Species diversity is often used as a simple way to compare the biodiversity of different regions of the world. A student read that species diversity decreases with increasing distance from the equator. The latitude at the equator is 0°. Latitudes increase north and south of the equator. The student selected data from a database which holds records of the annual bird count in North America. This annual count is carried out each year during one day in the winter. Volunteers count all the species of birds that they observe in each location. The area of each location is the same size. The student found data from 17 sample locations within the Delmarva Peninsula on the east coast of the USA for 2005. Fig. 2.1 shows the 17 locations within the Delmarva Peninsula. [Figure 2.1] The student used the data to see if there was any relationship between the latitudes of the sample locations and the number of species recorded at each location. The data are shown in Fig. 2.2.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

1. [1] idea of no (clear), relationship / trend; or as latitude increases, (bird) species diversity / numbers of (bird) species, (slightly) decreases / (might) show a downward trend;
2. [3] 1 data (for latitude and number of species) is, paired / linked ;
3. 2 number of bird species and latitude / (i.e. the data points) within samples are independent of each other;
4. 3 the data, is ordinal / is interval / is discrete / can be ranked ;
5. 4 (scatter) graph / Fig. 2.2, suggests a, (decreasing) relationship / correlation ;
6. 5 there are, 17 (paired) observations / more than 5 (paired) observations ;
7. 6 idea that bird species selected randomly / AW ;
8. [1] idea that there is no, correlation / relationship, between latitude and the number of (bird) species ;
9. [4] 1 critical value (for p = 0.05%) = 0.485 or critical value for p = 0.01% = 0.615 ;
10. 2 value for rs / calculated value, is < than critical value ;
11. 3 null hypothesis is accepted;
12. 4 there is no significant correlation (between latitude and number of bird species) ;
13. 5 there is a (weak) negative correlation (between latitude and number of bird species as shown by the negative value for rs);
14. [3] any three from all marking points are ideas that: limitations of the data
15. 1 only used counts of bird species (may not apply to all species);
16. 2 do not know the, number of individuals of each species / relative abundance of each species / species evenness ;
17. limitations of sampling birds
18. 3 hard to identify some (bird) species / miss some (bird) species / some (bird) species look similar / miss birds that fly away / birds migrate / only resident birds or species counted / qualified ref to volunteers / AW ;
19. latitudes sampled
20. 4 nothing above 40N / nothing before 37N / need wider range of latitudes / AW ;
21. 5 no data on latitudes south of the equator ;
22. sampling sites
23. 6 not random / only sampled in certain locations / sample locations do not cover the whole of the peninsula / many near the coast / locations may not be representative of the peninsula / only 17 sites / sampling sites do not extend beyond the peninsular / AW ;
24. habitats
25. 7 no information on habitats (at locations) / not all location may be equally suited for birds / different habitats have different conditions / AW ;
26. timings
27. 8 only sampled, on one day / in one year / sampled in, winter / one season ; ora
28. [3] any three from:
29. 1 catch birds within area and count total captured and mark and release them;
30. 2 detail e.g. idea of: marking technique not, harmful / too obvious e.g. idea of: giving time for populations to mix before second sample taken – days or weeks not more ;
31. 3 catch second sample and count total number of birds and number of marked birds ;
32. 4 ref. to Lincoln / Petersen, index ;