p2: populations and ecosystems

Question 1

define population

Answer 1

individuals of the same species occupying one area at one time that can potentially interbreed

Question 2

define habitat

Answer 2

an area where an organism lives

Question 3

define community

Answer 3

all the opulations of all the species in one area at one time

Question 4

define niche

Answer 4

the role an organism plays in the ecosystem and how it interacts with the biotic and abiotic factors

Question 5

define biotic factor

Answer 5

a living factor which affects the distribution of an organism

Question 6

define abiotic factor

Answer 6

a non-living factor which affects the distribution of an organism

Question 7

define carrying capacity

Answer 7

the maximum population size of a species that an ecosystem can support

Question 8

define ecosystem

Answer 8

consists of the community and the non-living components of its environment

Question 9

explain why sampling should be carried out at random

Answer 9

to ensure that all data collected is not biased

Question 10

describe how you would retrieve reliable and representative data when sampling

Answer 10

you must take a large sample

Question 11

describe the steps of how you would estimate the numbers of trees in a woodland by random quadrat sampling

Answer 11

1. two measuring tapes are arranged at right angles to eachother to form axis of a grid and co-ordinates are assifgned
2. co-ordinates are generated at random by using a random number generator on a calcuator and a quadrat is placed at these co-ordinates
3. the number trees in the quadrat is then counted
4. this is repeated a large number of times so when a running mean is calculated it shows little variation
5. the running mean value would then be used to estimate the total number of organisms in thw whole area e.g mean number of quadrats x how many quadrats can fit inot the area.

Question 12

describe the steps of how to see if succession was occurring from a rocky seashore, inland using a transect

Answer 12

• several belt transects replaced at parallel across an area and numbered.
• a transect is chosen at random using a random number generator button on a calculator
• a quadratic is placed along the straight line at regular intervals
• the percentage covered or number of each species are counted in each quadrat
• this is repeated a large number of times across parallel transects an a mean at each interval is calculated.

Question 13

what is a limitation of using belt transects

Answer 13

• a single transect might not go through a representative area

Question 14

explain when it would be appropriate to use the mark release recapture method to estimate the numbers of a species present in an area compared to using random quadrating

Answer 14

mark release recapture is used for motile organisms whereas random quadrating is used for non-motile or very slow moving organisms.

Question 15

describe the steps of how you would estimate the number of turtles on a local coral reef ( mark release recapture)

Answer 15

a sample of animals of a particular species are captured, counted, marked and released
- the mark should not affect the organisms survival
- the animal car left a long enough time to redistribute randomly back into the population
- a second sample is captured and the total number caught are counted as well a show many were marked.
- use formula:

(number caught 1st time x number caught 2nd time) / number marked in 2nd sample

Question 16

describe assumptions of the mark release recapture method

Answer 16

• birth rate = death rate
• marking does not influence survival
• no immigration/ emmigration
• long enough time fir marked to redistribute randomly
• large population

Question 17

describe the stage of how succession leads to a climax community

Answer 17

• startrs with colonisation of pioneer speciess in hostile environment in ostile conditions
• pinoeer species change the abiotic conditions e.g. form soil.
• the environmet becomes less hostile and more suitable for new species to colonise.
• the new species outcompete the pioneer species so the pioneer numbers decrease.
• from stag eto stage the species diversity increases
• eventually a climax community is reached

Question 18

describe the difference between primary and secondary succession

Answer 18

secondary succession does not start with a pioneer species