I still find it difficult to follow texts on phylogenetics but they interest me greatly and it is exciting to imagine the world in the times when the Earth looked so different.
I have been curious about the takeover of the Beringian wolves (closer ancestors to the present-day Holarctic grey wolves) and the apparent extinction of the Pleistocene Asian wolves without admixture that should have been greater in canids (that interbreed relatively easily) unless the takeover was swift.
As far as I understand, the Pleistocene wolves that are extant and that gave up their former ranges to the expanding populations from Beringia, were larger than modern-day grey wolves and possibly larger than the ancestors of these modern-day grey wolves that took over their lands.
How did it happen?
As I was reading some publications on tundra wolves and arctic wolves in North America, I began wondering if I am not mistaken in assuming that the Beringian wolves that arrived and expanded through Asia and Europe had the same ecology, including social habits, as most wolf populations that I know of.
Arctic and tundra wolves often demonstrate a pattern of denning during summer and then following the migratory prey species to their winter ranges.
In some populations, several wolf groups can even tolerate one another near these winter yards (e.g., Theberge, J. & Theberge, M., 2004) and some very large wolf groups (> 15 individuals) in the arctic are thought to have formed from several wolf families.
It is mainly in the temperate regions and not even all boreal regions wolves appear to settle down all year round maintaining territories that are smaller in summer and larger in winter.
Beringia was a tundra environment and at the time, the prey species likely migrated not only to winter yards but possibly also extending their range continually.
It is very likely that the wolves, too, followed these movements rather than forming stable and permanent territories.
It is possible that dispersal in these wolves occurred not as dispersal by individuals (as is common in residential wolf populations) but as dispersal by families where the wolf groups remained stationary during pup-rearing season while roaming very widely during winter when the pups could already follow.
During those times, it is also conceivable that wolf families did not migrate to follow localized ungulate groups to their traditional wintering ranges and to return to the known den sites in the spring to come.
As the ungulates were, too, colonizing, the wolves could have tracked them in family groups and denned every spring in a new site until they decided on staying somewhere.
Perhaps even several wolf families travelled together and the social organization in those wolves was not as family-unit-based as is observed nowadays.
Such mass movements would have provided an advantage for the Beringia immigrants over the Asian residents even if the residents had knowledge of the local environment and even if they could have been larger (which I do not attest to because I am not certain this was the case).
Resident wolves would have dispersed as single individuals (and pairs) who found it hard to usurp territories compared to migrating family groups who might challenge existing families and who would certainly outcompete individual dispersers.
This might also explain the relative lack of hybridization because dispersing families would not be on the lookout for new breeding opportunities unlike dispersing individuals in the ‘customary’ wolf social systems.
Similarly, if these Beringian wolves used to gather near wintering yards of ungulate prey (which could happen because winter likely restricted migration in ungulates due to snow cover and therefore the expansion of the colonizing ungulates would have followed a seasonal pattern halted by winter cold and fawning/calving), they might have found mates among other Beringian wolves reducing the ‘outbreeding’ apart from cases when resident Pleistocene Asian wolves joined the small populations as dispersers.
Perhaps the Beringian wolves initially tracked the expanding ungulates from the very same Beringia and while doing so, they were nomadic and not sedentary (and possibly forming social units different from those we observe today in grey wolves in most places).
As the ungulates settled down and as these wolves met the resident ungulate populations, they could have used their advantage of large groups to take over the resident Pleistocene Asian wolf territories.
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Another consideration of the relative success by the Beringia wave takeovers could be related to megafaunal extinctions disfavouring larger wolves with higher metabolic needs.
This could have contributed to competitive disadvantage in Europe.
For example, in North America it has been assumed that the relatively smaller red wolves (Canis rufus) and eastern wolves (C. lycaon) lived on the continent before the arrival of the ancestors of present day NA grey wolves (possibly, forming a unified species).
It is worth noting that these two wolf taxons are smaller than even grey wolves and grey wolves did not manage to overtake their distribution area completely.
They could have partitioned niche through hunting different-sized prey species while larger wolves could have been unable to keep subsiding on very large ungulates.
Notes by Ieva 