populations in ecosystems exam questions

Question 1

mark, release, recapture method can be used to estimate the size of a fish population.
Explain how. (4)

Answer 1

-capture, mark and release
-ensure marking is not harmful
-allow fish to distribute before collecting second sample.
population= number in first sample x number in second sample divided by number of marked fish in second sample.

Question 2

suggest why the mark release recapture method can produce unreliable results in very large lakes. (1)

Answer 2

less chance of recapturing fish

Question 3

succession occurs in natural ecosystems. Describe and explain how succession occurs. (4)

Answer 3

-pioneer plants colonise
-they make the abiotic conditions less harsh.
environment becomes less hostile for other species
increase in biodiversity
final seral stage- climax community.

Question 4

The sundew is a small flowering plant, growing in wet habitats such as bogs and marshes. The soil in bogs and marshes is acidic and has very low concentrations of some nutrients. The sundew can trap and digest insects.
(a) Describe how you could estimate the size of a population of sundews in a small marsh.
_________________________

Answer 4

-use a grid
-use random number generator to generate coordinates
-measure number of sundews in each quadrat
-large sample and calculate an average/mean
-multiply mean number of sundews in each quadrat by number of quadrats.

Question 5

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

Answer 5

-digestion of proteins
-provides amino acids

Question 6

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

Answer 6

-generate random coordinates using random number generator
-large sample
to calculate mean percentage divide the total percentage of beach grass by the number of quadrats.

Question 7

Dengue is a serious disease that is caused by a virus. The virus is carried from one person to another by a mosquito, Aedes aegypti. One method used to try to reduce transmission of this disease is the Sterile Insect Technique (SIT). This involves releasing large numbers of sterile (infertile) male A. aegypti into the habitat. These males have been made infertile by using radiation. (2)-

Answer 7

-do not reproduce
-compete with fertile males for food, mate

Question 8

The release of radiation-sterilisedour A. aegypti has not been very successful in controlling the transmission of dengue.
Suggest one reason why.
___________________________________________________________ (1)

Answer 8

-affects courtship behaviour/attractiveness/life span

Question 9

Ecologists studied a stream community before and after a flood. The flood reduced animal populations in the stream by 98%.
The table shows how the populations of six animal species found in the stream changed following the flooding.
Number of days after flooding
1 5 13 22 35 49 63 Mean number of organisms / thousands m−3
Animal species
Baetis quilleri Leptohyphes packeri Helicopsyche mexicana Cryptolabis paradoxa Pentaneurini guttipennis Micropsectra klinki
(a) Explain how the data in the table provides evidence of succession.
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
______________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
___________________________________________________________
(

Answer 9

-species that colnises
-changes abiotic factors e.g. food resources-
-so they are less harsh for x species
-x species declines as succession continues
-increase in species richness

Question 10

Suggest an explanation for the effect size when non-native species were introduced to communities.
___________________________________________________________

Answer 10

-non native species outcompete native speies for food and resources.
-some populations of native species may become extinct.

Question 11

Describe how you would investigate the effect of an invasion by a non-native species of plant (a biotic environmental factor) over many years on the abundance of a native species of plant in a community.
___________________________________________________________ (3)

Answer 11

-set up grid system with coordinates
-place large number of quadrats at random
-repeat a

Question 12

explain the increase in diversity of birds as the woodland developed. (3)

Answer 12

-more plant species
-more food sources
-more habitats/niches.

Question 13

hydrilla has become the dominant plant species.
suggest 2 reasons why. (2)

Answer 13

-outcompeted other species for resources
-few predators.

Question 14

the spread of hydrilla has economic consequences for commericla activities and for the government’s environmental agency.
suggest 2 economic consequences of the spread of hydrilla. (2)

Answer 14

-loss of income from fishing
-loss of income from tourism.

Question 15

scientist used percentage cover rather than frequency to record abundance of algae present. suggest why (1)

Answer 15

-difficult/too many to count

Question 16

population number of both species of lizard varied at different times of the year. Suggest two reasons why. (2)

Answer 16

-breeding of lizards
-preadators
-food sources/prey

Question 17

explain how these data suggest that succession has occcured from points A to E along the transect. (3)

Answer 17

-decrease in bare ground
-change in number of species as abiotic conditions change
-increased depth of soil as plants die and add a thin layer of soil/humus

Question 18

the diversity of animal species is higher at E than A. Explain why. (2)

Answer 18

-greater variety of food
-more variety of habitats

Answer 19

-marking is not removed
-no immigration
-same sampling method
-no births or deaths.

Question 20

explain the advantage of species occupying different niches. (1)

Answer 20

less competition for food/resources

Question 21

the increase in the index diversity is one indicator that succession is taking place.
describe the features of the succession that would bring about an increase in the index of diversity. (3)

Answer 21

-inital environment is hostile
-pioneer species change abiotic conditions
-more habitats/niches
-enabling other species to become established.

Question 22

the communities a - d are composed of different species.
explain how the change in species composition occurs in a succession

Answer 22

-pioneer species colonise and change abiotic conditions
-enabling other species to become established
-new species are better competitors.

Question 23

why is the climax community the most stable stage?

Answer 23

-more species present
-more complex food webs

Question 23

glaciers are masses of moving ice. when they shrink, the thick covering of ice dissapears to leave behind bare land. Land exposed by a shrinking glacier in alaska becomes covered by dense forest in 150 years.
Explain how succession resulted in the formation of the forest. (4)

Answer 23

-pioneer species colonise land
-change abiotic conditions e.g. food resources
-enables other species to become established.
-conditions change further to favour trees.