What is a species? (1 Viewer)

[jurek]

If so, and we are not able to consistently place taxa in the right box, then it could be argued that the system has gone too far and is too granular.

Yes, this is what I believe. Both in the case of species and families.

But if species can be properly defined and may or may not be cryptic, then correct allocation is purely a human problem. The library system is right, we just struggle to use it!

The concept of discrete species is biologically untrue, that is birds called species on major bird lists contain more than 5% of hybridizing and non-monophyletic populations.

I remarked before that the library system of discrete species and subspecies is not needed for us. The concept became wrongly fixated sometime in the 1990s when ornithologists started using lists of all birds and early computer spreadsheets and databases. This seemed to be the top technology then.

Now it is perfectly possible to use not discrete categories. You have computer programs which lets you write, for example, a gull is 80x20 Herring x Caspian Gull and you scored 305.2 on your life list.

It removes the problem of hybrids and distinctive subspecies, which are not nothing but not a full species either. For a birdwatcher, one can even award higher rank to distinctive species, like Lammergeier or a Frigatebird, than to one more warbler or flycatcher. Or a higher rank for a colorful breeding plumage. All birdwatchers feel one is better than another, but the traditional bird list lets you only put seen or unseen.

 

[Jon.Bryant]

Your autocorrect's made a tiny oops

I have a tendency to make loads of typos, which I then try to edit - if is was a fibber, I would blame it on auto correct, but in reality it is just typing to fast and not thinking!

 

[Jon.Bryant]

for example, a gull is 80x20 Herring x Caspian Gull and you scored 305.2 on your life list.

This would be very complicated. Unless we went around testing every bird, it would need to be an individual judgement - so we would then be into that mode of 'that Jon Bryant cheats and always over-estimates - that hybrid gull he saw the other day was 10% max and he is claiming it as 50%!' Not that I would mind, as I am not competitive and my list is my list!

Also what would you do if you saw another gull that was a judged a 60/40 split. Add 0.2 presumably. But what if the bird was from the other end of the hybrid spectrum - you could argue you have seen 60% of Caspian Gull genes, so 0.6.

For me (quite ironically as I am trying to develop a listing and recording programme) I am not that bothered about the numbers. I am not even sure what my world list is - I only have an approximate number in my head. But I do like the thought of recording to the highest level of granularity, and don't mind if this means some fuzzyness. I would personally record in my dairy 'Herring Gull showing some anomalous characters of Caspian Gull' and forget the impact on my list. If I saw a 'Russian' Common Gull that fell short of the full range of characters, I would record it as either a 'probable' or 'possible henei', depending on how far off the mark it fell.

The concept of discrete species is biologically untrue, that is birds called species on major bird lists contain more than 5% of hybridizing and non-monophyletic populations.

This may be true, but what percentage of individuals within that 5% are problematic - say Blyth's Reed and Marsh Warbler hybridize, so these are two of the birds in the 5% you mention. But how common or rare is this hybridization in these species. If this is only 1 in 1,000, I think most birdwatchers could live with this, and statistically if you have seen two or more individuals (not from the same nest) the chances everything was a hybrid becomes vanishing small ( 2 birds = 1 in 1,000,000 or a 99.9999% chance you have seen the real thing). If we were to extrapolate this principle to all species, what percentage of all the individuals birds we see fall into the grey? There are probably more things that are wrong on my list due to my ID capabilities (particularly with South American empids), than created due to taxonomic messiness.

 

[bevbeverly]

This would be very complicated. Unless we went around testing every bird, it would need to be an individual judgement - so we would then be into that mode of 'that Jon Bryant cheats and always over-estimates - that hybrid gull he saw the other day was 10% max and he is claiming it as 50%!' Not that I would mind, as I am not competitive and my list is my list!

Also what would you do if you saw another gull that was a judged a 60/40 split. Add 0.2 presumably. But what if the bird was from the other end of the hybrid spectrum - you could argue you have seen 60% of Caspian Gull genes, so 0.6.

For me (quite ironically as I am trying to develop a listing and recording programme) I am not that bothered about the numbers. I am not even sure what my world list is - I only have an approximate number in my head. But I do like the thought of recording to the highest level of granularity, and don't mind if this means some fuzzyness. I would personally record in my dairy 'Herring Gull showing some anomalous characters of Caspian Gull' and forget the impact on my list. If I saw a 'Russian' Common Gull that fell short of the full range of characters, I would record it as either a 'probable' or 'possible henei', depending on how far off the mark it fell.

This may be true, but what percentage of individuals within that 5% are problematic - say Blyth's Reed and Marsh Warbler hybridize, so these are two of the birds in the 5% you mention. But how common or rare is this hybridization in these species. If this is only 1 in 1,000, I think most birdwatchers could live with this, and statistically if you have seen two or more individuals (not from the same nest) the chances everything was a hybrid becomes vanishing small ( 2 birds = 1 in 1,000,000 or a 99.9999% chance you have seen the real thing). https://writingbros.com/essay-examples/ helps me with my biological science exercises. The inspiring essay samples give me birds' identification and writing skills. If we were to extrapolate this principle to all species, what percentage of all the individuals birds we see fall into the grey? There are probably more things that are wrong on my list due to my ID capabilities (particularly with South American empids), than created due to taxonomic messiness.

Hi people. Yup, testing every bird is unrealistic, but obviously we can use visual cues, behavior, and habitat to make educated guesses.🤔

I mean yeah, people might have different opinions and biases, but that doesn't mean all identifications are useless. With practice, we can get pretty good at it - and I am already.

Everything is just so simple. If I saw a gull judged as 60/40 split, I'd add 0.2 to the appropriate category. And if a bird is mostly one species but shows some characteristics of another, I'd note that in my records without worrying about its impact on my list.

It's a personal thing, so let's keep an open mind and enjoy birdwatching in our own way, that's all.🤷‍♀️

 

[Jon.Bryant]

Interestingly I was recently on the Antipodes (well doing a zodiac cruise around), where there are two endemic parakeets. According to the expedition geologist, the islands are only 200,000 years old. This suggests to me that either speciation occurs much quicker than we think, or that in this case that speciation much have occurred elsewhere prior to colonisation.

This seems a common problem with New Zealand in particular, which has some relatively young geology - the main alps are said to be only 5 million years old.

I wonder if geologists and taxonomist have banged heads together, to determine if the concept of 10million years separation as a species limit, matches our knowledge of geological time.

 

[THE_FERN]

Interestingly I was recently on the Antipodes (well doing a zodiac cruise around), where there are two endemic parakeets. According to the expedition geologist, the islands are only 200,000 years old. This suggests to me that either speciation occurs much quicker than we think, or that in this case that speciation much have occurred elsewhere prior to colonisation.

This seems a common problem with New Zealand in particular, which has some relatively young geology - the main alps are said to be only 5 million years old.

I wonder if geologists and taxonomist have banged heads together, to determine if the concept of 10million years separation as a species limit, matches our knowledge of geological time.

I think the southern Alps are around 15 million years old. NZ was once much larger and in the far past, part of Gondwana. The recent distributions we see are relicts---it's extremely unlikely that something as ancient and distinct as the Stephens Island wren actually arose and was always only found there.

10 million years is quite a long time, at least in the Northern hemisphere. I've not done a review but get the impression that many species there are younger than this

 

[Jon.Bryant]

I am relying on the expedition geologist who advised the NZ alps were 5 million years old (not the NZ landmass as part of Gondwana). Unfortunately I cannot find anything on the net to confirm the age. Interestingly, the geologist advised the last min ice age in NZ was only 16k years ago, when sea levels were much lower (and therefore presumably the land area much larger). Rock Wren (presumably as ancient as Stephens Island Wren) cannot have survived in the alps during that period, but presumably moved to lower altitudes, then recolonised the alps later.

The reason I think this interesting, is that one mooted measure of a species is 3% divergence in DNA, which some parties infer is equivalent to a separation of 10 million years. If the Antipodes are only 200k years old (but have two endemic parakeets) then does this imply 1/ our assessment of the geological history is wrong 2/ our assessment of the rate of genetic change is wrong 3/ speciation in this case took place long before the islands formed (and the parakeets colonised the islands from a now lost origin) 4/ These ‘species’ do not have a 3% difference in DNA.

If the latter, then it seems a bit arbitrary to now use this yardstick for new assessments.

I suppose that looking at species in ‘young’ islands would be the first port of call, when looking for apparent species that have evolved quickly (and hence may not pass either the 10mya, the 3% DNA measure, or both). If ‘species’ on young island do show a 3% divergence in DNA, then surely it means scientific estimates for the pace of genetic mutation and hence speciation are inaccurate.

 

[Jon.Bryant]

Now I am confused. According to good old Wikipedia ‘The Homo genus is evidenced by the appearance of H. habilis over 2 mya,while anatomically modern humans emerged in Africa approximately 300,000 years ago.’

So why is divergence of 10mya often quoted for bird species (which generally have a much shorter life and quicker reproductive cycle than great apes and humans)?

Seems like an arbitrary measure back engineered to fit our ability to differentiate taxa. If we used a much shorter measure, then presumably a lot of subspecies (including some rather subtly ones) would qualify as species.

 

[T.O.]

I am relying on the expedition geologist who advised the NZ alps were 5 million years old (not the NZ landmass as part of Gondwana). Unfortunately I cannot find anything on the net to confirm the age. Interestingly, the geologist advised the last min ice age in NZ was only 16k years ago, when sea levels were much lower (and therefore presumably the land area much larger). Rock Wren (presumably as ancient as Stephens Island Wren) cannot have survived in the alps during that period, but presumably moved to lower altitudes, then recolonised the alps later.

The reason I think this interesting, is that one mooted measure of a species is 3% divergence in DNA, which some parties infer is equivalent to a separation of 10 million years. If the Antipodes are only 200k years old (but have two endemic parakeets) then does this imply 1/ our assessment of the geological history is wrong 2/ our assessment of the rate of genetic change is wrong 3/ speciation in this case took place long before the islands formed (and the parakeets colonised the islands from a now lost origin) 4/ These ‘species’ do not have a 3% difference in DNA.

If the latter, then it seems a bit arbitrary to now use this yardstick for new assessments.

I suppose that looking at species in ‘young’ islands would be the first port of call, when looking for apparent species that have evolved quickly (and hence may not pass either the 10mya, the 3% DNA measure, or both). If ‘species’ on young island do show a 3% divergence in DNA, then surely it means scientific estimates for the pace of genetic mutation and hence speciation are inaccurate.

The one benchmark of speciation is that there are no benchmarks and it makes no sense to use a blanket one for genetic differences or time of separation. Nature is far too complicated for that.


Btw your 10 mya example is more often used for splitting or lumping genera than species. Many good species are only separated 1 million years or less.

 

[THE_FERN]

I am relying on the expedition geologist who advised the NZ alps were 5 million years old (not the NZ landmass as part of Gondwana). Unfortunately I cannot find anything on the net to confirm the age. Interestingly, the geologist advised the last min ice age in NZ was only 16k years ago, when sea levels were much lower (and therefore presumably the land area much larger). Rock Wren (presumably as ancient as Stephens Island Wren) cannot have survived in the alps during that period, but presumably moved to lower altitudes, then recolonised the alps later.

The reason I think this interesting, is that one mooted measure of a species is 3% divergence in DNA, which some parties infer is equivalent to a separation of 10 million years. If the Antipodes are only 200k years old (but have two endemic parakeets) then does this imply 1/ our assessment of the geological history is wrong 2/ our assessment of the rate of genetic change is wrong 3/ speciation in this case took place long before the islands formed (and the parakeets colonised the islands from a now lost origin) 4/ These ‘species’ do not have a 3% difference in DNA.

If the latter, then it seems a bit arbitrary to now use this yardstick for new assessments.

I suppose that looking at species in ‘young’ islands would be the first port of call, when looking for apparent species that have evolved quickly (and hence may not pass either the 10mya, the 3% DNA measure, or both). If ‘species’ on young island do show a 3% divergence in DNA, then surely it means scientific estimates for the pace of genetic mutation and hence speciation are inaccurate.

I don't recognise some of your numbers. In general, I think people tend to assume divergence of about 2% per 1 million years:

The Molecular Clock and Estimating Species Divergence

Southern Alps uplift started 15M years ago:

Geology of New Zealand | GNS Science | Te Pῡ Ao

Aotearoa New Zealand’s geologyThe New Zealand region lies in the southwest Pacific Ocean astride a distinct belt of volcanic and earthquake activity that surrounds the…

www.gns.cri.nz

I'm not aware of a proposal to treat 10 million years as a definition for recognising species. However, like any other approach to delimiting species that would be entirely arbitrary. Many currently recognised species are far younger than this.

There are many instances of "island hopping" species: species which evolved elsewhere on islands which subsequently disappeared. They are therefore older than we might expect from their current distribution

 

[Mysticete]

I think there is some misunderstanding here. The 2% figure mostly comes from comparing sister species that are considered each considered "good species", specifically birds (I rarely (if ever?) have seen people suggest using this for other critters, including mammals). A species can have more or less genetic difference from there closest relatives; differences don't necessarily accumulate at the same rate for all species, based on differences in lifespan, rates of reproduction, extinction, and natural selection. Its one line of evidence but it should never be viewed in isolation.

Island species specifically can evolve VERY quickly, because normally they have small founder populations, are isolated from larger populations of the same species, and lack of competitors/limited resources can cause them to change drastically

 

[Jon.Bryant]

Island species specifically can evolve VERY quickly, because normally they have small founder populations, are isolated from larger populations of the same species, and lack of competitors/limited resources can cause them to change drastically

Never considered this. I suppose that for a genetic ‘advantage’ to ripple out from the source throughout a widespread taxa could take thousands of years, whereas for limited island populations, an advantage would be incorporated across the whole population more quickly.

But then again, if we assume that genetic change is a blind random process, isn’t there a paradox that the larger the population the greater chance of a random change - every reproduction is another shake of the dice? For small island populations there would be fewer shakes of the dice, so presumably less chance of speciation?

I will check my numbers when back home - the figures of 3% and 10mya are from memory, but Oriental Birdclub Taxonomy Update definitely makes reference to separation of X million years - I understand that they are just compiling and summarising arguments presented in original papers - it is not their rule.

 

[jurek]

But then again, if we assume that genetic change is a blind random process, isn’t there a paradox that the larger the population the greater chance of a random change - every reproduction is another shake of the dice? For small island populations there would be fewer shakes of the dice, so presumably less chance of speciation?

There is a whole branch of theoretical ecology dealing with these topics. In reality, small populations on islands evolve faster, also trough non-adaptive genetic drift.

 

[Jacana]

Never considered this. I suppose that for a genetic ‘advantage’ to ripple out from the source throughout a widespread taxa could take thousands of years, whereas for limited island populations, an advantage would be incorporated across the whole population more quickly.

But then again, if we assume that genetic change is a blind random process, isn’t there a paradox that the larger the population the greater chance of a random change - every reproduction is another shake of the dice? For small island populations there would be fewer shakes of the dice, so presumably less chance of speciation?

I will check my numbers when back home - the figures of 3% and 10mya are from memory, but Oriental Birdclub Taxonomy Update definitely makes reference to separation of X million years - I understand that they are just compiling and summarising arguments presented in original papers - it is not their rule.

This is an assumption that is not safe to make. Mutations might be random(ish), but genetic change is far more than just random drift, especially in island biogeography settings.

There's often a founder effect, whereby only a subset of genetic variation of the whole population reaches a new island. By chance some of those random mutations and variations in the founding population will end up being more common than in the source population. This can really speed up the rate of change in phenotypic differences over time. Plumage is something that frequently changes due to this. A release from competitors, predators and parasites can very quickly change things like body size or (in birds) flight abilities.

 

[Jon.Bryant]

This is an assumption that is not safe to make.

My knowledge of genetics is pretty poor, and my assumptions on speciation based on ‘the blind watchmaker’, which is fairly dated. But how can the process be non-random? The process of gene replication (and bad copy) is surely non-selective.

There's often a founder effect, whereby only a subset of genetic variation of the whole population reaches a new island

I can see how this forms a dividing point (isolation eliminates further gene flow), but not sure how it would speed up the process. As an example, I am currently in NZ and was reading that Chatham Shag is probably descended from ‘Stewart Island’ Shag, which colonised the islands when sea levels were much lower. When sea levels rose, the shags would have been isolated, and of course the founders on Chatham may well have been ‘Otago’ shags, so have been genetically distinct from ‘Forveaux’ shag - but isn’t this just ‘adding together’ variation on the mainland and subsequent variation offshore, rather than fast tracking?

 

[njlarsen]

I am not sure I agree with the statement Jacana made, but the combined effect of mutation and selection is not random. With a small population, (and to my understanding, which might be wrong) a random but beneficial mutation has a much larger likelihood of becoming influential than if the population was large.
Niels

 

[Frank van Drogen]

My knowledge of genetics is pretty poor, and my assumptions on speciation based on ‘the blind watchmaker’, which is fairly dated. But how can the process be non-random? The process of gene replication (and bad copy) is surely non-selective.

Aside from being a birder, I have a hobby being a geneticist (or was it the other way around....?).

It is especially the selection that is non-random of course. However, chromatin architecture does somewhat influence mutation rate of different regions. Additionally, meiotic cross-over is not quite random either. Overal, it seems the evolutionary process has resulted in a slightly decreased chance if getting unfavorable mutations -- even though those still make up the far majority.

(This is not my real speciality though, so I am happy to stand corrected).

 

[Jacana]

Yep, there's a confusion here between genetic change and mutation rates. Frank gets it right, mutations are basically random, but some base pair combinations in some parts of the chromosomes are more likely to mutate than others.

Genetic change is a more woolly concept, that suggests that mutations spread in the population. This process is absolutely not random.

 

[Jon.Bryant]

With a small population, (and to my understanding, which might be wrong) a random but beneficial mutation has a much larger likelihood of becoming influential than if the population was large.

Yes this was my assumption.

But the counter to this is that if mutations occur per x replications, the larger the populations the more chance of a mutation occurring. There is probably a complex model that balances chance of mutation verses likelihood of becoming influential.

Speciation obviously does occur more often on isolated islands, but it would be interesting to determine if our theories on speciation match geological timeframes (especially for geological young islands).

Hybridisation has also been considered a possible fast track to speciation, and I recall that on the Galapagos (I think) a recent hybrid swarm (which to all accounts acts like a species) was recently fathered by a single ‘vagrant’. I think there are grounds to argue that hybridisation rates occur at higher levels in small populations of similar species (e.g hybridisation of Forbes and Red-crowed Parakeet occurred more regularly when the former had a very low population).

 

[Jon.Bryant]

Frank gets it right, mutations are basically random, but some base pair combinations in some parts of the chromosomes are more likely to mutate than others.

Interesting that rates vary. Doesn’t this make the calculation of when a species diverged highly complex? I.e a calculation of what mutations have occurred in which parts of the chromosome and at what assumed rate?

Presumably also some gene mutations are dominant? I can’t remember the ‘rules’ that determines human eye colour, but I seem to remember brown is dominant. If my unscientific understanding is correct, then a mutation of a dominant gene should spread more quickly than a mutation of a non-dominant one.