Hi Perdition,
In the Green Warbler example RAZD has brought up, there seems to be multiple species that can interbreed with the ones near them, until the ring closes and the two "ends" can't. Or is there only one species...or is there two, with some undefined line somewhere in the middle? The picture, with the multiple colors shading into each other seems to indicate multiple, interbreeding species.
They are currently classed as multiple varieties of the same species (hence the three part names with the first two being the normal species genus\species pair and the third being the variety name)
There are also four hybrid zones between the five daughter variety populations. The hybrids do not appear to infiltrate back into either of the neighboring variety populations, which leads me to conclude that the varieties are
demes (thanks Modulus):
quote:
Message 10: Groups that could produce offspring with outsiders but that do not breed with them are sometimes called 'demes':
quote:
In biology, a deme is a term for a local population of organisms of one species that actively interbreed with one another and share a distinct gene pool. When demes are isolated for a very long time they can become distinct subspecies or species.
Each of the daughter variety populations meet the definition for deme as given.
It certainly is. And Aiki says that the two populations can breed, but often don't because of the timing of their arrivals. Would a speciation event require them to be unable to interbreed, or is it enough to simply show that they tend not to?
It is not known (at least by me) that the two northern varieties of greenish warbler cannot interbreed, just that they don't: their behavior blocks them from seeing the other population as potential mates.
Similarly, with the blackcaps, we observe that they normally don't breed, due to timing (rather than behavior), BUT they also note that the migratory behavior is different for the few hybrids from captive breeding experiments:
Message 1: ... Breeding studies with captive Blackcaps have shown that the migratory direction is genetically determined. Two WNW-migrators produce WNW-migrating offspring, the same goes for the SW-migrators. Pair one of each, and the offspring set off to migrate in an intermediate direction. ...
Thus any naturally occurring hybrids would possibly not survive their altered migration, and this would help solidify the genetic differences.
As Wounded King (
Message 11) points out, there is variation on where biologists draw the line. There are some that are "lumpers" and some that are "splitters" with different opinions on how many individuals fall into the different species categories.
Message 9: Well, as with any mutation, they need to grant the ability to exploit a food source or exploit an old one better, to be beneficial. The fact that the food source is left out by people is almost irrelevant. If the people stopped, the mutation would no longer be beneficial, but this is no different than any other environmental change that removes a food source.
Indeed, this is an example of natural selection operating on the different varieties\behaviors, and if the opportunities and challenges change it is possible that the populations would merge, or that one or the other would die out.
Enjoy.
ps - also avid birder
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