Get a Grip On is a short series from the late 90's. I saw the whole series at a Barnes & Noble recently and didn't realize that they were from Time-Life; they are physically smaller than most Time-Life books and they really look different (they're paperback, etc. It's hard to explain.)
Anyway, I don't own these yet, but I've heard mostly good things about them. I am planning on running Get a Grip on Philosophy by my fiancee the philosophy major just to see what level the books are on, but as of yet I don't have too much insight into these.
The Get a Grip on Ecology volume was published in 2003, several years after the others, and it has proven difficult to track down (it isn't listed in Amazon or on the Library of Congress site yet) but Barnes & Noble has them in stock for $4.98 each.