In R. Wilson (ed.), Species: New
Getting Rid of Species?
Brent D. Mishler
University Herbarium, Jepson Herbarium, and Department of Integrative Biology, University of
California, Berkeley, CA 94720, U.S.A.
This paper explores the implications of generalizing the species problem as a special case
of the taxon problem. Once a decision is made about what taxa in general are to represent, then
species in particular are simply the least inclusive taxon of that type.
As I favor a Hennigian
phylogenetic basis for taxonomy, I explore the application of phylogenetics to species taxa.
Furthermore, I advocate a novel extension of the recent calls for rank-free phylogenetic
taxonomy to the species level.
In brief the argument is: (1) Species must be treated as just one
taxon among many; (2) All taxa should be monophyletic groups; (3) Because of problems with
instability and lack of comparability of ranks in the formal Linnaean system, we need to move to
a rank-free formal classification system; (4) In such a system, not all hypothesized monophyletic
groups need be named, but those that are named formally should be given unranked (but
hierarchically nested) uninomials; (4) The least inclusive taxon, formally known as "species,"
should be treated in the same unranked manner.
Finally, I explore the practical implications of
eliminating the rank of species for such areas as ecology, evolution, and conservation, and
conclude that these purposes are better served by this move.
The debate about species concepts over the last 20 years follows a curious pattern.
than moving towards some kind of consensus, as one might expect, the trend has been towards an ever-
increasing proliferation of concepts.
Starting with the widely accepted species concept that had taken
over in the 1940's and 50's as a result of the Modern Synthesis, the Biological Species Concept, we
heard calls for change from botanists, behaviorists, etc.
Despite the babel of new concepts, the BSC
continues to have fervent advocates (Avise and Ball, 1990; Avise and Wollenberg, 1997), and has itself
spawned several new variants. A recent paper by Mayden (1997) lists no fewer than 22 prevailing
It appears we can never eliminate any existing concept, only produce new ones.
Why is this?
The obvious conclusion one might draw, that biologists are contrarians who each
want to make their own personal mark in a debate and thus coin their own personal concept to defend,
is really not the case -- this is no debate about semantics.
The conceptual divisions are major, and real.
In my opinion the plethora of ways in which different workers want to use the species category reflects
an underlying plethora of valid ways of looking at biological diversity.
The way forward is to recognize
this, and face the implications: the basis of this confusion over species concepts is a result of heroic but