populations in ecosystems

Question 1

How can a lake have more species of fish compared to another lake?

4

Answer 1

-mutations
-different env conditions
-different alleles passed on
-eventually diff species cant breed to produce fertile offspring

Question 2

How does a loss of nutrients into a lake cause lower fish populations?

3

Answer 2

-more algae
-no photosynthesis so plants die
-less oxygen for fish to respire

Question 3

How does the mark-release-recapture method be used to estimate the size of a fish population?

4

Answer 3

-capture sample, mark and release
-ensure doesnt harm it
-allow time to randomly distribute back before collecting 2nd sample
-number in first sample × number in second
sample divided by number of marked fish in second
sample

Question 4

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

1

Answer 4

unlikley fish distributes randomly

Question 5

How does succession occur?

5

Answer 5

-colonisation by pioneer species
-change env thru forming nutrients
-env less hostile for new species
- increase biodiversity
- -to climax community

Question 6

Describe how you could estimate the size of a population of sundews in a
small marsh

5

Answer 6

-use a grid
-use random generator for co-ordinates
-count number in quadrat
-large sample and calculate mean per quadrat
- multiply this by number of quadrats to get total

Question 7

Suggest and explain how digesting insects helps the sundew to grow in soil
with very low concentrations of some nutrients.

2

Answer 7

-digestion of proteins
-provides amino acids

Question 8

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

5

Answer 8

-use a grid
-use random generator for co-ordinates
-count number in quadrat
-large sample
-divide total percentage by number of quadrats/

Question 9

put lots of sterile infertile male bugs into habitat by radiation

Explain how using the SIT could reduce transmission of dengue.

2

Answer 9

-intraspecific competition: compete with fertile males for mate/food
-don’t reproduce

Question 10

The release of radiation-sterilised A. aegypti has not been very successful
in controlling the transmission of dengue

1

Answer 10

-die due to radiation