There are plenty of animals that live in community settings. Communities can vary drastically from species to species. Predator groups work together to hunt larger prey and or hunt with more success. While prey groups stay together for protection and other benefits. There are many other benefits of community living, but there are also many risks that come with it.
Living in a group, as a prey organism, can help to deter predators from attacking. When a prey organism is by itself, it is unlikely that it would be able to defend itself from the predator. In a group, many animals attacking or running from a predator creates a dangerous situation for a predator. This might cause the predator to flee as the prey may not be worth the damage. In addition, spotting a predator is much easier with many eyes surveying the area.
Some animals use pack tactics to take down large prey. In the photo above, a wolf pack is surrounding a bison. This bison would be very difficult and probably impossible to take down by a single wolf, but a group of wolves cooperatively hunting the bison makes it quite possible. The bison and other larger prey make large meals for the hunters.
Community Rearing of Young:
Especially with closely related individuals within a population, the act of caring for children who are not one’s own is a common occurrence. Helping those who are related to you raise their children increases one’s fitness, their indirect fitness improves. They are helping some of their gene pool survive into the next generation.
In situations where their is no genetic relatedness between a helping individual, this behavior evolved because some sort of fitness is gained by the helper. This could be in the form of breeding areas, reciprocity, breeding partners and many of the other types of altruism in animals. This idea is talked about in more detail in another article by another KSC student.
There are likely other benefits that I have left out. Mention them in the comments!
Competition for Food:
When individuals of a population live close together, they start to compete for many resources such as space and food. In the case of group living this would be called intraspecific competition because members of a population are competing. Competition creates negative density dependence which means that as the population size grows, the per capita death rate increases and/or the per capita birth rate decreases. This is a form of population regulation, the population can only go up to a certain point which is the carrying capacity. This negative density dependence, in reference to food availability, is affected by the variety of food the population can and will consume. Diversity within a population, for this example what they can and will eat, will decrease competition to a point where it might not be as much of problem for the group.
Competition for Mates:
When a population contains groups that live closely together, they have to compete more than populations that do not. This also applies to accessing mates. Typically the males of the group have to fight or compete for access to females who are able to breed. This is the operational sex ratio. This arises because female gametes, eggs, are much more costly to make and maintain than sperm. The females must be choosy to ensure their offspring get the best genes and therefore have the highest chance of surviving and producing their own offspring. In some situations sexual selection can get out of hand, creating males with traits that make them less fit to the point that natural selection counters it. This phenomenon is called Runaway selection. This competition can even come down to the ability of sperm to fertilize the egg. It is intense! In some cases the females must compete for access to males, this is called a sex role reversal. Sex role reversals can even occur between generations.
In some cases where male competition could lead to fighting, it is avoided by asserting dominance. Instead of physically fighting the males will perform displays of dominance. The dominant males will gain access to the most females, while subordinate males often adopt alternative strategies to get mating in where they can.
When animals live in groups, they are easier to spot. When you are a prey species you may not want to be seen by a predator, when you live in a group you do not want to be singled out. When you are alone it is much harder to avoid a predator than when many of you are running at the same time. This also applies to predator species, a predator would like to catch the prey species off guard as to minimize their energy input for the energy gained from feeding on the prey.
When an individual is within close proximity to another individual who is infected with some sort of transferable disease they are more at risk than an individual who is farther away. This will vary with the amount of contact there is between individuals of the group. In highly social animals who come into frequent close contact interactions, disease would likely spread like wildfire. This can be seen in one study that compared the gut biomes of individuals in a group of rhesus macaques. The degree of contact between individuals had a positive correlation with the genetic similarity of the commensal E.coli in their gut. While some of the genetic similarity would come from relatedness between individuals, but it was more related to the social contact between individuals!