Why Taxonomy Matters
Who cares about all these esoteric Latinized words, anyway?
A wise man once said to me that "words define the limits of our world." Upon reflection, I realized that in few places is this more true than in it is in taxonomy.
Taxonomy is the biological system of names we have created to guide everything from research to conservation. Using Carl Linnaeus's two-name nomenclature, we have an internationally recognized reference system for all known species. Each name is a doorway to the vast catalog of human knowledge associated with it. In spotting Melanerpes erythrocephalus— Red-headed Woodpecker — at a swamp in upstate New York, for example, we tap into a web of information. For example, the area must have ample dead trees that the woodpeckers require for foraging and nesting. Perhaps there are relatively frequent fires that produce the dead trees. And somehow, invasive starlings haven't become too prevalent there to outcompete the woodpeckers for nest cavities. It's like opening a book; Melanerpes erythrocephalus is the title on the first page.

With birds, people have had the peculiar advantage of easily distinguishable species. Unlike with some groups of rodents, insects, many plants, or other more cryptic groups, we recognize a robin, a cardinal, a pigeon, etc. What humans have informally recognized as different "kinds" of birds are often recognized by scientists as evolutionarily distinct as well, sharing their own unique evolutionary histories, and rarely if ever interbreeding with each other. What this means is critical: our names for these birds reflect actual units of biodiversity, what we call a species.

It's like with family names. Let's imagine a perfect world where your last name is used only by your family and its ancestors. It would be misleading for your last name to be held by your family and a small group of strangers that are unrelated to you. Similarly, taxonomy seeks to give unique names only to populations that are in one genealogical line, a "monophyletic" lineage, not to a few unrelated groups that are here and there on the tree of life. Species, Genus, Family…they're all evolutionary terms, created to define organisms that are on one "branch" on the tree of life. Even though the names themselves may be arbitrary (why "Northern Cardinal" instead of "Crested Redbird"?), they are meant to represent something real.

Birds aren't always easy to separate into species. This is Mouse-colored Tapaculo, whose taxonomy has been a bewildering mess. Only this year, a study has clarified some of its population structure. Photo by Nick Athanas of antpitta.com.
Well, it turns out that not all birds are as simple as distinguishing robin from cardinal. Not all bird species will necessarily evolve differences in appearance, especially if they only split from a common ancestor within the past million years (a relatively short amount of time in evolutionary terms). This lack of simplicity leads to taxonomic ambiguity — names that don't represent actual units of biodiversity. In some situations, we think a few populations qualify as one species, but later find out that they aren't even closely related. In this case, we've effectively taken some organisms from one branch on the tree and some on another, and called them a species. In other situations, what we call one species actually includes a number of populations that are at the species level. In this case, we are underrecognizing the biodiversity that evolution has given us.
But...why do we care? Aren't names just names, human constructs that just exist in our minds and our textbooks?
We can't act on the nameless, the unknown unknowns, and we certainly can't study them. In this way, words do create the limits of our world.
Because the relationship between humans and the rest of biodiversity is complicated by human greed and the fragility of ecosystems, these names may be some of the most important words in our language. Keep in mind that we can only refer to and interact with something we are conceptually familiar with, and our go-to method of making something conceptually familiar is creating a word for it. This makes it a thing, something we can talk about, something we can observe, something we can think about, something we can protect. We can't act on the nameless, the unknown unknowns, and we certainly can't study them.

In this way, words truly do create the limits of our world.

Taxonomic names are what make the organisms around us something we can know. We refer to the organisms that share this planet by the names we give to them, and in doing so, we make it possible to observe them, study them, and protect them. But if our names recognize something that is imaginary, we experience a fatal pitfall:
we fail to protect biodiversity we didn't even know existed.
A male Vermilion Flycatcher photographed in Mexico by Greg Schlechter
A recent example demonstrates this fact with a fair dose of solemnity: Pyrocephalus dubius.

Out of most taxonomic groups (mammals, fishes, flowering plants, etc.), birds are one of the better studied, but this doesn't mean that their diversity is totally understood. Up until very recently, ornithologists have relied almost entirely on morphology to distinguish between species. But morphology can be misleading, be it because of convergent evolution or because morphological differences never evolved to begin with. Molecular methods for identifying species — like genetics — have resulted in a near-constant progression of taxonomic corrections, each working to ensure that our taxonomy accurately represents the earth's biodiversity. Even still, many taxonomic mistakes remain to be found, persisting in our field guides, encyclopedias, and anywhere else the erroneous name may be called upon.

Beyond just getting the species right, understanding the branching pattern of birds' evolution is the next big step. Only recently have many of the deep relationships among birds been resolved (though no one would be surprised if even this supposed resolution eventually came into question). Ornithology may be further ahead than some other fields, but in no way does that means it's finished.
Figure 1 from Carmi et al. 2016, in the journal Molecular Phylogenetics and Evolution. This study uncovered the diversity we had been missing within "Vermilion Flycatcher".
For a long time, the Vermilion Flycatcher — Pyrocephalus rubinus — of Central and South America was among these species awaiting revision. Historically divided into 12 subspecies, the Vermilion has long been recognized for its geographic variation. To the left, you can get an idea of just how many places you can find these Pyrocephalus flycatchers, and just how many different populations have traditionally been ranked as subspecies. Among these subspecies, some are migratory and some are not. Some migrants travel from north-to-south, while others travel from south-to-north. Some subspecies have even evolved different songs (for species in their family, the Tyrannidae, songs are innate rather than learned, and therefore require more evolution to change).

In addition to varying considerably across South America, Vermilion Flycatchers have even made it to the Galápagos, where two subspecies have long been suspected of deserving species status.

As such, the big question is this:
Recognizing only one Vermilion Flycatcher (or one species in the genus Pyrocephalus), are we underrecognizing the diversity in this genus?
According to a study that will be in print this September, the answer is a definite yes.

Using mitochondrial and nuclear DNA, Ore Carmi and colleagues inferred the evolutionary history of the 10 Vermilion Flycatcher subspecies they sampled. They found that at least 3 of the subspecies would be better classified as distinct species. Two of these would-be-species are nanus and dubius of the Galápagos, and the third is rubinus of Brazil and Southern South America. Conversely, some of the other 7 subspecies may not even deserve subspecies status (namely, flammeus and mexicanus of Central America, which are not distinguishable from each other). In just one study, the genus Pyrocephalus goes from containing one species to containing four.
This would all be well and good, except for one thing: one of these species is already extinct.
This taxonomic update is 30+ years too late for the Vermilion Flycatchers of San Cristóbal Island — Pyrocephalus rubinus dubius — the last individual of which was last seen in 1987. This is the first bird species extinction on the Galápagos Islands, and we're only recognizing it decades after the fact. And this is in part because we didn't think that the Vermilions of San Cristóbal Island were a "thing"; they're just a small, island population of Vermilion Flycatcher, right?

In fact, they were a totally separate evolutionary lineage. They were more genetically different from the other Galápagos Vermilion—Pyrocephalus nanus — than humans are genetically different from chimpanzees.

So, why does taxonomy matter? Taxonomy matters because it can influence the fate of a species. If our taxonomy for Pyrocephalus flycatchers was correct in the '80s, more conservation measures might have been taken for the evolutionarily unique San Cristóbal population. To lose just any population to introduced predatory rats and parasitic flies is one thing, but to lose an entire species is a biological tragedy, robbing the earth of an irreplaceable piece of its biodiversity, and denying future scientists potential answers that will forever be unattainable.

It's astonishing to think that something as seemingly insignificant as a different name might have saved Pyrocephalus dubius. But in the minds of many, including some who fund conservation, saving a subspecies is less appealing because, as one might say, "there's still the rest of the species." Such was the case with Peregrine Falcons, whose entire Eastern North American subspecies, called anatum, was eradicated by DDT. Instead of trying to find the last anatum, conservationists simply introduced Peregrine subspecies from elsewhere in their place. Such an action would have been unthinkable if anatum was its own species — though evolutionarily speaking, anatum certainly did not deserve species status.

In the case of Vermilion Flycatchers, exchanging Pyrocephalus rubinus dubius for Pyrocephalus dubius could have led to a much brighter fate, just as many hope it might for the other Galápagos Vermilion: nanus. In serious decline across its remaining distribution, nanus faces many of the same challenges that befell dubius, and ultimately led to its demise.

At least now, we are recognizing the biodiversity in the genus Pyrocephalus, and we word-loving primates can start to act accordingly.

Words matter, my friends. They matter because they allow us to recognize the diversity of life on earth, helping us to understand it more deeply and to better coexist with it. Indeed, perhaps more than anywhere else, words in taxonomy should not be taken lightly.

A Vermilion Flycatcher on the Galápagos, presumably nanus. Photo by Rhys Thatcher.
Citations:
Carmi, Ore, et al. "Phylogeography of the Vermilion Flycatcher species complex: multiple speciation events, shifts in migratory behavior, and an apparent extinction of a Galápagos-endemic bird species." Molecular phylogenetics and evolution (2016).

Platt, John. "First Bird Extinction In The Galápagos Islands Confirmed". Scientific American Blog Network. N. p., 2016. Web. 6 July 2016.


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