Population

Question 1

Whats the advantage of measuring the dry mass rather than the total mass of the carrot plants?

Answer 1

True indication of growth/water mass may vary.

Question 2

Describe and explain the changes that occur in the lemming and stoat populations. (6 marks)
Predator-Stoat
Prey- Lemming

Answer 2

1. 4 year cycles
2. Predator/stoat peaks after prey/lemming
3. Lemmings increase due to low no. of stoats/available food
4. More food for stoats so no.s increase
5. Increased predation reduces no. of lemmings
6. No. of stoats decreases due to lack of food/starvation

Question 3

Lemmings often live in isolated populations. From time to time some lemmings move and join other populations. Explain how this movement is important in maintaining genetic variability in lemming populations which have large fluctuations in size. (2 marks)

Answer 3

1. Smaller populations have fewer different alleles/smaller gene pool
2. Migrants bring in new alleles/increase gene pool.

Question 4

2 lemming populations are separated by a melting glacier forming an ocean. Explain how 2 species of lemming evolved from the original species. (4 marks) 6 points

Answer 4

1. Geographical isolation in populations
2. Variation present in population
3. Different environmental conditions
4. Different selection pressures/different penotypes selected.
5. Change in gene pools/allele frequency
6. 2 distinct populations so unable to breed to produce fertile offspring

Question 5

Explain how a quadrat can be used to obtain the mean density of the 2 species of periwinkle in each area. (3 marks)

Answer 5

1. Ref to use of random quadrat positions
2. Using random no. generator
3. . Ref to several or more than 2 readings.
4. Ref to known area of quadrat
5. No. of individuals in each quadrat counted
6. Density = total no. of each species divided by total area sampled

Question 6

What is an ecosystem? (1 mark)

Answer 6

A self supporting system in which all organisms/community interact with the physical environment with all its biotic and abiotic factors.

Question 7

NZ weed has been introduced into many ponds. Here it competes with naturally occuring plants. Suggest how the intro of NZ weed may lead to a reduction in the diversity of the community in a natural pond. (3 marks) 5 points

Answer 7

1. NZ weed competes for CO2/light/nutrients
2. Reduction in no.s of original plants
3. Some of original plant SPECIES lost
4. Loss of habitats/niches/shelter
5. Consumers die/some migrate