Is it exhibit suitability you need? If that's your problem, try using only their favoite foliage (the umbrella thorn tree I think), and place 4 of them in one square until placing a new one in a square turns up a red face. (to turn on grid, hit Ctrl + g)
Look at the zookeeper recommendations and play around with terrain until happy/sad faces tell you whether it's okay.
If you're still having trouble, you may want to check out Wisco's and go to the strategy center-it will tell you the best way to get the highest suitability possible.