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1. The island of Surtsey was formed in 1963 by a series of volcanic eruptions. Biologists have
studied the colonisation of this new island by plants and animals.
(a) The graph shows the number of species of plants found on the island each year for the
first seven years of its existence.
16
14
12
10
N um ber
o f s p e c ie s 8
6
4
2
0
1963 1964 1965 1966 1967 1968 1969 1970
Y ear
The development of the plant community on Surtsey illustrates the process of succession.
Explain why:
(i) very few species could grow on the island in the first few years after it was formed;
, (b) Animals also colonised Surtsey. One conclusion drawn from studying them was that
particular species of animals found here had broader ecological niches than they did on
the nearby mainland. Suggest why.
2. Heather is a woody plant found in many moorland areas on higher ground in Britain. Grouse are
chicken-sized birds which feed on the young shoots of heather. On many moorlands, the heather
is managed to produce better conditions for grouse. This involves burning large areas. After
burning, heather goes through the cycle of growth described below.
Pioneer phase New plants grow either from
0-7 years seed or from stem bases
undamaged by fire.
Building phase Phase of rapid growth
7-15 years producing dense cover of
heather plants.
Mature phase Plants still growing but gaps
15 - 25 years start to appear in the canopy.
Degenerate phase Branches break. Central part
25+ years of plant dies although outer
branches may remain alive.
2
,Table 1 summarises some data collected from a study of heather plants of different ages.
Age/years Total Biomass of green Percentage cover Light at ground level
2 –2 as percentage of light
biomass/g m shoots/g m
in open
5 287 78 10 84
10 1508 203 85 5
20 1924 208 76 22
30 1043 n/a 34 56
Table 1
Key:
n/a = figures not available
(a) To determine the total biomass, quadrats were used to collect the heather samples.
Describe the procedure you would have used to place these quadrats.
(iii) Management of heather by burning allows an area of land to support a larger
population of grouse than if the heather is unmanaged. Use the information in
Table 1 to suggest why.
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