Class Level
The character’s druid level. The druid’s class levels stack with levels of any other classes that are entitled to an animal companion for the purpose of determining the companion’s abilities and the alternative lists available to the character.
(Ranger) Animal Companion
This ability functions like the druid ability of the same name, except that the ranger’s effective druid level is one-half his ranger level. A ranger may select from the alternative lists of animal companions just as a druid can, though again his effective druid level is half his ranger level. Like a druid, a ranger cannot select an alternative animal if the choice would reduce his effective druid level below 1st.