🌱Biology Unit 6 Ecology

• Ecosystem

  A reasonably self-contained area together with all its living organisms, e.g. oak forest, deep sea, sand dune, rocky shore, moorland, hedgerow, garden pond, etc.
• Habitat

  The physical or abiotic part of an ecosystem, i.e. a defined area with specific characteristics where the organisms live. Most ecosystems have several habitats.
• Terrestrial

  An ecosystem on dry land
• Aquatic

  An ecosystem in water
• Marine

  An ecosystem in the sea
• Community

  The living or biotic part of an ecosystem, i.e. all the organisms of all the different species living in one habitat.
• Population

  The members of the same species living in one habitat.
• Species

  A group of organisms that can successfully interbreed
• Random sampling

  Used when you want a representative sample of the whole area under study. Measuring tapes are placed along two sides of the area, like axes of a graph, and random numbers (from tables or a computer) are used as coordinates to choose sampling points in the area.
• Systematic sampling

  Used when you choose where to take your samples, because you are investigating a specific pattern in the ecosystem, such as zonation in a rocky shore, sand dunes or hillside. The most common kind of systematic sample is a transect, where samples are taken along a straight line to see what changes there are along the line.
• Transect

  1. Line transect - organisms touching a piece of string stretched along the transect are recorded

  2. Belt transect - quadrats are placed at intervals along the transect and organisms in each quadrat are counted

  3. Interrupted transect - the sampling is not continuous, but there are gaps between the samples
• The data from a transect can be presented as a kite graph, which shows biotic data as "kites" and abiotic data as lines.
• Abiotic factors

  The non-living or physical factors in an ecosystem, usually measured with special digital electronic equipment.
• Biotic factors

  The living or biological factors in an ecosystem, measured by finding and identifying the organisms, and then quantifying them in various ways.
• Abundance

  The number of organisms in a sample, often divided by the sampling area to calculate density.
• Biomass

  The dry mass of living organisms, measured by drying samples to constant mass.
• Point quadrat


  A needle (like a knitting needle), with the point of the needle being the actual tiny quadrat
• Quadrats


  • Allow quantitative measurements of the abundance of plants
  • Provide a small, standard area for investigation
• Finding the best quadrat size

  1. Do a preliminary experiment "nesting" different-sized quadrats

  2. Count the number of species found

  3. Choose a quadrat size that is likely to catch all the species, but without wasting unnecessary effort
• Quantitative measurements using quadrats

  • Density
  • Species Frequency
  • Percent Cover
• Density

  Count the abundance, then divide by the area of the quadrat
• Species Frequency

  Record the number of quadrats in which a species was found
• Percent Cover

  Estimate the percentage area of the quadrat covered by a particular species (to the nearest 5%)
• Point Quadrats

  A needle is dropped through a frame till it touches the ground and whatever species the needle hits are recorded
• Abundance Scale

  A qualitative way to assess abundance using a 5-point scale (e.g. ACFOR: Abundant, Common, Frequent, Occasional, Rare)
• Techniques for sampling animals

  • Nets (e.g. sweep nets, D-nets)
  • Traps (e.g. pitfall traps, Longworth traps, light traps)
  • Sighting methods
• Null Hypothesis

  States that there is no difference between groups, or no correlation between variables
• In biology, a p-value less than 0.05 (5%) is usually taken as the cut-off for statistical significance
• Statistical tests for A-level biology

  • t-test
  • Spearman's correlation coefficient
• Using the t-test

  1. Calculate the t-value using the formula

  2. Calculate the degrees of freedom

  3. Look up the critical value of t in a table

  4. Compare the calculated t-value to the critical value to determine if the null hypothesis should be rejected or accepted
• If the critical value of rs is less than the calculated value

  p < 0.05, reject the null hypothesis and conclude there is a significant positive correlation with a strength of 0.77
• If the critical value of rs is greater than or equal to the calculated value

  p ≥ 0.05, accept the null hypothesis and conclude there is no significant correlation
• Food chain

  Relationships between members of a community in an ecosystem, with arrows representing flow of energy and matter
• Trophic level

  Each stage in a food chain
• Food chains always start with photosynthetic producers
• Producers

  Organisms that produce food from carbon dioxide and water using photosynthesis (plants, algae, plankton, photosynthetic bacteria)
• Consumers

  Animals that eat other organisms
• Types of consumers

  • Herbivores (eat plants)
  • Carnivores (eat other animals)
  • Omnivores (eat plants or animals)
  • Vegetarians (humans that choose not to eat animals)
• Autotrophs

  Organisms that manufacture their own food (= producers)
• Heterotrophs

  Organisms that obtain energy and mass from other organisms (= consumers + decomposers)