Tuesday, March 30, 2010

Grooming, group size, and feeding priority in female Rhesus macaques



(Photo by James Warwick/Getty Images. On the left is Esther, on the right is Terry, and they were two of my favorite focal animals ever!)

Here is the abstract of the poster I am currently working on for the AAPAs:

Grooming, group size, and feeding priority in female Rhesus macaques
M.A. Rodrigues¹, D.L. Hannibal²

The social brain hypothesis predicts that larger groups require greater investment in allogrooming for social cohesion. It has been suggested that low-ranking individuals allogroom to gain tolerance from high-ranking individuals for access to food resources. Here, we report on data collected from twenty-eight adult female rhesus macaques on Cayo Santiago, Puerto Rico. Contrary to the social brain hypothesis predictions, we found that individuals in large groups (10.3%) do not invest more time in grooming than individuals in small groups (13.6%) (F=1.302, p=0.263). Furthermore, time spent allogrooming does not explain access to food resources among middle- and low-ranking females (F=0.403; p=0.533), nor does the interaction of group size and grooming (F=0.032; p=0.859), the interaction of rank and grooming (F=0.005, p=0.943), or the interaction of group size, rank, and grooming (F=2.684; p=0.118). The interaction of group size and rank was significant (F=6.123, p=0.022). Removing grooming from the model, however, negates the significance of the group size and rank interaction. The benefits of membership in a large group outweigh the disadvantages of increased intragroup competition for low-ranking individuals. In smaller groups, however, low-ranking individuals are constrained by both intergroup and intragroup competition. Furthermore, grooming does not appear to offset the disadvantages of low rank or small group size. While increasing group size and rank improve access to food resources, and the contribution of grooming for tolerance was not significant in this study, further investigation on the role of grooming in the complex dynamics of intergroup and intragroup competition for food resource is warranted.

4 comments:

  1. So, if grooming up the ladder doesn't produce tangible (food) benefits, what's the purpose of grooming in this group?

    And, how likely is it that this finding: Contrary to the social brain hypothesis predictions, we found that individuals in large groups (10.3%) do not invest more time in grooming than individuals in small groups (13.6%)...... is due to sampling error?

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  2. Unfortunately, we don't have the data on grooming distribution to test some other hypotheses, but I suspect that they are concentrating grooming around their matriline, ie, investing in kin. Thus, I would hypothesize that females with the most most kin would have the highest grooming rates... I really wish we had the data to test it (the project was focused on feeding, so the only data that we have on grooming is time spent grooming).

    As for sampling error, it something that can't be ruled out, but we sampled pretty thoroughly... We followed randomized lists for focal observations, and did 20-minute focals throughout the day--we also did extended data collection hours to cover the day from 6 am to 6 pm, which is pretty rare on Cayo (most projects follow the normal boat hours, so data is usually collected between 7:30ish and 3ish).

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  3. I'd "Like" this post if I could. :D

    Is it possible for me to get a hold of the paper? When will it be published and where?

    Are these rhesus macaques from a wild population? What about their food source ... do they have a big range when they look for food or they get their food source from humans?

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  4. The rhesus are at Cayo Santiago, Puerto Rico, where they are provisioned with monkey chow. However, the also do forage on the island, and lower-ranking individuals often don't get enough access to the chow, and thus have to spend more time foraging for their own food (which is really interesting--mostly leaves and occasionally flowers, but we have seen a couple cheek-pouch young coconuts and even an anole! I also wonder if some of them have figured out how to find iguana eggs yet...). As for right now, it's only a poster, but I can send you a copy when it's final...

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