Ecological Concepts Population

  • Different groups making up the ecosystem consist of populations of plants and animals.
  • Population: a group of interbreeding organisms of the same kind occupying a particular place

 Ecological Genetics Population cont.

  • Populations: Form a structural component through which energy flows and nutrients cycle
    • Characterized by density (# of individuals/unit of space)
    • Has age structure (ratio of one age class to another)
    • Acquires new members via birth/immigration, loses members via death/emigration

 Ecological Genetics Population cont.

  • Populations: serve as genetic units because they are composed of interbreeding organisms
    • each individual carries a unique genetic component
    • combined genetic information within a population called the gene pool

 Ecological Genetics Evolution

  • Involves changes in the gene pool and physical expressions of the genetic constituents
  • Cumulative result of the adaptiveness of its individuals


  • 1744-1829: Lamarck – inheritance of acquired characterstics
  • 1809-1882: Darwin – developed thoery of evolution (species evolved through natural selection and adaptation to their ever-changing environment
  • 1823-1913: Wallace – supported Darwin’s theory
  • Present theory of evolution by natural selection


  • Evolution acts upon populations through the organism
  • Species have the potential to reproduce beyond the carrying capacity (or close to)
  • competition for limited resources will increase
  • not all of the organisms will survive and reproduce offspring


  • Inherited characteristics that will allow some to compete more successfully, and will most likely survive and reproduce
  • Adaptive characteristics will become fixed in the population
  • Other characteristics will continue to accumulate over generations of time
  • May be thought of as differential reproductive success within a population

;NATURAL SELECTION;Survival of the fittest

  • Darwin’s term: refers to a species’ ability to successfully reproduce within its environment
  • Biologically Fit: best adapted to their environments

Ecological Genetics;Discontinuous vs. Continuous;DISCONTINUOUS

  • Variation in a specific character or set of characters which separates individuals into discrete categories (age groups, sex, color phases)
  • May be tabulated as a frequency distribution ; graphed as a histogram

Ecological Genetics;Discontinuous vs. Continuous;CONTINUOUS

  • Variation in specific character or set of characters which can be placed along a range of values (length, weight, size, and shape)
  • May be tabulated as a frequency distribution ; graphed as a histogram


  • GENOTYPE: sum of hereditary info carried by individual
  • PHENOTYPE: external or observable expression of genotype, may be influenced by external and internal conditions
  • PHENOTYPIC PLASTICITY: ability of genotype to give rise to a range of phenotypic expressions under different environmental situations


  • Primary genetic control mechanism found within DNA and RNA, forming primary heritable components of chromosomes

;SOURCES OF VARIATION;Mitosis vs. Meiosis

  • Mitosis: cellular reproduction/duplication
  • Meiosis:; chromosome material split to form gametes/spores


  • Single units of heritability within DNA molecules individual gene
  • Locations on a chromosome termed loci
  • Genes occupying same loci on a pair of chromosomes termed alleles
  • If both alleles affect a given trait in same manner, the two are homozygous (heterozygous if they differ)

;SOURCES OF VARIATION;Recombination of genetic material

  • Combination of gametes to form a zygote
    • # of possible combinations of parental material are infinitely large, provides immediate and major source of variation
    • does not result in change of genetic info, provides different combination of genes which selection can act
    • # of recombinations depends on # of chromosomes and frequencies of crossing-over


  • An inheritable change of genetic material in the gene or chromosome


  • Point Mutation
  • Alterations in DNA sequence of one or a few nucleotides
  • May be a change in order, substitution, deletion, or transposition


  • Alterations in chromosome structure or number
  • Polyploidy, duplication, deletion, translocation, inversion


  • An explanation for gene frequencies, genotype, and phenotype coming into equilibrium within a population as genes are passed from generation to generation in absence of evolutionary forces

;HARDY-WEINBERG EQUILIBRIUM;For it to hold true (never is 100%), we must assume:

  • Population is infinitely large
  • Mating is random and occurs in proportion to frequencies of genotpyes within popuation
  • Population is free from evolutionary forces
    • mutation, genetic drift, migration, natural selection

;HARDY-WEINBERG EQUILIBRIUM;Must be considered theoretical

  • Provides a distribution pattern against which actual observations can be compared
  • After one generation of random mating, genotypic frequencies within a population will remain in the proportions

;HARDY-WEINBERG EQUILIBRIUM;p + q = 1p2 + 2pq + q2 = 1

  • p2: frequency of AA
  • 2pq: frequency of Aa
  • q2: frequency of aa
  • p is the allelic frequency of A
  • q is the allelic frequency of a


  • If a population is in genetic equilibrium, two results may be expected:
    • 1) frequencies of alleles do not change from one generation to the next
    • 2) genotypic frequencies will be in the proportion p2, 2pq, and q2 after one generation and will remain in these frequencies as long as equilibrium is maintained

;;Variation within a population

  • Seldom constant from one generation to the next.; Results from:
    • Gene mutation
    • Nonrandom mating/reproduction
    • Differential survival of individuals
    • Fecundity rates

;;Genetic Variation and Population Size

  • Reduced genetic variation can be due to three factors
    • Inbreeding
    • Genetic Drift
    • Neighborhoods and effective population size

;Genetic Variation and Population Size;Inbreeding

  • Mating among close relatives
  • Occurs mostly in social animals
  • Survivorship declines as inbreeding increases

;Genetic Variation and Population Size;INBREEDING EFFECTS

  • More inbred, the quicker the variation in a population drops
  • Juvenile mortality increases in captive/inbred populations
  • Most pronounced in small populations
    • Has important ramifications in real world

;Genetic Variation and Population Size;GENETIC DRIFT

  • Changes in allelic representation by chance alone
  • Sampling error
  • All of an individual’s genes will be represented somewhere among its gametes, but not in any two of them

 Genetic Variation and Population Size Genetic fixation &Founder’s Principle

  • Genetic fixation: permanent loss of an allele within a small population (result of genetic drift)
  • Founder’s principle: small group of colonists from a population establish new population in unfilled habitat

 Genetic Variation and Population Size PROBABILITY

  • Higher in small populations
  • Likelihood of rare alleles increases in small/isolated populations vs.

    large populations

  • Small populations will lose % of their variation over time
  • Can be countered by immigration

 Genetic Variation and Population Size 50 Rule

  • Populations under 50 suffer highly from genetic drift
  • Seems insignificant but is magnified over time

 Genetic Variation and Population Size Neighborhoods & effective population size

  • Large populations have genetic risks if mating takes place in neighborhoods
  • Some animals only breed within a small distance of birthplaces
  • Some individuals breed, others don’t

Genetic Variation and Population Size;Neighborhoods ; effective population size;NE = (4NMNf)/(NM+Nf)

  • NE: Effective population size (breeding individuals)
    • Vital for conservation projects
  • NM: Number of breeding males
  • Nf: Number of breeding females

Changes in population gene pool over time may be due to selection
;;MODES OF SELECTION;Directional, Stabilizing, Disruptive

  • Directional: favors one extreme phenotype at the expense of all others
  • Stabilizing: favors the average expression of an optimum intermediate at the expense of both extremes
  • Disruptive: favors both extremes, although not necessarily to the same extent, at the expense of the average


  • Selection operatin on a population as a unit depends upon:
    • More than 1 group within a large entity (subpopulation within a regional population)
    • Different frequencies of adaptive alleles in groups
      • traits will benefit the group at the expense of individual
      • altruistic


  • Selection acting on small groups of closely related individuals
  • Theoretically increases the average genetic fitness of the group at the expense of some individuals

;Group and Kin Selection Background

  • Ecologists suggest populations regulate themselves – Ex. Birds:
    • territorial birds – exist in areas that hold less than the prey can support
    • Emigration
    • Varation reproductive rates

;Group and Kin Selection Background;V. C.

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  • Came up with Group slection
  • Most groups of individuals purposely control their rate of consumption of resources; and rate of breeding to ensure group would not become extinct
  • There should be no selfish behavior
  • Should avoid competition

;Group and Kin Selection Background;Individual Selection

  • Individuals are selfish and act only in their best interest
  • Mutation Example:
    • Bird lays only two eggs, plenty of resources
    • ensures replacement of parents, prevents explosion
    • Mutation allows 3 eggs, still plenty of resources
    • larger broods get same advantage, max # of offspring

;Arguments AGAINST Group Selection;IMMIGRATION;

  • Selfish individuals can migrate into the area.
  • Never isolated


  • For group selection to work, some groups must die out faster than others.
  • In nature, whole groups don’t die out – individuals do so they would be the more powerful evolutionary force


  • For group selection to work, individuals must be able to assess and predict future availability of food and the population density within their own habitat.
  • Little evidence that organisms can.


  • Giving a benefit without any reward or where there may even be a cost
  • Behaviors include:
    • Grooming, cooperation, give warning signals
  • Explained in genes

 ALTRUISM Coefficient of relatedness

  • Each parent gives .5 of their genes
  • Coefficient of relatedness (r): probability that a parent and offspring share a copy of a particular gene
  • If an organism can pass on its genes through parental care, it can pass them on by caring for siblings, nieces, nephews, and cousins

 ALTRUISM Inclusive & Direct Fitness, Kin Selection

  • Inclusive Fitness: pass on genes by other than direct means
  • Direct Fitness: genes passed on to children
  • Kin Selection: selection for a behavior that increases inclusive fitness relative to direct fitness

MICROevolution: change in gene frequency in a populationMACROevolution: change at the species level and above
 SPECIATION Biological

  • A group of actively or potentially interbreeding populations that are reproductively isolated from other such groups

 SPECIATION Morphological

  • Discrete units to which specific names have been given
  • System of classification defined by Carl vonLinne


  • Morphologically similar or identical natural populations that are reproductively isolated


  • Origin of isolating mechanisms within the dispersal area of the offspring of a single cline
  • Takes place in center of patchy environment
  • Results in formation of multiple sibling species

 SPECIATION Allopatric

  • Separation of a widely distributed population by some extrinsic barrier that interrupts gene flow

 SPECIATION Parapatric

  • Evolution of a species as a continuous population in a continuous cline
  • Differs from founder effect:
    • 1) No spatial isolation is required, 2) level of vagility is low, 3) Reproductive isolating mechanisms arise by selection at same time genetically unique individuals colonize or exploit a new environment


  • Significant differences often exist among populations or different geographic regions
  • Variants reflect the environmental selective forces acting on genotype


  • Continuous variation across a species’ geographic range results from the intergradation of gene pools between local populations

;;CLINE;The result of…

  • Result of phenotypic response to environmental selective pressures that vary on a gradient;/ continuum
  • Most prevalent among organisms with continuous ranges over a continental area
  • Usually associated with an ecological gradient such as temperature, moisture, altitude, light


  • A population or group of populations that is prevented by some extrinsic barrier from effecting a free flow of genes with others of the same species


  • An aggregate of local populations of a species inhabiting a geographic subdivision of the range of a species and differing taxonomically from other populations of the species


  • Populations connected by intermediate forms or intergrades, so that it is virtually impossible to separate them


  • The occurrence of several distinct forms of a species in the same habitat at the same time
  • Forms are distinct and the characteristic involved are discontinuous – NO overlap


  • Species which may reproduce themselves in some nonsexual manner
  • Agamospecies
    • Those which lack true sex reproduction
    • Reproduce via runners, bulbs, corms
    • Self-ferilization

Spontaneous generation of new species through alteration of chromosome numbers

  • Formed by doubling the chromosomes in any individual of the species

Formed by doubling the chromosomes of a hybrid individual

  • Direction and degree to which a population diversifies
  • Influenced by the preadaptability of the species population to a new situation
  • By selective pressures of climate and competition
  • By the availability of ecological niches

;MAINTENANCE OF SPECIES;Isolating mechanisms
The means by which species maintain diversity
;MAINTENANCE OF SPECIES;Ecological mechanisms
Include habitat isolation and temporal/seasonal isolation
;MAINTENANCE OF SPECIES;Ethological mechanisms
Differences in courtship and mating behavior
;MAINTENANCE OF SPECIES;Mechanical Isolating mechanisms
Structural differences that make copulation or pollination between closely related species impossible
;MAINTENANCE OF SPECIES;Reduction of Mating Success
Does not prevent waste of gametes but highly effective in preventing crossbreeding
Breakdown in isolating mechanisms