The definition of endemic

I think it’s worth considering that any line we draw on a map is a line we drew on a map. Political boundaries certainly aren’t intended to reflect patterns of biodiversity, sure. There is no taxon-agnostic natural classification of the landscape, though. If you want to capture variation in aquatic or wetland organisms, you’ll likely find a watershed-based landscape classification is the best bet. If you’re interested in alpine plants, you’ll probably find that the watershed boundaries are worse than useless, dividing every peak.

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I don’t think we diverge as much as you might think. I fully recognize and appreciate the scientific value of knowing where a species was most recently native without human influence. My “day job” as a Natural Heritage botanist for Nevada has given me the privilege of working for the past 31 years with about 140 endemic plant taxa, defined both by our state boundary and by their (usually) much smaller geographic ranges within. We also have two of the most prominent centers of endemism in North America (if not beyond): the Spring Mountains and Ash Meadows. And we pay just as much attention to another 160 or so taxa that we don’t call endemic because they also occur in neighboring states, but that are still just as vulnerable within their small natural ranges.

A few of our species have “lost” their endemic status over the years, mainly due to taxonomic re-interpretations. (And also gained a few by discovery of new species.) One example is a species that was formerly considered “objectively” endemic to the Spring Mountains of Nevada, but is now “objectively” considered conspecific with populations in the Wasatch Range of Utah. I use the term “objectively” advisedly here, because there is always an element of human judgment in such taxonomic decisions, and they are always subject to future further judgment as new research is conducted. All designations of “endemic” worldwide exist within a taxonomic context.

A few other species have “lost” endemic status to one area because apparently native populations have subsequently been discovered outside that area. We once thought we had dropped a state endemic because of an apparently introduced population that turned up along a California highway near our border. But that population ended up not becoming naturalized (so far). If it had, though, its formerly endemic status could still have been preserved, in an iNaturalist context, by marking it Native in its “naturally” endemic range, and Introduced outside of that.

My sense is that we wouldn’t be having this debate if species never became naturalized outside their “native” ranges by human-aided dispersal. Above I used the phrases “most recently native” and “without human influence” intentionally to illustrate the arbitrary decisions that are still unavoidable when defining endemism that way.

most recently native

Our designations of “endemic” depend on where we take our “snapshot in time.” As you noted, species ranges grow, shrink, and/or shift over time for a multitude of natural causes, not least of which “recently” have been Pleistocene climatic cycles. Some current centers of endemism, like strongly isolated “sky-island” mountain ranges, or actual oceanic islands, were probably centers of endemism throughout the Pleistocene (though their “taxonomic contents” may well have changed during that period). The Spring Mountains example fits here. Other current centers of endemism, climatically isolated wetlands like Ash Meadows for example, are likely more ephemeral in time and/or location, and less informative historically.

Where we take our snapshot in time:

without human influence

Very recent historical introductions are often (but not always) easy to identify. As one goes back a little farther, in some parts of the world the advent of human-aided dispersal is relatively easy to pinpoint in time. And the native ranges of species just prior to that pinpoint may in some cases be relatively easy to deduce. In other regions and for many other species, it only gets harder to make those calls. For these reasons I suggest that it is inherently impossible to determine where something is “native” objectively and consistently across the globe. It will always be subject to an element of human judgment.

So where does this leave things for iNaturalist? As I see it, we can go with either

  1. Endemic = “native here and nowhere else” and apply it easily to some species while having endless debates about many other species. Or,
  2. Endemic = “native and occurs nowhere else” and usually be able to objectively determine that status (spatially, if not taxonomically), and use the Native and Introduced options to add more information where possible and Endemic does not apply.
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My thoughts on “Endemic” are biased from having Howard Frank as an advisor. And he proposes dropping the term and using other terms. The problem of what exactly is meant my “here” remains though. Also, you can tell he worked on biological control from the divisions of adventive.
A. Native (= indigenous)

  • Precinctive (native and occurring only here)
  • Native but not precinctive (native and occurring elsewhere, too)

B. Adventive (= “non-indigenous”, arrived from somewhere else)

  • Immigrant (arrived uninvited).
  • Introduced (introduced deliberately by people)

More info https://ipm.ifas.ufl.edu/Education_Extension/gloss.shtml#5

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“Evolved in this region or arrived by non-anthropogenic means.”

If you think about it, this means that every species in the world was originally endemic to one locality – the locality where it first evolved. Probably one single hillside, or valley, or stream, or rock face. When we think of species so rare that they are known only from the type locality – that is how every species got started.

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Also many groups that are now endeic to one region were distributed much wider, so endemism is a concept of “here and now”.

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