Evolutionary history of wolves – choices wolves made to be together

Last weekend I was sitting by the river and watching a spot where sometimes deer can be seen (not at the moment, though).

Suddenly, I recalled the piece of information that deer had evolved from a woodland species.

Then I remembered that wolves, in turn, (genus Canis) had evolved essentially during Pleistocene where woodland was scarce and where the landscapes were dominated either by arctic tundra or grasslands.

Thus, I began wonder how it follows that nowadays deer are among the dominant prey species of the wolves and wolves – where they have the opportunity – tend to locate their home ranges accounting for the presence of forests.

Certainly, deer (cervids) are not the only wolf prey species and wolf diet is opportunistically and flexibly based on the available resources.

For example, wolves in British Columbia are ‘sea food’ gourmets and some wolf families on islands there even do not hunt ungulates at all (according to McAllister, I. in his book ‘Last Wild Wolves: Ghosts of the Rainforest’, 2007 where the island-living Surf Pack had no access to mountain goats, nor moose (and maybe little or no access to deer) and where this family preyed on scavenged sea lions, seals, seabirds, shorebirds, eggs, fish (including salmon), rodents, clams and mussels (pp. 90)).

However, in most regions, wolves mainly prey on ungulates (cervids, bison, wild boar, mountain sheep and goat etc.) and many of these most preferred ungulates are often associated with forest (although they might not live entirely in the forest or in forest ecotones and might make extensive use of grasslands which, however, have forests in their vicinity.

In many cases, species (plains bison, mountain ungulates etc.) that are not forest-dwellers are hunted when wolves move out of forest cover to travel along their hunting routes which typically do not lead through dense forest but through more open areas (e.g., riparian areas, old roads, other types of forest openings etc.).

Wolves appear to make second-order habitat selection decisions (choosing where to establish home relative to the regional landscape) based on tree cover as well as based on the proximity of resident wolf populations (but not necessarily so).

However, when that choice has been made, wolves will not utilize forests exclusively and, I have mentioned before, they might even prefer to travel along non-forested or sparsely-forested features where it is easier to locate and kill prey.

There are, of course, wolf populations (e.g., arctic wolves) who do not have access to forests and tree groves and these wolves have adapted accordingly.

But where there are forests, wolves would probably associate with them.

It is not know whether forests are sought for refuge from human persecution (thusly, it cannot be claimed with utmost certainty that wolves have always selected for forests because the changes in the global landscapes might have affected wolves’ decisions over the past centuries or even millennia), or forests and forest proximity is where wolf-preferred prey can be found, or forests are important during some life cycle stages (e.g., denning), or a combination of the aforestated factors plus some.

Denning in tree cover appears important to wolves (although wolves can also den in more open areas if needed or they can choose riparian shrub cover instead of thick forest in areas where forests do not grow easily due to cold and/or dry climate, poor soils).

For example, some wolves that prey on migratory caribou, would remain below or near timberline during the denning season (see, e.g., Heard, D.C. & Williams, T.M., 1992) even though caribou migrate away from forests in spring to oversummer in the tundra and to return in late summer/early autumn.

The timberline likely provides structural support for den digging (roots prevent dens from collapsing, the soil is better drained and sandier) and the absence of the caribou is relatively short but the wolves still have to travel rather far in order to hunt their prey (the caribou).

It would appear that denning is an important consideration in opting for forest cover and the presence of the trees.

However, I would like to look into the evolutionary history of the wolves in order to find out more about how these associations between wolves and cervids as well as wolves and forest have come about.

Firstly, the early ancestors of wolves (but also of foxes, bears, racoons etc.) that could be described as canid-like taxons were tree-dwellers.

Humans are not the only species that has ‘climbed down from the trees’. So have wolves.

One of these ancestors (as far as we know, the earliest) was the extint Miacis.

Miacis lived ca. 52 million years ago (Eocene) and they preyed on insects, birds and reptiles as well as fruits and seeds.

Some 10 – 20 million years later (still during Eocene), Hesperocyon evolved that is no longer an ancestor shared with bears but it is an ancestor shared with foxes, racoons, jackals etc.

These pre-canids or canid-like animals retained their arboreal lifestyle but a shift in their diet had occurred.

Their diet began to include fewer insects and more birds (plant resources remained unchanged).

I find this detail to be significant.

Both these taxons lived in North America which during the former part of Eocene was warm and humid; but toward the latter part of Eocene, the climate changed – it began to cool and became more arid.

In fact, the same changes occurred in Eurasia and Africa where mass extinctions were observed as wetlands dried out and tree covered areas likely turned into grasslands.

Wetlands are highly important for insect life and it might be expected that under the cool and dry conditions of late Eocene, insect prey became far more abundant and many invertebrates became extinct.

Thus, their predators had to adapt to new diets.

However, there are differences in behaviour and morphology of species that prey on insects vs. larger prey species (if these prey types dominate in their diet).

Invertebrates can often be found in more abundant aggregations and they do not request for roaming far and wide.

It is possible that predators preying on invertebrates would have smaller home ranges, would travel less and they would spend a lot of their time in one spot interacting with relatively similar prey (while there is a great diversity of insects, many insectivores develop their methods, e.g., digging, that they apply to a great number of invertebrate species; these canid-like species probably did not dig but they could have, as well, evolved a strategy that allows to capture many different prey taxons by the application of the same skill set).

If the Hesperocyon reoriented themselves toward bird prey, they probably had to evolve new skills and new traits.

Birds do not form such abundant clustered aggregations as invertebrates do and frequently the social bird species have alarm signals to notify the rest of the flock of the presence of a predator.

Bird predators might have to move greater distances, become stealthier, diversify their hunting techniques (unless the Hesperocyon preyed mainly on chicks which they might have).

The social life of the species might also change as its home range grows and interactions with conspecifics might become reduced.

Reproductive activity could shift, as well, due to the increased scarcity of mates and perhaps also the necessity to centralize near the den (which could have been a tree cavity perhaps or a hole in the ground in the roots) which could have been further from the foraging grounds than previously when invertebrates could have been found nearer the young at all times.

As there could have been several litters per year, the female and the male home range sizes and foraging patterns might have diverged resulting in polygamous systems.

Cool temperatures might have added to the metabolic needs contributing to even larger home ranges and more solitary lifestyle (I am not trying to claim that these species were social in the usual sense of the term meaning cooperating; I simply think that larger home ranges would have reduced contact with conspecifics and perhaps some territoriality even might have arisen which, in a tropical forest, however, might have been vertically structured as well as horizontally structured).

Increased rate of carnivory would have affected morphology, e.g., jaw structure, dentition, speed, agility, endurance.

Some of these factors could have led to larger body size but apparently it did not because Hesperocyon were not significantly bigger than Miacis.

However, it is possible that, for example, digestive adaptations (gut microbiota) might have made a return to insectivory unprofitable.

Comparing Miacis and Hesperocyon, it is clear that the changes were not dramatic.

The species retained its omnivorous habit and much of the bird prey could have consisted of eggs and chicks that do not ask for active chase.

However, it has been stated that Hesperocyon had teeth similar to those of canids and this might suggest that they did catch adult birds, as well.

Meanwhile, ungulate ancestors had been around since about the same time (early Eocene), also inhabiting forests, but the first deer ancestors appeared around the same time as Hesperocyon – already in the cooler, drier late Eocene (35 mya) / early Miocene.

These ‘early deer’ were, in fact, twice as long and more than 35 times as heavy as Hesperocyon (with which they might have cohabited in North America although one on ground level and the other in the trees).

It is perhaps interesting to note (because history will sort of repeat itself) that, in this situation, the deer ancestors and these early canids evolved under similar circumstances which were those of a cooler, drier climate, albeit still in a forested biotope.

From then on, their paths diverged, however.

The ancestors of ‘true deer’ (Cervidae) evolved earlier (ca. 30 million years ago in Eurasia) than the ancestors of what might be described as ‘true wolves’ or wolf-like canids (2 – 3 million years ago although it is not very clear whether in North America or Eurasia and some claim that it happened 5 million years ago).

Also, these deer ancestors (which resembled the nowadays chevrotains or mouse deer) lived in tropic forests and they were tiny while the first wolf-like canids were probably about the size of foxes or jackals and they lived largely in grasslands.

However, it must be noted that by the time the ‘true deer’ had evolved into Cervinae (7 – 9 mya) and, more so, by the time wolves appeared (2 – 3 mya), the deer had, once more, surpassed wolves in size and some of them had adapted to partly open habitat-based diet (grasses, forbs).

How did this transition come about?

We left the wolf evolutionary history at the Hesperocyon pre-canids, ancestors to wolves, foxes, jackals and racoons, more carnivorous than their predecessors, and we left it at the end of Eocene and the beginning of Miocene.

Out of the Hesperocyon, the first Caninae (canines) evolved, and these taxons emerged ca. 7 – 8 million years ago during Miocene.

At the time, the temperatures were still moderately warm although the began to cool down leading into the Pleistocene glacials and interglacials.

The period was mostly characterized by aridity which led to development of grasslands, savannas and even deserts.

Thusly, the ancestors of wolves, foxes, jackals, coyotes etc. truly evolved at a time when grasslands and open habitats (e.g., grasslands with scattered trees and shrubs) dominated the landscapes.

It is perhaps not surprising that the arboreal Hesperocyon disappeared but it had given rise to forms that were more similar to canids in their appearance and their tails probably shortened while their bodies adapted to ground-living.

It might be interesting to compare why some of the Hesperocyoninae and the closely related Borophaginae went extinct while the Caninae did not.

The two former taxons were omnivores (but so were the Caninae).

The Borophaginae appeared to have reverted to some (ground-based) insectivory but they relied on meat quite heavily (1/3 of diet) as well as on fruit and other plants.

Their strong jaws have given them the name of ‘bone crashers’ but it is not known to what degree they hunted and to what degree they scavenged.

However, bird bones were unlikely calling for bone-crashing, nor birds were abundantly caught in these open habitats (for a non-tree-dwelling species).

Similar traits and behaviours were probably shaping the Hesperocyoninae.

Some of these species reached the size of a coyote or even a wolf (e.g., Osbornodon fricki).

Apparently, the Leptocyon did not evolve such massive jaws and they relied on smaller prey as well as agility.

Perhaps this was what secured their survival once the climate cooled to the point that either very large animals or very small animals could carve a niche for themselves under the new conditions of ice ages and interglacials.

Not opting for the largest and necessarily most powerful form within their capacity has been an strategy which has helped wolves not just once during their history of evolution as will be demonstrated later.

It almost seems as if canids learned these lessons from the extinctions of their ancestral and sister groups.

With the onset of glaciation and with the shifting of the landscapes from savannas to grasslands with no trees and from grasslands to tundras (in the respective georegions), it was likely that either very large herbivores survived who could endure the cold and who could feed on bulk (rather than being selective and relying on woody shoots, leaves and forbs) or very small herbivores survived who could burrow into the soil or even into the soil subsiding on even dwarf shrubs and the seeds of the grasses.

Under such conditions, the competition among scavengers was probably enormous but active hunting could occur among smaller predators (such as fox-sized predators) who could catch rodents in the grasses and beneath the snow, or among very massive predators who could pursue the megafauna.

Meat-eaters who had not relied on rodents but who were unable to subdue the megafaunal herbivores probably went extinct.

There was also the choice of remaining omnivorous (utilizing many different types of food that would become suddenly available during some climate shifts) which was opted for, e.g., by the foxes, or becoming predominantly carnivorous.

I suppose that in order to evolve mainly carnivorous lifestyle, the predators either had to become the largest and most powerful of the apex carnivore guild or they had to become highly efficient at hunting more modest-sized prey and protecting it from other carnivores and omnivores.

Thereby, it could be that both the growing size of prey as well as the fierce competition with scavengers shaped the evolutionary paths of the canids.

Foxes apparently selected remaining small and utilizing a variety of smaller prey (as well as scavenging) but also retaining the possibility to sustain themselves on occasional plants, amphibians, reptiles etc. where and when those were available.

Their strategy was that of flexibility and multi-trophism which allowed to survive during harsher periods but also facilitated rapid colonization of recently more abundant and diversified habitats.

Jackals (and later coyotes), too, did not specialize overly but they were more carnivorous which was perhaps a combined plot to both retain the utilization of small and medium-sized prey (medium-sized rodents, lagomorphs) but also to be able to scavenge more securely from larger predators and to sometimes make larger kills by themselves when the circumstances allowed (e.g., when the circumstances allowed pack formation).

Wolves that we know today were some of the last to diverge from their canid ancestry (although some wolf species in Africa and Asia diverged sooner perhaps due to isolation induced through glaciation).

However, it should be noted that, for example, in North America, dire wolves apparently appeared from local (South America) canid-like ancestors already 5 million years ago (some argue that dire wolves are not wolves).

Thusly, it is interesting to consider what ‘makes wolf a wolf’ and how it is that some of these canids became jackals or coyotes, or dogs, but others became wolves or retained their ‘wolf legacy’ even after having been separated from the more extensive wolf populations by glaciers, mountains and seas.

In this post, I will, nevertheless, keep the track of the late Pleistocene wolves and grey wolves (that evolved 2 – 3 million years ago).

I believe that these animals opted for a larger size than their relatives (other canids) but they did not attempt to reach a size which would allow them to take down megaprey, either, at least not on individual basis.

Some late Pleistocene wolves were larger than the grey wolves but it is likely that they all preyed mainly on the large ungulates that had evolved by that time.

For example, reindeer evolved 5 – 6 million years ago, bison – ca. 2.6 million years ago, moose evolved ca. 2 million years ago. The Cervus spp. were around since already ca. 7 million years ago.

I believe that wolves chose to mainly prey on these animals some of which were adapted to tundra and grasslands while others moved north and south in a closer association with the retreating or recolonizing forests.

However, wolves probably also hunted larger prey which was very important if wolves wished to inhabit regions further north during glaciations.

I suppose that some wolves evolved a larger size (but it should be noted that these wolves, e.g., dire wolves and late Pleistocene Eurasian wolves went extinct or were assimilated as the slightly smaller grey wolves took over after the megafauna went extinct and rules changed).

But I think that wolves decided to rely not on individual strength but on the strength of a family.

However, in order to form packs, wolves had to be large enough to be able to fend off other predators and scavengers (which is one of the reasons why other social canids do not always form packs that are comprised from more members than the mated pair and their offspring of the year) but they had to remain small enough to be able to sustain the family (which might have been nuclear with several generations of offspring but which also might have been extended with other kin included) on the range and prey available to them.

The larger the animal, the greater its energy demand and thereby, the greater the amount of prey it needs individually.

In very large species, it may be difficult to maintain group living, especially, if the species is predominantly carnivorous, hunting large prey, as the prey biomass necessary for the group of individuals can be only found on large ranges that need to be defended, as well.

It is not known clearly when social living evolved in canids and, moreover, when the social groups began expanding beyond parent-offspring of the year bond including older offspring, other relatives and at times even non-relatives (as can be observed today in wolf packs).

However, I believe that among the strategies available to them, wolves carved a niche out for themselves that was based on the following conditions:

• becoming dominant over mesocarnivores in order to reduce losses to scavenging;
• becoming large enough to hunt the medium-sized group of large prey but not becoming too large to become dependent on either huge home ranges or megafauna exclusively;
• ensuring themselves against other large and larger predators;
• ensuring the ability to sometimes hunt larger prey which can ensure survival during glaciations when the medium-sized ungulates retreat with the forests and the tundra is dominated by giant herbivores.

These goals could be achieved through forming cohesive, large, multi-generational family groups.

I believe that when given the choice between becoming some of the mightiest lone predators or remaining small enough to subsist on the already numerous predators of rodents and lagomorphs (and other smaller prey), wolves opted to stay in the middle which was accomplished not through individual strength but through the flexibly adjustable (through dispersal or inclusion) strength of the group.

A larger or smaller group of wolves could take down medium-sized prey but also much larger prey (when and where circumstances necessitated such strategy).

Social cooperation could also protect the wolves both against the abundant mesocarnivores and against the powerful top predators who were often solitary.

Group size could be adjusted to the dynamic conditions (as characteristic of the Pleistocene period) but a body morph remains rather fixed setting the fates and reducing the broadness of the niche.

Thus, for example, wolves living through the coldest periods or living furthest north could group up and also become slightly larger in order to be able to hunt the larger prey of the cold climate, to protect themselves in the fierce competition and to survive the climate extremes.

Wolves living through the warmer periods of living farther south could, once again, group up and perhaps evolve smaller body phenotypes in order to hunt slightly smaller prey, in order to compete with the scavengers and not to starve or overheat (as large-bodied animals might in warmer climate).

The cold/northern climate wolves may have also formed larger packs than the warm/southern climate wolves.

During interglacials, these phenotypes might have met and interbred ensuring an adaptive pattern of body size, prey selection and social living in the entire global wolf population.

I think that wolves realized that it was more risky to adapt themselves to the consistently unpredictable future than it was to adapt their social habits.

It was proven wise as the larger carnivores (as well as the larger wolf species) went extinct during late Pleistocene, and part of the reason could have been their inability to adapt to the new conditions following the termination of the more extreme ice age cycles.

But also, these large species might have found themselves less capable of evolving immunity against some diseases characteristic to the warm climate and increasingly overcrowded habitats.

Wolves had avoided these troubles as they had maintained populations in all types of climatic conditions (developing immunity) and they had found for themselves a place in the diverse community of both large and small mammals.

It is worth asking also why grey wolves had such success replacing (or assimilating) the larger Pleistocene wolf species and how grey wolves ended up associating themselves with forest and forest edge habitats?

I do not believe that the larger Pleistocene wolves could not have survived because they were not enormous and they could have still preyed on the largest among non-megafaunal ungulates (e.g., bison, aurochs, moose etc.).

Perhaps it was becoming more difficult as the forests were taking over (even the former grassland species had to perhaps live at least partly in forests) and the larger wolf species could not defend such big territories.

But I also believe that perhaps they were not as efficient socially as the grey wolves.

As I mentioned before, larger canids would need larger ranges to tolerate larger social groups.

Meanwhile, slightly smaller canids could adapt their group size to the size of the range.

Grey wolves do not necessarily form larger packs where their territory is larger (although as the group grows, sometimes they might seek to expand although the causality here is not the same because it is the increase in group size that leads to an increase in territory size, and not the other way around).

However, under more strikingly different environmental conditions, group sizes can be adapted (such that in more open habitats or arctic habitats groups are often larger than in forested habitats).

There is the basic family unit of parents + offspring + perhaps older offspring. But, under some conditions, two basic units can either unite (two breeding females or even two breeding pairs in one group) or thy can live as neighbours extending the influence of their kin and maintaining cooperation.

This is different from a family model in larger wolf species where the metabolic needs would limit the group size disallowing to add another unit to the existing unit (where it benefits the pack) or disallowing to engage with neighbours (a daughter/son split-off).

I believe that these larger wolves had a difficult time defending their ranges against the more efficient and even intercollaborative packs of smaller grey wolves.

For example, during these times, much migration by the prey probably occurred as waves of mammals pushed out from Beringia and into continents.

If a two family unit group of grey wolves could migrate along, they could find a range where they thought it wise to settle and then they could split first occupying the far and the near end of the range surrounding a late Pleistocene wolf pack.

Then they could have either pushed the other wolves out or they could have had their offspring breed with them incorporating the non-grey-wolf family unit into theirs.

I find it curious that besides split-offs or ‘donations’ of portions of territories to new pairs consisting of the pack’s offspring + their new mate, I, personally, observe that sometimes a wolf pack’s offspring would disperse a short distance from their parental pack and settle in a range that is, however, not adjoined to that of their parents.

Then the both packs would close the gap between their ranges as the offspring pack produces more young and expands.

Perhaps it is a reminiscence of an ancient takeover strategy that was once used by the Beringian grey wolves to conquer Eurasia and North America.

Interestingly, grey wolves did not overtake the lands where the putatively endemic red wolves and eastern timber wolves lived in North America.

Apparently, the smaller, forest-based Canis rufus and Canis lycaon were better adapted to the new conditions to withstand the colonization by the grey wolves (while the dire wolves, for example, disappeared).

With regard to the association with forests, the grey wolves themselves could have taken on the niche of slightly more open habitats that, as some scientists think, still existed (not all was taken over by closed forests) or at least the grey wolves could have utilized their chance to occupy the niche of hunting the largest of prey (instead of competing with other similar-sized (to wolves) predators over the medium-sized ungulates).

Of course, in some areas, they did and there are still wolf populations that depend on, e.g., moose, muskoxen, bison.

However, it seems that wolves, once more, overall (on a global population level) stuck to their strategy of choosing the middle way (e.g., if roe deer, red deer and moose were equally available, the wolves would be likelier to hunt the red deer).

They also seemed to prefer the species of more forested regions although it could be argued that, at the time, forested regions predominated (therefore, wolves simply might have adapted) and that, later on – as the humans began to keep livestock and eventually to farm crops, it was better to stay out of their way and to use the remoteness of the forestland.

However, for thousands of years, humans did not begin cropping, and livestock was often grazed in forests or other natural habitats that were not always explicitly separated from ‘official pastures’.

Maybe the wolves did use both open and closed habitats.

But I think that they preferred forested habitats because of how it helped the wolves develop their social strategies.

I believe that wolves found it more efficient to form smaller family groups (parents + pups + older offspring) than to form larger social units consisting of several families (as observed in some cold, non-forested, large-prey-based regions).

Forested landscape perhaps facilitated the formation of nuclear families and the union of several such families not in the capacity of one large social group but in the capacity of related neighbours.

In forested landscapes, such social structure would allow to use the land and prey resources more efficiently and to be at all times knowledgable of what was happening in the wolf family’s home.

The large, several family unit is more efficient while following migratory or far roaming or very widely dispersed prey.

Thusly, the strategy of the wolves could have been one of pursuing a specific social structure that is efficiently realized in forested landscapes (including ecotones) where prey tends to be more sedentary, where prey is smaller and does not form massive herds that are scattered widely in the region.

Such family units are far more adaptive.

Modifications to their size can be achieved through regulating the retention/dispersal of older offspring (instead of splitting in two families and losing around half of the pack total numbers).

I also think that prior to the mass persecution of wolves, their ability to form neighbouring kin packs (or perhaps kin packs interspersed with non-related neighbours) was sufficient to maintain a local population that could perhaps at times share resources, tolerate forays into their territories (e.g., when one related pack was suffering hardships while prey was still abundant on another related pack’s territory), sometimes exchange pack members or provide babysitters and territory patrolling crew if the prey temporarily shifted its range and if longer travels were needed to hunt.

It is a rather curious social organization whereby localized clans would be formed that consisted of families (and that were sustained through the wolves’ ability to disperse far and to reach other clans for finding mates).

To conclude, I believe that wolves, during their evolution, selected the strength of family over individual strength and they also selected neighbouring but separated single monogamous parental pair-offspring families (faciliated by forested landscapes) over large formations of several united families (or polygamous large families).

Wolves appear to have always chosen ‘the middle’ way choosing cooperation to pursue their interests and refraining from evolving anything that is too enormous to be regulated by a parental pair.

Essentially, just like leadership in wolf packs in the leadership based on parent-offspring relations, their entire population is governed by the same principle – by the choices made within a monogamous family that is limited enough to account for its every member, to know every member’s potential and needs.

Their population is governed by every family that it comprises.

And thus far wolves who chose this strategy, seem to have prevailed where other predators and other wolf species failed.

***

I would also like to mention that, I believe, wolves were one of the perhaps few species in the evolutionary history to make a decision regarding their future niche (rather than being more passively selected by environmental, reproductive and other factors).

For example, many species form social groups where resources are abundant and where the living arrangement (home range) is restricted (thereby avoidance of others is perhaps difficult to achieve and costs more than it is profitable).

However, wolves appear to have formed larger groups, e.g., in higher latitudes and in harsher climatic conditions during Pleistocene.

Such circumstances would not favour natural group formation (by ‘natural’ I hereby mean to refer to group formation which is not decided upon by the individuals (internally) but which occurs because it is convenient, pleasant, profitable, affordable etc. and which can be cancelled by the same external factors that encouraged the social group formation).

If wolves evolved from ancestors who pursued smaller prey, such prey would be scarcer in colder climate.

Many predatory/carnivorous species form smaller social groups (frequently, only mother and her offspring) in regions where vegetation growing season is short and snow covers the ground for much of the year because it is challenging to sustain oneself as it is.

Thus, wolves had to realize that, by sticking together in large, cooperative groups, they could overcome the obstacles imposed by the environment and they could profit from increased resourcefulness (being able to direct focus from smaller prey to larger prey), defense etc.

However, I do not think that this could be achieved by simply following the natural social developments and I believe wolves had to make a decision and an effort to maintain their social cohesion in order to stay together.

For the wolves to be able to hunt efficiently, as a group, in these cold climate conditions, they had to roam over large areas while remaining together, and individuals had to also stay with the group during the denning period (rather than venturing off by themselves to seek prey elsewhere without the competition by one’s social group members).

Social group formation in wolves, during Pleistocene, was not something that I can see as easily encouraged by ‘Mother Nature’ (locally abundant prey, small home ranges), and I think it requested determination because wolves had to tolerate the group’s needs during the denning period and they had to learn to travel together as a group during winter.

By selecting social life, wolves necessarily became larger (because they needed larger prey for the whole group to survive) and, thus, they could no longer sustain themselves on smaller prey.

Meanwhile, they could not become too large (see above) which meant that they could not, by themselves, hunt megafauna and large prey without serious risk.

Wolves, thereby, selected against the traits that could have allowed to ensure survival for them as individuals (because individuals who were smaller or larger than wolves, would have been able to better survive on their own).

I do not see how the natural environment and climate during Pleistocene favoured group living in wolves in a manner that would come about ‘unconsciously’ (as in many species where social group formation is subject to environmental fluctuations and it is not really a decision to be made, nor it necessarily imposes morphological adaptations that disallow individualistic survival).

I believe that in order to profit from their chosen lifestyle, wolves had to make deliberate pact to remain together because, only through applying conscious effort to become highly cooperative, they could benefit from their social living.

Through making this effort, wolves became highly successful and adaptive but I think that they were able of foreseeing this success and benefit and that they pursued it (rather than succeeding and benefitting from social group lifestyle at once and thence evolving these traits).

***

I will also include the following text which is a part of an e-mail message I sent to present my consolidated theory:

Wolves evolved during Pleistocene when climate fluctuated but when frequently the survival of the species was determined by their ability to adapt to grassland/savanna habitats where smaller prey and megafauna dominated (granted that most medium-sized prey such as deer depend on woody vegetation and only partly subside on grasses, some more than others).

As wolves seem to have evolved from ancestors which might have been more similar to coyotes and jackals in that their diet was dominated by smaller mammals (with medium-sized prey taken under favourable environmental and social circumstances), wolves were subject to a certain choice.

Namely, if the Pleistocene habitats provided very large prey and rather small prey in abundance, any carving of a niche was dependent on the ability by the predator to compete with either mesopredators or megapredators. Mesopredators were already abundant (high competition) while evolving into becoming a megapredator was probably risky (as demonstrated by their due extinction) because of high metabolic needs and inability to sustain oneself on smaller prey.

Being a scavenger was also a hazardous occupation at the time.

Moreover, the climatic fluctuations favoured adaptive species who could take smaller prey and larger prey during colder periods and who could make a stand as scavengers against the numerous competitors. But also such species would have thrived that, during the warm-ups, could make use of medium-sized prey (which very small predators such as foxes could not, outside of the calving/fawning season).

I believe that many species made a choice (the choice was made for them) to become very large or to remain of a medium size (which enabled them to survive on smaller prey under dire circumstances but which also allowed them to be sneaky and to scavenge while, during warmer periods, such species might have produced social groups and attacked even deer and similar ungulates).

Wolves, meanwhile, appear to have selected neither. They became too large to subside on rodents efficiently for prolonged periods but they were not large enough to kill megafauna. Wolf size was truly adaptive (if we are speaking on an individual basis) only during warmer periods when medium-sized ungulates (or beavers etc.) were available. 

At the same time, wolves appear to have succeeded in distributing themselves all over the place.

Wolves, as individuals, would have been rather inefficient during the colder periods because they could not easily take megafauna and it was probably hard or impossible for an individual wolf to compete with megapredators; wolves also needed lots of food (because they were bigger than mesopredators) and could not hunt as effectively under the snow etc. Although larger than mesopredators, a single wolf would have also had a difficult time competing with scavengers.

Due to these (and some other) reasons I believe that wolves, at this time, decided not to focus on their individual size because it was, in fact, more profitable to have a size that fluctuates according to the habitat, climatic period, prey availability, enemy etc.

As an individual cannot attain a fluctuating size (of course, there can be phenotypes but I am speaking of a more dynamic fluctuation which can be evoked in shorter time spans, even during mere months or separate incidents), I believe that wolves decided to focus on adjusting their group size.

I believe that rather than opting for being megapredators or mesopredators, wolves became social predators where the individual size was subject to social requirements (see below) but where the group size could fluctuate for its members to succeed in many of the circumstances they were facing (in a dynamic and highly contrasting environment).

The adaptable group size provided what could not be achieved through selection of individual body size. It would have insured wolves as competitors with larger predators, with scavengers, with mesopredators but also wolves would have been able to adapt to varying prey size taking megafauna, medium-sized prey and also smaller prey during some periods.

The wolf’s individual size was probably the result of having to live in a group. A group has to account for the availability of resources. Socially living individuals (especially, predators) cannot grow too large because they would exhaust their prey. Which is why wolves probably became larger than mesopredators (to be able to provide group defense but also to be able to hunt larger prey cooperatively and to survive the cold) but they did not turn into megafauna, either, because this would have prevented them from social cooperation.

On the other hand, the social individual could not be too small, either, because their objective was now to provide for the entire group (and not merely for themselves) which would demand greater physical strength.

Wolves were, in some respects, a megafaunal species but only a social megafauna (their social group being a meta-organism comprised of individual wolves and able to fluctuate in adjustment to the dynamically changing conditions and to an environment of stark contrasts).

The stark contrasts are represented by the very large or the very small herbivores (and their predators) whereby the small species could benefit from burrowing in the snow and seeking shelter in soil/crevices available to them due to their compact body size while the large species would have been better able to withstand exposure.

I believe it is highly interesting but I also think that wolves made a choice to use this strategy. 

Namely, there are other species that team up to achieve what individuals cannot achieve (although these species appear to have evolved their social strategy in perhaps a more static environment, not as a strategy to survive climatic fluctuations and to distribute themselves along vast gradients of habitats and latitudes).

But I think that mostly this strategy has been the result of natural selection favouring group living.

When I consider wolves, however, it appears ‘strange’ that they developed social cooperation to respond to a cold and unproductive climate.

Mostly, the degree of sociality in species depends on the climate and resource availability.

Social species become ‘more social’ when the environmental conditions (food, climate, predation pressure) enable them or force them to form larger groups. It is more probable for a social species to develop larger groups when it is warmer and when resources are more abundant. When it is cold and resources are scarce, the social species can live singly, in mother-offspring groups, parent-offspring groups but not truly in more extended groups.

Accordingly, I suppose that the evolution of sociality in many species has been driven by favourable conditions to developing a large group size and these species would have maintained this group size to adapt to the specific conditions (thusly, species with a rather fixed social structure, the social structure would be the product of adaptations to a particular environment and to a particular niche rather than a strategy to survive along an ample environmental/niche gradient).

It is counterintuitive that wolves would have naturally evolved large social groups under Pleistocene harsh conditions. Namely, it would have been more natural for social groups to shrink under such circumstances.

Therefore, I think that wolves had to decide to rely on social cooperation vs. allowing for the environment to dictate their ultimate body size and niche.

It was the social factor that dictated wolf evolution, instead. Additionally, for an individual wolf, the attained morphology might not have been the most profitable. It would have been difficult for a single wolf to survive during Pleistocene. By selecting social cooperation as their evolutionary strategy, wolves, essentially, traded off individual security.

I, personally, believe that during some warmer conditions, wolves might have been able to form larger social groups (much like coyotes) and they might have begun hunting larger prey than rodents. When the climate changed, I think wolves were not willing to give up their group living due to the bonds they had formed. There might have been some factor in wolf social living that seriously enhanced, e.g., oxytocin production and social affiliation but currently I cannot tell what this factor is.

Under harsh circumstances, it would have been more beneficial for the parental pair if their offspring dispersed. Especially, while wolves were perhaps still smaller in size and individuals were able to survive by hunting smaller prey in the snow.

I believe that wolves did not select adjustable social groups because it was somehow natural or even easy for them. I think that they did not want to lose their social living and they adapted to retain in which turned out to be a profitable choice.

Maybe you would be inclined to laugh at such supposition.

A species making a conscious evolutionary decision to stay together and to cooperate despite losing some of the individual fitness potential and having to adapt its lifestyle sounds much like a Christian society which acts out of a vision for a better future in which everyone treats one another as brothers and sisters. Not something we would think of wolves.

However, I wanted to propose this theory. It is perhaps easier to accept that wolves selected adjustable group size vs. inflexible body size that narrows the available niche. It is more challenging to accept that wolves may have had to acted thusly out of attachment to their group members and despite initial (as well as some permanent) obstacles to this course of evolution.

Still, as I mentioned above, during Pleistocene, the climate would not have naturally (sort of automatically, out of natural behaviour governed by environmental factors) favoured large groups of above-average-sized predators, and the size of the wolf seems to be derived from social requirements rather than environmental mandate during Pleistocene.

Well, perhaps you might be entertained by my theory. I believe that wolves belong to one of the probably very few species that has made an evolutionary decision which has been that of maintaining group affiliation. And that they adjusted their niche to group living which, in the end, was proven to be a remarkably adaptive choice.

References

Heard, D.C. & Williams, T.M. 1992. Distribution of wolf dens on migratory caribou ranges in the Northwest Territories, Canada. Canadian Journal of Zoology. 70(8): 1504-1510. https://doi.org/10.1139/z92-207

McAllister, I. (2007). The last wild wolves: ghosts of the rain forest . University of California Press.