Friday, November 9, 2007

Week 13: Scaling part 2

The following papers are required readings for next week. A few optional papers are in the ereserves folder as well.

*Hamilton M. et al. 2007. The complex structure of hunter-gatherer social networks. Proceedings of the Royal Society of London, Series B.

* Bettencourt, L. M. A., J. Lobo, D. Helbing, C. Kuhnert, and G. B. West. 2007. Growth, innovation, scaling, and the pace of life in cities. Proceedings of the National Academy of Sciences 104:7301.

*Moses, M. E., and J. H. Brown. 2003. Allometry of human fertility and energy use. Ecology Letters 6:295-300.

28 comments:

dtinucci said...

Bettencourt et al. imply that theoretically there are no limits to the size cities can achieve. However, since a city's physical presence impacts the environment on a material plane, wouldnt it be subject to the same constraints as organisms drawing on resources in a bounded area?

Isnt there some law of property that applies to this situation?

Oskar said...

Excellent questions - there's really a lot to chew on in this paper.
So, lets keep in mind that the predicted limits on growth depend on the type of variable that is driving it. So if you only consider wealth and innovation without resource limitations, growth can go on indefinitely. Or if you look only at the human goods and services that scale linearly, their model predicts unlimited growth. But look at figure 3 where the predicted results for each of the scenarios they consider are depicted. (see also Table 2) Factors related to infrastructure (sublinear) predict that growth will cease (plot a) whereas growth based on innovation and wealth with resource constraints built in predicts that the society will collapse (plot d). So they do include the sorts of constraints that are analogous to those that act on biological organisms. Consider also their statement at the beginning of their section on the urban growth equation, "Growth is constrained by the availability of resources and their rates of consumption."
So, I think you are exactly right to point out that a city's presence has an impact and that it is constrained by resources. They also address how innovation and resource limits might interact...
hasta luego.
O

Michael said...

Would the 10 nations excluded from Moses and Brown analysis due to extremely high per capita energy production produce any recognizable trend when plotted against fertility rates? Even though Kuwait and Turkmenistan all have high production values, unemployment in these countries varies from practically non-existent in Kuwait to around 60% in Turkmenistan.

Wenyun said...
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Wenyun said...

One of the optional paper(West et al., 1999), they assume that li->li'=lambda*li, then they get equation 4,5,6. However, I wonder whether we really need constant lambda to get equation 6. I thought even we assum li->li'=lambda.i*li. We can still follow steps from equation 4 to equation 6. Finally, we still get a'==lambda^epsilon.a. This result means that arbitray scale transformation on the network: li->li'=lambda.i*li still support 3/4 theory.

Fred Whiteman said...

Hamilton et al. are particularly interested in the idea that the flow of genes, other information, and material resources may all scale similarly. How could this be tested more specifically? If these three scale similarly, we ought to be able to figure out the rates of transfer among groups of different sizes and see if they all scale to a similar power.

Steven M. said...

Hamilto et al look at fractal nature of group hierarchies in hunter gather socities.

What data are availible to look into the same trends in modern society?

dodegard said...
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Justin Smith said...

I'm confused about what's being measured by Moses and Brown. They're supposedly testing how human energy consumption relates to fertility, but leave out ten nations marked as outliers due to their extremely high energy production. Which is it?

tlvandeest said...

In their discussion, Bettencourt et al mention that in principle there is no limit to the size of a city. But going back to the Tainter et al article, with the example of the collapse of the Roman Empire due to inability to sustain the wealth needed to feed the organization, wouldn't lack of resources eventually win out over the pace of innovation? No matter the rate of innovation, will it always be able to stay far enough ahead of the limited resources to continue urban growth? And, if innovation needs to accelerate with each cycle, what happens when innovation cannot happen fast enough to continue driving growth? Wouldn't that indicate that there must be a minimum time scale for innovation?

Fred Whiteman said...

In the Bettencourt et al. paper, the authors state that cities which have growth rates constrained by wealth and innovation will eventually crash unless “successive cycles of superlinear innovation” take place. What would constitute these? If innovation is causing the growth, how can it also slow down the growth?

dodegard said...

How could adaptive cycles be used to reach sustainability by unerstanding the Life History/energy pc trends in Moses and Brown's paper?

helen elizabeth said...

My question is in line with Justin's. I see that the outliers are major oil producers. I would be interested to know which oil countries are outliers. When looking at trends in fertility and education, you often see that with increased education you have lower fertility rates, except in the Middle East. I wonder if this is echoing that same pattern.

Michael said...

What is the defined population threshold for urban used by Bettencourt et al.?

helen elizabeth said...
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Wenyun said...

Fertility rates of primates are known to be lower than other mammals. Does this mean the energetic investment in each offspring higher in primates than other mammals? Why should this happen?

helen elizabeth said...

Why just focus on group size - vague references to efficient or optimal energy/information transfers within networks without considering
resource base, soil condition, or other geographical features that increase energy concentration--Is this where nodes start? Probably.

Senorita Myra said...

This idea of pace in the Bettencourt paper makes me curious as to whether it is spatial, temporal, or pace of exchange of energy between systems? The idea of it sounds Holling-like, or am I just thinking that cause I'm a Holling fan? Pace in this paper assumes there is a cycle and certain stages to the cycle right?

Dan said...

Taking queue from Marcus, but in the opposite direction, it may be fruitful to look at power functions with respect to the next level up from the urban systems, namely regional systems. Urban systems are reliant on regional networks to provide food and other energetic commodities such as oil. How far can these biological power functions take us? Would this give us a more complete picture of what will affect population growth,, levels of social and economic development, and the ecological footprint of modern man?

Tracy Brannan said...

I like the idea of relating a city to an organism. It has to be resource dependent and I would think that the resource dependence would be more prone to supply failures interupting "organism" function.

Tracy Brannan said...

The Fertility paper was interesting especially regarding decreased fertility resulting from the high cost of energy production.

Have there been any additional studies of this type?

tlvandeest said...

Moses and Brown discuss how the flow of energy within modern post-demographic transition societies increases, as well as an increase in the time invested in that energy and the infrastructural cost of its transport. I thought that it was interesting they point out that there is a virtual infrastructure in place along side physical infrastructure, taking into account the role of government and research. They place the research they and others are conducting into the equation and feeding part of the system, rather than placing it outside or on the periphery as implied by many studies. Do others also address directly the place of the research we are reading about and the products of that research into the systems and scaling patterns?

tlvandeest said...

Moses and Brown discuss how the flow of energy within modern post-demographic transition societies increases, as well as an increase in the time invested in that energy and the infrastructural cost of its transport. I thought that it was interesting they point out that there is a virtual infrastructure in place along side physical infrastructure, taking into account the role of government and research. They place the research they and others are conducting into the equation and feeding part of the system, rather than placing it outside or on the periphery as implied by many studies. Do others also address directly the place of the research we are reading about and the products of that research into the systems and scaling patterns?

dodegard said...

What could a closed island-nation like Cuba show about the relationship between life history traits and energy used?

Dan said...

In the Bettencourt et al article it was a little unclear why demand on infrastructure (linear association with city size) would decrease while there is faster than exponential growth (See page 7306 2nd paragraph. Wouldn't demand on infrastructure per capita remain static?

Anonymous said...

Along with Helen's question: I wonder if middle eastern country populations also have similar life spans as other countries included in the study? It seems to me that either there is little variation in expected human life span around the globe, or either these papers are ignoring a very important life history trait that affects reproduction.
Myra

Aaron McCarty said...

Just a thought...Moses and Brown cite unspecified "social and economic conditions" to explain the high fertility of the wealthy Gulf states and the low fertility of the comparatively poor former Soviet republics and Cuba. One possibility:

Education, as well as being expensive, is also time consuming—time that could have been spent finding mates and raising children is instead spent obtaining knowledge and skills that will make one an attractive mate in the first place. In the energy-rich states of the Middle East, it is possible to become successful and wealthy by literally “striking it rich,” or by having connections to a powerful family. Thus, compared with Western democracies, a higher education may not be as important to success, and fertility could remain higher. Likewise, Cuba and the former Soviet republics place a heavy emphasis on education (Cuba has the world’s highest literacy rate); even though they are currently relatively poor, there may nonetheless be strong social selection to delay reproduction.

Aaron McCarty said...
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