The need for socialization is not exclusive to human beings. Instances of social activity can be found in many species in the animal kingdom. Some animals connect, interact and live together in a more complex way than we could imagine. When thinking of animals that display this kind of behaviour, chimpanzees or elephants tend to be the first to come to mind. These animals represent the social connection in their species with their behaviour, but there are many others.
One of the main characteristics of social interaction is living in groups; in other words: living together. Animals gather together to optimize the profit of their environment. However, this environment is not always the same, and there are often local variations (due to physical, chemical or biotic factors, amongst others) that differentiate some groups within the same species, as they will present different grades of cohesion or interaction. Despite this fact, animals do benefit from a series of advantages by living in groups:
A more stable body temperature
When the individuals of a population stay together and close to each other, the surface-volume ratio (S/V) is reduced, achieving a minimum loss of heat. On the other hand, when animals are more exposed, there is a greater dissipation of body heat to the surroundings.
Improved locomotion capabilities
The advantage here is obtained by animals that move in a fluid medium, as they save energy by travelling in group. For example, birds that travel in a V-shaped formation during migrations do so more efficiently, benefiting from the thrust generated at the ends of the wings of the birds that fly in the first rows of the group. Together, they are able to generate the advantage of turbulence, converting a turbulent flow (more chaotic) into another laminar flow (more organised).
Enhanced reproductive capacity
Living in a group increases an individual’s possibilities of meeting potential partners and also increases its reproductive success or that of its family members (inclusive effectiveness).
Protection against predators
It is one of the most remarkable advantages of group leaving, as it allows to identify predators more efficiently, as well as to locate prey. But grouping not only means protection against interspecific competitors; it can also bring protection against predators within the same species. For example, groups of lionesses can protect their young from errant males, thus preventing infanticide, which is common in certain species.
On the other hand, the surveillance time of individuals is considerably reduced as the size of the group grows, as well as the percentage of those that are in charge of watching out, who feel more secure when surrounded by their peers. For example, a Carduelis carduelis will raise its head twice as often when it is alone, compared to when it is in a flock of six. However, according to a study of my own, it has been proved that there are significant differences in the groups ofIberian wild goats in the Guadarrama mountain range (Spain), in which surveillance is more efficient when the size of the group is smaller.
A larger group also causes two known effects that may favour the survival of individuals: they are called “dilution effect” and “confusion effect”. Thanks to the effect of dilution, the probability of being preyed upon (or parasitized) is smaller for an individual when living in a group. In short, in a larger group, it is “more likely” for it to happen to another individual. For example, Camargue horses establish more numerous groups in summer, decreasing the probability of being attacked by parasites.
Regarding the confusion effect, it seems that predators find it difficult to maintain focus on a prey when facing a large group. They find difficulties to choose an individual, due to the overload of moving targets in their visual canal, as well as sensitive confusion.
Finally, large groups have a greater capacity to manoeuvre against predators, such as the flocks of Sturnus vulgaris, which cause polarization and the formation of vacuoles around the predator, generating empty spaces around it. This is a very visual defence mechanism, in which each individual perfectly controls its movements and speed, in order to avoid any type of collision.
Efficient food search
This becomes more effective as the size of the group increases, because, as we have already mentioned, there is a more efficient detection of prey. In addition, if we refer to shoals of fish, the larger groups are less visible in front of the prey, due to the superposition of the detection spheres and the optical properties of the water, so they become effective predators (against isolated individuals). This is not the case with birds, where larger flocks are more visible than isolated ones (they acquire other advantages, such as locomotion). In fact, there are few species of birds that form flocks, while more than 4,000 species of fish group in shoals.
Despite the great advantages of group living, it also comes with certain costs that can be damaging to the group: an increase in the rate of disappearance of food, an increase in competition, stress, appearance of unwanted agonistic behaviour, dominance… Costs that are side effects but, ultimately, beneficial to the group.