populations in ecosystems

• ecosystem:

  • all the biotic and abiotic components and their interactions
• population:

  • individuals from the same species living in the same habit
• carrying capacity:

  • the maximum size of a population the ecosystem can support
• biotic:

  • living factors
• abiotic:

  • non-living factors
• community

  • populations of different species within a given ecosystem
• habitat:

  • the place where an organism lives
• trophic level:

  • primary, secondary, tertiary in food chain
• niche:

  • refers to where an organism lives and what it does there
• interdependence:

  • species relying on each other to carry out life processes
• reasons why population growth is limited:

  • availability of food
  • shelter
  • light
  • water
  • oxygen
  • accumulation of toxic waste
  • predators
  • disease
• abiotic factors affecting population growth

  • temperature: optimum temperature/pH for enzyme activity. if temperature significantly differs from the optimum temperature, organisms use a lot of energy to maintain body temperature, leaving less energy to grow, reducing reproductive rate. carrying capacity is reduced
• abiotic factors affecting population growth p2:

  • light: increased photosynthesis, increased growth rate, more seeds produced, increasing carrying capacity. more plants for consumers to feed on, increasing their carrying capacity
  • pH: enzyme activity
  • water: humidity affects transpiration rate in plants and evaporatio of water in animals
• intraspecific competition:

  • competition that occurs within the same species
  • determines the size of a population
  • availability of resources affects intraspecific competition
• interspecific competition:

  • occurs between different species
  • when there is competition between two species, one will have a competitive advantage over the other.
  • this population will grow in numbers, while the other one diminishes, leading to complete removal of the outcompeted population (competitive exclusion principle)
• predation and its effects on population size

  • predators eat their prey, reducing the population of prey
  • fewer prey available, so predators compete with each other fro food sources
  • predator population is reduced as some predators are unable to feed on prey enough for survival and reproduction
  • fewer predators, fewer prey are eaten, more prey survive and reproduce, increasing prey population
  • more prey available as food source, so predator population also increases
• selection pressure is the force that acts on an organism to change its phenotype
• types of quadrat:

  • frame quadrat
  • point quadrat
• frame quadrat are usually 0.5m x 0.5m
• sampling

  • lay out two long measuring tapes at 90 degree angles in the study area
  • using a random number generator, obtain a set of coordinates
  • place the quadrat at the coordinates and record the species within it
• systematic sampling along belt transects:

  • stretch tape across the ground in a straight line
  • lay the frame quadrat alongside the tape and record species within it
  • move it along the line so that the species are recorded in a continuous belt
• for reliable results

  • sample size must be large
  • many quadrats must be used
  • mean of all samples must be obtained
• mark release recapture

  • known number of animals are caught and marked
  • marked animals are released back into the community
  • some time later, randomly collect a given number of individuals and the number of marked animals are recorded
• calculating population size

  A) estimated population size

  B) total number of individuals in first sample

  C) total number of individuals in second sample

  D) number of marked animals recaptured

  
• assumptions made:

  • marked individuals when released, distribute themselves evenly amongst the population
  • marking does not affect their chances of survival
  • no immigration or emigration of population
  • few deaths and births within population
  • mark does not come off
  • ratio of marked to unmarked in second sample is same as ratio of marked to unmarked in whole population