Wildlife of Ecuador: A Photographic Field Guide to Birds, Mammals, Reptiles, and Amphibians by naturalist Andrés Vásquez Noboa, witih photography byablo Cervantes Daza, covers mainland Ecuador (but by "mainland" we also mean ocean mammals). Focusing only on non-piscine verts, you will need to go elsewhere for your inverts and plants and such. But you get the point. This book covers most of what you are looking for when you are out in the wild looking for animals.
This is not a comprehensive guide, but covers the most frequently seen animals, totaling to 350 distributed across over 400 plates.
There is a good chance that if you are an American or European going to Ecuador, you are visiting the Galapagos, in which you will want to check outg Wildlife of the Galápagos: Second Edition. A rather broad gulf of evolutionary change and outlandish biogeography separates Ecuador from its famous island possessions. But there is a good chance that if you are going to teh Galapagos, you are making at lease one nature related stop, so this is the book for you.
This is a well done nicely bound standard field guide of field guide size and format with animal info and excellent photos on the same pages, and organized by taxonomic category (not all field guides are!). You might think a tiny country like Ecuador does not need range maps, but the topography is highly variable with conditions running from lowland moist to alpin-ish and from wet to dry, so there are, indeed, range maps as needed. And, that ecological diversity is explained in the preface material.
I highly recommend this book for travelers to the region.
If you want more ecology and evoluitonary biology with your field guides, check out my review of the Neotropical Companion, here.