Agree. So for us humans we might think that one "hybrid" event every year or every few years will make no difference and the populations will remain "distinct". But because of the speed at which many [not all] genes evolve [slowly] then even this low level of genetic interchange can be enough to prevent the populations diverging genetically.Puzzled. If a bird from one population/species breeds successfully - even only once - with, and within the range of, birds of another population/species then that is gene-flow between those populations, even if only in one direction and minute.
and not because they have smith genes but because of intraspecific variation
The recent research on redpolls proposed lumping them because it found that they "lack population genetic structure by either geography or ecotype [phenotype] boundaries" and that genetics failed to group the individuals according to their current species classification. The researchers suggest that phenotypic differences are probably driven by environmental factors.Yes we can see different more or less well marked phenotypes but then we can for redpolls too...
Well I've asked about this before. I'm unaware of any good recent molecular studies. I'd be keen to know what and how extensive any differences are. For example, I'd be willing to bet many [herring, caspian etc] are less divergent than mainland and Gran Canaria robins. There are small but consistent differences between populations of humans... [that's how we can reconstruct past migration patterns of H. sapiens out of Africa etc] ...but sensible people still treat us as one species.The recent research on redpolls proposed lumping them because it found that they "lack population genetic structure by either geography or ecotype [phenotype] boundaries" and that genetics failed to group the individuals according to their current species classification. The researchers suggest that phenotypic differences are probably driven by environmental factors.
I don't think there has been any suggestion of similar issues with gulls. EHG and AHG do have consistent genetic differences (albeit small ones) between populations.
Thanks I was [vaguely] aware of this. See Fig 1.2 f), the bit highlighted in the rectangle for an example of what I was talking about. This clade is unresolved—genetically indistinguishable. Without being able to read the details, I can see from Fig 3.9 that at best divergences are very recent for larger gulls: of the order of <=500,000 yrs. I understand Fig 3.14 to indicate [very] incomplete lineage sorting.If you're into genetics, The Fern, the dissertation work of Viviane Sternkopf might be of interest to you, attached. But I doubt you would be able to read it as it is in german. Maybe some of the figures give you some insight, though.
Just to clarify this aside to this interesting thread - re Lesser Black-back Gulls - turns out they colonised Greenland in the 1980s. Whence wintering birds and then more latterly start of breeding birds to N America came from (earlier vagrants from Iceland or elsewhere).I was thinking of it as an example where in the recent past (last couple of centuries?) it wasn't an American breeder - presumably the earliest ones in N America would still also have hybridised with AHG. (As an aside - how recent is the Greenland population of LBBG?) as an example of a vagrant hybridising.
One difference between large gulls and redpolls is that, with a few notable exceptions (the whole Thayer's/Kumlien's/Iceland conundrum, for example), a lot of large gulls breed in areas where lots of ornithologists and field birders live. Thus, even leaving aside instances of hybridisation/gene flow, we can almost intuitively grasp that, say, (European) Herring and Lesser Black-backed Gulls behave as good species, regardless of the genetic differences. We can see what goes on, and they clearly act as separate entities most of the time. Therefore, while grasping that a species is actually a human concept to help us make sense of the natural world around us, these two birds would qualify as 'species' under any species concept, and many other large white-headed gulls are similar. Redpolls, on the other hand, largely breed in remote northern areas, at least most of the taxa do, so we have far less of an idea of what is going on where taxa meet. Though, being selfish, as I've only seen Lesser Redpoll myself, I'd not be averse to a lump of them all...I don't think there has been any suggestion of similar issues with gulls. EHG and AHG do have consistent genetic differences (albeit small ones) between populations.
Here's the nub of it. Imposing a discontinuous taxonomy ("species", "genera" etc) on a continuously varying thing (populations of individuals) will never be anything other than subjective. So "... Intuitively grasp...would qualify as 'species'..." can only really be understood as your personal view (which you're welcome to of course). I try to come to my own position on these things---and it may differ from yours. We'll both be equally right (or wrong).Thus, even leaving aside instances of hybridisation/gene flow, we can almost intuitively grasp that, say, (European) Herring and Lesser Black-backed Gulls behave as good species, regardless of the genetic differences. We can see what goes on, and they clearly act as separate entities most of the time. Therefore, while grasping that a species is actually a human concept to help us make sense of the natural world around us, these two birds would qualify as 'species' under any species concept