| Date | May 2010 | Marks available | 1 | Reference code | 10M.2.SL.TZ1.1 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 1 |
| Command term | Calculate | Question number | 1 | Adapted from | N/A |
Question
The grey partridge (Perdix perdix) is a species of bird that is found on farmland. Sparrowhawks (Accipiter nisus) and buzzards (Buteo buteo) are birds of prey that kill and feed on birds, including grey partridge. The number of grey partridges in a region of southern England was monitored from 1970 to 2004. The numbers of sparrowhawks and buzzards, seen from sampling positions during regular observation periods, were counted. The results are shown in the graph below.
The density of grey partridge (number per square kilometre) varied considerably in different areas within the study region. The graph below shows the correlation between the density of grey partridges and the density of birds of prey.
The highest density of birds of prey was found in areas used for recreational shooting. In these areas, other species of partridge were bred and released. Food and shelter were provided for the released birds. These measures tended to increase the number of both released and wild birds.
The causes of death of grey partridge were investigated in one of the areas that was used for recreational shooting. The pie chart below shows the causes of death.
Outline the trends, over the period of time shown in the graph, in the number of grey partridges, buzzards and sparrowhawks.
Grey partridges: ........................................................
Buzzards: ........................................................
Sparrowhawks: ........................................................
Identify the correlation between the density of grey partridges and birds of prey.
Suggest a hypothesis to account for this correlation.
Calculate the percentage of deaths due to birds of prey.
Using the data provided, discuss the causes of the correlation between the density of grey partridges and the density of birds of prey.
Markscheme
grey partridge numbers/pairs reduced;
buzzard numbers increased;
sparrowhawk numbers no clear trend/no overall rise or fall/constant/stable/ fluctuates;
negative correlation/inverse proportion/bird of prey density falls as partridge density rises
partridges eaten by birds of prey;
fewer partridges present where more birds of prey present / more partridges present where fewer birds of prey present;
partridges move to areas with fewer birds of prey;
fewer birds of prey enable growth (by reproduction) of grey partridge population;
18%/18.1% (18 needed but no penalty if significant figure error)
birds of prey attracted from outside to shooting areas because of abundant food (grey and released partridges) / birds of prey living in
shooting areas increase in numbers because of abundant food;
non-hunting human involvement (food and shelter) influenced the correlation between the densities;
more grey partridges shot than killed by birds of prey / many grey partridges shot in shooting areas;
correlation not only due to birds of prey eating grey partridges/human involvement;
grey partridges compete with released partridges for food and shelter (decreasing the density of grey partridges);
Examiners report
The answers here were usually fine, but sometimes candidates faltered because they never summarized an overall trend or reached any conclusion about a trend. Just noting yearly population fluctuations for individual bird species was not enough to gain marks.
Answers were divided between giving the term negative correlation or inverse proportion or using a sentence such as "birds of prey density goes down as grey partridge density rises." Either style was acceptable.
Those answers that gained the maximum of two marks provided a prediction/observation supported by some reasoning. For example, “fewer partridges are present when more birds of prey are seen because partridges are eaten by birds of prey.” Another acceptable reason was that the partridges moved to areas with fewer birds of prey. Converse accounts also gained credit such as “more grey partridges can exist (through reproduction) when fewer birds of prey are around.” Some candidates just repeated their response from 1(b) (i) and gained no credit.
A correct percentage was usually calculated. Although it was not required, many candidates applied significant figures rules in determining their answer.
Answers were quite varied. Many candidates had difficulty using the data provided. The discussions of some candidates covered more than the maximum number of marks while others wrote vague and ambiguous explanations for no credit. Many candidates showed some sort of reasoning. All the marking points eventually appeared over the range of scripts. Often, candidates mentioned that birds of prey were attracted from outside to the shooting area because of the abundant food i.e. the released partridges and grey partridges.
