Population
- Created by: maryam
- Created on: 12-02-15 11:58
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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
- Abiotic factors that limit the size
- the 2 main processes that occur in an ecosystem are
- population has a definite boundary no immigration and emmigration
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