Galapagos: The Islands That Changed the World
Filled with pictures, this narrative describes the geologic and biologic history of the islands: how they formed and how life evolved once there. Several chapters are devoted to describing the wildlife on the islands and in the surrounding waters. Several other chapters relate human history on the islands (including an entire chapter devoted to Darwin's studies), and the recent struggle to conserve the ecosystem.
What makes the Galapagos islands so special is that in contrast to other islands (like Hawaii), these were uninhabited by humans until relatively recently. Fresh water is hard to find, so although the giant tortoises were an attractive food source, settlement was difficult. As a result, the wildlife remained relatively untouched by the time Darwin got there. He was able to observe the careful balance of populations on each , and how they are adapted to a particular niche. Once people settled, bringing goats and pets, that balance was upset, and endemic species were threatened.
I picked up this book when looking for something to read about Galapagos (in preparation for my trip there next spring), and it happens to be the companion to a BBC miniseries I got from Netflix. Both the miniseries and the book are very good, and they don't overlap much at all.