ecology and the environment

• Population


  A group of organisms of the same species living in the same place at the same time
• Community


  All of the populations living in the same area at the same time
• Interdependence


  Organisms living in the same habitat depend on each other, a change in one species will affect other species
• A habitat is the place that an organism lives
• Ecosystem


  All of the organisms that live in an area, and their interactions with the living (biotic) and non-living (abiotic) factors in their environment
• Living organisms interact with both the living components (each other) and the non-living components (e.g. the temperature and rainfall) of their environment
• Quadrat


  A square frame that is placed on the ground to study the organisms within it
• Abundance


  How common a species is within a quadrat, can be used to estimate the size of a population
• Measuring abundance within a quadrat


  1. Recording whether or not a species is present

  2. Counting the number of individuals of a species

  3. Estimating percentage cover
• Percentage cover is often used to measure the abundance of a species where individual organisms are difficult to tell apart, e.g. grass or barnacles
• Placing quadrats randomly avoids bias in an investigation
• Variables to keep the same when using quadrats to compare population sizes in two areas (CORMMS)


  • Size of quadrat
  • Number of quadrats sampled
  • Time of day / time of year
  • Knowledge of species identification
• Challenges of using quadrats to investigate populations include: it can be easy to miss organisms when counting, some species might be difficult to identify
• Increasing the number of quadrats will increase the likelihood that any results accurately represent the habitat sampled
• Biodiversity


  The variety of different species found in a habitat, including the number of different species, the size of each population and the differences between individuals of a species
• Benefits of high biodiversity


  • Increased availability of food and shelter
  • Increased resilience to change
• Low biodiversity decreases ecosystem stability
• Distribution


  Where a species occurs within its habitat
• Variables that could be measured when using quadrats to investigate biodiversity (CORMMS)


  • The number of species in each quadrat
  • The abundance of each species in each quadrat
• A quadrat that contains more species is likely to have higher biodiversity
• Abiotic factor


  Non-living factors that influence ecosystems, e.g. temperature, sunlight, pH, salinity, precipitation
• A decrease in water availability

  The population size might decrease, the population might change its distribution by leaving one area for another in search of more water
• An increase in temperature from 20 °C to 30 °C would result in an increased population size for a plant species
• Biotic factor


  Living factors that affect organisms in an ecosystem, such as competition, predation and disease
• Biotic factors that could affect populations


  • Predators
  • Competition
  • Availability of food organisms
  • Pathogens /disease
• A decrease in the size of a prey population will most likely result in a decrease in the size of a predator population
• Competition


  Organisms fight for the same resources, e.g. food or mates
• Populations that compete for the same resources are likely to be smaller than equivalent populations that are not experiencing competition