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Referee Comments: Referee 1

Posted by PLOS_ONE_Group on 21 Jan 2008 at 09:57 GMT

Referee 1's review:


This paper describes sharing of cultivated crops in the Bossou population of chimpanzees. Sharing of this food, which appears to be stressful to obtain is more common than wild fruits. Males shared most with adult females. The 'food for sex/grooming' or 'showing off hypotheses' seem most suitable to explain this behaviour. This is an interesting paper that is well written. I would like to see the addition of some extra data, and more information reported for the statistical tests reported.


Abstract - here and in other places in the paper you say that sharing of cultivated foods occurs with similar frequencies to meat sharing. Please provide some frequencies for meat sharing at this or other sites to substantiate this claim.


1. Please provide data on how often this community crop raid. Then present a percentage of crop raiding events in which they share the food in. Sharing may be 'regular', but it may still be uncommon, and this is not clear in the Ms at present. My guess is that they crop raid much more often than they share, in which case the difference between this and meat sharing is still significant, and this should be highlighted.

2. What unit are the RSS figures measured in (scratching bouts/hour? - please specify otherwise the numbers are meaningless)

3. For each binomial test please report the chance level against which you are testing. E.g. if testing against 50% chance: Binomial (0.5), p=0.004). Without this information it is not clear to the reader what you are testing and the meaning of the results.

4. Please also state the number of other crops which were shared in the 13 cases that are not discussed in detail, so the reader has a complete picture of the data set.

5. I am confused how the chimps can crop raid in the forest (comparison of likelihood of sharing crops obtained in different locations of exposure: forest vs village). Please explain.

6. It needs to be made clear that by 'presence of humans', you mean local people who live in the village: as you witness the events there are always humans present with the chimps.


It seems that most of the sharing data is heavily influenced by one female. I think therefore that this should be highlighted when discussing the data in terms of food for sex/grooming hypotheses. Although in her case this is the best explanation the reader should be aware it is an interpretation driven principally by one female and therefore may not be totally representative of the process as a whole.

Materials and methods.

How many observation days were there in the study period?
Please specify the number / range of adult females in the group over the study period.

N.B. These are the general comments made by the reviewer when reviewing this paper in light of which the manuscript was revised. Specific points addressed during revision of the paper are not shown.