Why Do Levels of “Cooperation” Diminish as Pack Size Increases?
Originally published in slightly different form on November 9, 2012 at PsychologyToday.com.
Should Game Theory Be Applied to Wolf Pack Behaviors?
One area of great interest in current biology is animal altruism and cooperation. These qualities are said to exist at all levels of life, from aggregations of cells to human society.
In their paper, “The evolution of cooperation and altruism,” (2006) Lehmann & Keller write, “One of the enduring puzzles in biology and the social sciences is the origin and persistence of intraspecific cooperation and altruism in humans and other species.”
Because cooperation and altruism in non-human animals really is so puzzling animal researchers rely on disciplines like experimental economics and game theory—designed to explain cooperation in human society—and apply them to non-human animals.
Wolves are often cited as a prime example of cooperation in animals. Yet research shows that hunting success peaks at about ± 4 wolves. The larger a pack gets, the less successful they are.
Why is this so?
In a 2011 article, McNulty, Smith, Mech, et al say that there are 2 prevailing hypotheses for why group-specific hunting success (Hn) declines in larger packs. The interference hypothesis proposes that Hn is limited because individual predators impede each other’s actions. The other possibility is the “free-rider” hypothesis, a term borrowed from economics, where “free riders” are defined as those who consume more than their fair share of a resource, or shoulder less than a fair share of the costs of its production. (Economics is what gave us the mistaken idea that dogs know when they’re being treated unfairly: see here, and here.)
Defining Pack Hunting Behaviors
The wolf researchers measured levels of participation by pack members during various stages of the hunt, using an ethogram (an objective scientific inventory of a set of behaviors) developed a few years earlier by McNulty, Mech & Smith (2007).
Search..................... Traveling without moving toward prey.
Approach................. Fixating on and traveling toward prey.
Watch..................... Fixating on prey while not traveling.
Attack-Group............. Running after a fleeing group.
Attack-Individual......... Running after a solitary individual.
Capture.................... Biting and restraining prey.
The idea that hunting success was negatively impacted because wolves in packs with >4 members withheld effort was generally borne out by the fact that the rate of decline was most apparent for the most dangerous task above: capture, or biting and restraining prey. In other words, as pack size increased fewer wolves felt like going in for the kill.
McNulty et al conclude: “Our study suggests that [some] wolves in large groups (>4 hunters) withheld effort … and likely participated merely to be at hand when a kill was made.”
I think that’s very unlikely. Don’t get me wrong; this is a dedicated group of scientists who are at the top of their field. They’ve done a wonderful job of compiling research and applying the principles of group cooperation as put forth in previous animal studies based on economic theory, etc. But while their conclusion is right and proper within that specific context it still requires the wolves to engage in some very high-level, humanlike thought processes.
Morgan’s Canon & Information Theory
Morgan’s canon states that, “In no case is an animal activity to be interpreted in terms of higher psychological processes if it can be fairly interpreted in terms of processes which stand lower in the scale of psychology and evolution.”
Yet these are the thought processes a wolf would have to engage in for the reasons given above: “I’ll withhold my own efforts (requiring a sense of self) knowing that the other wolves (requiring a sense of self-and-other) will probably do all the work for me (requiring hypothetical thinking) so that later on (requiring mental time travel), when the elk has been killed (requiring an ability to project hypothetical thoughts onto hypothetical future events via mental time travel), I’ll be able to eat my fill anyway (more mental time travel, more hypothetical thinking).”
None of these forms of cognition have been found to exist in canids.
McNulty et all would probably counter by saying they’ve drawn no such conclusions. They’re only presenting the data, using a widely accepted scientific model.
This is true. The problem isn’t with their research. As I see it, the problem is with the model. A wolf pack is not an economic system. There are no goods and services being sold or bartered, no markets or distribution points, no currency changing hands. (There are some similarities of course, but not enough, in my opinion, to make total sense when applied to most non-human animals.) But while there’s no currency exchange there is an exchange of information. So I think applying information theory would give us a more parsimonious explanation as to why “cooperation” in wolves decreases as pack size increases.
More Wolves = More Noise?
In the ethogram developed by McNulty, Mech & Smith, pack hunting behaviors are described in the most objective of terms. There isn’t the slightest hint or suggestion as to why the animals are exhibiting any of these behaviors. Can lack of success in larger packs also be explained without attaching humanlike reasons for behaviors?
Yes, but in order to do so we have to look at the hunting process through the wolf’s eyes. That doesn’t necessarily mean we’re pretending to know that the wolf’s experience is. We’re just making objective observations about where the wolf’s attention is focused.
When a single wolf hunts small prey on his own he only has to focus on 2 primary external stimuli: 1) the prey’s movements and 2) the terrain both animals are moving through. When the same wolf is hunting with his pack mates, he has another set of stimuli to focus on (at least peripherally), 3) the movements of his confederates.
In wolf packs of optimal size (± 4 members), each wolf is processing information via ± 4 sets of signals: ± 3 sets coming from his fellow pack mates and 1 set coming from the prey animal. As the number of wolves increases, so does the number of signals each individual wolf has to process. As the number of signals increases the potential for “noise” in the system increases as well.
McNulty et al write, “Several lines of evidence suggest that decreasing individual performance resulted from declining effort in response to high hunting costs.” That may be true, but I would suggest that decreasing individual performance resulted from a decreasing ability to differentiate between information and noise.
Is it that simple?
Yes and no. For instance, while all members of a large pack were less likely to engage in the attack and kill behavior, breeding wolves still engaged in those behaviors more often than non-breeders did.
This could be explained through a kind of anti-green beard effect where the individual wolf’s genes were running the show. Or it could be explained through differences in channel capacity (or carrying capacity); the operating thesis being that in most cases, breeding wolves are also the so-called “pack leaders,” and as such have to routinely pay attention to more sets of signals than their subordinates. So whether through experience, or genetics, or both, breeding wolves would hypothetically be more capable of receiving multiple streams of information without experiencing them as noise. Since the final act of the hunt is the most dangerous, it also requires the most intense focus. Non-breeders would be less able to tune out system noise, which would hypothetically be what’s actually inhibiting them from going in for the kill or actively participating in other aspects of the hunt.
Finally, a simple conjecture: British anthropologist Robin Dunbar has suggested that for human beings there’s a limited number of people with whom one can maintain stable social relationships and that “this limit is a direct function of relative neocortex size.”
My conjecture is that there may be a kind of Dunbar’s number for pack size as well. If hunting success decreases in inverse proportion to any pack of >4 wolves, it may well be because there’s a limited number of wolves with whom each wolf can maintain a stable hunting relationship. This wouldn’t require some wolves to withhold their efforts, “pretending to participate” in the hunt in order to get a free meal. I’ll leave it to you to decide which model makes more sense.
“Life Is an Adventure—Where Will Your Dog Take You?”
1) Computer models show that wolves don’t need to form the intent to cooperate while hunting, which suggests, by contrast, that they probably don’t withhold their efforts, pretend to cooperate, or fail to cooperate either.
cooperation in dogs and wolves