KA 2: Distribution of Organisms

• How can the number of plants and animals in an ecosystem be estimated?

  By counting a sample
• Why is it important to take many samples when estimating the number of organisms in an ecosystem?

  To obtain reliable estimates
• What tool is used to sample stationary animals or plants?

  A quadrat
• What does a quadrat mark?

  A region of known square area
• What is an example of a quadrat size?

  0.25 m²
• What is the term for the number of small squares in a quadrat containing one or more organisms?

  Abundance
• How can the validity and reliability of quadrat results be improved?

  By placing quadrats randomly, counting all organisms, and placing them frequently
• What type of animals can be sampled using a pitfall trap?

  Small soil animals, usually invertebrates
• What method can be used to identify organisms?

  A paired-statement key
• What are the requirements for placing pitfall traps?

  They should be placed randomly, level with the ground, and covered
• What abiotic factors can be measured using electronic instruments?

  Light intensity, temperature, pH, and soil moisture
• What precautions should be taken when determining abiotic factors?

  Readings should be taken consistently and averaged
• How can the distribution of organisms in an ecosystem be controlled?

  By various abiotic factors
• What is a transect used for in ecological studies?

  To investigate the effect of an abiotic factor on the distribution of organisms
• How can the presence of a plant species be related to abiotic factors?

  By taking samples along a transect
• What are indicator species?


  Species that indicate environmental quality or levels of pollution
• How can pollution in ecosystems be monitored?

  By counting the presence/absence and number of indicator species
• What can freshwater invertebrates be used for?

  To assess the quality of freshwater
• What can lichens be used as an indicator species for?

  Assessing local air quality
• What are the key steps to ensure valid and reliable results when sampling organisms in an ecosystem?

  • Take many samples
  • Use a quadrat for stationary organisms
  • Place quadrats randomly
  • Count all organisms
  • Place quadrats frequently
• What are the precautions to take when measuring abiotic factors?

  • Take readings in the same way each time
  • Take many readings
  • Calculate an average value from the readings
• What is the relationship between abiotic factors and the distribution of organisms?

  • Abiotic factors can control the distribution of organisms
  • Samples taken along a transect can relate plant species presence to abiotic factors
• Factors that influence the distribution of organisms include climate, temperature, precipitation, altitude, soil type, water availability, sunlight, wind patterns, topography, vegetation cover, human activities, and natural barriers such as mountains or oceans.
• What are biotic factors that affect ecosystems?

  Competition for resources, disease, food availability, grazing, and predation
• What are abiotic factors that affect ecosystems?

  Light intensity, moisture, pH, and temperature
• What is the importance of measuring abiotic factors in an ecosystem?

  • Helps understand environmental conditions
  • Assists in assessing habitat suitability
  • Aids in studying organism distribution
• What are some possible sources of error when measuring abiotic factors?

  Inaccurate instruments, environmental fluctuations, and human error
• How can errors in measuring abiotic factors be minimized?


  By calibrating instruments and taking multiple measurements
• What methods are used for sampling plants and animals?

  • Quadrats for stationary organisms
  • Pitfall traps for ground-dwelling organisms
• What are some limitations of using quadrats for sampling?


  They may not represent the entire area and can miss mobile organisms
• What are some sources of error in using pitfall traps?


  Traps can be affected by weather, and animals may escape
• What is the purpose of paired-statement keys in biology?


  • To identify organisms based on characteristics
  • To simplify the classification process
• How do biotic and abiotic factors affect biodiversity?


  They influence the variety and distribution of organisms in an ecosystem
• What are indicator species?


  Species that indicate environmental quality or levels of pollution
• Why are indicator species important in ecology?

  They help assess the health of an ecosystem