The Organism in the environment

• Definition of population 

  A group of organisms of the same species in a particular area
• Definition of community 

  All the different populations in the same habitat
• Definition of a habitat 

  The place where an organism lives
• Definition of an ecosystem 

  All the biotic factors and all the abiotic factors that interact within an area at one time 
• What is a biotic factor 

  Living components of environment (eg plants+animals)
• What is an abiotic factor 

  non-living components of environment (eg light intensity)
• What are examples of abiotic factors 

  Light intensity

  temperature

  wind speed

  moisture levels

  soil pH

  mineral content

  wind intensity/direction

  CO2 and O2 levels
• How abiotic factors affect community: light intensity 

  More light leads to an increase of photosynthesis rate, thus an increase in plant growth rate 
• How abiotic factors affect community: temperature 

  Affects rate of photosynthesis. (Low temp= low photo, high temp= high photo, too high temp= denaturing+no photo)
• How abiotic factors affect community: moisture levels 

  Both plants and animals require water to survive 
• How abiotic factors affect community: soil pH and mineral content 

  Soil pH affects rate of decay, thus how fast mineral ions return to soil. Different plant species are adapted to different pH levels and nutrient concentration levels 
• How abiotic factors affect community: wind intensity+direction

  Wind speed increases transpiration rate which affects photosynthesis rate as it ensures water and mineral ions are transported to leaves 
• How abiotic factors affect community: carbon dioxide levels 

  Higher the CO2 levels, higher rate of photosynthesis 
• How abiotic factors affect community: oxygen levels 

  Some aquatic animals (eg fish) only can survive in water with high oxygen concentration
• What are examples of biotic factors 

  Availability of food, new predators, new pathogens, competition  
• How biotic factors affect community: availability of food

  More food means organisms have a high survival chance, thus higher rates of reproduction, increasing populations
• How biotic factors affect community: new predators 

  Can make ecosystem unbalanced- too many predators can wipe out prey population
• How biotic factors affect community: new pathogens 

  Can wipe out a population as populations living in ecosystem won’t have immunity/resistance to it
• How biotic factors affect community: competition 

  If 2 species compete for same resources and one is better adapted to take advantage of them, that species will outcompete the other. Continues until there’s too few members of lesser adapted species to breed successfully
• Practical: Investigating Population Size

  • Ecology is the branch of biology that studies:
  • The distribution of species
  • The abundance of species
  • Interactions between species
  • Interactions between a species and its abioticenvironment
  • Ecologists are biologists that study these interactions by investigating ecosystems
  • One piece of equipment that might be used to investigate population size is a quadrat
• Quadrants

  • Quadrats are square frames made of wood or wire
  • They can be a variety of sizes eg. 0.25m2 or 1m2
  • They are placed on the ground and the organisms within them are recorded
  • Plants species are commonly studied using quadrats to estimate the abundance
• What quadrats can be used to measure

  • Quadrats can be used to measure abundance by recording:
  • The number of an individual species: the total number of individuals of a single species (eg. buttercups) is recorded
  • Species richness: the total number of different species (but not the number of individuals of each species) is recorded
  • Percentage cover: the approximate percentage of the quadrat area in which an individual species is found is recorded (this method is used when it is difficult to count individuals of the plant species being recorded eg. grass or moss
• Investigating population size in 2 different areas using quadrats

  Apparatus

  • 2 tape measures
  • Quadrat
  • Random number generator
  • Species key
• results

  • Once the results have been collected and the averages calculated, we can compare the abundance of the study species in each survey area
  • Species abundance is likely to be influenced by biotic factors such as:
  • Competition
  • Predator-prey relationships
  • Interactions with other organisms within the food chain or food web
  • The abundance will also be influenced by abiotic factors such as:
  • Light intensity
  • Mineral availability
  • Water availability
  • pH
  • Temperature
  • Salinity
• limitations

  • It can be easy to miss individual organisms when counting in a quadrat, especially if they are covered by a different species
  • Solution: Use a pencil or stick to carefully move leaves out of the way to check if there is anything else underneath
  • Identifying species may be tricky
  • Solution: Use a species key to identify the species
• CORMS

  • C - We are changing the study area where we are collecting the data
  • O - We will count the same species of organism in each quadrat
  • R - We will repeat the investigation several times to ensure reliability
  • M1 - We will count the number of the designated study species found across all quadrats
  • M2 -  this isn't really relevant in this scenario
  • S - We will control the size of the quadrat, the random way that quadrats are placed on the ground, the day that the results were collected