7: Genetics, populations, evolution and ecosystems Flashcards
Describe the process of succession [6]
- (Colonisation by) [named] pioneer species;
- Pioneers cause change in environmental abiotic / biotic factors (give an example);
- Pioneers make the environment less hostile for new species;
- New species change/make conditions less suitable for previous species;
- Change/increase in diversity/biodiversity;
- Stability increases [population/richness/abiotic factors];
- Climax community [represented by…..];
Explain how succession results in a wide variety of fish living on coral reefs. [2]
- Increase in variety/diversity of species/plants/animals; OR Increase in number of species/populations; OR Increase in species richness / biodiversity
- Provides more/different habitats/niches OR Provides greater variety/types of food OR becomes less hostile;
Describe random sampling
[estimation of population density]
[5]
- Use a grid / split area into squares/sections OR Map the area
- Method of obtaining random coordinates / numbers, e.g. random number generator;
- Count number/frequency of plants in a quadrat;
- Large sample (20+ quadrats) AND Calculate mean/average number (per quadrat/section);
- Valid method of calculating total number of ……… e.g. mean number of plants per quadrat/section/m2 multiplied by number of quadrats/sections/m2 in area;
Describe systematic sampling [3]
- Transect/lay line/tape measure (from one side of the dune to the other);
- Place quadrats at regular intervals along the line;
- Count plants/percentage cover/abundance scale (in quadrats) OR Count plants and record where they touch line/transect;
Which type of sampling would you choose?
On a beach
RANDOM
Which type of sampling would you choose?
Along a beach
SYSTEMATIC
Which type of sampling would you choose?
In a wooded habitat
RANDOM
Which type of sampling would you choose?
On a coral reef
RANDOM
Which type of sampling would you choose?
Investigate how the distribution of species changes across a sandune away from the sea.
SYSTEMATIC
Describe how you would determine the mean percentage cover for beach grass on a sand dune. [3]
- Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
- Large number/sample of quadrats; (min 20)
- Divide total percentage by number of quadrats/samples/readings;
Describe the mark, release, recapture technique [4]
- Capture sample, mark and release;
- Appropriate method of marking suggested / method of marking does not harm fish;
- Take second sample and count marked organisms;
- No in No in Population =
(No in sample1 × No in sample2) divided by Number marked (recaptured) in sample 2;
The mark-release-recapture method can be used to estimate the size of a fish population.
Explain how. [4]
- Capture/collect sample, mark and release;
- Ensure marking is not harmful (to fish) OR Ensure marking does not affect survival (of fish);
- Allow (time for) fish to (randomly) distribute back into population before collecting a second sample;
- (Population =) number in first sample × number in second sample divided by number of marked fish in second sample/number recaptured;
Suggest why the mark-release-recapture method can produce unreliable results in very large lakes [2]
- Less chance of recapturing fish OR Unlikely fish distribute randomly/evenly;
- Fish may remain in one area OR fish may congregate
Describe how you would determine how many quadrats to use when investigating a habitat. [5]
- Calculate running mean/description of running mean;
- When enough quadrats, this shows little change/levels out (if plotted as a graph);
- Enough to carry out a statistical test;
- A large number to make sure results are reliable and representative;
- Need to make sure work can be carried out in the time available;
What is meant by carrying capacity?
- Maximum number of individuals of each species an ecosystem can support.
