Question 19M.3.SL.TZ2.12
| Date | May 2019 | Marks available | [Maximum mark: 9] | Reference code | 19M.3.SL.TZ2.12 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Analyse, Describe, Outline, State | Question number | 12 | Adapted from | N/A |
A survey was made of the intertidal zone at Butter Lump Bay, Great Cumbrae, Scotland. The three species of barnacle found were Elminius modestus (EM), Chthamalus montagui (CM) and Semibalanus balanoides (SB). The kite diagram shows the vertical distribution of these three species from the low tide mark at 0 m to 2.25 m above low tide.
[Source: reprinted from Estuarine Coastal and Shelf Science, 152, M C Gallagher, et al., The invasive barnacle species,
Austrominius modestus: Its status and competition with indigenous barnacles on the Isle of Cumbrae, Scotland,
pages 134–141, 2014 with permission from Elsevier]
Outline how the data could have been obtained.
[2]
a. transect across area to be studied ✔
b. count/record barnacles «per species» in quadrats at regular intervals ✔
The data in this question was a kite diagram showing the distribution of three barnacle species. In part (a) most strong candidates could outline how the data was obtained though many failed to use specific vocabulary and did not mention transects or quadrats.
Describe the distribution of C. montagui and S. balanoides barnacles in Butter Lump Bay.
[2]
a. both species present throughout the range ✔
b. C. montagui has small number of individuals «throughout»
OR
C.montagui occupies «mostly» upper shore/intertidal zone
c. S. balanoides «mostly» occupies low tide area ✔
OR
S.balanoides has large number of individuals «throughout» ✔
OWTTE referring to maximum numbers at specific heights.
Candidates were able to describe the distributions of the barnacles very well in part (b).
E. modestus is an invasive barnacle while the others are native species. Analyse the data to show how it supports this statement.
[2]
a. native species/C. montagui and S. balanoides have niches that don’t overlap much / are distinct
OR
range of E. modestus overlaps with both native species ✔
b. niches of native species «which don’t overlap much» shows competition between native species
OR
E.modestus invades habitats of C. montagui/S. balanoides resulting in competition with «both» native species ✔
c. EM has a wide niche/higher tolerance/covers entire «intertidal» range making it easier to invade the habitat ✔
Candidates had difficulty finding data to support E.modestus being aninvasive barnacle in part (c).
State one abiotic factor that could have determined the distribution of barnacles.
[1]
a. exposure/tides/waves ✔
b. temperature ✔
c. surfaces «of attachment» ✔
d. resource availability/nutrients ✔
e. pH ✔
f. light ✔
g. salinity ✔
Do not accept biotic factors eg: “competition or predation”
Barnacles are sensitive to pollution. Outline how it might be possible to use these organisms as indicator species.
[2]
a. indicator species need particular environmental conditions
OR
indicator species tolerate only certain environmental conditions ✔
b. increase/decrease in population size «over time» shows effect of environmental conditions ✔
c. used to calculate biotic index/index of cleanliness ✔
d. index of 10/high index number indicates totally unpolluted
OR
index of 2 or 1/low index number indicates severe pollution ✔
In part (e) some candidates chose to describe invasive species in general (without using the data) and others described the data but were not able to attach this to the idea of an invasive species. Many repeated the information given in the question.