Group living

It is extremely difficult to distinguish between solitary living and group living. Distinctions between the two are relatively artificial. This is because many species of animals who spend a majority of their life alone, at some point in their life, will join a group or engage in social behavior. Some examples of this happens during mating, parental care of their offspring, or even aggregations of conspecifics to an area to exploit resources of food or shelter. defines a group as “any set of organisms, belonging to the same species, that remain together for a period of time while interacting with one another to a distinctly greater degree than with other conspecific organisms." This definition cannot be applied to situations such as moths drawn to a lamp, or when animals aggregate around a watering hole, == Evolution of group living ==

There have been multiple different hypotheses proposed to explain how group living evolved in animals. Research shows that grouping habits may differ between individuals, and this tendency to group can be inherited. Research also shows that grouping tendency depends heavily on the interaction of many genes, as well as experiences gained by an individual and the environmental conditions surrounding the individual. Other studies argue that the main driving force of the evolution of social grouping is phylogenetic inertia alongside ecological pressure. However, it is still unclear how exactly animals have evolved from the ancestral state of solitary life. == Benefits of group living ==

Information access and transfer A key advantage to group living is the ability for individuals in a group to access information gained by other group members. Once a high-quality resource is found, the individuals may produce signals or cues that guides other members of the group to the location of the resource. In some species, for instance the forest tent caterpillar (Malacosoma disstria), foraging behaviors change depending on food source. On less favorable food sources, caterpillar groups tend to splinter, thereby potentially increasing the risk for predation, but increasing the potential of finding a more favorable food source. Increased defense from predators Another advantage of living in a group is seen in many prey species in their ability to increase defenses against predatory animals. A way that a group may increase its defenses against predators is through the ‘many-eyes effect’. This effect states that larger groups of animals are better at detecting predators compared to smaller groups. This allows the individuals within a group to more effectively identify predators, allowing these individuals to flee or adopt postures to alert the predators that their presence is known. An example can be seen in a study conducted by Siegfried and Underhill (1975) on laughing doves, in which large groups react to a mock-predator much more rapidly than smaller groups. Another way in which a group may have decreased risk of predation is through the dilution effect. Breeding It is hypothesized that reproductive success of a female is determined by the number of eggs she can produce, while reproductive success of a male is determined by the number of females he mates with. Furthermore, according to Bateman's principle, it is expected that females of a population will select mates that result in the best quality offspring, while males compete among each other to mate with a female. Group living provides the presence of social information within the group, allowing both male and female members to find and select potential mating partners. Alongside this, living in a group allows for higher reproductive success as individuals have access to a greater number of potential mates, and the possibility to choose between them. Therefore, individuals living in groups have a higher chance of finding a mate and successfully reproducing, on the basis that larger groups present a greater number of accessible mates nearby. == Costs of group living ==

Despite the many benefits of living in groups, individuals of the group may also incur costs when forming groups. Ectoparasitism and disease When individuals of the same species aggregate to form groups, there is an increased risk of diseases and parasites spreading throughout the group. Because individuals of a group live together in close proximity, when one individual is infected with a disease or parasite, they bring this disease or parasite into a habitat full of susceptible individuals. Also, larger groups of animals will produce larger amounts of waste material, allowing for a favorable environment for pathogens, that may spread to individuals. Thus, transmissions of diseases and parasites are more likely to occur and more rapidly than if an individual lived alone. A great example was shown in colonies of cliff swallows by Brown and Brown (1986). Cliff swallows are commonly parasitized by swallow bugs and this study showed that the number of swallow bugs per nest increased significantly with an increase of the number of cliff swallows per colony, which thus reduced the survivability of the nests’ offspring by up to 50%. Another study shows that bank swallows have an increased likelihood of flea infestations per burrow with the increase of colony size, which also increased mortality rates of offspring in infected burrows. Intraspecific competition A consequence that may arise from forming large groups is the increased intraspecific competition between group members. If resources in a group’s environment becomes limited, group members will then have to compete with one another for the available resources. The increased competition then results in reduced nutritional intake in some individuals compared to others. An example of this can be seen in a study conducted on leaf monkeys. This study showed that females in a larger group of leaf monkeys had a reduced energetic intake than females in groups of smaller sizes. The reduction in energy gain seen in females of the larger group also then negatively affected the development rates of any infant offspring. Therefore, despite the benefits of animals forming groups that increases foraging efficiency due to the presence of social information, This means some individuals will have a reduction in their reproductive success as it now competes with other group members. An example can be seen in a study conducted on the Eurasian badger (Meles meles). Individual group members in group sizes much larger or smaller than the optimum may have increased stress levels. Individuals in groups much larger than their optimum group size may have increased stress levels due to competition for food resources or mates. In contrast, individuals in groups smaller than their optimum have increased stress levels arising from inadequate defense from predators. An example of this can be seen in a study conducted on a species of ring-tailed lemurs (Lemur catta). This study predicted that the optimum group size of ring-tailed lemurs is 10-20 individuals. The study then showed that groups within the optimum group size produced the lowest level of cortisol (an indicator of stress), while groups larger or smaller than the optimum group size had a significant increase in cortisol production. Therefore, group sizes that are not maintained within their optimum size may incur a cost of increased stress levels of individuals within those groups. Inbreeding Another proposed cost of group living is the increased risk of inbreeding. As members of the group in close proximity to one another over long periods of time, this increases the chances that offspring of the group may mate with related individuals. Offspring resulting from inbreeding have an increased chance to be affected by recessive or deleterious traits, thus reducing its survivability and ability to reproduce. The risk of inbreeding however, is only prevalent in smaller, isolated groups, as larger group sizes dilutes the chance of an individual mating with its relatives. == Further reading ==