[ExI] Multiplicity of similar species: what's the mechanism/explanation?

[BillK]

On 9/28/09, Max More wrote:
> The Angry Evolutionist
>  By Richard Dawkins
>  http://www.newsweek.com/id/216140
>
>  (1) Dawkin says: "My favorites, however, are the free-living turbellarian
> worms, of which there are more than 4,000 species: that's about as numerous
> as all the mammal species put together."
>
>  That made me think again about the curious fact (I least I think it's a
> fact, without checking) that there are vastly more species of insects
> (especially ants) and arachnids as there are mammals or "more complex"
> creatures. I realized that I don't really know why that's the case. Right
> now I'm too lazy to try to find an answer in my biology books. I can make
> some guesses (like "a simpler/smaller genome varies more, and each variant
> finds sufficient room in the same ecological niche"), but I'd like to hear
> if there is a well-developed and compelling explanation.
>


I think this answers your first question.

<http://www.sciencedaily.com/releases/2007/04/070403112553.htm>

Why Are There So Many More Species Of Insects?
Because Insects Have Been Here Longer

ScienceDaily (Apr. 4, 2007) — J. B. S. Haldane once famously quipped
that "God is inordinately fond of beetles." Results of a study by Mark
A. McPeek of Dartmouth College and Jonathan M. Brown of Grinnell
College suggest that this fondness was expressed not by making so
many, but rather by allowing them to persist for so long.

This is a surprisingly simple answer to a fundamental biological
puzzle. They accumulated data from molecular phylogenies (which date
the evolutionary relationships among species using genetic
information) and from the fossil record to ask whether groups with
more species today had accumulated species at faster rates.

Animals as diverse as mollusks, insects, spiders, fish, amphibians,
reptiles, birds, and mammals appear to have accumulated new species at
surprisingly similar rates over evolutionary time. Groups with more
species were simply those that had survived longer. Their analyses
thus identify time as a primary determinant of species diversity
patterns across animals.
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BillK