succession

Question 1

what is succession

Answer 1

the process by which an ecosystem changes over time

Question 2

primary succession

Answer 2

occurs on an area of land that has been newly formed or exposed and there is no soil or organic material present to begin with e.g. bare rock, where volcanoes have erupted to create new surface, where sea levels have dropped exposing a new area of land

Question 3

secondary succession

Answer 3

occurs on areas of land where soil is present, but it contains no plant or animal species

Question 4

what are the main seral stages of succession

Answer 4

• pioneer community
• intermediate community
• climax community

Question 5

what happens at each seral stage

Answer 5

key species can be identified that change the abiotic factors especially the soil, to make it more suitable for the subsequent existence of other species

Question 6

pioneer community

Answer 6

begins by colonisation of an inhospitable environment by pioneer species which arrive as spores or seeds carried by wind from nearby land masses or from the droppings of birds/animals passing through e.g. algae, lichen

Question 7

adaptations of pioneer species

Answer 7

• ability to produce large quantities of seeds or spores which are blown by wind and deposited on new land
• ability to photosynthesise to produce their own energy because light, rainfall and air are only abiotic factors present
• tolerance to extreme environments
• ability to fix nitrogen from the atmosphere so adding to the mineral content of the soil

Question 8

intermediate community

Answer 8

• weathering of bare rock produces soil
• organisms die and decompose so organic products released into soil (humus)
• soil can now support growth of plants (secondary colonisers) as it contains minerals/nitrates and retains water
• pioneer species provide food for consumers so animals start colonising
• environmental conditions continue to improve and tertiary colonisers arrive (plants) with waxy cuticle to retain water
• more erosion, mass of organic matter increases, nutrient-rich soil, grasses then shrubs then trees
• better adapted organisms outcompete species that were previously present and become the dominant species which are most abundant

Question 9

climax community

Answer 9

• stable state and shows little change over time
• a few dominant plant/animal species, depending on the climate
• biodiversity increases, but climax community is not biodiverse
• biodiversity reaches peak in mid-succession then decreases due to dominant species outcompeting pioneer and other species so they are eliminated
• the more successful the dominant species, the less biodiverse the ecosystem

Question 9

plagioclimax

Answer 9

the final stage when succession is stopped artificially as a result of human activities and doesnt reach the climax community

Question 10

deflected succession

Answer 10

when human activities prevent succession

Question 11

examples of deflected succession causes

Answer 11

• grazing and trampling of vegetation by domesticated animals -results in large areas being grassland
• removing existing vegetation to plant crops- crops become final community
• deforestation burning- increase in biodiversity as provides more space and nutrient-rich ash for species to grow like shrubs

Question 12

distribution of organisms

Answer 12

where the individual organisms are found within that ecosystem

Question 13

how to measure distribution in an ecosystem

Answer 13

• line/belt transect with samples at regular intervals (systematic sampling)

Question 14

abundance

Answer 14

• the number of individuals of a species present in an area at any given time
• it may fluctuate due to immigration and births, or emigration and deaths

Question 15

how to measure abundance of plants in an ecosystem

Answer 15

• using sampling techniques
• quadrats placed randomly with the following equation used:
  estimated number in population (m^-2)= (number of individuals in the sample)/(area of sample m^2)

Question 16

how to measure abundance of animals in an ecosystem

Answer 16

• capture-mark-release-recapture:
• capture as many individuals possible in a sample area and mark them and then release them
• recapture as many individuals as possible in the original sample area and record the number of marked and unmarked individuals present
• use the Lincoln index:
  (estimated population size)= (number of individuals in first sample x number of individuals in the second sample)/ number of recaptured marked individuals