Lately I have been reading up on the wolf species in Africa – the African wolf (Canis lupaster) and the Ethiopian wolf (Canis simensis).
As far as I understand, Africa has been colonized and recolonized by grey wolf immigrants from Asia (e.g., across the Red Sea) several times during the history of the evolution of the local canid species.
It appears that the Ethiopian wolf diverged from what were later Holarctic grey wolves the first (2 – 1 million years ago, possibly, ca 1.5).
The African wolf diverged later – 0.6 – 0.4 million years ago.
What I find interesting is that both wolves are small mammal specialists rather than ungulate specialists like grey wolves.
It has been assumed that at least the Ethiopian wolf (you can find a list of useful publications on the Ethiopian Wolf Conservation Programme’s website) was adapted to preying on rodents prior to reaching Africa because during glacials southeast Europe and Middle Asia, as well, were covered in cold and dry steppe habitats where small prey might have been more abundant than large grazers and not at all browsers (due to the retreat of tree species to refugia).
I was wondering why mostly small mammal specialist canids arrived in Africa.
I have developed a few hypothesis:
1.
The regional populations simply grew abundant and the dispersal occurred naturally as a result of increasing small mammal specialized-canid densities.
2.
There were other large predators in Africa that were formidable competition and that had occupied the niche of ungulate specialists.
3.
The migration into Africa was caused not by the population densities but rather by changes in climate that drove the expansion of forests and the associated wolf species that preyed on large ungulates and that were likely, correspondingly, larger than the small mammal-specialists.
Whereby, the small mammal specialists were pushed out into the periphery and sought their refuge (paradoxically, refuge during interglacials and not glacials) in Africa.
***
There is much I do not know or that, generally, is not known.
For example, the Ethiopian wolf’s earliest fossil in the southeastern Ethiopian Highlands has been dated at 1.6 – 1.4 million years indicating an Early Pleistocene presence of the species in Africa (Martínez-Navarro, B. et al., 2023).
However, this is not telling of when the species’ ancestors arrived exactly.
I find it interesting to entertain the third hypothesis.
The advancement of forests and forest species during the onset of interglacials would have favoured larger wolf (sub)species.
Meanwhile, the smaller wolves that may have specialized on small mammals while in Europe/Middle East already would have been pushed out by the larger species as is common in the nature where the larger species frequently prevails unless some particular environmental factors are at play favouring the smaller species.
The route into Europe would have been cut off by the slowly expanding forests and the associated competition as well as the comparative disappearance of the larger-sized of the small rodents and lagomorphs.
While the glaciers had not retreated (and even afterward), route toward India and the Himalayan plateu would have been proven unconquerable.
Meanwhile, if forests expanded all over Asia, the Central Asia could have been flooded by dispersing ungulate specialists that multiplied and migrated.
The best route might have led toward Africa while the interglacial period had not melted enough of the ice to rise the sea levels and to close the land bridges.
As the land bridges disappeared (if they did which I do not really know with certainty), migration out of Africa would have been temporarily halted and as the climate changed in Africa, as well, the small mammal specialists would take to the highlands or other types of steppe habitats to partition niche with larger prey specialists.
I find it interesting to consider this but I severely lack data regarding what the landscape truly looked like during those times and, also, when and how the migrations occurred by the larger canids across Asia and Europe.
Still, I do not believe it contrived to assume that such migrations if they happened, affected the competitors, as well, and, similarly to Migration Period which is thought to have led to the fall of the Roman Empire (as well as some smaller empires and kingdoms along the way), would have shifted whole subspecies of wolves and other mammals.
Of course, the small prey specialist population density hypothesis is also appealing and it is simpler (as demanded by Occam’s razor principle).
Notes by Ieva 