Isn’t it also true, I remember reading but dont have the literature handy and am out so not in a great place to search that reproductive viability varies in 1st generation bird hybrids by gender?
I see to remember reading at least in ducks and other waterfowl where hybrids are not uncommon there is a difference in the fertility between male and female
Red herring was probably the wrong word, being mischaracterized is probably better. This post may be me reading into meaning a little too much, but I think it is important to clarify how significant hybridization is, both for understanding the threats to spotted owls and potential management options.
Most birds in the area are one of the parent species, not F1 hybrids or back crosses even after swamping with barred owls. There may be certain pressures favoring hybrid pairing, but that has not been shown, and there are strong pressures against hybrids (evidenced by the dominance of parent species in overlap zones). Predominantly one group (spotted owl) is being replaced by another group (barred owl). I’m not saying that there are not species concepts that would call this situation one species, but when looking these groups at a population level it seems to be predominantly an example of interspecific competition vs intraspecific competition.
What is not happening is widespread or even detectable levels of gene flow between the parent groups. (I’ll cite this time 
)
Not necessarily, this paper refers to a hybrid between two subspecies of barred owl, maybe you can use that to read further into how the authors feel about the significant genetic difference between the two subspecies. 
That is true, it is called “Haldane’s Rule”, and it is the pattern that the sex that has two different sex chromosomes (XY male mammals or ZW female birds, etc) tends to suffer from reduced hybrid fitness earlier during the divergence of two species than the other sex (XX female mammals or ZZ male birds). So, in birds when hybrids have reduced fitness, it tends to be reduced more in females than in males. That could partly explain why male hybrids are seen more often than female hybrids (on top of the fact that male birds are often easier to identify).
I had decided against mentioning infraspecific hybridization for the sake of simplicity, but I suppose the broader way of putting what I meant is “it’s hybridization because they’re different taxa”.
Do birds have different sex chromosomes than mammals O_O ? I don’t think they ever taught that in my high-school biology courses.
I googled it right after I posted. I’m just mildly shocked that no one taught me that in school (or perhaps I just forgot). I remember my HS bio teacher was very excited to tell everyone that strawberries have octoploid DNA, but it seems odd that he wouldn’t have mentioned this.
For sure! There is a tonne of variation in sex determination systems in different animals. In some it is not even genetic, and in others it is at the whole genome scale with diploid females vs haploid males. A lot more complicated than XX and XY!
Temperature dependent determination in some reptiles such as crocodilians being one I assume. What other types are there?
Some clownfish change sex based on social cues. Protandrous clowns that live in groups move up through the group from neuter to male to female based on their size relative other members of the group. Sequential hermaphroditism is genetically based, I suppose, but in a very different way than XY and ZW work.
Temperature dependance is probably the most common non-chromosomal sex determination system, and then there are species that change sex based on social or chemical cues like pmeisenheimer mentioned. Some species use sequential hermaphroditism, where they start out one sex when young and then transition to a different sex when they are larger. One pretty unique system is a worm Bonellia viridis which will develop as male if the larvae touch a female, otherwise they will become female. Some ferns do something similar, where gametophyte ferns that are growing near a female can become male in order to promote outcrossing, but could otherwise become hermaphroditic if they did not sense a female nearby. A lot of diverse strategies out there!
Blockquotey some widely accepted definitions of species that means they are not reproductively isolated and therefore not separate species.
I thought the biological species concept was more or less gone? Given the occurrence of ring species in birds and salamanders, the hybridizations between coyotes and red wolves, the truly weird hybridization you can see in herps…I thought that concept had more or less fallen out of favor. I know it wasn’t taught as the gospel truth back when I was attending college (pre-07).
Do you have a particular example in mind?
This is interesting. I’m learning quite a bit on this topic.
It certainly should be gone but it is still widely cited, including on iNat. Take a look at how the red deer/wapiti/sika deer complex, a more or less obvious candidate for ring species, is referenced. As I said, there are other species concepts that work at least as well.
Application of species concepts varies greatly among taxa. Even among the community that readily acknowledges the inadequacy of the biological species concept there is a lack of clarity about what a species actually is. It doesn’t help that some management bodies have adopted legal definitions of species that lump species, subspecies, varieties, populations , etc. There is a tendency these days to use mitochondrial nucleic acids as measures of isolation but the measurement of divergence of base sequences is just a proxy for time since divergence of lineages and passage of time does not equal speciation. It’s a useful proxy but it doesn’t follow from any definition of what a species actually is that is consistent across taxa.
Ultimately, the concept of species is an artifact from the days of natural history when it was taken as given that the study of taxonomy was a matter of cataloguing the magnificence of Biblical creation. Species were assumed to have been created as unique expressions of a divine plan. It’s a rigid, angular framework forced on a messy, amorphous biological reality where there are exceptions to almost every generalization.
The concept of evolutionarily significant units was originally proposed, in part, to deal with the fact that conventional taxonomy failed to reflect genetic diversity among subsets of many species. It, or something like it, is probably a more useful way of talking about a lot of conservation biology. As for the barred owl-spotted owl interaction, it is pretty clear that each is evolutionarily significant, however one prefers to describe their taxonomic status.
I would like to thank everyone so far for their thoughtful responses. The thread sort of wandered off topic a bit, but it has been wonderful side trip. I’ve learned so much, not only about spotted owls, but about sexual determination and species definition as well.
One of the things that struck me early on was how complicated things were. Whatever happens with the spotted owl will likely be related to some sort of political decision - I struggle to see how successfully politicians can navigate (or understand) all the complexities - both biological and social - of an issue like this. And I would like to reiterate that I have no agenda here.
It has been interesting, thanks for kicking it off. I do think the social/political aspects of issues such as this (or the issue of logging, as mentioned in your original post) are fascinating in what they reveal in values and biases in individuals, societies and government. I very much doubt the US could pass something like the Endangered Species Act today, we seem to be a long way from that era of the 1960s and 1970s when acts like the Wilderness Act, Clean Air and Clean Water acts, the Endangered Species Act, were passed. You asked a question a few posts back -
If most extinctions are the result of mortality or habitat loss/degration as a result of the human population (the space required for it, the exploitation needed to produce the resources to feed its economic engine, as well as the many exhaust products of that economic engine), it’s of interest to look at the US population growth. In 1973 when the ESA was passed, the estimated US population was a little over 215,000,000. In 2020, the estimate was a little over 331,000,000, a 45% increase in the 47 yr time span, and if current trends continue the estimate for 2050 is 438,000,000, which would double the population of the year the ESA was passed. So yeah, i think for the first part of your question, it would seem unavoidable that extinction become inevitable for some species.
That is interesting. Today, in the same Newspaper that started this off, was an opinion column - " Climate strategy must embrace equity and justice". It was all focused on Human equality and justice, and made no mention of the non-human life that would also will be affected. So I believe that for the most part, “values” and equality are applicable only to us (humans).
I’ve read a number of papers on how plant community and animal distributions may shift as a result of modeled climate change, but one thing i’ve yet to see are papers detailing how the human footprint may need to change, whether or to what extent human population or agricultural centers will need to shift. How that footprint will need to change would seem to be a large determinant of how or where biodiversity might be conserved in the future, since it seems likely or even logical that our species will prioritize its needs over that of other species.
This paper discusses some of what you are referring to, about how the ideal niche of humans will shift with climate change (quite disturbing results) “Future of the human climate niche” https://www.pnas.org/content/117/21/11350 (Open access)
It seems that a lot of the densely-inhabited areas of the world will become much less suitable for humans, but whether people will actually be able to migrate to track their niche is another question that will depend on social and political factors.
Thank you much for posting the reference. Figures 3 and 4, and the associated text, are very sobering. Will have to dig around in the lit cited for more.