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Author Topic:   Evolution Occurs Faster at the Equator
Quetzal
Member (Idle past 3982 days)
Posts: 3228
Joined: 01-09-2002


Message 16 of 18 (312371)
05-16-2006 9:35 AM
Reply to: Message 15 by fallacycop
05-16-2006 12:29 AM


The problem with the article, and indeed this discussion, is that the factors influencing biodiversity are extremely complex. As scoff noted, the geology of the region in question has a lot to do with biodiversity, as does the availability of niches (heterogenous vs. homogenous habitat, for instance). Observations have shown that niches seem to be more finely divided in the tropics than elsewhere, but the causal explanation is still wanting.

In the case you mention (the effect of genetic drift on small populations) rate of evolution may increase, but rate doesn't necessarily increase biodiversity - which is the heart of my quibble with the article. Take the case of the Galapagos as a for-instance, which scoff mentioned. It is actually a biodiversity-impoverished area overall. However, it has a very high level of endemism and both speciation and incipient speciation, indicative of a high rate of evolution. The islands are only about ~10 my old. Part of the explanation is geologic, some is topologic and climatic, some is ecological (dispersal ability, colonization sampling error, etc).

Mutation, of course, is the primary means of increasing inheritable variability in a population over time. It therefore stands to reason that whenever you see a high rate of endemism and/or speciation, the rate of mutation is also high. The cause of the mutation rate can be argued, as can the relative contribution of drift.

I think another issue we may be having trouble with is the use of the term "biodiversity". How you measure this is problematic, with a number of differing definitions leading to variant results. For example, in my work we usually use "total number of plant species" as the yardstick. This is consistent with the IUCN's definition, and is how global biodiversity hotspots are determined. Another widely used (and useful) definition is the rate of endemism. As you can plainly see, if we use the endemism scale the Galapagos show very high biodiversity, whereas if we use the species number definition, Galapagos is impoverished. I suppose as long as everybody knows which measure is being used, there isn't a problem.


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DrFrost
Inactive Member


Message 17 of 18 (312479)
05-16-2006 2:08 PM


biodiversity
The most diverse place near my location (as far as plants are concerned) has nothing to do with heat or radiation. There's a small section of wilderness near where I live with far more plant species than any other area within thousands of miles. It's not the warmest or highest spot by any means. It turns out, due to it's location and geology, that as glaciers moved across the area they would naturally deposit some of the material they had picked up at this location (rocks, dirt, seeds, etc.). This led to it's rich soil and wide diversity of plant species (or so I've been taught).

It causes me to wonder if there could be another explanation for the biodiversity in these cloud top forests other than radiation.

Edited by DrFrost, : EDIT: Fixed syntax errors.

Edited by DrFrost, : Fixed mispelling (I really should have proofread this better the first time).


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 Message 18 by Quetzal, posted 05-16-2006 3:31 PM DrFrost has not yet responded

  
Quetzal
Member (Idle past 3982 days)
Posts: 3228
Joined: 01-09-2002


Message 18 of 18 (312502)
05-16-2006 3:31 PM
Reply to: Message 17 by DrFrost
05-16-2006 2:08 PM


Re: biodiversity
It causes me to wonder if there could be another explanation for the biodiversity in these cloud top forests other than radiation.

I think that's a given. The article made a simplistic equivalency that falls apart when you look at the details (not the quality work I usually see in PNAS). Higher heat = higher metabolism = higher mutation rate = higher evolution rate = higher biodiversity. I don't think that is justified by the evidence. They used what appears to be a very biased sample that showed the effect they were looking for. What a surprise.


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 Message 17 by DrFrost, posted 05-16-2006 2:08 PM DrFrost has not yet responded

  
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