612 Commentary [Auk,Vol. 99 By studying and defining this variation, orni- lutionary units and thus would not be referable thologistsare able to add to the knowledgeof to the same subspecies.Graves (1980) re-ex- the earth's history. Obviously, not all variation amined the Colombianpopulation of Diglossa among closely related bird populations has (carbonaria) brunneiventrisand found that the progressedto the point at which those popu- population was separablefrom the Peruvian lations merit speciesstatus. To recognizethese birds. I feel that his action was correct in that populationsby naming them as subspeciesis the Colombian and Peruvian brown-bellied to acknowledgetheir existenceand to dem- birds, which are separatedby all-blackpopu- onstrate how the earth's history has affected lations, are separate evolutionary units and them. This idea is nowhere better illustrated should not be placedtogether under one name. than in the Andes, where geographicvariation To make the subspeciesconcept embrace an is obvious and populations are often isolated evolutionary unit would not affect its conve- from each other. I think that the subspecies nience, would make it more useful, and would concept is a valid one but that it should be get rid of the need to differentiatebetween the connectedto an evolutionary unit. If subspe- "evolutionary" and the "taxonomic" implica- cies are evolutionaryunits, then the usefulness tions that seem to be so often misused. I have of the conceptis greatly enhanced.If there is obviously oversimplifiedmany of the prob- no break in gene flow (i.e. a smooth cline), lems and have left out a great amount of in- then all populationsin that "aggregateof pop- formation that warrants discussion, but this is ulations" should be consideredto belong to necessarybecause of space constraints.I do, one form. When there is a break in the gene however, find the conceptto be very valuable flow by any type of separation (geographic, and very useful in the 1980's. ecological, etc.) then recognition of a second unit or subspecieswould be warranted. Vari- LITERATURE CITED ation within a cline can be discussed and de- GRAvEs,G. R. 1980. A new subspeciesof Diglossa scribed, but only a single name need be ap- (carbonaria) brunneiventris. Bull. Brit. Ornithol. plied. Two subspecies that seem to be Club 100: 230-232. morphologicallyalike but are separatedby a MAYR, E. 1963. Animal speciesand evolution. Cam- form that is different would be separate evo- bridge, Massachusetts,Harvard Univ. Press. SUBSPECIES AND SPECIES: FUNDAMENTALS, NEEDS, AND OBSTACLES ALLAN R. PHILLIPS 1 Populations are nature's building blocks. one or more of thesecomplexes does vary geo- When they do not differ consistentlyfrom oth- graphically,forming more-or-lesswell-defined er (usually more or less adjacent)populations, subspecies.There may alsobe areaswhere the the whole seriesforms a single subspecies•or variations are inconstant;such variable popu- species if essentially isolated reproductively. lationsshould not be arbitrarilysqueezed into Character complexes commonly varying, at one or another of the truly distinct subspecies. these levels, are measurements, details of Common patternsof racial or subspecificvari- colors, or more rarely facial patterns or colors ation are clinal or convergent,open-ring, bro- of soft parts. In most widespread species(es- ken-ring or divergent, parallel, and nonclinal pecially if not stronglymigratory or nomadic), or random (which should normally not be named) (Phillips 1959). Treatmentof speciesand subspecieshas var- Apartado Postal 370, San Nicolas de los Garza, ied widely. Most Europeansbefore Hartert re- Nuevo Le6n, M•xico 66400. jected the subspeciesconcept, calling every July1982] Commentary 613 recognizableform a species.Hellmayr, at the though this may be hard to measure.We must other extreme, considerednearly every allo- not be blind slaves to statistics. patric form a subspecies,paving the way for Note that the membersof the populations Mayr and Amadon (1951)to reducethe world's must differ; entire populations are not com- Recent avifauna to 8,519 species.Mayr's fol- pared. White and dark geeseare color phases lowers have most recently(Bock and Farrand or "morphs"; while eachoccupies certain parts 1980) conceded that at least 9,021 speciesexist, of the breeding range exclusively, in other a figure surelywell shortof reality. [I still con- parts they mix, and no one recognizesSnow sider my guess(Phillips 1959)of about 10,000 and Blue geeseas subspecies.Selander's pro- speciesa reasonable one.] But instead of these posal (1959)to recognizeraces based on occur- guesses,we urgentlyneed field studiesand ex- rence of "morphs" is unacceptable;what hap- plorations.Mayr, Bock,and Farrandare quite pens when unexpected individuals turn up in wrong in stating that "the biological species other populations, and how do we identify concept . becomesless and less applicable single specimens?True subspeciesare more to populationsreplacing one another over in- substantial. creasing geographicaldistances." Biology is Subspeciesare no new discovery;they have not dependent on distance,and only slightly been known longer than sibling species, on ecology. Mayr and his followers would do though at first termed species or varieties. well to familiarize themselves with avian bi- Thus, 3 subspeciesof Motacilla fiava (Yellow ology:nests, eggs, flesh colors,behavior (in- Wagtail) from northern Eurasia had been cludingvocalizations), and skeletalstructures. named by 1789and 6 palearcticraces of M. alba Their belief that all forms of Morus, Anhinga, (White or Pied Wagtail) were described by Haematopus,etc. are allopatric does not prove 1838, whereas before 1811 only 1 species (2 that these forms are subspecies(cf. Brodkorb subspecies)of the various EurasianPhyllosco- 1963, Morus; Phillips et al. 1973, Phillips MS, pus warblers had been described,and only 1 Polioptila;Baker 1974,Haematopus). Simple vi- of the 5 speciesof easternNorth American Em- carlance of surviving taxa does not determine pidonaxflycatchers. Only the most distinctive their taxonomic levels. As Coues long ago of the other, western United States Empido- wrote, species are better determined in the naceswas recognizablydescribed before 1856; field than in the closet!An excellentexample indeed the status and nomenclature of these of the sort of field approachthat is neededis speciesin North Americawas not finally set- provided by Lanyon's(1978) vocalization play- tled until 1973!Other sibling species,like sub- back studiesof Myiarchusflycatchers. Such in- species, continue to turn up. vestigationsare urgentlyneeded of many more In the past 30 yr, severalwriters have sought genera, especiallyin the tropics. to convincethe unknowing that subspeciesare Subspecies are morphologically or geo- a fictional concept, unstable in time, and that graphically significant populations whose their recognitionis at best dubious. Uniform- members differ morphologically, at some ly, they studiouslyignore the many truly dra- stage, from those of other populations (of the matically different subspecies, such as the species)to a conventionaldegree; commonly, above Motacillae, Canada Geese, flickers, vari- we insist that at least 75% of the birds must be ous juncos, and other sparrows,etc. Johnston distinguishablefrom 99% of those of other and Selander's"House Sparrows: rapid evo- populations. This convention has been mis- lution of races in North America" (1964) may interpreted to mean they must differ in some be instructive.They claimedthat recentfall se- one character to that extent. Often, however, ries from 20 points in North America (plus more than one character is involved, and at Hawaii and Bermuda) showed that each pop- least 75% of the birds must be separablefrom ulation "has differentiatedto greateror lesser other populationsin one or another character. degreefrom any otherand from the Old World Single-characterraces are, in fact, unusualand stock,"and that this was geneticallycontrolled often rather weak. If a bird is darker, this will (including a "conspicuous yellow wash" at usually affect various parts of the plumage; if Oaxaca, Oax., M•xico, where in fact Passerar- an insularbird's bill is larger,it will usuallybe rived not long before 1962). They correlated both longer and deeper (or perhaps wider), colorvariation with temperatureand humidity 614 Commentary [Auk,Vol. 99 but ignored soot, smog, or other discoloration leaving less room for doubts and disagree- in urban populations, plus the basic fact that ments. the birds were not washed before skinning. The utility of subspecieswould undoubtedly They concluded:(a) "levels of differentiation be enhanced if all competent taxonomists ... are fully equivalent to those shown by agreed on all details. This utopian ideal is un- many polytypic native species .... applica- attainable, if for no other reason than differ- tion of subspecifictrinomials to certain New encesin ocular acuity, combinedwith the dif- World populations .... would be fully war- ficulty of verbally expressing differences ranted . ."; and (b) much of the "differentia- visible to the eye. Nevertheless,much could tion" must have occurred in the present cen- be done to improve the presentunsatisfactory tury; this they found concordantwith changes situation. within historic time in other groups, citing For one thing, I am constantlyimpressed by amongother authorsWilson and Brown (1953). the minute taxonomicvalue of the average In cold fact, the differentiation in color had museum's