Ratio of body mass to group size?

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Offline Rincewind

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Ratio of body mass to group size?
« on: 18/11/2008 05:36:04 »

this is a question based on a memory of a biology teacher back when I was at school.

I'm pretty sure she said one day that there is a linear relationship between the body mass of individuals in a species and the average size of a group of that species.

As I remember, she put a graph up on the OHP with average body size on one axis and average group size on the other and there were several points plotted each representing a mammalian species, I think.

Although it was a line of best fit and the points were not all very close to the line, there did seem to be a relationship using the points that were plotted.

It was important because humans apparently fall at about 130 individuals per group given our body mass, which seemed like a nice social group to me, and it was this incident that convinced me that this is a true and natural (albeit flexible) fact.

However thinking about it, I'm not sure if it is.  I've had a search on the internet and don't seem to be able to find any research on this fairly simple relationship.

Can any biologist out there help?


Offline dentstudent

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Ratio of body mass to group size?
« Reply #1 on: 18/11/2008 11:23:37 »
Do you remember whether it was a positive (ie as BM increases, group size increases) or a negative relationship (ie as BM decreases, group size increases, or as BM increases, group size decreases)?

I'll assume in this case that it is a positive trend (because it is unlikely to be a negative trend).

However, I'm not sure how this would work - I think that there would be many outliers (observations that do not fit the model) for example Wildebeest, who have a relatively high BM, but also gather in huge numbers, as opposed to whales who have a rather large BM but are often solitary. It is probably a correlation rather than a causation, which means that although there may be an apparent linear link, the real reason is something entirely different. It may be that smaller animals require many individuals in order to live (ant colonies for example) whereas larger animals can be more self-sufficient and hence require smaller groups. Therefore, there would appear to be a link between size and numbers, when in actual fact it is a link between social requirements in order to survive and numbers.
« Last Edit: 18/11/2008 11:26:19 by dentstudent »