| Sampling at random method | - Set up a grid – (10m X 10m would be reasonable)
- Generate random co-ordinates using a random number table (to prevent bias)
- Place the bottom left hand corner of a 1m X 1m quadrat at the generated coordinates
- Measure the limpet closest to the centre (to eliminate bias)
- Repeat for 30 limpets (30 is good for statistical analysis !) this allows you to calculate a reliable mean.
- To make data valid – same species of limpet, same height from sea level, same time of year |
| Mark-release-recapture | - A method of estimating mobile populations |
| Mark-release-recapture process | - Capture first sample
- Mark the sample e.g. tag on foot (must be non harming and not make the animal conspicuous to predators)
- Release the sample
- Allow the sample to mix with the population
- Capture second sample
- Count the number of marked and unmarked |
| The size of the population is then calculated as follows: | estimated population size =
total number of individuals in the first sample x total number of individuals in the second sample
/number of marked individuals recaptured |
| This technique relies on a number of assumptions: | - No migration
- No deaths or births
- All specimens have an equal chance of being caught |
| To make a valid estimation | - Mark does not harm animal
- Mark does not make animal more susceptible to predators
- Mark does not come off
- Animals are not trap happy/shy
- Animals integrate fully into population |
| When to use log | - Use of log when there is a large difference between the numbers |
| Four basic population parameters | - Emigration
- Morality
- Natality
- Immigration |
| Population parameters | - Affect population density |
| Birth rate calculation | Birth rate = no. of births per year/total pop that yr x 1000 |
| Why per 1000? | per 1000 to compare different country pops |
| Factors that lead to increased brith rate | - Lack of contraception
- Religious/social reasons
- Economic instability |
| Factors leading to decreased birth rate | - Economic stability
- Improved contraception
- Political reasons (e.g. china) |
| Death rate calculation | Death rate = no. of deaths per yr/total deaths that yr x1000 |
| Factors leading to increased death rate | - Natural disasters
- Famine
- Disease |
| Factors leading to decreased death rate | - Improved sanitation
- Improved medical care
- Improved nutrition |
| Average life expectancy | - The age 50% of pop is still alive |
| Demographics | - Study of pops |
| Age population pyramid | - Shows % of males + females alive at different ages |
| Survival curve | - Graph to show % of pop alive at each age |
| Demographic transition | - A model to show how pops change over time |
| Stable population | - Pop where birth rate = death rate |
| How to measure abundance | When species is clearly identifiable
Count
When species too many o cannot identify individual plants
% cover (so area of the plant divided by the total cover of quadrat x100) |
| Species richness | - No. of species |
| Species diversity | - No. of each species |
| Ecosystem | - Interactions between abiotic + biotic factors in a specific area |
| Population | - All of a group of interbreeding organisms of are species in a specific habitiat |
| Community | - All of the population in a specific area at a specific time |
| Habitat | - The place where an organism lives |
| Ecological niche | - The role of an organism in its environment |
| How many quadrats (for measuring species present)? | - Plot a graph of no. of quadrats against the cumulative no. of species, see where it plateaus, select number before that - that is the right no. of qudrats as beyond this it is pointless + waste of time |
| Transects | - Used for sampling a transition e.g. light to shaded area
- 2 types: belt + line |
| Process of using transects | - Lay out 50m tape along the environmental gradient from e.g. exposed to sheltered area
- Every 1m record species
- To improve: can use quadrat to turn it into a belt and therefore measure abundance
- Repeat, statistical test |
| Increasing relability | - Large sample - representative
- Repeat many times - get reliable mean |
