Natural selection


Selection pressures:

  • the environmental factors that limit the population of a species

Gene pool:

  • the total number of all the alleles of all the genes of all the individuals within a particular population at a given time

Carrying capacity:

  • refers to the resources available, enabling a population to survive

Fundamental niche:

  • refers to the resources available to species in the absence of competition

Realised niche:

  • refers to the resources available to species as an outcome of competition

The process of evolution by means of natural selection depends upon a number of factors including:

  • organisms produce more offspring that can be supported by the available supply of food, light, space etc
  • there is genetic variety within the populations of all species
  • a variety of phenotypes that selection operates against

Evolution through natural selection:

1 - because the individuals of a species population vary genetically, their characteristics are slightly different from one other

2 - resources (food, space, mates) enabling species populations to survive are limited

3 - organisms have the potential to over-reproduce. however, species populations fluctuates in numbers but, on average, numbers remain stable in the medium term because the individuals of


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