It's common to talk about animal species that are threatened, endangered, or extinct. Many times these are cute, fuzzy creatures that elicit emotional responses (and thus a desire to contribute to their conservation). But a major part of what leads to a particular adorable species' ability to persist is the environment in which it lives. A new study out this week in the journal Science analyzes data from the International Union for the Conservation of Nature's Red List of Threatened Species, as well as the World Database of Protected Areas to name the most irreplaceable protected areas on our planet.