Species limits and taxonomy in birds (1 Viewer)

[jurek]

The Fern is absolutely correct. I don't know why people are arguing about taxonomy not having a degree of subjectivity. Scientists have discussed subjectivity in what is or isn't a species for hundreds of years. Charles Darwin even wrote about it in the Origin of Species.

This is because the species is a folk concept, coming from the pre-science period.

Ancient people did not deal with the problem that e.g. the same animal could look different in faraway locality. The concept of species was used already when people did not yet even know that individuals of one species are biologically related. In the times of Aristoteles, it was believed that e.g. mice and flies are created spontaneously from dead matter wherever there is rotting food.

So scientists try to fit themselves into what is a practical concept used by humanity. Strangely, however, they never tested their creations. It would be logical e.g. to create a poll among birdwatchers, hunters and farmers what is one species and what is not, and choose the definition which fits it the best.

As speciation is a constant and continuous process, there are going to be species that phenotypically (or genetically, or ecologically) reside in a gray zone between "clearly not distinguishable" and "absolutely a distinct and obvious separate species".

That is why genetic difference is better than species-based description. Genetic difference is just a number getting bigger as subspecies turn into species. One needs not to know or care whether populations crossed the limit and for which definition of species.

For the purpose of describing conservation value of e.g. a national park or an Important Bird Area, one can sum these numbers just as one counts species. The number will be uneven, but it will still describe the conservation value of the place, and could be prioritized. This solves lots of problems, including how to define the conservation value of places where weak species / strong subspecies are numerous, due to their geological history. Examples are Mexico vs USA or Cape Verde Islands vs. mainland Europe.

 

[Mysticete]

This is because the species is a folk concept, coming from the pre-science period.

Ancient people did not deal with the problem that e.g. the same animal could look different in faraway locality. The concept of species was used already when people did not yet even know that individuals of one species are biologically related. In the times of Aristoteles, it was believed that e.g. mice and flies are created spontaneously from dead matter wherever there is rotting food.

So scientists try to fit themselves into what is a practical concept used by humanity. Strangely, however, they never tested their creations. It would be logical e.g. to create a poll among birdwatchers, hunters and farmers what is one species and what is not, and choose the definition which fits it the best.


That is why genetic difference is better than species-based description. Genetic difference is just a number getting bigger as subspecies turn into species. One needs not to know or care whether populations crossed the limit and for which definition of species.

For the purpose of describing conservation value of e.g. a national park or an Important Bird Area, one can sum these numbers just as one counts species. The number will be uneven, but it will still describe the conservation value of the place, and could be prioritized. This solves lots of problems, including how to define the conservation value of places where weak species / strong subspecies are numerous, due to their geological history. Examples are Mexico vs USA or Cape Verde Islands vs. mainland Europe.

This assumes that all taxa accrue genetic differences at the same predictable rate, which we know is completely false.

 

[jurek]

This assumes that all taxa accrue genetic differences at the same predictable rate, which we know is completely false.

No. Since genetic difference is what is irreplaceable once lost - humans cannot, at present, resurrect living organisms - this is what is conserved.
If two populations somehow accrued few genetic differences, they are little different so little is lost.

 

[THE_FERN]

For the purpose of describing conservation value of e.g. a national park or an Important Bird Area, one can sum these numbers just as one counts species. The number will be uneven, but it will still describe the conservation value of the place, and could be prioritized. This solves lots of problems, including how to define the conservation value of places where weak species / strong subspecies are numerous, due to their geological history. Examples are Mexico vs USA or Cape Verde Islands vs. mainland Europe.

Actually there are better ways. You could read one of my few (cough) published papers on the subject... [DOI 10.1007/s004420050804], and my thesis stuff on phylogenetic covariance. Old hat now, I suspect. (You can't sum genetic distance in the way you suggest. And you have to decide what distance metric to use—see previous posts.)

 

[THE_FERN]

No. Since genetic difference is what is irreplaceable once lost - humans cannot, at present, resurrect living organisms - this is what is conserved.
If two populations somehow accrued few genetic differences, they are little different so little is lost.

No completely disagree. Much genetic difference is irrelevant—it doesn't represent DNA which codes, which performs a regulatory or a structural function. I've mentioned this several times in the thread...

...It also ignores the sometimes large phenotypic effects of quite small genetic changes. Well-known ones in humans include thalassemia, sickle cell etc which confer some benefits to populations where they are prevalent (resistance to malaria) in the face of the obvious downside of genetic disease. Not all genetic differences are equal.

You equate difference solely with [presumably DNA] sequence differences. This ignores the emerging information we have about epigenesis, prions etc. A purely sequence-focused approach gives a very limited view of biology's rich tapestry, I suggest.

We are increasingly able to manipulate the biochemical background of organisms. This will eventually allow us to produce strong copies of extinct species [probably only recently extinct ones]. The importance of all the other things—things we might call "culture"—will become much more obvious then. We will struggle to get our reconstituted mammoth to integrate into the environment—even if we can find suitable habitat for it—because it will not have the benefit of other mammoths to learn from.

 

[njlarsen]

For the purpose of describing conservation value of e.g. a national park or an Important Bird Area, one can sum these numbers just as one counts species. The number will be uneven, but it will still describe the conservation value of the place, and could be prioritized. This solves lots of problems, including how to define the conservation value of places where weak species / strong subspecies are numerous, due to their geological history. Examples are Mexico vs USA or Cape Verde Islands vs. mainland Europe.

I really, really hope you did not actually mean what you wrote here. It reminds me of a story I read many years ago: Someone in charge of a reserve wanted to change the management of the reserve to increase the biodiversity within the area. They wanted to do that by changing part of the old growth forest to roads and semiopen areas so that there would be a greater variety present within the park. They completely ignored that the added species would be very widespread species with no conservation concern while some of the species negatively impacted were highly localized species with a very low density even where they did exist. Long live bookkeepers!

Niels

 

[jurek]

*add - I mean endemic species or unique species. This is how biodiversity hotspots are calculated normally.

By the way, I expected criticism that birds are nothing compared to genetic diversity of microorganisms. Which is countered that microorganisms are widespread - as far as known.

 

[Peter Kovalik]

Kevin Winker. An overview of speciation and species limits in birds. Ornithology, ukab006, https://doi.org/10.1093/ornithology/ukab006

Abstract:

Accurately determining avian species limits has been a challenge and a work in progress for most of a century. It is a fascinating but difficult problem. Under the biological species concept, only lineages that remain essentially independent when they are in sympatry are clearly species. Otherwise, there is no clear line yet found that marks when a pair of diverging lineages (e.g., in allopatry) become different enough to warrant full biological species status. Also, with more data, species limits often require reevaluation. The process of divergence and speciation is itself very complex and is the focus of intense research. Translating what we understand of that process into taxonomic names can be challenging. A series of issues are important. Single-locus criteria are unlikely to be convincing. Genetic independence is not a species limits requirement, but the degree of independence (gene flow) needs to be considered when there is opportunity for gene flow and independence is not complete. Time-based species (limits determined by time of separation) are unsatisfactory, though integrating time more effectively into our datasets is warranted. We need to disentangle data signal due to neutral processes vs. selection and prioritize the latter as the main driver of speciation. Assortative mating is also not likely to be an adequate criterion for determining species limits. Hybridization and gene flow are more important than ever, and there is a condition not being treated evenly in taxonomy: evolutionary trysts of 2 or more lineages stuck together through gene flow just short of speciation over long periods. Comparative methods that use what occurs between good species in contact to infer species limits among allopatric forms remain the gold standard, but they can be inaccurate and controversial. Species-level taxonomy in birds is likely to remain unsettled for some time. While the study of avian speciation has never been more exciting and dynamic, there is no silver bullet for species delimitation, nor is it likely that there will ever be one. Careful work using integrative taxonomy in a comparative framework is the most promising way forward.

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