Populations

• Community


  all the populations of different organisms living and interacting in a particular place at the same time
• Population


  group of individuals of the same species occupying the same habitat at the same time
• Habitat


  place where an organism usually lives
• Niche


  all conditions and resources needed for an organism to survive and reproduce, how an organism fits into the environment

  governed by abiotic and biotic conditions
• Ecosystem


  all the interacting biotic and abiotic features in a specific environment
• Abiotic factors


  non living features of an environment e.g temperature, PH, light
• Biotic factors


  living features of an environment
• Using quadrats


  set up a grid

  choose random coordinates using random number generator

  measure percentage cover or species frequency in a quadrat

  place a large number of quadrats on coordinates and calculate a mean per quadrat
• Percentage cover


  measures abundance

  an estimate of the area within a quadrat a specific plant species occupies

  useful when counting individual organisms is impractical e.g too many

  underestimates small organisms and overestimates large organisms
• Species frequency


  number of individuals of each species in a quadrat
• Random sampling 


  avoids bias
• Deforestation/removal of hedges


  fewer species, less habitats, fewer food sources, increase of carbon dioxide in the airsince less photosynthesis

  farmers benefit from hedges as they have more predators for pests
• Transects


  used when there is a transition in the environment

  place quadrats at regular intervals along the line

  count plants or percentage cover in each quadrat

  use several quadrats

  may not be representative of area
• Mark release recapture


  capture sample mark and release

  apply mark that doesnt harm

  take second sample after organisms have had chance to disperse and count marked organisms

  population is number in sample one times number in sample two divided by number recaptured
• Carrying capacity


  ecosystem can only support populations of a certain size

  affected by abiotic factors, inter and intraspecific competition and predation
• Assumptions of mark release recapture

  no emigration

  no losses to predation

  marking doesnt affect survival

  birth rate and death rate is equal

  all belong to one population
• Intraspecific competition


  competition between members of the same species
• Interspecific competition


  competition between members of different species

  happens until one outcompetes the other for things like food, space, light, breeding
• Predator prey relationship


  hard to show in a lab

  data from natural environments should be taken with caution