Red squirrels are now so scattered they could split into different species

Swampy said:
A tad of a melodramatic headline, methinks....

Needs a caveat of ".....in a few tens of thousands of years", added.
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Now that you mention it, I see what you mean. It would depend on the amount of time that these Red squirrel populations have separated to determine whether speciation has occurred or not.
 
Here is a potentially relevant paper from The Journal of Zoology, mind you it is from 2020.

Morphological and functional variation between isolated populations of British red squirrels (Sciurus vulgaris)

Abstract

Isolation due to habitat fragmentation can lead to morphological and functional variation between populations, with the effect being well documented in rodents. Here, we investigated whether such morphological variation could be identified between British populations of the Eurasian red squirrel (Sciurus vulgaris). This species was once widespread across Great Britain, but suffered a severe population decline across the 20th century, leaving a highly fragmented distribution. The aim was to test for morphological and biomechanical variation of the mandible between the remaining British red squirrel populations, and between British and continental European red squirrels. Linear and geometric morphometric methods were used to analyse shape in a sample of over 250 red squirrel hemi-mandibles from across Britain plus a sample from Germany representing the central European subspecies. Procrustes ANOVA identified significant shape variation between populations, with particularly distinct differences being noted between red squirrels from Germany and several British red squirrel populations, which may reflect their evolutionary history. Linear biomechanical measurements showed that the red squirrels from Formby and Jersey had a significantly lower mechanical advantage of the temporalis muscle than other British populations, suggesting they were less efficient at gnawing. This functional difference may be related to many factors, such as founder effect, potential inbreeding and/or past supplemental feeding with less mechanically resistant food items.

https://zslpublications.onlinelibrary.wiley.com/doi/full/10.1111/jzo.12829
 
UngulateNerd92 said:
Here is a potentially relevant paper from The Journal of Zoology, mind you it is from 2020.

Morphological and functional variation between isolated populations of British red squirrels (Sciurus vulgaris)

Abstract

Isolation due to habitat fragmentation can lead to morphological and functional variation between populations, with the effect being well documented in rodents. Here, we investigated whether such morphological variation could be identified between British populations of the Eurasian red squirrel (Sciurus vulgaris). This species was once widespread across Great Britain, but suffered a severe population decline across the 20th century, leaving a highly fragmented distribution. The aim was to test for morphological and biomechanical variation of the mandible between the remaining British red squirrel populations, and between British and continental European red squirrels. Linear and geometric morphometric methods were used to analyse shape in a sample of over 250 red squirrel hemi-mandibles from across Britain plus a sample from Germany representing the central European subspecies. Procrustes ANOVA identified significant shape variation between populations, with particularly distinct differences being noted between red squirrels from Germany and several British red squirrel populations, which may reflect their evolutionary history. Linear biomechanical measurements showed that the red squirrels from Formby and Jersey had a significantly lower mechanical advantage of the temporalis muscle than other British populations, suggesting they were less efficient at gnawing. This functional difference may be related to many factors, such as founder effect, potential inbreeding and/or past supplemental feeding with less mechanically resistant food items.

https://zslpublications.onlinelibrary.wiley.com/doi/full/10.1111/jzo.12829
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Here is another potentially relevant paper, though this is from 2006.

Morphological changes in a British mammal as a result of introductions and changes in landscape management: the red squirrel (Sciurus vulgaris)

Abstract

British red squirrel populations have been subject to landscape management practices resulting in large-scale fragmentation and defragmentation of habitat, as well as numerous historical introductions of closely related subspecies. This unique population history allowed us to examine: (1) the morphological changes to a rare native species probably caused by hybridization with introduced subspecies; (2) the impact of landscape management, specifically reforestation, on the spread of these morphological changes across the north of England. British red squirrels represent a peripheral population of
Sciurus vulgaris, which is regarded as a separate subspecies (S. v. leucourus) to populations found on the European continent. British populations are in danger of extinction because of the introduction of the North American grey squirrel S. carolinensis. Repeated translocation of continental European S. vulgaris individuals to Britain over 150 years may be responsible for an alteration of the morphological characteristics of populations compared to the original subspecies description. The majority of examined populations possessed the coat colour characteristics associated with continental European subspecies. Only populations in the western region of Cumbria possessed coat colour characteristics similar to the described subspecies S. v. leucourus. Changes to landscape connectivity in Britain during the 1980s greatly altered dispersal patterns, resulting in an increase of gene flow from populations in the north-east of England and the Borders into Cumbria. The morphological characteristics of the Cumbrian population also changed over this period, from traits similar to the British subspecies before 1980, to traits similar to the continental European subspecies after 1980. This study demonstrates the threat landscape management practices and the introduction of closely related subspecies can present to rare peripheral populations.

https://zslpublications.onlinelibrary.wiley.com/doi/abs/10.1017/S0952836903003595
 
More likely in the shorter term populations could die out due to inbreeding. What is needed is some metapopulation management, i.e. occasionally moving some animals from one population to another.
 
MRJ said:
More likely in the shorter term populations could die out due to inbreeding. What is needed is some metapopulation management, i.e. occasionally moving some animals from one population to another.
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Transplanting British red squirrels sounds like it would be a helpful strategy in their conservation. This would be beneficial for re-wilding projects as well.
 
UngulateNerd92 said:
Linear biomechanical measurements showed that the red squirrels from Formby and Jersey had a significantly lower mechanical advantage of the temporalis muscle than other British populations, suggesting they were less efficient at gnawing. This functional difference may be related to many factors, such as founder effect, potential inbreeding and/or past supplemental feeding with less mechanically resistant food items.

https://zslpublications.onlinelibrary.wiley.com/doi/full/10.1111/jzo.12829
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I've heard in the past that the Formby Red squirrels are descended from pet squirrels that were released and may have been European in origin. I'm not sure what the latest thinking on that is. Similarly are the Jersey Squirrels more closely related to those in France, given the geographical nearness.
 
Pertinax said:
I've heard in the past that the Formby Red squirrels are descended from pet squirrels that were released and may have been European in origin. I'm not sure what the latest thinking on that is. Similarly are the Jersey Squirrels more closely related to those in France, given the geographical nearness.
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Very interesting, it looks like we are starting to connect some dots here.
 
UngulateNerd92 said:
Very interesting, it looks like we are starting to connect some dots here.
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A quick search indicates Red Squirrels were introduced to Jersey around 1885, and the founders were a mix from both England and the continent(France). Some photos I found of Jersey squirrels appear to resemble more the continental forms.
 
Pertinax said:
A quick search indicates Red Squirrels were introduced to Jersey around 1885, and the founders were a mix from both England and the continent(France). Some photos I found of Jersey squirrels appear to resemble more the continental forms.
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That is quite fascinating! admixture from both the British and mainland European red squirrel populations, no wonder why the population on Jersey might have appeared to have some distinctness...
 
Some populations are a result of a mixture from other British populations (eg. Anglesey). Complete fallacy that British reds are unique as continental animals were introduced in the past (Jersey is probably an exception). Given that squirrels are fast-breeding/short-lived rodents, any differences between groups is mostly due to inbreeding.
 
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