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Re: Big-brained birds evolve faster



Clearly the gold medal for the greatest diversity goes to the Insecta (or more broadly the Arthropoda). Not much in the way of brains though. It would seem that diversity is more closely linked with body size. A group with small body size can more effectively partition the environment into specialized niches and achieve greater diversity.

Dan

Erik Boehm wrote:
--- On Fri, 8/22/08, Roberto Takata <rmtakata@gmail.com> wrote:

Well, we have at least four independent natural experiments
with wings
that we could correlate with biodiversity: insects,
pterosaurs, birds
and bats.

So then should we examine the natural experiments with big brains, and see their effect on diversity:

Elephants: 2 extant species.

Homonids: 1 extant species (and the earlier homonids were rather small brained, 
bipedalism before large brains).

Dolphins: a fair amount of diversity, but declining, mainly due to human 
activity (so not really applicable), but relatively low to begin with.

All the above species are rather large, and mammals, and small size tends to 
lead to larger populations and increased diversity anyway.

Where does one draw the line at "big brained"? Wings ars a fairly obvious 
trait, but brain size (which is continuous)?

A whale could have a much smaller brain:body mass ratio, and still have a lot 
more brain mass directed towards cognitave function.

Do we include all primates? (as mentioned, primates, including most homonids, 
have small brains relative to the likes of humans and the above mentioned 
mammals)

Whales? Pinnepeds? Crows? Raptors?

Do we include Parrots? is parrot diversity due to intelligence, or habitat 
isolation and sexual selection? Does increased intelligence lead to more 
complex mating displays, and more diversity on the basis on sexual selection?

Are we talking species diversity, or diversity of ecological niches?

Around here we have "wild" peacock and "wild" turkey (I don't think either are 
native), as far as I can tell, they do the same darn thing - both walk around mostly, are about the 
same size and build, and will run away quite a bit before attempting to fly, which they do 
clumsily, and seem to visit the same areas, one day a flock of peacocks may be foraging in one 
area, the next week, same area, its turkeys... as far as I can tell they are occupying the same 
niche, whith the only difference being plumage for sexual display.

I assume the point is to try and link intelligence with diversity?

Surely intelligence can open up new niches, which should increase diversity, but it can also allow for one form to make use of many niches, decreasing diversity(the best example of this being humans).


Given the difficulty in assesing intelligence, the continuous nature of brain size, and the limited data points available, difficulty of distinguishing the effects of brain size vs some other morphological characteristic, I doubt any convincing argument for a correlation can be made one way or the other, but it is interesting to think about.






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