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180 comments on DrumBeat: August 13, 2006

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Leanan on August 13, 2006 - 8:24am Permalink | Subthread | Comments top
Got the Sept. 2006 issue of Discover yesterday.  (It's a special issue on "Does NASA have a future?")  

There was an interesting bit about urban sprawl. ("Is Urban Sprawl an Urban Myth?")  Turns out, it's not as bad we think.  Cities have grown, but the development is not more scattered.

[University of Toronto economist Mattheew] Turner's observations of individual cities are also surprising.  Miami, for example, is about a third more compact than New York or San Francisco, while Pittsburgh sprawls more than even Atlanta or Washington.  He attributes about 25 percent of difference to topological factors like groundwater accessibility, weather, and mountains.  The rest is pure human influence: Cities constructed during the automobile era are more scattered, while cities where employment is centralized and taxpayers shoulder more infrastructure costs tend to build on a relatively cheaper and more compact scale.
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Robert Rapier on August 13, 2006 - 8:31am Permalink | Subthread | Parent | Comments top
There was an interesting bit about urban sprawl. ("Is Urban Sprawl an Urban Myth?")  Turns out, it's not as bad we think.  Cities have grown, but the development is not more scattered.

I guess it depends on your metric. If you compare us to Europe, then we have horrendous sprawl. Over there, you come upon a compact little village, and then leaving the village you are back into farmland unspoiled by half a dozen little subdivisions. Here, it seems like we have just sprawled all over good farmland, and I think we will ultimately regret that.

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alistairC on August 14, 2006 - 4:33am Permalink | Subthread | Parent | Comments top
Depends where you look, Robert... France has sprawled catastrophically over the 20 years I've been commuting here. though, it's true, generally by expansion around the nucleus of existing villages, rather than green-field development. But there has been a major phenomenon of urban flight, and it's still going on. Will probably take a few years, and political will, to turn around before we start re-densifying the places with the good infrastructure.

When visiting the US, I was struck by the impression that only the best, easiest agricultural land is used. e.g. the hills of North Carolina : all that superb rainforest was destroyed, the land grazed or cropped for a little while (a generation or two?) and is now reverting to forest. What happens next? Clear the forests again to plant biomass for fuel?

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Leanan on August 13, 2006 - 8:32am Permalink | Subthread | Parent | Comments top
Another interesting bit from this issue: an estimate  of how much energy it takes to evolve a new species.  Turns out, life ain't cheap.  It's actually incredibly expensive.

Drew Allen, an ecologist at UC Santa Barbara, worked out how much energy it takes to generate a new species.

The answer: a staggering 10^23 joules, more energy than is released by all the fossil fuels burned on Earth in a year.

...He found that although the amount of energy required is constant, new species form more quickly near the equator because heat speeds up both metabolism and the rate of genetic mutations.  

Even Darwin noticed that biodiversity is more plentiful in the tropics.  "But the idea that temperature affects speciation rates through its effects on molecular-level processes is brand new," Allen says.

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odograph on August 13, 2006 - 8:50am Permalink | Subthread | Parent | Comments top
I may have to get to the library for that, sounds interesting.   FWIW, I remember that African Chchlids are sometimes put forward for the "reocrd" in speciation, but at 15K years or so it's not exactly fast on a human timescale.

"Interestingly, Lake Victoria dried up approximately 12,00-15,000 years ago (before becoming a lake again), suggesting that the rate of speciation in Lake Victoria cichlids is the fastest ever reported for vertebrates."

http://animaldiversity.ummz.umich.edu/site/accounts/information/Cichlidae.html

Thanks for the great load of articles Leanan.

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FossilFool on August 13, 2006 - 9:03am Permalink | Subthread | Parent | Comments top
That's not good. I read a book about agriculture and such. We need to change the varieties of crops every five years to keep up with developing resistances of pests and other such things. That won't be good when the farmers don't have that.
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Engineer-Poet on August 13, 2006 - 9:30am Permalink | Subthread | Parent | Comments top
10^23 joules is about what Earth receives from the Sun in 16 hours.
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ET on August 13, 2006 - 12:27pm Permalink | Subthread | Parent | Comments top
Diamond discusses the issue of more species at the equator. I forget whether it was in 'Guns Germs & Steel' or 'Collapse' but doesn't posit any root causes. I really am suspicious of this energy calculation though. Energy necessary to form a new species??? How the hell can that be measured? Bacteria can form a new species in a few hours. I don't think this can be either accurate to any degree or useful except in a 'golly, gee whiz' kind of way.
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Robert Rapier on August 13, 2006 - 3:52pm Permalink | Subthread | Parent | Comments top
Energy necessary to form a new species??? How the hell can that be measured? Bacteria can form a new species in a few hours.

Yeah, I thought the same thing. The nylon-digesting bacteria resulted from a frame-shift mutation. That was just a normal division process that got screwed up. All it takes is one division in some cases, as you say, to form a new species.

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ET on August 14, 2006 - 11:10am Permalink | Subthread | Parent | Comments top
Actually, gene-swapping or 'horizontal-gene-transfer' is ubiquitous among bacteria so it doesn't take mutations at all for them to form new 'species' however one defines a species among bacteria. Good evidence exists that HGT occurs somewhat higher up the evolutionary ladder as well.
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Apuleius on August 13, 2006 - 10:09pm Permalink | Subthread | Parent | Comments top
The definition of species is dependent on context. For sexually reproducing organisms 'species' is much more easily defined, and the pace of speciation is worth studying. Speciation in bacteria is a more subjective matter.
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