Ecology

• Community = all the populations of different species living together in a habitat
• ecosystem = the community of organisms & non-living components of an area & their interactions
• population = all organisms of the same species living with one another in a habitat
• habitat = the place where an organism lives
• abiotic factors = the non-living aspects of an ecosystem

  • eg temperature, light intensity, moisture, soil pH, carbon dioxide & oxygen levels etc
• biotic factors = the living components of an ecosystem

  • eg food availability, pathogens, predators & other species
• distribution = the spread of living organisms in an ecosystem

  • it is affected by environmental changes which may be seasonal, geographic or man-made
• food chain = describes the feeding relationships between organisms & the resultant stages of biomass transfer
• food web = a network of food chains that shows how energy flows through an entire ecosystem
• Interactions between organisms include feeding & competition
• feeding:

  • plants, animals & decomposers are continually recycling the same nutrients throughout an ecosystem
• competition:

  • animals compete for food, shelter, mates & nesting sites
  • plants compete for carbon dioxide, mineral ions, light & water
• interactions between organisms & the environment:

  • plants = absorb mineral ions, co2 & water from environment; plants also give off water vapour & oxygen into environment
  • animals use materials from environment to build shelters
  • temp of environment affects processes within organisms = processes within organisms also affect temperature of environment as all produce heat
• quadrats are used to estimate the abundance of organisms within a large area by looking at a few small samples
• quadrats:

  • place quadrat randomly on ground & count organisms within quadrat, record number
  • repeat at different areas before finding mean
  • find area of quadrat & area of sample site
  • find scale factor = area of site / area of quadrat
  • find estimated population size = mean no of organisms x scale factor
• Abiotic factors:

  • light intensity = required for photosynthesis, affects rate of plant growth
  • temperature = affects rate of photosynthesis
  • moisture levels = all plants & animals need water to survive
  • Soil pH & mineral content = affects rate of decay & therefore how fast mineral ions return to soil. Different plants need different nutrient levels
• biotic factors:

  • food availability = more food allows population to increase
  • New predators
  • New pathogens = population has no resistance & can be wiped out quickly
  • Competition = if one species is better adapted, it will outcompete other species until numbers decrease
• Decomposers are bacteria & fungi that break down dead animal’s body & waste for energy, using enzymes
• Producers = organisms that make their own food by photosynthesis, eg plants & algae
• primary consumers = herbivores that only eat plants (producers)
• secondary consumers = carnivores that eat primary consumers
• tertiary consumers = carnivores that eat secondary consumers

  • they have no predators & so are called apex predators
• Food webs are a collection different food chains to show how all the organisms in a habitat interact = shows interdependence & therefore how population number changes can effect entire ecosystem

  
• pyramids of numbers show the population of each organism at each trophic level of the food chain

  • producers are at the bottom & usually get smaller as you go up

  
• Pyramids of biomass show relative biomass at each trophic level

  • shows relative dry mass of material at each level
  • there is less biomass as you move up trophic levels
• not all food converted by an animal is converted into biomass = therefore the organism in the level above in a pyramid of biomass will always be higher

  • as not all the organism eaten can be consumed & converted into biomass
• Producers transfer 1% of incident energy from light for photosynthesis as not all light lands on photosynthesising areas
• Approximately 10% of biomass of each trophic level is transferred as:

  • not all biomass can be eaten
  • not all biomass is converted into biomass of animal eating = as glucose used in respiration, producing waste co2; urea released in urine; biomass lost as faeces
  • energy used for movement, repair of cells or lost as heat to surroundings
• As less biomass is transferred each time, there is often:

  • limited number of trophic levels
  • less animals in higher levels
• carbon is a component of all major biological molecules
• stages of carbon cycle:

  • photosynthesis
  • respiration
  • fossilisation
  • feeding & assimilation
  • combustion
• photosynthesis = carbon dioxide are absorbed by plants & used during photosynthesis to make glucose (containing carbon atoms)
• respiration = produces carbon dioxide as glucose, then broken down using oxygen to release energy
• fossilisation = some living things don’t fully decay when dead due to soil conditions

  • fossil fuels are formed
• feeding & assimilation = pass carbon atoms already present in organic compounds along food chains
• combustion = releases carbon dioxide into atmosphere when fossil fuels are burned