Populations Population Genetics Population Growth Interactions Among Populations Ecological Succession

Population Genetics A population is a group of individuals of the same species occupying the same habitat at the same time The gene pool of a population is all of the different genes that occur within the population A deep gene pool results when there is great variation within a population A shallow gene pool results when there is little diversity in a population

Population Genetics For a given trait the frequency of each phenotype can be calculated The frequency of each genotype can be estimated The frequency of each allele can be estimated

Population Genetics The Hardy-Weinberg equilibrium predicts that allelic frequencies remain constant over time provided five conditions are met A population at equilibrium is not evolving with respect to the trait A population that has its equilibrium disturbed is evolving with respect to the trait

Population Genetics Microevolution is the directional change in frequency of alleles over time Change in allele frequencies can occur due to: Genetic Drift: the reproductive success or failure of an individual in a small population

Population Genetics Mutation: new mutations can add new alleles or change existing alleles that could be advantageous or disadvantageous Gene Flow (Migration): Disproportionate movement of individuals into or out of a population

Population Genetics Non random mating due to preferences based on inheritable characteristics The founder effect decreases diversity in the population of descendents of a small founding population The bottleneck effect decreases genetic diversity when a large population is reduced to a small population by selective pressure Natural Selection is the result of any of the above factors

Population Genetics Change in allelic frequencies can result in speciation Speciation can occur if populations of the same species become reproductively isolated

Population Growth Measures of population growth include Size: determined by census or sampling Density: population size per unit area or volume Per Capita Growth Rate: the growth of a population per individual (due to immigration, emigration, natality and mortality) Growth Rate: the growth of a population over time

Population Growth Characteristics of populations include Distribution (random, uniform or clumped) Growth Curve : J-shaped (exponential) or S-shaped (sigmoidal) Ecological Niche: the role played by a population in an ecosystem

Population Growth Geographic Range: a region where a population can be found Habitat: the physical conditions that support a population Population Pyramid (Histogram): a graph representing the age and gender distribution of a population

Population Growth Reproductive Strategy: k or r selected strategies Environmental Resistance: factors that limit population growth (density dependent or density independent) Biotic Potential (Fecundity): maximum reproductive rate under ideal conditions

Population Growth Tolerance Range: the minimum and maximum levels of an environmental factor that can support population growth Law of the Minimum: of the number of essential substances required for growth, the one with the least concentration is the controlling factor Open or Closed: an open population is influenced by immigration, emigration, natality and mortality (closed has no immigration or emigration)

Interactions Among Populations All populations exist within a biological community such that populations must interact Population interactions include: Interspecific Competition: competition between two different species (-/-) Gause’s Principle: no two species can occupy the same niche without one being reduced in numbers or being eliminated Intraspecific Competition: competition among individuals of the same species(-/-)

Interactions Among Populations Predation: A predator population feeds on a prey population (+/-) Mimicry Symbiosis: Two different organisms live in close association with each other Parasitism (+/-) Commensalism (+/0) Mutualism (+/+)

Ecological Succession Ecological succession is the progessive replacement of one community by another during the development of vegetation in an area Primary succession refers to the occupation, by plant life, of an area not previously covered by vegetation Secondary Succession refers to an area that was previously covered

Ecological Succession Succession progresses from a pioneer community, through several seral stages to a climax community As succession progresses biomass of the ecosystem increases As succession progresses biodiversity increases and then declines when a climax community is reached