7.4 populations in ecosystems

• what is a community

  all the populations of different species living in the same place (habitat) at the same time
• what is an ecosystem

  a community and the non-living (abiotic) components of its environment

  ecosystems can range in size from very small to very large, they are dynamic systems (populations rise/fall overtime)
• what is a niche

  the specific role of a specific species within its habitat e.g what it eats, where and when it feeds

  governed by its adaptation to both abiotic (non-living) and biotic (living) conditions
• explain the advantages 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 e.g light intensity, temperature, soil pH & mineral content, humidity

  interactions between organisms - interspecific competition (between organisms of different species), intraspecific competition (between organisms of the same species), predation (predators kill and eat other animals, called prey)
• explain how abiotic factors may affect population size/carrying capacity

  if conditions favourable, organisms more likely to survive & reproduce so increasing carrying capacity

  e.g increasing light intensity increases 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 well adapted species declines

  potentially leading to extinction
• explain how INTRAspecific competition may affect population size

  as population size increases, resources per organism decreases so competition increases

  so chances of survival and reproduction decreases so population size decreases

  as population size decreases, resource availability per organism increases so competition decreases

  so chances of survival and reproduction increases so pollution size increases
• explain the changes which occur in populations of predators and prey

  prey population increases so predators have more food

  so more predators survive and reproduce

  predator population increases so more prey killed and eaten

  so less prey survive and reproduce

  prey population decreases so predators have less food|

  so predators less likely to survive and reproduce

  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

  divide area into a grid/squares e.g place 2 tape measures at right angles

  generate a pair of coordinates using a random number generator e.g on a calculator

  place a quadrat here and count number/frequency of (named species)

  repeat a large number of times (10 or more) and calculate mean per quadrat

  population size=(total area of habitat/quadrat area) x mean per quadrat
• describe how the mark-release-recapture method can be used to estimate the size of a population of motile organisms

  capture sample of species, mark and release

  ensure marking is not harmful/does not affect survival rate

  allow time for organisms to randomly distribute before collecting second sample

  population=(number in sample 1 x number in sample 2)/number marked in sample 2
• what assumptions does the mark-release-recapture method make

  sufficient time for marked individuals to mix/distribute evenly within the population

  marking not removed and doesn't affect chances of survival/predation

  limited/no immigration/emigration

  no/few births/deaths/breeding/change in population size (or birth and death rate are equal)
• suggest why the mark-release-recapture method can produce unreliable results in very large areas

  unlikely that organisms will distribute randomly/evenly

  less chance of recapturing organisms (that were marked initially)
• describe and explain how primary succession occurs

  colonisation by pioneer species (first to colonise)

  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)

  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

  as succession goes on biodiversity increases

  climax community reached which is final stable community (no further succession)
• succession

  change in a community overtime due to change in abiotic factors/species
• describe features of a climax community

  same species present/stable community over a long time

  abiotic factors (fairly) constant over time

  populations (fairly) stable (around carrying capacity)
• explain how conservation of habitats involves management of succession

  further succession can be prevented to stop a climax community forming

  by removing or preventing growth of species associated with 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 habiats/niches are not lost
• describe the conflict between human needs and conservation as well as the importance of managing this

  human demands for natural resources (e.g timber) is leading to habit 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