A hierarchy of species concepts: the denouement in the saga of the species problem
Abstract
At least 22 concepts of species are in use today and many of these are
notably incompatible in their accounts of biological diversity. Much
of the traditional turmoil embodied in the species problem ultimately
derives from the packaging of inappropriate criteria for species
into a single concept. This results from a traditional conflation of
function of concepts with their applications, definitions with concepts,
taxonomic categories with groups, and the ontological status of
real species with teleological approaches to recover them. Analogous
to classifications of supraspecific taxa, our forging inappropriate and
ambiguous information relating to theoretical and operational discussions
of species ultimately results in a trade-off between convenience,
accuracy, precision, and the successful recovery of natural
biological diversity. Hence, none of these expectations or intentions
of species or classifications is attainable through composite, and possibly
discordant, concepts of biological diversity or its descent.
Reviewing and evaluating the concepts of species for their theoretical
and operational qualities illustrates that a monistic, primary
concept of species, applicable to the various entities believed to be
species, is essential. This evaluation reveals only one theoretical concept
as appropriate for species, the Evolutionary Species Concept.
This conceptualization functions as a primary concept and is essential
in structuring our ideas and perceptions of real species in the natural
world. The remaining concepts are secondary, forming a hierarchy of
definitional guidelines subordinate to the primary concept, and are
essential to the study of species in practice. Secondary concepts should be used as operational tools, where appropriate, across the
variance in natural diversity to discover entities in accord with the
primary concept. Without this theoretical and empirical structuring
of concepts of species our mission to achieve reconciliation and
understanding of pattern and process of the natural world will fail.