The. Strength of the 狼, オオカミ is the pack. What dose it mean?

The "wolf" draws strength from its brother (or sister) 狼, オオカミ pack members...strength in numbers....

It means that no matter how strong the 狼, オオカミ is によって itself and no matter how much power and force it has によって itself, the whole sense of a pack and all the オオカミ working together as one strengthens the bond between them and makes them so so much stronger plus gives a sense of teamwork and power even more.

The main strength of the 狼男 is in numbers and in the teamwork and co-ordination their mental link gives them.