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“Our knowledge of iguanid diversity will likely increase as
different philosophical approaches to species are applied

and further insights into relationships revealed” (Hollingsworth
2004). Why should we care?

Not too long ago, I wrote an article about animal classifica-
tion (Powell 2002), in which I suggested that even the experts,
systematic biologists who study the evolutionary relationships
among animals, differ in their views of species and higher cate-
gories. If the experts cannot agree, why should those of us who
merely want an accurate name to attach to a particular type of
animal seek an inevitably elusive answer or merely put up with
what seems like a constant litany of taxonomic changes that
accrue when the systematists use new data to change a name that
seemed to serve our purposes just fine?

I suggest that we should care and that we also should toler-
ate — and even welcome — the inevitable confusion that comes
with new knowledge, for reasons both philosophical and practi-
cal. As an educator, I strongly believe that knowledge for its own
sake is valuable, not just because it conceivably could lead to prac-
tical applications (pretty far-fetched when discussing lizard phy-
logenies), but because a knowledge of real relationships reflected
in an accurate taxonomy is, in effect, a search for truth. Both in
the scientific and human realms, this is a worthy goal, even if no
cure for cancer is forthcoming.

The practical aspect reflects our commitment to conserving
biodiversity. “Species in peril rightly receive more attention than
subspecies [or populations] in peril” (Malone and Davis 2004).
Even though any population of an endangered animal is worthy

Species and Subspecies: What Do They
Mean and Why Should We Care?

Robert Powell

Avila University, Kansas City, Missouri

108 IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 POWELL

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The three traditionally recognized subspecies of Cyclura rileyi , C. r. rileyi (above), C. r. cristata, and C. r. nuchalis, show essentially no genetic 
differentiation (Malone and Davis 2004) and probably should not be recognized taxonomically. Investing sparse resources to manage them as 
distinct entities may not be appropriate. Photograph by John Binns.



IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 109SPECIES AND SUBSPECIES

of conservation, especially the very tiny, fragmented populations
that characterize the distributions of so many island-dwelling
iguanas, that statement reflects the unfortunate reality that
resources allocated to conservation are limited and “some form
of triage is necessary in any conservation plan” (Malone and
Davis 2004). I have heard even professional natural resource
managers say that “it’s only a subspecies,” as if that rendered the
entity in question of no value.

So, where should the lines be drawn? Species concepts range
from wanting to designate as “full species” every isolated popula-

tion with its own “evolutionary fate” to a rigid application of the
“biological species concept,” in which reproductive isolation (an
inability to successfully reproduce under natural conditions) is
the defining criterion. The former would create an unmanage-
able morass of new names, many of them applied to populations
indistinguishable from one another, whereas the latter leads
inevitably to highly subjective conclusions when parthenogenetic
groups, asexually reproducing organisms, or geographically iso-
lated populations are considered.

If species are difficult to delineate, what about subspecies?
This concept has been variously applied to everything from
“incipient species” (itself an undefined entity) to localized pattern
variants and geographic isolates of uncertain status (Powell and
Henderson 2003a). Because of the ambiguity of subspecies, the
entire concept has fallen into disfavor in recent years. For exam-
ple, only four new subspecies of West Indian amphibians and
reptiles have been formally described in the last decade, in stark
contrast to the convention that reigned throughout much of the
1950s and 1960s, when hundreds of subspecies were described,
many of them placed in the same “species” for reasons no more
substantive than an overall similarity in appearance.

If species and subspecies are difficult, if not impossible, to
define accurately, how can we distinguish between them? In most
instances, the criteria used for this purpose involve “degrees of dif-
ference.” If two groups of obviously related animals can be dis-
tinguished consistently by means of one or several unambiguous
characters, most experts would agree that we’re dealing with two
species. If, however, the diagnostic features are few or don’t apply
in all cases, especially if we have evidence that hybridization
occurs regularly, a dilemma exists. Are we dealing with species

Cyclura cychlura has long been considered to have three subspecies, C. c. cychlura (above), C. c. inornata, and C. c. figginsi, but recent studies 
suggest that only the latter two genetically and geographically defined units exist (Malone et al. 2003). Photograph by Chuck Knapp.

Cyclura carinata bartschi is not genetically distinct from the nominate
subspecies (Malone and Davis 2004) and probably should not be rec-
ognized taxonomically. Photograph by John Bendon.



that have yet to evolve the differences that allow us to accurately
distinguish them, are we dealing with something best defined as
a subspecies, or are we really only dealing with slight geographic
variations unworthy of any taxonomic recognition? What makes
this decision even more difficult is the realization that the evolu-
tion of new species usually is not a sudden occurrence, but takes
time measured in many generations, sometimes extending over
millennia or even periods of time best defined by geological
means. Consequently, at any time, such as the present, for exam-
ple, we are likely to encounter populations in various stages of
that process, with the almost infinite number of possible varia-
tions represented by at least some groups.

Does a solution exist? Not really. In spite of inevitable gaps
and errors that will have to be “fixed” down the road, we have to
strive to evaluate all of the available and pertinent evidence in an

effort to construct a taxonomy that most accurately reflects real-
ity as it currently exists — and we should never recognize a
species based on anything other than evolutionary relationships.
For example, using the need to protect a population to justify its
designation as a full species would be wrong. Similarly inappro-
priate would be letting a desire to draw hard lines where none are
possible or blind allegiance to a traditionally accepted name or
concept stand in the way of objectively evaluating new informa-
tion or interpretations.

So, if we want to conserve imperiled iguanas and we accept
the unfortunate reality that populations recognized as species are
going to be given more consideration than those that are not,
what do we do? We could designate every isolated population a
species, but that would not reflect reality nor would it be legiti-
mate or even really helpful. If faced with a large number of

110 IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 POWELL

Cyclura stejnegeri (top), from Isla Mona (see article on p. 98), and C. onchiopsis (above left), from Navassa Island and extinct since the late 19th cen-
tury, were considered subspecies of C. cornuta (above right) until the application of modern species concepts resulted in a reevaluation of distinctive
characters (Powell 1999, 2000). Cyclura stejnegeri is less distinctively different from C. cornuta morphologically than is C. onchiopsis, but biological dif-
ferences may provide sufficient justification for recognition as a full species (e.g., Wiewandt 1977, Powell and Glor 2000). Photographs by Robert Powell.



IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 111SPECIES AND SUBSPECIES

“species” and still-limited resources, the criteria used in the
inevitable triage would simply be adjusted. Consequently, the
only realistic solution is to evaluate each situation independently,
endeavoring to apply the relevant criteria as consistently and
accurately as possible, given the uneven states of knowledge and
the inevitable disagreements regarding taxonomic ranks.

References
Burton, F.J. 2004. Taxonomic status of the Grand Cayman Blue Iguana.

Caribbean Journal of Science 40: in press.

de Queiroz, K. 1987. A new Spiny-tailed Iguana from Honduras, with com-
ments on relationships within Ctenosaura (Squamata: Iguania). Copeia
1987:892–902.

Grismer, L.L. 1999. An evolutionary classification of reptiles on islands in the
Gulf of California, México. Herpetologica 55:446–469.

Grismer, L.L. 2002. Spiny-tailed Iguanas, insular evolution, and Seri indians:
How long does it take to make a new species and does it matter who
makes it? Iguana Times (Journal of the International Iguana Society)
9(1–2):3–8.

Hollingsworth, B.D. 2004. The evolution of iguanas: An overview of rela-
tionships and a checklist of species, pp. 19–44. In: A.C. Alberts, R.L.
Carter, W.K. Hayes, and E.P. Martins (eds.), Iguanas: Biology and
Conservation. University of California Press, Berkeley.

Köhler, G. 2002. Schwarzleguane: Lebensweise, Pflege, Zucht. Herpeton Verlag
Elke Köhler, Offenbach, Germany.

Iguana iguana, as traditionally defined, is actually a complex of closely
related species (Malone 2000), and all translocations of Green Iguanas
between South America, Central America, and the Lesser Antilles should
cease in order to prevent the loss of unique genetic variation and dis-
ruption of locally adaptive gene complexes (Malone and Davis 2004).
Photograph by Thomas Wiewandt.

Until about 10 years ago, some authorities thought that the variable
morphology and lack of definitive characters used to distinguish
Ctenosaura acanthura (top), C. pectinata (center), and C. similis (bot-
tom) would result in these three species being subsumed into a single
species that ranged from Sinaloa, México to Panamá (Köhler 2002).
Recent, detailed studies have since revealed several consistently diag-
nostic characters, and these have been confirmed using modern molec-
ular techniques. Top and center photographs by Gunther Köhler, bottom
photograph by John Binns.



112 IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 POWELL

Cyclura lewisi (below) was until recently treated as a subspecies of 
C. nubila (above) (Burton 2004, Malone et al. 2000, Powell and
Henderson 2003b). Although considerable effort had been made to
conserve what may be the world’s most endangered lizard when it was
generally considered to be “only” a subspecies, its elevation to full
species status is a much more accurate reflection of real relationships
within the genus Cyclura. Top photograph by John Binns, bottom photo-
graph by Fred Burton.

Ctenosaura oedirhina (above) from Isla Roatán, Honduran Bay Islands,
was considered a second population of C. bakeri (below), known only
from Isla Utila, until the distinctiveness of the two populations was rec-
ognized (de Queiroz 1987). Top photograph by Randy McCranie, bot-
tom photograph by Gunther Köhler.



IGUANA  •  VOLUME 11, NUMBER 2  •  JUNE 2004 113SPECIES AND SUBSPECIES

Malone, C.L. 2000. Phylogenetic systematics and conservation genetics of
Caribbean iguanas. Unpubl. Ph.D. dissertation. Texas A&M University,
College Station.

Malone, C.L. and S.K. Davis. 2004. Genetic contributions to Caribbean
iguana conservation, pp. 45–57. In: A.C. Alberts, R.L. Carter, W.K.
Hayes, and E.P. Martins (eds.), Iguanas: Biology and Conservation.
University of California Press, Berkeley.

Malone, C.L., C.R. Knapp, J.F. Taylor, and S.K. Davis. 2003. Genetic con-
sequences of Pleistocene fragmentation: Isolation, drift, and loss of diver-
sity in Rock Iguanas (Cyclura). Conservation Genetics 27:1–15.

Malone, C.L., T. Wheeler, J.F. Taylor, and S.K. Davis. 2000. Phylogeography
of the Caribbean Rock Iguana (Cyclura): Implications for conservation
and insights on the biogeographic history of the West Indies. Molecular
Phylogenetics and Evolution 17:269–279.

Powell, R. 1999. Herpetology of Navassa Island, West Indies. Caribbean
Journal of Science 35:1–13.

Powell, R. 2000. Cyclura onchiopsis. Catalogue of American Amphibians and
Reptiles (710):1–3.

Powell, R. 2002. Understanding animal classification. Iguana Times (Journal of
the International Iguana Society) 9:18–26.

Powell, R. and R.E. Glor. 2000. Cyclura stejnegeri. Catalogue of American
Amphibians and Reptiles (711):1–4.

Powell, R. and R.W. Henderson. 2003a. The taxonomic and conservation sta-
tus of giant Hispaniolan Celestus (Anguidae). Caribbean Journal of Science
39:237–240.

Powell, R. and R.W. Henderson. 2003b. A second set of addenda to the
checklist of West Indian amphibians and reptiles. Herpetological Review
34: 341–345.

Wiewandt, T.A. 1977. Ecology, behavior, and management of the Mona Island
Ground Iguana, Cyclura stejnegeri. Unpublished Ph.D. dissertation,
Cornell University, Ithaca, New York.

Ctenosaura conspicuosa, C. hemilopha, C. macrolopha, and C. nolascensis (above), from the circum-Gulf of California region of northwestern México,
were considered subspecifically related until reevaluated in light of modern species concepts (Grismer 1999). Of particular interest is the sugges-
tion that C. conspicuosa evolved from ancestors whose original populations on islas Cholludo and San Esteban may have had a human facilitated
origin (Grismer 2002). Photograph by John Binns.

Populations of Iguana delicatissima show very little genetic differentia-
tion (Malone 2000). However, because of the ongoing threats that
endanger all of the species’ fragmented populations and their vulnera-
bility to stochastic events, each should be afforded the highest level of
protection possible. Photograph by Glenn Gerber.


