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

HISTORY OF MODERN EVOLUTIONARY THOUGHT

• 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

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

NATURAL SELECTION

• 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

Ecological Genetics

GENOTYPE, PHENOTYPE, & PHENOTYPIC PLASTICITY

• 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

SOURCES OF VARIATION

• 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

SOURCES OF VARIATION

GENES

• 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

SOURCES OF VARIATION

Mutation

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

SOURCES OF VARIATION

Micromutation

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

SOURCES OF VARIATION

Macromutation

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

HARDY-WEINBURG EQUILIBRIUM

• 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 = 1

p² + 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

GENETIC EQUILIBRIUM

• 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

N_E = (4N_MN_f)/(N_M+N_f)

• N_E: Effective population size (breeding individuals)
• Vital for conservation projects
• N_M: Number of breeding males
• N_f: Number of breeding females

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

MODES OF SELECTION

Group Selection

• 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

MODES OF SELECTION

Kin Selection

• 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. Wynne-Edwards

• 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

Arguments AGAINST Group Selection

INDIVIDUAL SELECTION

• 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

Arguments AGAINST Group Selection

RESOURCE PREDICTION

• 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.

ALTRUISM

• 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

EVOLUTION

MICROevolution: change in gene frequency in a population

MACROevolution: 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

SPECIATION

Sibling

• Morphologically similar or identical natural populations that are reproductively isolated

SPECIATION

Sympatric

• 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

GEOGRAPHIC VARIATION

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

CLINE

• 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

GEOGRAPHIC ISOLATE

• 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

GEOGRAPHIC ISOLATE

Subspecies

• 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

GEOGRAPHIC ISOLATE

Geographic Races

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

GEOGRAPHIC ISOLATE

Polymorphism

• 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

SPECIATION

Asexual

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

MECHANISMS OF SPECIATION

Polypoidy

MECHANISMS OF SPECIATION

Autopolypoidy

• Formed by doubling the chromosomes in any individual of the species
• AABBCCDD → AAAABBBBCCCCDDDD

MECHANISMS OF SPECIATION

Allopolyploidy

MECHANISMS OF SPECIATION

Adaptive radiation

• 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

MAINTENANCE OF SPECIES

Ecological mechanisms

MAINTENANCE OF SPECIES

Ethological mechanisms

MAINTENANCE OF SPECIES

Mechanical Isolating mechanisms

MAINTENANCE OF SPECIES

Reduction of Mating Success

MAINTENANCE OF SPECIES

Hybridization