A problem in designing conservation strategies is a lack of species baseline information. I would argue that this is the case even in the developed world. Therefore, when faced with expanding human population, the best approach is to preserve large blocks of land containing a variety of habitat types that are connected to each other. Often, efforts directed to a single species have benefits for other species. For example, seasonal trapping of the brown-headed cowbird, a nest parasite for the endangered least Bell's vireo, benefits other rare and declining riparian avian species that are parasitized such as the willow flycatcher and yellow warbler.
Lands preserved and mitigation measures imposed for one species usually benefit most other wildlife.
The book by Shafer on Conservation Biology is worth a read.