🔴️Population
All organisms of 1 species in a habitat
Community
All of the populations of all the species
🔴️How to use quadrats to estimate the number of bluebells in a field
- Lay out 2 tape measures at right angles.
- Then find coordinates using a random number generator
- Count number of plants in a quadrat and repeat this many times. Do this for different locations
- Calculate mean bluebells per quadrat
- Divide the mean by the area to get bluebells/m2.
- Multiply this by the total area of the field to estimate the bluebells present.
🔴️How would you decide on the number of quadrats to use in order to collect representative data for number of plants
- Do enough to carry out statistical test
- Try to do a very large number to make sure the results are reliable
- but not too much as we need to make sure it can be done in the time allotted
- Calculate a running mean of species
- When the quadrats are enough, it levels out (if plotted): species against quadrat
🔴️Explain why we should measure the population size immediately when using the MCR
- Rules out changes in the population
- This could be due to births/deaths/migration
🔴️Ecological niche
- Refers to an organism’s feeding role (what it eats)
- And its abiotic role (where it lives in terms of conditions it needs)
🔴️Assumptions made in Mark Capture
- Marking doesn’t wear off
- Marking isn’t toxic or conspicuous
- No births or deaths
- No immigration and emigration
- Mixes randomly with population
🔴️How can you tell if 2 organisms are the same species
- Breed them together if they produce fertile offspring then they’re the same species
What information is required in order to calculate the growth rate of a population?
- Birth rate and death rate
- Emigration and Immigration;
Describe one method the scientists could have used to ensure that the sites were chosen without bias.
- Number the sites
- Use a random number generator
Factors which lead to a decrease in the death rate in a human population.
- Improved medical care
- Improved quality and quantity food
- Improved sanitation so less disease
When looking at survival curve, look out for:
1 Death and Birth rate.
2 Average life expectancy
A girl collected 17 lizards and marked them before releasing them back into the same area. Later, she collected 20 lizards, 10 of which were marked.Calculate the number of sand lizards
No= (N1 x N2)/ N3
No= (17x 20)/10
Using the mark-release-recapture method, describe how to estimate the number of one species of fish in the lake.
1 Capture sample using a trap. Count them, then mark and release (N1)
- Make sure marking does not harm fish or make them conspicuous
- Wait SUFFICIENT time so they reintegrate into population,
4 Then take second sample (N2) and count marked organisms (N3)
- Calculation
Why won’t the MCR method work if there are many births?
- The calculation only works if the population is constant.
- Births would change the population between the first and second sample
How to use transect lines to measure the population of grass
- Lie a tape measure from one side of the field to another
- Place quadrats at regular intervals along the line
- Count plants in quadrats and record where they touch transect
- Calculate per M2
Birth rate
Births per thousand per year
Why won’t the MCR work if birds are forming separate territiories
1 Birds in territories not mixing with population
2 Territory sample not representative of population
Death rate
Number of deaths per 1000 each year
What factors affect birth rate?
- economic: availability of contraceptives/ pre-natal care / better nutrition of mother;
- education on family planning
- cultural/governmental influence on family size
Changes that occur to birth and death rate during demographic transition
-Birth and death rate fall and then levels out (stabilises)
Changes in the size of the population during a demographic transition
-Population size increases then levels out (stabalises)
Ethical issues involving fieldwork?
- People walking may cause soil erosion.
- This can be combated by restricting where you walk to a specific area being studied
Why does the pest population fluctuates due to predators
- As pest numbers increase more food for predators, so they increase;
- Increased predation of pests reduces numbers;
- Low number of pests results in less food for predators, so their numbers decrease;
- Low predator numbers allow pest population to reproduce as fewer are eaten;
