| Date | November 2011 | Marks available | 2 | Reference code | 11N.3.HL.TZ0.1 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Outline | Question number | 1 | Adapted from | N/A |
Question
A study of two populations of Darwin’s finches, medium ground finch (Geospiza fortis) and cactus finch (Geospiza scandens), was undertaken between 1973 and 1998 on the Galápagos Islands. The graphs below show the mean beak size in each year from 1973 to 1998 compared with the long-term mean size.
State the year in which G. fortis had the greatest change in relative beak size.
Compare the trends in relative beak size of G. fortis and G. scandens.
Outline possible reasons for the trends in relative beak size in finches.
Markscheme
1977 / 1978
N.B. Some responses are interpreting this as a change between years.
both species increased (relative) beak size at the beginning of the study/ between the years 1973/1974 to 1977/1978;
no similarity in trend for both species after 1977/1978/1979 / no relationship between the two species in the years of increase and decrease;
more occurrence of decrease in (relative) beak size in G. fortis whereas G. scandens showed more increases in (relative) beak size;
G. fortis shows wider fluctuation in (relative) beak size than G. scandens;
Do not accept year by year comparisons.
changes in environment/rainfall/ocean currents/migration / drought;
change in food supply;
hybridization/crossbreeding between species;
natural selection / selection pressure;
Examiners report
N/A
The lack of sufficient explanation in the question, "mean beak size‟ for each species or for the two species together, led to a wide variety of answers that scored poorly. Many also quoted values for individual years which did not describe a "trend.‟
Factors contributing to different beak size between species were stated (different food sources) instead of reasoning which factors cause that a given species change its size.
