Evolution of separate species with similar range (1 Viewer)

I've always wondered why there seems to be such a variety of species that are so very similar, and why separate species have evolved apart on similar ranges with separate distribution.

Some examples I can think of (there are many) and they vary to different degrees include-

Bewick's Swan and Whooper Swan
Marsh Tit and Willow Tit
Chiffchaff, Iberian Chifchaff and Willow Warbler

even Chaffinch and Brambling, or Greenfinch and Goldfinch -
species which show very little morphological difference but can have strikingly different plumages.

Would these populations have ever been separated entirely or do they genuinely occupy separate niches so that the population could simultaneously live alongside each other yet branch into a separate species

Are you familiar with the basic idea of speciation? One original species somehow becomes split into two eg by a new barrier developing or a colonisation of a new area by a small subgroup. The two populations diverge, partly by random drift, and partly by adaptation to the somewhat different conditions in the two areas. Eventually the populations meet again, and, in essence, there are barriers to mating - possibly the populations have already diverged, or, possibly more likely, intermediates are less successful, so choosy parents who mate with their own type leave more offspring. In this model, you would expect recent splits to be geographically close and morphologically similar. Species which choose mates by voice eg warblers would be expected to diverge more in song than plumage. Plumage will diverge more when it needs to be distinctive to prevent "wasteful" hybridisation. Does this help?

What we're talking about here is 'sympatric speciation': speciation that occurs without geographical isolation. It's quite controversial and I'm not expert enough to boil down a succinct summary here, but the Wikipedia article on the topic discusses a few proposed mechanisms, and Google will send you to a few .edu sites with good material.

With your examples, we don't know the history of the species concerned and whether some kind of isolation existed in the past. Maybe goldfinches have only recently colonised the range occupied by greenfinches, but they were geographically separated 5 million (or whatever) years ago.

Or maybe there was some kind of 'disruptive selection': within the ancestral species, the greenfinch ancestor's more muscular build and heftier bill was perfect for one food source, the goldfinch ancestor's more gracile structure was perfect for another, and the in between structure of a hybrid wasn't as good as either. I made that example up without evidence, but it illustrates how homozygosity for a variable trait might be rewarded and that might drive divergence.

I think not all are cases of sympatric speciation. I think the chiffchaff case could be allopatric.
But like many things in biology nothing is completely black or white but there are several shades of grey in between.

- A biology student

Gladiator96 said:

I think not all are cases of sympatric speciation. I think the chiffchaff case could be allopatric.
But like many things in biology nothing is completely black or white but there are several shades of grey in between.

- A biology student

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Zebras, penguins and Black-and-white Warbler.....

John

what I meant to say is that in evolutionary biology, most of the time, you can't give a 100% definite answer since it's always the result of various factors interacting with each other.

MoshoeshoeII said:

Would these populations have ever been separated entirely or do they genuinely occupy separate niches so that the population could simultaneously live alongside each other yet branch into a separate species

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The examples you give are all separated to a greater or lesser degree, either by region, or by habitat preference. The biggest overlap between any of them is between Chiffchaff and Willow Warbler, which will nest in the same locations, and even (very rarely) interbreed.

Greenfinch and Goldfinch have recently been shown to be much less closely related to each other than thought in the past, so that example doesn't really apply any more.

Nutcracker said:

The examples you give are all separated to a greater or lesser degree, either by region, or by habitat preference. The biggest overlap between any of them is between Chiffchaff and Willow Warbler, which will nest in the same locations, and even (very rarely) interbreed.

Greenfinch and Goldfinch have recently been shown to be much less closely related to each other than thought in the past, so that example doesn't really apply any more.

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I just find it bizarre that avian populations can diverge so radically when they can be so mobile - for example a migratory species which is diverging will frequently come into contact with its root population on wintering grounds- if not on breeding grounds. (I am sure there are many example of species which share either or both)

What prevents, for example, a lost migrant Bewick's Swan type joining up with Whooper Swans and hybridising OR legitimately breeding for the millions of years speciation apparently takes?

Another good example I can think of is of Gulls, who proliferate in species and yet seemingly have separated at certain boundaries. Maybe LBBG and Herring Gull are the best divergent species I can think of where it seems arbitrary for one to be slightly daintier with slight plumage variation - at least from a modern view point!

MoshoeshoeII said:

I just find it bizarre that avian populations can diverge so radically when they can be so mobile - for example a migratory species which is diverging will frequently come into contact with its root population on wintering grounds- if not on breeding grounds. (I am sure there are many example of species which share either or both)

What prevents, for example, a lost migrant Bewick's Swan type joining up with Whooper Swans and hybridising OR legitimately breeding for the millions of years speciation apparently takes?

Another good example I can think of is of Gulls, who proliferate in species and yet seemingly have separated at certain boundaries. Maybe LBBG and Herring Gull are the best divergent species I can think of where it seems arbitrary for one to be slightly daintier with slight plumage variation - at least from a modern view point!

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Caspian, Yellow Legged and Herring are all considered separate species these days but interbreed regularly. Similarly the Western North American ones do and their offspring are known as Olympic Gulls, so where the separation is not too distant, maybe, then hybridisation occurs more often. Man has caused a lot of this to happen, by fishing, using rubbish dumps, which provide an easy source of food, especially in the winter.
Mallards will hybridise with anything. I'm not sure how much some of the hybridisation would occur naturally if the collectors in times of yore hadn't imported exotic species and kept them on artificial ponds in parks. Escapes want to breed and if they can't find a partner of their own species, then they hybridise. Some vagrants that make an Atlantic crossing and stay will attempt to breed if a mate can be found from a similar species and this undoubtedly occurs.

Its only humans that want to categorise everything. If you look at distribution within a species you will finds clines with different traits. The further awy from the originals they get the more pronounced the differences and they you get sub species and evenually the difference is great enough to cause mankind to say that they are another species. So geography plays a key role in diversification. If you consider how the Atlantic Puffin population is being affected by the movement of sand eels, you will also see that birds are creatures of habit and will always return to the same colony, despite there being little readily available food. Either the colony fails, or they dicover a new site nearer their food by accident and a new colony is formed. Is there much genetic variation in eastern and western colonies of Puffins? If colonies in the middle fail, will the variation be greater in the future as they adapt to new food sources? You need look no further than Darwins Finches to see what isolation does when the only choice is specialise or fail. Rember not all birds migrate and possibly only started to because as they expanded their range and adapted to their surroundings, they found that they coudn't survive winter or drought and had to migrate. I'm not a biologist or any type of scientist, so my ramblings might not make sense or be wrong, but thats my thoughts on the subject.

Migratory birds may come into contact with closely related species on the wintering grounds but, unless they are a species that completes pair formation before migrating back to the breeding areas, differences in vocalisations, minor habitat preferences ( Common Chiffchaff require tall trees as songposts, Willow Warbler can make do with scrub that's all the same hight ) or slight differences in behaviour can, and do, keep species separated. In the wild taxa of large 'white-headed' Gulls, ducks and a surprising number of North American passerines do hybridise regularly, but not in sufficient numbers to create a blurring between species. It only takes a quite small 'barrier' for the evolution of separate species to start, and then it's just a matter of time. Phylloscopus Warblers, Empidonax Flycatcher, Poecile Tits, many Babblers and Bulbuls are very similar in looks but minor ( to humans ) differences, often based on vocalisations or niche exploitation, serve to keep taxa separated. It may, initially, appear to be better to be a generalist when it comes to food, habitat choice or whatever, as the options are greater, but specialisation to a finer and finer degree eliminates opposition, therefore increasing the probability of successful transmission of the species genes to future generations.

chris butterworth;3099185[B said:

]Migratory birds may come into contact with closely related species on the wintering grounds[/B] but, unless they are a species that completes pair formation before migrating back to the breeding areas, differences in vocalisations, minor habitat preferences ( Common Chiffchaff require tall trees as songposts, Willow Warbler can make do with scrub that's all the same hight ) or slight differences in behaviour can, and do, keep species separated. In the wild taxa of large 'white-headed' Gulls, ducks and a surprising number of North American passerines do hybridise regularly, but not in sufficient numbers to create a blurring between species. It only takes a quite small 'barrier' for the evolution of separate species to start, and then it's just a matter of time. Phylloscopus Warblers, Empidonax Flycatcher, Poecile Tits, many Babblers and Bulbuls are very similar in looks but minor ( to humans ) differences, often based on vocalisations or niche exploitation, serve to keep taxa separated. It may, initially, appear to be better to be a generalist when it comes to food, habitat choice or whatever, as the options are greater, but specialisation to a finer and finer degree eliminates opposition, therefore increasing the probability of successful transmission of the species genes to future generations.

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Thanks for pointing that out Chris.
What happens to the 1st winter individuals that fly the wrong way then?
If they make it home in springtime, do they return to the same place the following year and will their offspring do the same? Or do they not survive, generally? I can see this hit and miss method as a means of accidental species spread, but the conditions would need to be suitable for survival for that species.

Andy Hurley said:

Thanks for pointing that out Chris.
What happens to the 1st winter individuals that fly the wrong way then?
If they make it home in springtime, do they return to the same place the following year and will their offspring do the same? Or do they not survive, generally? I can see this hit and miss method as a means of accidental species spread, but the conditions would need to be suitable for survival for that species.

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In my opinion they generally don't survive - and the numbers involved are, under normal circumstances, too low to make a difference to the overall species.

There is a tenuous but possible example of a Dusky Warbler ringed in spring at the Calf of Man obs and subsequently controlled/recovered (can't remember) at the same place in the autumn. The supposition would be that in the intervening period it migrated to normal Dusky Warbler range and then returned by its learned route, rather than summering nearby.

Its persuasive on a romantic level and not unreasonable as likely behaviour of a long-distance migrant - albeit there is no way of knowing how far towards normal Dusky Warbler range it went, just that we know that on its original migration it must have come that far, ergo it is possible.

John

Thanks John. It would be interesting to know if it bred successfully and if subsequent DW's start using the route. One to watch for.