Evolution

• • Within a population there will always be a competition for resources and impact of disease and predators leading to natural selection.
  • Wide range of phenotype due to genetic and environmental factors. Primary source of genetic variation is mutation, meiosis and random fusion of gametes.
• • Predators, disease and competition lead to selection pressures. Organisms with phenotypes giving a selective advantage are more likely to survive.
  • More likely to produce more offspring and pass on favourable alleles to next generation changing the allele frequency overtime.
• Types of selection

  • Stabilising 
  • Directional
  • Disruptive
• Disruptive selection

  when individuals contain alleles coding for either extreme traits and more likely to survive and pass on their alleles. So allele frequency change and more individuals possess allele for extreme trait and middling trait allele less frequent. Continued disruptive selection can lead to speciation.
• Speciation

  • Creation of new species, occurring when one original population of the same species become reproductively isolated.
  • This isolation means, two populations of the same species cannot breed together.
• Speciation

  • Leads to differences gene pools, due to mutations, to the extent the two populations unable to interbreed to make fertile offspring so classed as two different species.
• Two different ways populations can become reproductively isolated:

  • Allopatric (geographically)
  • Sympatric ( Changes in reproductive mechanisms)
• Allopatric

  • Populations can be separated geographically leading to reproductive isolation.
  • new mountain ranges
  • New bodies of water separating land masses
  • This separates the original population into 2, unable to reproduce due to geographical barrier.
  • Both separate populations will continue to accumulate different beneficial mutations overtime to help survive in their environment
  • Due to change of DNA base sequence differences overtime, two populations so genetically different, unable to interbreed to create fertile offspring.
• Sympatric

  • Reproductively isolated due to differences in behaviour.
  • Due to random mutations within population could impact reproductive behaviour. May cause different courtship ritual so opposite sex won't recognise their ritual and will not reproduce with them or for individuals to be fertile at different times of year.
  • So no gene flow between two groups within population.
  • These reproductive isolated populations accumulate different mutations to extent that DNA base sequence is so different that they cannot interbreed to create fertile offspring . Classed as two different species.
• Genetic drift

  • Change in the allele frequency within a population between generations.
  • Always be genetic drift from one generation to the next but continual but substantial genetic drift leads to evolution.
  • Smaller a population is the bigger the impact allele frequency changes has, this is why evolution often occurs more rapidly in smaller populations.
• Key words:

  • Niche: Organisms role within an ecosystem, including position in food web and habitat
  • Carrying capacity: Maximum population size an ecosystem can support.
  • Abiotic factors: Non-living conditions of an ecosystem.
  • Biotic factors: Impact of the interactions between organisms
• Abiotic factors

  •  Can affect size of different populations.
  • Range from, temperature, oxygen, CO2 concentration, light intensity, pH and soil conditions.
  • Plants and animals are adapted to abiotic factors within their ecosystem.
  • These adaptations develop through processes of natural selection over generations.
  • Less harsh the abiotic factors, e.g plenty of water and light, the larger the range of species and larger population sizes
• Biotic factors

  • IntERspecific: Members of different species are in competition for the same resources in limited supply, the individual better adapted to environment is more likely to succeed.
  • IntRAspecific: Members of the same species are in competition of resources and a mate. Mating relates to courtship rituals. Individuals fitter have more energy to perform a more impressive courtship ritual/ colourful feathers to attract a mate. 
• Predator-Prey relationships

  Graphs always follow the same pattern:

  • Size of predator and prey population both fluctuate
  • Always more prey than predator
  • Size of population will change the prey and then the predators. As prey eaten first then run out so predator diet out.