Unit 4 Populations

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1.1 Populations and ecosystems
Key Words Definition
Ecology The study of the inter-relationships between
organisms and their environment
Abiotic Non-living factors e.g. Climate
Biotic Living factors e.g. competition
Biosphere Life supporting layer of land, air and water
Ecosystem The way the biotic and abiotic features of a specific
area interact
Population A group of individuals of the same species that
occupy the same habitat at the same time
Community All the populations of different organisms interacting
in the same place at the same time
Habitats Where a community of organisms live
Ecological Niche Describes how an organism fits into an environment
i.e. where it lives and what it does there
1.2 Investigating Populations
There are 3 factorsto consider when using quadrats:
The size of the quadrat to use - depends on size of animals being
investigated and the area of land
The number of sample quadrats - the more quadrat samples taken, the
more reliable the results
The position of each quadrat - Random Sampling should be used
How to obtain random sampling
1. Lay out a line transect
2. Obtain a series of coordinates by using a random number generator on
3. Place quadrat at the intersection of each pair of coordinates and record
the species within it
Measuring Abundance

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Percentage Cover
To obtain reliable results, there should be a large sample size,many quadrats
used and the mean of all samples is obtained
Mark-Release-Recapture Technique
1. Take a sample
2. Count and mark them
3. Release
4. Capture a second sample
5. Count the number of them and how many are marked
1.3 Variation In Population Size
Population Curve
1. A period of slow growth
2. A period of rapid growth as individuals reproduce - population size
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H- Affects enzymes and how efficiently they work
Water and humidity - Where water is scarce, populations are small and
consist of organisms that are well adapted to
survive there. Humidity affects transpiration rates
1.4 Competition
Intraspecific Competition
Occurs when individuals of the SAMEspecies compete with each other
Interspecific Competition
When individuals of DIFFERENT species compete with each other
One species will increase in size where the otherwill eventually
This is known as the competitive exclusion principle
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Factors affecting Birth Rates
Economic Conditions - LICs tend to have higher birth rates
Cultural and Religious Backgrounds - Some religions are opposed to
birth control
Social pressures and conditions - In some areas, large families
improves social standing
Birth Control - The extent to which contraception and abortion are
Political Factors - Governments influence birth rate through taxation
Factors affecting Death Rates
Age Profile - if there are more elderly, death rate will be high
Life expectancy at birth - those in…read more


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