Populations and Ecosystems

• Definition of an environment.

  An organism's surroundings
• Definition of population.

  All the organisms of the same species living in the same environment.
• Definition of a community.

  All the organisms of different species living together in the same environment.
• Definition of habitat.

  place where organisms live
• Definition of a niche.

  The role of an organism within its ecosystem
• What is an ecosystem ?

  All the organisms living in a certain area and all the non living conditions found there (biotic and abiotic factors)
• What are biotic factors ? Give 4 examples.

  Living features of an ecosystem

  1. Predators
  2. Disease causing organism
  3. Intraspecific competition
  4. Interspecific competition
• What are abiotic factors ? Give some examples.

  Non living features of an ecosystem.

  • light
  • temperature
  • water availability
  • oxygen availability
  • carbon dioxide availability
  • wind
  • pH of soil
• How does predation affect population size ?

  decreases the number of prey population
• What is the difference between interspecific and intraspecific competition ?

  Intraspecific competition is between members of the same species and interspecific competition is between two different species competing for the same resources.
• What is the carrying capacity ?

  Maximum population size an environment can support.
• How does temperature affect population size of plants ?

  As the temperature increases so does enzyme activity up to a point, after which enzymes denature.
• How does light intensity and CO2 concentration limit population size of plants ?

  limiting factor for the rate of photosynthesis
• Interspecific competition :

  If they share the same source of resources, there will be less available to both of them. Both populations have less energy for growth and reproduction, so the population sizes decrease for both species. If two species are competing but one is better adapted to its surroundings than the other, the less well adapted species is likely to be out-competed.
• What resources would species compete for ?

  food, space or oxygen
• Intraspecific competition :

  1.Species population increases when resources are plentiful.

  2. Resources become limiting — population then begins to decline.

  3. Smaller population - there's less competition for space and food which increases growth and reproduction — so the population starts to grow again.

  This cyclical pattern then continues.
• What is predation ?

  When an organism (predator) kills and eats another organism (prey).
• Describe how a predator prey relationship affects population size.

  1.As the prey population increases, there's more food for predators so the predator population grows.

  2. As the predator population increases, more prey is eaten so the prey population then begins to fall.

  3. This means there's less food for the predators, so their population decreases, and so on.
• What is succession ?

  The change in communities over time due to a change in the environment caused by the species present.
• What are the first organisms to invade and colonise a new site known as ?

  pioneer species
• State some hostile factors faced by pioneer species.

  -Limited water availability = no soil to retain water

  -A few minerals or nutrients = no soil

  -High light intensity, exposure to wind and rain and fluctuating temperatures = area is exposed to sun and the elements
• Give examples of pioneer species.

  -Marram grass = grow on sand dunes near sea

  -Lichens = fungus and algae

  -Shrubs
• How does marram grass on sand dunes benefit from having deep roots ?

  obtains water and salt tolerant
• What do lichens (fungus) secrete acids ?

  to erode the rock and release minerals
• What is each stage is succession called ?

  sere
• Describe the process of succession.

  1. The initial environment is hostile with very few organisms adapted. Abiotic factors dominate.
  2. Initial colonisation by pioneer species.
  3. Death and decomposition of these organisms change the environment e.g. formation of new soil / hummus
  4. This enables new, better adapted species to colonise/survive and out-compete the present species.
  5. The process is repeated over time.
  6. This increases biodiversity, niches and habitats
  7. Over time the environment becomes less hostile and more stable. Biotic factors dominate.
  8. Climax community has been reached.
• What is deflected succession ?

  When human activity prevents succession continuing.
• Give some examples of deflected succession.

  -Sheep grazing prevents grasslands developing into woodlands

  -Using herbicides

  -Burning of heather moorland

  -Trampling
• State 4 ways population size can be measured ?

  Abundance, Frequency, Percentage cover and distribution
• Definition of abundance.

  The number of individuals of one species in a particular area.
• Definition of frequency.

  The number of samples a species is recorded in.
• Definition of percentage cover.

  How much of the area you're investigating is covered by a species.
• Definition of distribution.

  Where a particular species is within the area you're investigating.
• When is random sampling favoured ?

  When estimating the population of a stationary species.
• When is systematic sampling favoured ?

  When investigating the change in distribution of species across an area.
• Describe the procedure of random sampling.

  1. Divide the area to be sampled into a grid+
  2. Generate a large number of random coordinates for the grid+
  3. Count plant species using a quadrat at each coordinate
  4. Calculate a mean+
  5. Estimated population size = mean x size of area / area of 1 quadrat
• Describe the procedure of a systematic sample.

  Use in conjunction with a transect e.g. place the quadrat every 10m intervals along a transect.
• What are the advantages of using random sampling ?

  avoids bias
• What are the advantages of using systematic sampling ?

  good coverage of the study area can be more easily achieved
• What are the disadvantages of random sampling ?

  Can lead to poor representation of the overall population as large areas may not be chosen by the random numbers generated.