populations

• population: group of organisms of the same species living in the same habitat
• habitat: part on an ecosystem in which particular organisms live
• community: all the populations of different species in the same area at the same time
• ecosystem: a community and the non-living components of an environment, ranging in size
• niche: an organism's role within an ecosystem, including their position in the food web and habitat. each species occupies their own niche governed by adaptation to both biotic and abiotic conditions
• carrying capacity: the maximum population size an ecosystem can support
• abiotic factors: non-living conditions of an ecosystem
• biotic factors: impact of the interactions between organisms
• disruptive selection: when individuals which contain the alleles coding for either extreme trait are more likely to survive and pass on their alleles
• speciation: creation of new species by an increasing difference in the gene pool until they no longer can breed to produce fertile offspring
• two types of speciation:

  • allopatric
  • sympatric
• allopatric speciation:

  • geographically isolated, gene pools separate
  • adapt to survive in different environment
  • accumulate beneficial genetic mutations
  • adapted organisms breed
  • changes allele frequency
• sympatric speciation:

  • same habitat, reproductively isolated
  • mutation causes change in reproductive behaviour
  • no gene flow
  • change in allele frequency
  • disruptive selection
  • eventually species cannot interbreed to produce fertile offspring
• genetic drift:

  • change in allele frequency between generations
  • continual, substantial genetic drift results in evolution
  • smaller population, larger impact of allele frequency changes (proportionally) so evolution occurs more rapidly
• factors affecting population size:

  • abiotic factors
  • biotic factors
• abiotic factors:

  • plants and animals are adapted to the abiotic conditions within their ecosystem
  • by natural selection over time
  • less harsh abiotic factors, larger range of species and population
  • examples - temperature, minerals, pH, oxygen, light intensity
• biotic factors: intraspecific and interspecific competition
• interspecific competition:

  • members of different species are in competition for the same resource that is in limited supply
  • individual more adapted to the environment is more likely to succeed
• intraspecific competition:

  • members of the same species are in competition for resources and a mate
  • fitter individuals have more energy to perform a more impressive courtship ritual or have fur in better condition to attract a mate
• predator prey relationships:

  • both population sizes fluctuate
  • prey population always greater than predator
  • predator population change delayed from prey
• Selection pressures: Environmental factors that drive evolution by natural selection and limit population sizes e.g. competition, predation and disease
• pioneer species: first to colonise the new area and can survive in hostile environments
• Gene pool: All the alleles in a population
• why can genetic mutations not be passed between species?

  • mutations are spontaneous
  • only rate of mutation is affected by environment
  • different species do not interbreed
  • so mutation can not be passed from one species to another
• why is there a time delay for between selection pressure and time for species to accumulate a mutation?

  • initially one insect with favourable mutation
  • individuals with favourable alleles have more offspring
  • takes many generations for favourable mutation to become the most common allele of this gene
• mark recapture release equation?

  $population=$$\frac{number in first sample\times total of second sample }{number of marked in second sample}$
• suggest why mark-release-recapture method can produce unreliable results in large lakes?

  unlikely fish distribute evenly and less chance of recapturing fish
• describe and explain how succession occurs:

  • colonisation by pioneer species
  • decomposition changes environment or habitat
  • environment becomes more suitable for new species
  • increase in biodiversity
  • to climax community
• describe how you could estimate the size of a population of a plant species?

  • use a grid
  • randomly generate numbers
  • count frequency in quadrat
  • large sample and calculate average
  • multiply average by total area of habitat
• explain how the results shown were due to succession taking place?

  • name pioneer species
  • change the abiotic factors
  • more suitable for named species
  • name climax community
• give 3 features of a climax community?

  • same species present over long time
  • abiotic factors constant
  • populations stable
• secondary succession:

  • succession is disrupted and plants are destroyed
  • soil is already created, so succession restarts but not from bare rock
• explain how the mark-recapture release method can be used to estimate a population:

  • capture sample, mark and release
  • ensure marking is not harmful to animal
  • allow time for animals to redistribute before second sample
  • calculate using equation