populationfounding population

6.6. The bottleneck effect decreases genetic The bottleneck effect decreases genetic diversity when a large population is reduced diversity when a large population is reduced to a small population by selective pressureto a small population by selective pressure

7.7. Natural Selection is the result of any of the Natural Selection is the result of any of the above factorsabove factors


• Change in allelic frequencies can result Change in allelic frequencies can result in in speciation

• Speciation can occur if populations of Speciation can occur if populations of the same species become the same species become reproductively isolatedreproductively isolated

http://bcs.whfreeman.com/thelifewire/content/chp24/2402001.html


• Measures of population growth includeMeasures of population growth include1.1. Size: determined by census or Size: determined by census or sampling2. Density: population size per unit area or : population size per unit area or

volumevolume3.3. Per Capita Growth Rate: the growth of a Per Capita Growth Rate: the growth of a

population per individual (due to immigration, population per individual (due to immigration, emigration, natality and mortality)emigration, natality and mortality)

4.4. Growth Rate: the growth of a population over Growth Rate: the growth of a population over time time

http://www.pbs.org/saf/1204/teaching/teaching3.htm

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• Characteristics of populations includeCharacteristics of populations include

1. Distribution (random, uniform or (random, uniform or clumped)clumped)

2.2. Growth Curve : J-shaped (exponential) Growth Curve : J-shaped (exponential) or S-shaped (sigmoidal)or S-shaped (sigmoidal)

3.3. Ecological Niche: the role played by a Ecological Niche: the role played by a population in an ecosystempopulation in an ecosystem

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4.4. Geographic Range: a region where a Geographic Range: a region where a population can be foundpopulation can be found

5.5. Habitat: the physical conditions that Habitat: the physical conditions that support a populationsupport a population

6.6. Population Pyramid (Histogram): a (Histogram): a graph representing the age and gender representing the age and gender distribution of a populationdistribution of a population

http://www.uni.edu/gai/India/India_Lesson_Plans/India_Population_Pyramids_files/image002.gif

http://populationpyramid.net/


7.7. Reproductive Strategy: k or r selected Reproductive Strategy: k or r selected strategiesstrategies

8.8. Environmental Resistance: factors that Environmental Resistance: factors that limit population growth (density limit population growth (density dependent or density independent)dependent or density independent)

9.9. Biotic Potential (Fecundity): maximum Biotic Potential (Fecundity): maximum reproductive rate under ideal conditionsreproductive rate under ideal conditions


10.10. Tolerance Range: the minimum and Tolerance Range: the minimum and maximum levels of an environmental factor maximum levels of an environmental factor that can support population growththat can support population growth

11.11. Law of the Minimum: of the number of Law of the Minimum: of the number of essential substances required for growth, the essential substances required for growth, the one with the least concentration is the one with the least concentration is the controlling factorcontrolling factor

12.12. Open or Closed: an open population is Open or Closed: an open population is influenced by immigration, emigration, natality influenced by immigration, emigration, natality and mortality (closed has no immigration or and mortality (closed has no immigration or emigration)emigration)

Interactions Among Interactions Among PopulationsPopulations

• All populations exist within a biological community All populations exist within a biological community such that populations must interactsuch that populations must interact

• Population interactions include:Population interactions include:1.1. Interspecific Competition: competition between two Interspecific Competition: competition between two

different species (-/-)different species (-/-)• Gause’s Principle: no two species can occupy Gause’s Principle: no two species can occupy

the same niche without one being reduced in the same niche without one being reduced in numbers or being eliminatednumbers or being eliminated

2.2. Intraspecific Competition: competition among Intraspecific Competition: competition among individuals of the same species(-/-)individuals of the same species(-/-)

Interactions Among Interactions Among PopulationsPopulations

3. Predation: A predator population feeds on a : A predator population feeds on a prey population (+/-)prey population (+/-)

4. Mimicry

5.5. Symbiosis: Two different organisms live in Symbiosis: Two different organisms live in close association with each otherclose association with each other

i. Parasitism (+/-) (+/-)

ii. Commensalism (+/0) (+/0)

iii. Mutualism (+/+) (+/+)

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• Ecological succession is the progessive Ecological succession is the progessive replacement of one community by another replacement of one community by another during the development of vegetation in an during the development of vegetation in an areaarea

• Primary succession refers to the occupation, Primary succession refers to the occupation, by plant life, of an area not previously by plant life, of an area not previously covered by vegetationcovered by vegetation

• Secondary Succession refers to an area that Secondary Succession refers to an area that was previously covered was previously covered


• Succession progresses from a pioneer Succession progresses from a pioneer community, through several seral stages community, through several seral stages to a climax communityto a climax community

• As succession progresses biomass of As succession progresses biomass of the ecosystem increasesthe ecosystem increases

• As succession progresses biodiversity As succession progresses biodiversity increases and then declines when a increases and then declines when a climax community is reachedclimax community is reached