Can someone explain an aspect of endemic that I’m curious about, please? Can a species become endemic? For example, if something was formerly widespread in the Palaearctic but is now restricted to a mountain range, would it be considered endemic to the mountain range? And if so, does timescale matter? If it had been widespread in a previous interglacial but restricted to the mountains in the current interglacial, would that be treated differently from if it has been wiped out over most of its range in just the last few centuries?
That’s a really fascinating perspective/question on the time scale of endemism! The implication is that endemism has both a geography and a time frame as context. Being a relatively short-lived and “new” species on this planet, our human frame of reference for endemism is typically short-sighted, i.e., we speak of a taxon’s current distribution and ignore (or set aside for a different discussion) the topic of why/how its present distribution came to be.
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In an evolutionary sense, you could speak of endemism in both time and space. This is actually a concept in geology: biostratigraphy determines a rock’s age by the fossils found in them - if you find two rocks with the same fossils, it’s likely they are likely laid down at the same time, because that species was “endemic” at that particular time.
As noted in this thread, every species on Earth can be considered endemic to its range. If a species is now only found in a specific area, but found in a larger area before, it’s hard to define where it “became endemic” - because it always was. In the practical sense, though, your question has a real life application: in conservation, where species get re-introduced or allowed to spread tends to be within the species’ natural range as we know it has had, and therefore likely to not disrupt the ecosystems it’s brought into. We know that beavers were once endemic to all of Europe, so while they have been hunted to extinction in many countries, they’re fine to re-introduce as an “endemic” species to the continent.
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Thanks for the responses. So according to the Wikipedia article, a species with a restricted distribution that was widespread thousands of years ago is a paleoendemic. One that has been lost from most of its range in historic times may be a cryptoendemic.
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Even though endemism is geographical in essence, time is always to be considered, and relatives (…or lack thereof) as well. Palaeoendemics can be loners, “the last of their lineage”; however other endemics (schizo- patro- apo- etc.) are assessed in relation to close coeval taxa.
The flip side of this question is can a species lose its endemic status through human intervention or natural dispersal? The Knight Anole was endemic to Cuba but is now in Florida and the Bahamas. By some definitions it is still a Cuban endemic.
I agree that there is a big temporal aspect to how we define something as endemic. Like most terms we use in biology, it doesn’t always work for all situations. What we call a species is itself a temporally defined concept for a lineage of organisms.
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Yes, of course if it disappears everywhere except in a small part of its old area of distribution. They are called palaeoendemics.
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Not sure my reply belongs in this topic. I posted this with the intent that maybe iNat could adopt Frank’s terminology and abandon the word “endemic”. Don’t have an opinion on endemism over time. I probably could have said that rather than relying of which reply button I pressed (threading and subthreading is not handled well in this forum).
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No worries, I moved it back.
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Interesting paper (love the key p.5!), a century late to the party. In the meantime the word ‘endemic’ has invaded the biogeography literature. 
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