Topic 7

• What is an ecosystem?


  All of the organisms living in a certain community
• What is a community?


  Populations of different species living in the same environment or habitat
• Examples of abiotic factors:

  • Light intensity
  • Amount of water
  • $CO_2$ concentration
  • $O_2$ concentration
  • wind intensity + direction
• Examples of biotic factors:

  • Food availability
  • New predators arriving
  • New pathogens
  • Competition
• What can biotic and abiotic factors lead to?

  • competition
  • reduction in prey species/ predator species
  • Migration
  • Natural selection
  • Extinction
• What is a niche?


  The organism's role in the ecosystem or community. Each organism must be different if they live in the same area to avoid competition.
• What can niches differ by?

  • what they eat
  • where they eat
  • when they eat
  • how they catch or find food
  • what time of year they breed
  • temperature range they can survive in
• Adaptation:

  • a feature that members of the same species have that increases their chance of survival + reproduction
  • There is three types --> structural (anatomy), behavioural + functional (physiology)
• What is carrying capacity?


  Maximum, stable population size of a species that an ecosystem can support
• Exponential growth:

  • continuous growth in population size
  • only possible where there is an infinite supply of resources (in real ecosystems this is not the case)
• Limited resources:

  • Individuals are competing for resources
  • Adaptations allow species to gain resources better than other species (these species are more likely to reproduce)
  • Reproduction causes the size of a population to increase
• Abiotic factors affecting variation in population size:

  • amount of resources available - light, space + water
  • Temperature
  • Chemical composition of their surroundings - soil pH
  • suitable --> population increases, successful breeding, fast growth
  • not suitable --> slow growth, less successful breeding, population decreases
• Biotic factors affecting variation in population size:

  • intraspecific competition (same species)
  • interspecific competition (different species)
• What is abundance?

  number of individuals of one species in a particular area. Can be estimated by counting the number of individuals in a sample.
• What is frequency?


  number of samples a species is recorded in
• What is percentage cover (non-mobile/slow moving species)?


  how much of the area being investigated is covered by a species
• What is distribution?


  where a particular species is within the area you're investigating
• Types of quadrats:

  • frame quadrat (square)
  • point quadrat
• What are things to consider about quadrats?

  • size of quadrat - depends on size of species
  • number of samples - more samples, more reliable
  • position of each quadrat - try to be unbiased
• Transects:

  • belt transect
  • interrupted belt transect
  • transect sampling is more of a systematic technique but can be adapted to a random technique if needed
• Mark-release-recapture:

  • measures abundance of motile organisms
  • capture a sample of species
  • count them
  • mark them in a harmless way
  • release them back into habitat
  • wait a suitable length of time
  • take a second sample from the same population
  • count how many of second sample are marked
• What is the equation for estimated population size?

  estimated pop size = number caught in 1st sample x number caught in 2nd sample/number marked in 2nd sample
• Accuracy:

  • marked sample has time to mix back with population
  • marking doesn't affect chance of survival for the organism
  • no changes in population due to births, deaths + migration during period of study
  • ethical concerns = organisms need to be handled carefully for as little time as possible to minimise stress
• What is succession?


  the process by which an ecosystem changes over time. Ecosystems are always changing due to complex interactions between organisms and their environment
• Dynamic ecosystems:

  • are affected by change in structure + composition of communities within them
  • can be affected by environmental disturbances (e.g. volcanoes and earthquakes)
  • together these factors make ecosystems dynamic
  • over time, an ecosystem can change dramatically
• What is the climax community?


  the ecosystem that results from succession
• Human impacts:

  • prevents succession
  • stops a climax community forming
  • when it is stopped artificially climax community is called plagioclimax
• climatic climax community:

  • climax community for a specific climate
  • species within an ecosystem depends on the climate within the ecosystem
• What is conservation?

  protection and management of species and habitats in a sustainable way
• Main reasons for conservation:

  • personal - maintain our planet, our life support system
  • ethical - should be able to coexist with other species who have occupied Earth for longer
  • Economic - living organisms have a huge gene pool with the capacity to make millions of substances that could be valuable for the future
  • cultural + aesthetic - habitats + organisms enrich our lives adding variety and interest
• Managing grasslands:

  • many rare + protected species can be found in grasslands
  • without management they would quickly turn into shrubs + then woodland by succession
  • managing them prevents succession from taking place
• Managing techniques:

  • grazing - animals graze to prevent growth of vegetation
  • burning - kills vegetation + allows secondary succession to take place
• Managing heather moors:

  • provide an ideal habitat for game birds like red grouse
  • red grouse feed on young shoots + nest on longer heather
  • is burnt every 12 years to manage succession
  • if left to succession it would be unsuitable for red grouse
• Need for conservation:

  • humans pose a threat to biodiversity
  • human threats - population growth + resource exploitation
  • helps oppose effects from humans
  • protects ecosystems + species within them, increasing biodiversity
• Methods of conservation:

  • protected areas (e.g. national parks) - protect habitats
  • seedbanks - store seeds to avoid extinction
  • protected species - avoid extinction
  • fishing quotas - prevent overfishing
• Conflict - needs + conservation:

  • exists between human needs and conservation
  • conservation can be expensive
  • human population growth means there's a high demand for resources (food, space). Conservation can make meeting these demands difficult
• primary succession:

  • takes place of newly exposed/newly formed land
  • land is colonised by living things
  • pioneer species - first species to colonise exposed land, are specialised due to harsh conditions of land (no soil so limited nutrients and water)
  • soil formation - dead pioneer species decompose to contribute, they break down substances
  • colonisation by new species - less hostile due to soil formation, new species colonise less hostile land
  • altering abiotic conditions - when species die, soil composition changes, new species may alter the environment so pioneer species can no longer survive
• Secondary succession:

  • takes place where part of an ecosystem was disturbed + remnants of previous community remains
  • pioneer species - colonise damaged land, tend to be larger, environment is more nutrient-rich as there is already soil
  • colonisation by new species - soil becomes more nutrient-rich + stable as pioneer species die, new species out-compete the older species + become dominant, competition cause shift in species present
  • increased complexity
  • climax community - reaches an equilibrium point, is where species composition is no longer changing + resembles previous community
• What is allopathic speciation?

  A form of speciation that occurs when two populations become geographically isolated.