Pack
Generally speaking, a pack of wolves has between four and nine members, but they can also be as little as two wolves and even up to 30 wolves, although this is very rare and a pack that size will not last very long. A pack of wolves is almost like a little society, with a leader, a second in command, and even your poor old beggar. While there is a lot of hostility for positions within the wolf pack, these animals rely on each other and they all recognize this fact. The group is very sophisticated and abides by very strict laws. The pack is less about flat out violence, and more about order and keeping wolves in line. Even the leader yields his/her food to pups before they themselves dig in. You can generally tell what class a wolf is in based on their body language. Any pack will follow a certain layout of social classes including the Alpha, Beta, Subordinate, and Omega.
Alpha
The alpha is the leader of the pack and will not be afraid to drill that into the minds of the wolves in his/her group. The alpha is usually male, but the leader is judged on strength and not gender. Hunts and any activity of the pack is led by the alpha. When any wolf steps out of line is the Alpha's responsibility and privilege to punish that wolf. Alphas carry themselves in the highest esteem: tails straight up, head held up etc. Generally speaking, the Alpha's mate and offspring will be the only related wolves in a pack. This position is a highly coveted spot within the team and everybody wants it. In Call of the Wild this position belonged to Spitz and later, Buck.
Beta
If the Alpha was the president, the Beta would be the vice president. The Beta doesn't really have any select special job to do. This position is filled up by the strongest subordinate and is around to do the Alpha's duties when the Alpha is not around. The Beta, however, will not be afraid to challenge the leader at a moment's notice. Any weakness in the Alpha's routine may be enough for the Beta to challenge the leader. The Beta can treat subordinates and the omega however he or she desires. On the other hand, the Alpha will not give the Beta a second glance except maybe to watch his/her back. This position belonged to Buck, and then later, Sol-leks.
Subordinate
The subordinates are the ordinary dogs in the pack. They are the core of the pack and will follow the Alpha or Beta's lead. There can be cases where subordinates fight eachother but this generally doesn't happen unless the Alpha or Beta starts the fight. They are the ordinary citizens in the group and will have decently proud body language, except around the Beta and especially the Alpha. The only dog beneath the subordinates is the omega. Subordinates in Call of the Wild include, but are not limited to: Pike, Dub, Dolly, Teek, Koona, Joe, and Dave.
Omega
The omega is the weakest dog in the pack. When another dog is having a bad day this dog is the one to get picked on. He or she holds him/herself in the lowest esteem and this shows with drooping body language. The omega oftentimes will get so upset at the disrespect he/she is receiving from his/her packmates that it will leave the pack. In Call of the Wild, the Omega for most of the book is Billie. He, however, didn't get as bad of a break as other omegas because Billie had Joe and Buck protecting him.