Male Chimps Hang In Familiar Home Range

Beethoven Home court advantage matters when it comes to food and reproduction. So, where does a big male ape sit? Wherever he wants to....

... and if you are an adult male chimp, this means in the same part of the forest that you used to hang out with mom, when you were still more or less attached to her metaphorical apron strings.

The next issue of Current Biology will have a paper by Carson Murray, Ian Gilby, Sandeep Mane and Anne Pusey on adult male ranging patterns. The conclusion of the research is that adult males essentially inherit their mother's habits of space use.

The study is based on years of data collected at the research site of Gombe, in Tanzania. This is the longest running chimpanzee research site, and over the last several years the longevity of this project has been paying off with results that would not be possible from data collected over the shorter term.

These particular results are not surprising. Theory predicts that there are advantages in dispersal. This would suggest that male mammals, or seeds from some tree, or lots of other organisms would gain an advantage by going far from their cite of conception, under certain circumstances. Theory also predicts that there are advantages to not dispersing. This might sound like the theory is cheating, having it both ways, but that is not the case. Whether dispersal or conservatism in territory use is most advantageous depends on two kind of things: 1) The raw advantage or disadvantage of either strategy, weighing the costs and benefits; and 2) The severity of competition with other individuals to achieve the optimal result. This second effect may see a bit subtle but it is not at all. For instance, your most effective way to obtain loads of cash may well be to rob the local bank. But there are other people who do not want you to do that, and they will try very hard to stop you. With social animals such as chimpanzees or humans, the optimal outcome for the individual is more often than not a matter of negotiations.

The reason that a tendency for adult males to range in the home range of their mother is not surprising is that it appears that in chimps male strategies associated with he transition to adulthood are driving the system more so than female strategies, probably owing to the physical and social dominance of males over females in this species.

Among chimps, females tend to have relatively stable social rankings once they reach adulthood. In contrast, male rank may vary much more dramatically over time. There are probably foraging advantages to getting to know a particular area. Because of various social effects, males are faced with the problem (compared to females) that, despite the fact that they need more energy than females do, they need also to spend less time foraging for it. All these factors taken together predict that males should a) forage alone sometimes and b) are at risk when doing so because of the chance of encountering other males that outrank them. One solution to this set of conflicting factors is to get to know a foraging territory well (while growing up with mom) and then have that be one's primary area of use later on in life.

Given that high rank can be ephemeral, foraging in an unknown area might be disadvantageous to dominant males. Although additional data are needed to rigorously test the effects of dominance rank on male ranging, our results suggest that social status, habitat quality, and age are not strong determinants of male site fidelity. Rather, maternal space use during dependency drives adult-male spatial patterns.

Murray, Carson M., Ian C. Gilby, Sandeep V. Mane and Anne E. Pusey. (2008) Adult Male Chimpanzees Inherit Maternal Ranging Patterns. Current Biology. In Press. doi:10.1016/j.cub.2007.11.044