D4.1

• Natural selection :


  Process where different environments & their factors influence survival & reproduction of organism due to variations/adaptations.

  Caused by evolution as some variations -> more favourable for an environment -> survive longer.
• Process of natural selection :

  Overproduction of offspring -> variation occurs through mutations & meiosis (crossing over or random assortment).

  Struggle to survive due to large population -> more adapted individuals survive & go on to reproduce.

  Individuals reproduce -> pass on variations to offspring.

  Over time, frequency of favourable variation increases & frequency of unfavourable variations decreases.
• Sources of variation :

  Mutation.

  Meiosis.

  Sexual reproduction.
• Mutation as a source of variation :

  Changes in the sequence of a DNA.

  Leads to no changes in phenotype.

  Typically dead-end mutation if it doesn’t affect cell that produce gametes -> unable to be passed on.

  Majority of time mutations have a neutral effect, but rarely it can have both + or - effects.
• Meiosis as a source of variation :

  Produces haploid cells from diploid cells -> produce 4 genetically different cells (50% of genome).

  Crossing over & Random assortment (Metaphase I) allow for variation in genes.
• Sexual reproduction as source of variation :

  Asexual reproduction -> genetically identical individuals -> if badly adapted to environment -> quickly die out.

  Sexual reproduction -> fusion of gametes -> allows random gametes to fuse -> leads to new & unique combination of alleles.
• Observations for theory of evolution :

  Ecological -> population has the ability to grow exponentially -> until reaches certain size -> remains stable -> natural resources are limited -> not all individuals survive due to lack of resources -

  Hereditary -> Individuals in the same species have lots of different characteristics -> characteristics are heritable -> some individuals able to reproduce & survive due to better adaptations.

  
  

  Uses inductive reasoning to form this (observation -> theory)
• Pragmatic theory :

  Has practical consequences & useful in real life scenarios
• Coherence theory :


  Fits within a larger pool of knowledge.
• Correspondence theory :


  Accurately describes the real world.
• Difference between variation & sexual reproduction :

  Mutations are random, wheras sexual reproduction occurs with meisosis.

  Variations promoting survival get passed on.

  Variations reducing survival do not get passed on.
• Benefits of overproduction of offspring :

  Overproduction & not enough natural resources -> causes evolutionary pressure.

  Increases the odds that some offspring survive until adulthood.

  Lots of genetic variation -> if change to environment occurs -> individuals better adapted to situation survive & pass on alleles.
• Carrying capacity :


  Maximum population size that an environment can support.

  Less resources -> decrease capacity.

  More resources -> increase capacity.
• Competition types :


  Direct.

  Indirect.
• Direct competition :


  1 individual affects another individual ability to obtain resources.

  E.g : male elk use aggression to prevent other males from mating with females.
• Indirect competition :


  1 individual indirectly affect another individual’s ability to obtain resources.

  E.g : bear further up the riverstream eating salmon causes bear down the river to obtain less resources.
• Resources that limit population size :

  Food/Prey/Nutrients.

  Land.

  Water.

  Shelter.

  Mates.
• Example of overproduction of a species :

  Leatherback turtles lay 80-100 eggs -> only a few survive.
• Selection pressures :


  Variables in envrionment that causes a certain phenotype of an organism to have a better chance of surviving and/or reproducing.

  Can be negative (decreases frequency) or positive (increases frequency).

  Driving forces of evolution.
• Biotic selection pressures :

  Result of living things :

  • Predation.
  • Competition.
  • Disease.
  • Finding/Attracting mates.
  • Availability of food.
• Abiotic selection pressures :

  Result from non-living things :

  • Temperature.
  • Water availability.
  • Light availability.
  • O & CO2 concentrations.
  • Natural disasters.
  • Pollutants.
  • Wind.
• Density independent factors :

  Tend to be abiotic factor -> act the same no matter the population density.
• Density-dependent factors :


  Affect the size of population & dependant of poplation.

  E.g :

  • Availability of food.
  • Availability of water/shelter/resources.
  • Spread of pathogens.
  • Presence of predators.
  • Finding mates.
• Importance of selection pressures for variation :

  Allows for individuals who are best suited for the environment to survive & reproduce.
• Biological fitness :


  Ability of an organism to reproduce & pass on genetic material to offspring.

  Determined by :

  • Environment it lives in -> fitness varies with environmental condition changes.
  • Survival value -> traits enabling individuals to survive & reach reproductive age.
  • Reproductive potential of individual -> capacity to produce offspring -> ability to attract mates/produce viable gametes/parental care.
• Effect of selection pressure on more/less adapted individuals :

  Less suitable adaptations are unable to compete & thus more likely to die before reproductive age -> lower frequency of their variation.

  More suitable adaptations are able to compete & more likely to mate after reproductive age -> higher frequency of their variation.
• Pacing of evolution :

  Can change based on strength of selection pressures.

  • High pressure -> rapid evolution.
  • Low pressure -> gradual evolution.
• Adaptation :


  Forms that allow for them to be adjusted to an environment.

  Consequence of natural selection.
• Intraspecific competition :


  Competition between individuals of the same species.

  E.g : 2 trees growing close together -> compete for space, water, nutrients & sunlight.

  Density dependent -> increase in population size & reaches carrying capacity of environment -> competition for resources rises -> fitter individuals have a greater chance of acquiring resources & reproducing.

  • Decreases growth rate of population.
  • Traits from fitter individual passed on to offspring -> overtime causes population to be better adapted & emergence of new species (long run).
• Heritable traits :

  Must be part of individuals DNA & able to be passed on to future generations.

  In sexually reproducing organisms, only gametes pass on DNA.

  If beneficial -> increases likelihood of surviving & passing onto future generations.
• Acquired traits :


  Characteristics acquired in the lifetime of an individual due to environmental factors -> behavioural/physical.

  Only affects phenotype as not part of genetic material -> not genotype.

  Can affect genotype only if it doesn’t affect gametes.

  Unable to be passed onto offspring.
• Sexual selection :


  Selection for traits that don’t necessarily have a survival advantage, but instead a mating advantage.

  Intra/Intersexual selections.

  • Intra - between individuals of same sexes to mate with individual of other sex (male to male) -> fights/displays of strength (Deer) -> evolution of secondary sexual characteristics.
  • Inter - between individuals of same sex selecting who to mate with of other sex (females selecting male) -> based on appealing features (peacock) -> frequency of more appealing trait increases in a population over a time period.
• Factors of sexual selection :

  Colour, Size, Strength, Courtship behaviour.

  E.g : Male peacocks = colour.

  E.g : Male peacock spider = mating ritual is a dance.
• Sexual dimorphism :


  Morphological difference between males & females -> not visible in youth -> development of secondary sexual characteristics.
• Males who are adapted to sexual selection :

  Much more vibrant & more feathers -> good health/genetics as these have high energy costs & much more visible -> irresistable to females.
• Cryptic colouration :


  Colour of females are dull/dark -> not eye catching to be less likely to be noticed.
• Endler’s experiment :

  1. Guppies breed in an artificial pond -> considerable variation -> left alone for 6 months to reproduce multiple times -> increase in mean number of spots in male guppies -> more attractive for females.
  2. Split population into 3 ponds -> left alone for 20 months -> average number of spots calculated for each.

  • A - only guppies -> no predation.
  • B - Rivulus present -> predate on baby guppies irregularly
  • C - Pike cichlids present -> biggest predator of guppies

  3. Pond A & B evolved into more spots + Pond C evolved to be more drab to survive.
• Results & Reasoning to Endler’s experiment :

  A - no predation -> sexual selection present only -> more spots = more attractive -> trait increases over a period of time.

  B - predation of juvenile -> secondary sexual characteristics are’nt present -> randomly consumed -> more spots = more attractive -> trait increases over a period of time.

  C - Predation present -> natural selection & sexual selection present -> survival is more important -> more spots = higher likelihood to be detected -> trait decreases over a period of time.
• Selective pressures in Endler’s experiment :

  Predation -> more biologically fit organisms (blend into environment) -> allow for it to survive longer.

  Sexual selection -> more prevalent traits (standing out) -> allow it to be more attractive to reproduce.