Populations in ecosystems

• What is a Community?

  All the populations of different species living in the same habitat at the same time
• What is an Ecosystem?

  • A community and the abiotic components of its environment
  • They are dynamic (populations rise and fall over time)
• What is a Niche?

  • The specific role of a species within a habitat e.g. what it eats, where and when it feeds
  • Governed by its adaptation to both abiotic and biotic conditions
• Explain the advantage of species occupying different Niches:

  • Less competition for food / resources
  • If two species tried to occupy the same niche one would outcompete the other
• What is carrying capacity?

  The maximum (stable) population size of a species that an ecosystem can support
• List the factors that influence carrying capacity:

  Abiotic Factors:

  • Light intensity
  • Temperature
  • Soil pH and mineral content
  • Humidity

  Interactions between organisms:

  • Intraspecific Competition
  • Interspecific Competition
  • Predation
• Explain how abiotic factors may affect population size / carrying capacity:

  • If conditions are favourable organisms are more likely to survive and reproduce -> increasing carrying capacity
  • E.g. increasing light intensity increases the rate of photosynthesis in plants

  -This increases carrying capacity of a variety of plant species

  -So increases the number and variety of habitats, niches and food sources for animals

  -So increasing carrying capacity of a variety of animal species
• Explain how interspecific competition may affect population size:

  • Reduces [named resource] available to both species, limiting their chances of survival and reproduction

  -So reduces population size of both species

  • If one species is better adapted it will outcompete the other

  -So population size of less adapted species decline potentially leading to extinction
• Explain how intraspecific competition may affect population size:

  1)As population size increases, resource availability per organism decreases, so competition increases

  • So chances of survival and reproduction decrease -> population size decreases

  2)As population size decreases, resource availability per organisms increases, so competition decreases

  • So chance of survival and reproduction increase -> population size increases
• Explain the changes which occur in populations of predators and prey:

  1)Prey population increases so predators have more food

  • So more predators survive and reproduce

  2)Predator population increases so more prey are killed and eaten

  • So less prey survive and reproduce

  3)Prey population decreases so predators have less food

  • So less predators survive and reproduce

  4)Predator population decreases so less prey killed and eaten

  • So more prey survive and reproduce (cycle repeats)
• Describe how the size of a population of slow-moving or non-motile organisms can be estimated:

  1. Divide the area into a grid
  2. Generate a pair of coordinates using a random number generator
  3. Place a quadrat here and count frequency of [named species]
  4. Repeat a large number of time (10 or more) and calculate a mean per quadrat
  5. Population size = (total area of habitat / quadrat area) x mean per quadrat
• Describe how the Capture-Recapture method can be used to estimate the size of a population of motile organisms:

  • Capture sample of species
  • Ensure marking does not affect survival
  • Allow time for organisms to randomly distribute before collecting sample
  • Population = (number in sample 1 x number in sample 2) / number marked in sample 2
• What assumptions does the capture-recapture method make?

  • Sufficient time for marked individuals to distribute evenly within the population
  • Marking not removed and doesn't affect chances of survival / predation
  • Limited Migration
  • No / few births / deaths / breeding / change in population size
• Suggest why the Capture-Recapture method can produce unreliable results:

  • Unlikely that organisms will distribute evenly / randomly
  • Less chance of recapturing organisms
• What is Succession?

  Change in community over time due to change in abiotic features / species
• Describe and explain how primary succession occurs:

  1)Colonisation by pioneer species (first to colonise)

  2)Pioneer species (and other species at each stage in succession) change abiotic conditions

  • E.g. they die and decompose, forming soil which retains water (humus / organic matter)

  3)So environment becomes less hostile / more suitable for other species with different adaptations and less suitable for previous species, so better adapted species outcompete previous species

  4)As succession goes on biodiversity increases

  5)Climax community reached - final stable community
• Describe features of a climax community:

  • Same species present / stable community over a long time
  • Abiotic factors constant over time
  • Populations stable (around carrying capacity)
• Explain how conservation of habitats involves management of succession:

  • Further succession can be prevented to stop a climax community from forming - by removing or preventing growth of species associated with later later stages e.g. by allowing grazing
  • This preserves an ecosystem at a certain point / in its current stage of succession (plagioclimax)
  • So early species are not outcompeted by later species and habitats / niches are not lost
• Describe the conflict between human needs and conservation as well as the importance of managing this:

  • Human demand for natural resources is leading to habitat destruction / biodiversity loss
  • Conservation is needed to protect habitats / niches / species / biodiversity
  • Management of this conflict maintains the sustainability of natural resources - meeting current needs without compromising the ability of future generations to meet theirs
• What are methods of conservation?

  • Controlled Burning
  • Coppicing
  • Hedgerows
  • Grazing
  • Seed Banks
  • Captive Breeding
  • Fishing Quotas
  • Protected Areas
• Controlled Burning:

  Benefits:

  • Necessary for new growth in some areas
  • Prevents climax community

  Issues:

  • CO2 release
  • Burning can get out of control
• Coppicing:

  Benefits:

  • Stops climax community - increases biodiversity
  • Allows light penetration

  Issues:

  • Humans should not be involved
  • Need some climax
• Hedgerows:

  Benefits:

  • Allow species movement
  • Prevents monoculture
  • Greater food sources

  Issues:

  • Less land for agriculture
  • Pests
  • Reduce yield
  • Have to be maintained
• Grazing:

  Benefits:

  • Prevents movement through succession - Plagioclimax

  Issues:

  • Reduces forage quality
• Seed Banks:

  Benefits:

  • Backup in case of extinction
  • Breeding programmes increase genetic diversity
  • Stored indefinitely

  Issues:

  • Expensive to maintain
  • Most focus on agricultural plants, risking other
  • Many plants reproduce asexually
• Captive Breeding:

  Benefits:

  • Protects endangered species
  • Increases genetic diversity
  • Help public awareness

  Issues:

  • Hard to reintroduce into environment
  • Can disrupt climax community
  • Stress and unnatural behaviours in captivity
• Fishing Quotas:

  Benefits:

  • Limiting quantity or species of fish that can be caught
  • Do not deplete marine resources

  Issues:

  • Impossible to enforce
  • Exploitation of other species
• Protected Areas:

  Benefits:

  • Habitat conservation
  • Maintains biodiversity
  • Can be used for research
  • People can explore nature

  Issues:

  • Often tourist destinations
  • Can't represent all habitats
  • Isolated - Reducing genetic diversity