Topic 13 - Populations in Ecosystems Flashcards
Why is a large sample size important?
Increases the reliability of the data.
Why are repeats important?
More reliable means.
What are point quadrats?
- Frequency
- Horizontal bar supported by 2 legs.
- Holes that long pins can be dropped in.
- Each species that the pin touches is recorded.
What are frame quadrats?
- Percentage cover.
- Square frame divided into equally sized subdivisions.
- Abundance of each species within quadrat recorded.
What are three things to consider when using quadrats?
1) Size of quadrat - depends on the size of the species being measured.
2) Number of samples being taken
3) Position of each quadrat - to produce unbiased results, random sampling must be used.
Estimating population size: Randomly placed quadrats
- Is used in a fairly uniform area.
- Avoids bias.
- Data is therefore reliable.
- Allows the use of statistical tests.
Random sampling:
1) Set out a grid.
2) Obtain random pair of coordinates using random number generator.
3) Place quadrat at pair of coordinates.
4) Count/collect organisms.
5) Record data and repeat at least 10 times.
Estimating population size 2: Quadrats along a belt transect
- Appropriate when an area varies greatly over a relatively short distance = an environmental gradient is present.
Method: Systematic sampling
1) Lay out tape measure and place a frame quadrat at right angles to line at regular intervals.
2) Using a point quadrat, lower pins into vegetation and record the organisms.
3) Flip the frame quadrat over on the opposite side.
How do you measure the abundance (number of individual species within a given area)?
Frequency of a species = (Number of quadrats containing the species / total number of quadrats) x 100
What is the Mark Release Recapture method?
Used if wanting to study animals that move without harming them.
1) Capture a number of animals.
2) Carefully mark them.
3) Release them and allow time to reintegrate with population.
4) Collect 2nd sample.
5) Count and record number of marked and unmarked organisms.
6) Use MRR formula to estimate population size.
Estimated total population =(No. of organisms in sample 1 x No. of organisms in sample 2) / No. of marked organisms recaptured
What assumptions are made with the mark-release-recapture method?
- Proportion of marked:unmarked in 2nd sample is same as whole population.
- Marked individuals mix fully with unmarked.
- No immigration or emigration.
- No births or deaths.
- Method of marking doesn’t harm the animal.
- Mark can’t be removed.
What is succession?
Change in community over time due to changes in abiotic factors and/or species present.
What are the stages of primary succession?
1) Pioneer species colonise area.
2) Weathering of rock and death/decomposition of pioneer produces sand or soil.
3) Pioneer species die and decompose, adding nutrients to the soil.
4) Other plants like mosses, ferns etc start to colonise the area, increasing the biodiversity. Abiotic factors change (e.g. humidity increases).
5) Larger plants like shrubs and trees colonise.
6) Climax community is reached, there is a balanced equilibrium of species.
Why do pioneer species gradually become replaced by other plant species during succession?
They become outcompeted for resources by other species.
What is a climax community?
A stable community where no further succession occurs.
What is an ecosystem?
Made up of a community and all abiotic factors of environment.
