Seems to be a lot of questions lately about totem/tribe type numbers and growth. I went back into the archives and found the update that details the current mechanics.
Excerpt from the March 7, 2011 update follows :
We're testing some tribe revisions. Tribes will now have 4 sizes.
Homesteads 1-4 starting members.
Bands 5-9 starting members.
Clans 10-19 starting members.
Tribes 20+ starting members.
This will allow smaller groups to form tribes with a decent claimed area but without crowding the world due to the maximum tribe size.
Each of the tribe types can grow in radius beyond the size of the next type, so their maximum radius anticipates some growth.
Homesteads have a fixed radius.
Bands grow in size up to 15 members.
Clans grow in size up to 25 members.
Tribes grow in size up to 80 members.
If your group drops below the minimum number, it will change to the next size tribe. We will not implement tribe and homestead overlap for now due to potential complicated situations. We'll think about further revisions to the system in the future when we expand the green mist.
Aside from the maximum growth size there is no difference between these tribe types. The member counts were chosen based on current tribe sizes to provide some balance.
We may slightly adjust the numbers after some more tests tomorrow.