The silvery gibbon, Hylobates moloch, lives in the rainforests of the Indonesian island of Java. It was the first species to be protected by law in Indonesia in 1925 and is now on the IUCN Red List of Threatened Species.
Two recent estimates of the population of silvery gibbons in the Dieng Mountains are shown in the table below.
Year |
Method |
Population Size |
2010 |
Line transect |
881 |
2021 |
Fixed point count |
1092 |
(i)
Calculate the percentage increase in silvery gibbons in the Dieng Mountains between 2010 and 2021.
[2]
(ii)
The fixed point count in 2021 was completed by setting up listening posts at each sampling site to identify the calls of the gibbons.
The researchers identified two potential explanations for the data gathered. The first explanation was that the population size of gibbons had increased between 2010 and 2021.
Suggest another explanation for the apparent increase in population size.
[2]