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  • Population
    • the 2 main processes that occur in an ecosystem are
      • the flow of energy from one organism to another
      • the recycling of elements such as nutrients
    • Investigating population
      • Abundance - number of individuals within a given space
      • random sampling using quadrats
        • Position of quadrat
        • Size of quadrat depends on size of organism /distribution
        • Number of samples
        • layout tape measure at a right angle, obtain coordinates place quadrat at the intersection
      • Mark release recapture
        • population size = no. in 1st sample X no. in 2nd sample / no. marked in 2nd
        • assumes that:
          • the difference between marked and unmarked in the 2nd sample is the same as the population as a whole
          • individuals marked in the 1st sample distributed evenly
          • population has a definite boundary no immigration and emmigration
          • few deaths/births in the population
          • marking is not toxic/ more conspicuous
          • marking doesnt rub off
      • systematic sampling
        • more informative than random sampling
        • line transect/string stretched across the ground organisms that pass across it recorded
      • after collecting the raw data abundance can be measured - frequency - likelihood of occurrence and percentage cover
    • Variation in population size
      • Abiotic factors that limit the size
        • Temperature - further away from the optimum enzymes work less effectively so metabolic rate is reduced - pop. grows more slowley
        • Light - photosynthesis increases as light intensity increases - more plants, more food for animals pop. grows
        • pH - enzymes will work less effectively
        • water and humidity - humidity affects transpiration rates - low humidity water evaporates from plants and animals
      • Biotic factors that limit populations size
        • Predation - predators eat prey, prey pop. decreases less food for predator thus predator pop deacreases no predators to eat prey thus prey pop. increases then predator po increases more food
      • Human population
        • population growth = births + immigration - deaths + emmigration
        • percentage population growth = population change/population at the start X 100
        • Factors affecting birth rate
          • Age, life expectancy at birth food supply, safe drinking and sanitation, medical care, natural disease and war
        • Death rate = number of deaths per year/total pop. in that same year X 1000
        • population structure
          • Demographic transition - transitioning through to industrial revolution
          • stable = birth rate and death rate in balance increasing population = high birth rate and high death rate wider base and narrow tip decreasing = lower birth rate and lower death rate
          • survival curve plots the percentage of people still alive after an event or % of pop. alive at different ages
            • average life expectancy is the age at which 50% of individuals still alive
  • population has a definite boundary no immigration and emmigration


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