Unit 7- Pops in Ecosystems

Question 1

Method for estimating pop size of slow-moving or non-motile organisms.

Answer 1

1. split area into a grid
2. cooridinates generated from a random no. generator
3. larger no. of quadrats
4. count no. / % cover in each quadrat
5. calculate mean
6. calculate sampled mean per area of quadrat –> multiply by area to estimate total pop in whole area

Question 2

Method for estimating pop size of motile organisms.

Answer 2

Mark-release-recapture:
1. capture a sampl
2. mark
3. release + give time for random distribution
4. capture 2nd sample –> count total no. + no. of marked individuals
5. calculate pop size = n1 x n2 / nm

capture mark release

n1- initially caught ; n2- 2nd sample ; nm- marked

Question 3

Ethics associated with mark-release-recapture technique.

Answer 3

x permanent harm- mark must be:
- non-toxic
- x ↑ chance of predation
- x ↓ chance of reproduction

Question 4

Assumptions made when using the mark-release-recapture method.

Answer 4

1. proportion of marked to unmarked in 2nd sample = proportion in whole pop
2. individuals distribute evenly amongst pop after released
3. pop has definite boundary- x immigration/ emigration
4. x/ few births + deaths

Question 5

What is succession?

Answer 5

change in community over time
∵ abiotic factors

Question 6

What is the starting point for primary succession?

Answer 6

bare ground (e.g. rock)

Question 7

What is the start point for secondary succession?

Answer 7

community is damaged –> soil left –> plants colonise
e.g. when woodland is felled

Question 8

What is the end point of succession?

Answer 8

climax community- stable + x further succession

Question 9

What happens in the pioneer stage of succession?

Answer 9

1. species colonise new land surface
2. seed + spores blown in wind –> grow
3. harsh abiotic conditions- only pioneer species adapted + grow
4. pioneer species make abiotic conditions ↓ hostile (change carbon cycle)
5. new organisms can colonise
6. species diversity ↑
7. communities ↑ complex
8. ↑ habitats formed
9. ↑ food sources available
10. organisms bigger + live longer
11. ↑ biomass

Question 10

What happens in the later stages of succession?

Answer 10

1. plants + animals better adapted to improved conditions out-compete existing species –> dominant species
2. ecosystem ↑ complex
3. ↑ biodiversity (old + new species)
4. plants create ↑ habitats
5. abiotic conditions ↓ hostile

Question 11

What are the 2 forces affecting genetic variation?

Answer 11

1. genetic drfit
2. natural selection

Question 12

What is genetic drift?

Answer 12

change in allele freq. in small pop

Question 13

What is natural selection?

Answer 13

↑ freq of alleles that enhance fitness of individuals

Question 14

What is evolution?

Answer 14

change in allele freq. in a pop