7 - Ecology

• Ecosystem


  The interaction of a community of living organisms with the non-living parts of their environment
• What is a community made up of?

  The populations of different species or organisms that are all interdependent in a habitat
• Habitat


  The environment in which an organism lives
• Population


  The total number of organisms of the same species living in the same geographical area
• Interdependence


  The way in which each species within a community depends on other species for food, shelter, pollination, seed dispersal etc
• Competition


  The process by which living organisms compete with each other for limited resources (such as food, light or reproductive partners)
• What do organisms require to survive and reproduce?

  A supply of materials from their surroundings and from the other living organisms there
• What do plants often compete with each other for? (4)

  Light, space, water, and mineral ions from the soil
• What do animals compete with each other for? (3)

  Food, mates and territory
• Stable community


  Where all the species and environmental factors are in balance so that population sizes remain fairly constant
• What happens if one species is removed from a community?


  It can affect the whole community
• Abiotic factors


  Non-living factors
• Biotic factors


  Living factors
• Name 7 abiotic factors and how they might affect a community

  Litmuswoc

  1. Light intensity - photosynthesis, breeding cycles linked to day length

  2. Temperature - photosynthesis/plant growth, therefore animals which can survive

  3. Moisture levels - both plants and animals need water to survuve

  4. Soil pH and mineral content - distribution of plants, most struggle to grow where there is few mineral ions; low pH inhibits decay and therefore release of mineral ions

  5. Wind intensity and direction - shape of trees and landscape, increases plant transpiration

  6. Availability of oxygen - aquatic animals e.g. fish require high levels of dissolved oxygen

  7. Availability of carbon dioxide - photosynthesis
• Name 4 biotic factors and how they might affect a community

  FPOP

  
  

  1. Availability of food - food allows animals to survive and breed successfully

  2. New predators arriving - organisms with no defences against these predators may die out

  3. One species outcompeting another so the numbers are no longer sufficient to breed - e.g. grey squirrels in Britain

  4. New pathogens - organisms have no resistance so populations can be wiped out
• Adaptations


  Features which enable an organism to survive in the conditions in which they normally live
• Adaptations may be...


  ...structural, functional or behavioural
• Examples of structural adaptations (4)


  Features of body structure, shape or colour - e.g. animals living in cold environments have small ears (low SA:vol ratio), Arctic foxes have white fur, whales have blubber, herbivores have teeth for grinding up plant cells
• Examples of behavioural adaptations (3)

  Basking, migration, tool use - e.g. reptiles bask to absorb energy from the sun and warm up, birds migrate, nocturnal to avoid heat of day
• Examples of functional adaptations (3)

  Processes inside body like metabolism and reproduction - e.g. delayed implantation of embryos, reduced sweating, organisms in extreme winter temperatures produce a chemical in cells which acts as an antifreeze
• Extremophiles


  Organisms that live in very extreme environments, such as high temperature, pressure or salt concentration
• Example of extremophiles


  bacteria living in deep sea vents (at very high pressure, no light, acid pH)
• Photosynthetic organisms are...


  ...the producers of biomass for life on earth
• How can feeding relationships within a community be represented?

  With food chains
• Describe the structure of food chains, giving examples. (3)

  1. All food chains begin with a producer which synthesises molecules e.g. green plants, algae, which make glucose by photosynthesis

  2. Primary consumers eat producers

  3. In turn these may be eaten by secondary and then tertiary consumers
• Predators


  Consumers that eat and kill other animals
• Prey


  Animals eaten by predators
• In a stable community, the numbers of predators and prey...

  ...rise and fall in cycles
• What are 2 methods used by ecologists to determine the distribution and abundance of species in a ecosystem?

  Transects and quadrats
• Quadrat


  A square made of wire used to estimate population size of plants or slow moving animals. It may have smaller squares of wire within it.

  
• How do you use a quadrat?

  1. Choose a sample area at random (e.g. by closing your eyes, spinning around and throwing it)

  2. Count the number of organisms in the quadrat

  3. Repeat this several times

  3. Find mean number of organisms per metre squared
• How can we ensure this quadrat investigation is a fair test?

  1. Sample as many areas as possible to increase sample size and make the results more valid

  2. Use the same quadrat each time

  3. Randomly sample areas - could improve this by using a random number generator
• What is an issue with quadrat investigations?

  Time consuming and difficult if animals are present
• Sampling is also used to...

  ...measure changes in the distribution of organisms over time. Repeat measurements at regular time intervals and calculate mean. Finding the range of distribution and the median and mode of your data can also be useful.
• What factors could you investigate in an experiment about the distribution of species? (3)

  1. Trampled/untrampled grass

  2. Light levels

  3. Soil pH

  ENSURE YOU DECIDE ON YOUR SPECIES BEFORE DOING THE INVESTIGATION. (e.g. dandelions)
• Quantitative sampling


  Records the number of organisms rather than just the type
• Mean


  Sum of values divided by number of values
• Median


  The middle value of the range
• Mode


  The most frequently occuring value
• How does a line transect work?

  1. Stretch a tape between 2 points.

  2. Sample organisms at regular intervals along the line using a quadrat