All individuals rely upon the same resources, such as; food, shelter and finding a mate. So, why do some decide to live in groups while others prefer to live their lives in solitude? The costs and benefits of each method would make either a viable option for an individual depending on their specific needs.
Solitary individuals are very territorial. They have to be in control of their domain in order to have enough resources to survive. If resources are abundant an individuals will only need to protect a small patch of land. However, if resources are scarce the individual will need to control a larger territory. Animals will “mark” their territory to warn others that the land is already claimed. Aggression can also be witness in organisms in defense of their territory. Robins in early spring will attack other robins who invade their territory. Individuals in the species will usually only come together for mating purposes. This is because otherwise they would be in constant competition for food and space. The energy put into protecting ones territory seems very costly, but if they are able to acheive this they reap the full benefits of all resources.
On the other hand species who live in social groups share their resources. Individuals can either be found in large or small colonies/groups. In this kind of social aspect the group can work together to to build their nest or collect food. They have the added benefit of being able to better defend each other against predators. The disadvantage to this is that now they have to compete with eachother in the social group for division of the reasources, such as food and mates. When picking a social group it all comes down to what advantages and disadvantages can you live with.