Speciation, Investigating Populations & Succession

Question 1

Describe the process of succession

Answer 1

Pioneers cause change in abiotic/biotic factors (give an example e.g INCREASE SOIL DEPTH);
• 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;

Question 2

Explain how succession results in a wide variety of fish living on coral reefs

Answer 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;

Question 3

Describe random sampling [estimation of population density]

Answer 3

Use a grid / split area into squares/sections;
• Method of obtaining random coordinates / numbers, e.g. calculator/ computer/random numbers table/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 wood;

Question 4

Describe systematic sampling

Answer 4

• 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;

Question 5

Describe how you would determine the mean
percentage cover for beach grass on a sand dune.

Answer 5

• 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;

Question 6

Describe a method that could be used to determine the
mean percentage cover of algae on a coral reef.

Answer 6

• Method of randomly determining position (of quadrats) e.g. random numbers table/generator;
• Large number/sample of quadrats; (>20)
• Divide total percentage by number of quadrats/samples/ readings;

Question 7

Describe the mark, release, recapture technique

Answer 7

• Capture sample, mark and release;
• Appropriate method of marking suggested / method of marking does not harm fish;
• Take second sample and count marked organisms;
• Number in Population =
[No. in sample1 x No. in sample2]

Question 8

Describe how you would determine how many quadrats to use when investigating a habitat.

Answer 8

• Calculate RUNNING MEAN;
. When enough quadrats, this shows little change/levels out (plotted as a graph);
• Enough to carry out a statistical test:
• A large number to make sure results are reliable;
• Investigation must be done in set time frame

Question 9

Suggest why the mark-release-recapture method can produce unreliable results in very large lakes

Answer 9

• Less chance of recapturing fish OR Unlikely fish distribute randomly/evenly;
• Fish may remain in one area
OR fish may congregate

Question 10

The mark-release-recapture method can be used to estimate the size of a fish population.
Explain how.

Answer 10

• Capture, mark and release sample;
. Ensure marking is not harmful to fish/affect survival
• Allow (time for) fish to (randomly) distribute before collecting a second sample;
• Population =
No. 1st sample X No. 2nd sample
/ divided by no. Fish marked in 2nd sample/recaptured

Question 11

Describe what is meant by speciation (ALLOPATRIC) (5)

Answer 11

• geographical isolation;
• separate gene pools/no interbreeding (between populations);
• variation due to mutation;
• different environmental/abiotic/biotic conditions/selection pressures;
• selection for different/advantageous alleles;
• differential reproductive success /(organisms) survive and reproduce;
• leads to change in allele frequency;
  (no longer can breed/mate to produce fertile offspring)

Question 12

Describe what is meant by speciation (SYMPATRIC) (5)

Answer 12

• NOT geographical isolation;
• leads to reproductive isolation;
• separate gene pools/no interbreeding (between populations);
• selection for advantageous alleles;
• differential reproductive success/(organisms) survive and reproduce;
• leads to change in allele frequency;
  (no longer can breed/mate to produce fertile offspring)

Question 13

Describe how bacteria can become resistant to antibiotics.

Answer 13

• variation/mutation;
• some bacteria have allele to survive and grow/live in high concentration of antibiotic;
• adapted bacteria survive and reproduce / (differential) reproductive success;
• increase in allele frequency;
• no interbreeding (with other populations of bacteria) / separate/different gene pool