Populations in Ecosystems

Question 1

describe when and how to use a belt transect?

Answer 1

• used when there is a transition in habitats and communities through an area

method:
- a tape is run along the ground in a straight line
- at regular intervals a frame quadrat is laid down along the tape and the species within it are recorded
- the percentage cover or the frequency of the species can be recorded

Question 2

why is it important to use a larger number of quadrats when sampling?

Answer 2

to make sure the results are representative

Question 3

what is the equation for estimated mean density?

Answer 3

total number of individuals counted ⁄ (n of quadrats x area of each quadrat)

Question 4

describe the mark-release-recapture method?

Answer 4

• capture a representative sample of organisms from the population, record the number and mark them
• release them back into the habitat and leave them for a suitable amount of time to mix randomly into the population
• capture a second sample of organisms and count the number of marked individuals
• use equation to estimate population size

Question 5

what is the equation for estimated total population

Answer 5

= (n marked in first sample x n captured in second sample)/n marked in the second sample

Question 6

what assumptions does the ‘mark release recapture’ method rely on?

Answer 6

• organisms must mix randomly with the population
• organisms disperse evenly within the geographical area of the population
• changes of population size due to death birth immigration and emigration are negligible
• the marking doesn’t hinder the survival of the organisms

Question 7

what are some abiotic factors that affect population size

Answer 7

• light availability
• pH (of soil)
• Temperature

Question 8

what is interspecific competition?

Answer 8

• competition between different species

Question 9

what is intraspecific competition?

Answer 9

• competition between the same species

Question 9

what is a climax community?

Answer 9

• the end point of primary and secondary succession
• a very diverse and stable community

Question 10

describe the process of succession

Answer 10

• pioneer species are the first to colonise an area
• the pioneer species may change the abiotic environment making the environment less hostile and making it more suitable for new species with different adaptations to colonise the habitat
• the new species may outcompete the previous reducing their abundance
• succession usually proceeds to form a climax community which is stable due to the complexity and variety of the food webs.

Question 11

how is succession managed/prevented?

Answer 11

grazing - seedlings of herbaceous plants and shrubs are continually eaten preventing any succession beyond grassland

ploughing - the seedlings are broken up and buried preventing germination and the use of herbicides maintains an established community