Principios de Taxonomia

18j 2 Why is there a Species Problem?
Figure 2.4 Taxonomic classification may be
performed based on an assessment of trait
similarity (B þ C) or phylogenetic relatedness
(A þ B). The grouping of organisms based on
trait similarity results in artificial groups
(B þ C), whereas the grouping of organisms by
kinship results in natural groups (A þ B). It may
result in inconsistencies or contradictions to
combine both grouping attempts into a
common taxonomic system.
However, there is a different mode of arrangement. You can also combine
branches A and B in a group not based on trait resemblance, but because they are
more closely related (Figure 2.4). They are descendants of a recent common ancestor.
Many people will consider such a group to be natural because common ancestry is not
the product of a human sorting mechanism. There therefore appears to be natural
groups, in contrast to artificial groups (Chapter 3).
Today, many biologists and natural philosophers share the opinion that a
monistic species concept, that is, the species, cannot exist (Wilson, 1999). The
species is viewed pluralistically, meaning that it depends entirely on the respective
concept of how classifications and demarcations are performed. This is frustrating
and means that in principle, species cannot be counted (Hey, 2001). Every
statement of species number depends on the formation of the respective concept,
especially if the species numbers of different phyla of animals and plants are
compared to each other (Mishler, 1999). If a certain family or order of rotifers
contains 200 species, but a certain family or order of mammals contains only
30 species, then a comparison of these species numbers is futile, but it is made
anyway.
This is even true for much more closely related groups. The species numbers of
butterfly families and the species numbers of ant families are therefore not
comparable. Butterflies are combined into species in much larger entities compared
to ants. Butterfly taxonomists hold to subspecies and combine several subspecies into
a common species in many cases, while ant taxonomists, following the advice of E. O.
Wilson, award the rank of species to many subspecies (Jim Mallet, personal
communication, 2008). A statement such as 800 ant species but only 200 butterfly
species live in this tropical region hence becomes meaningless. Imagine a physicist
saying How many kinds of atoms and how many elements there are on Earth
completely depends on our classification principle.