What is a species?
These are both Teagueia
sancheziae in spite of their different color.
A red/yellow polymorphism is common in several
of these new Teagueia species.
The new Teagueia species are remarkably variable in
flower color, leaf size and shape, and even leaf texture. It
is quite a challenge to divide them up into good species. To
do it right, we have to think carefully about the meaning of
the “species concept” in biology. In the past, the
concept of a species was oriented towards identification and
classification, and forms which were visually very distinct
from each other were usually classified as separate species.
Forms which showed lots of variability were often all dumped
into a single all-encompassing species. These decisions were
made on the basis of intuition and individual judgement, and
like all matters of individual taste, were subject to all kinds
of fruitless debate among “splitters” and “lumpers”.
However, in recent decades a more objective “species concept”
has arisen in biology, and this concept removes some (though
not all) of the arbitrariness of our taxonomic decisions. In
modern biology a “species” is a population that
has the potential to freely exchange genes, and evolves through
time as a single unit. Thus two populations that live in the
same place but don’t exchange genes are two distinct species,
even if they seem very similar to us. On the other hand two
plants that look very different may both belong to the same
species, if there are lots of intermediate forms between those
extremes in the population.
species concept is easiest to apply at a single site. I try
to look at the populations and identify forms that seem to be
distinct. Then I try to get a big enough sample to assess the
variability of each of these forms. Sometimes two forms that
at first seemed distinct are seen to be part of a single highly
variable population. Sometimes two superficially distinct color
forms turn out to be structurally identical, and the color forms
turn out to be just a simple polymorphism (like the occasional
white or semi-alba Cattleya in a population of lavender
individuals). Other times a group of forms that seemed very
similar prove to have subtle but consistent differences in multiple
characters; these are distinct species.
get more difficult when I try to decide whether two forms from
different mountains belong to the same species. I first ask
myself what would happen if the two forms were to grow together.
Could they both share the same pollinator? I look at lip and
column structure and size to help me decide this, and pay less
attention to the parts of the flower that have less contact
with the pollinator. If two forms from different mountains could
not share the same pollinator, then they are not exchanging
genes, nor could they potentially exchange genes in the future
if their ranges were to someday overlap. These forms are thus
two distinct species, each on their own evolutionary pathway.
Unfortunately our knowledge of the pollination biology of Teagueia
is almost zero, so much of this is guesswork. I try to be conservative
and allow a lot of leeway for geographical variation, so I usually
end up lumping similar forms from different mountains into the
same species. Nevertheless my decisions, right or wrong, are
testable by pollination experiments and perhaps by DNA analysis.
This is the big advantage of the biological species concept.
There are still gray areas, of course, especially during a speciation
event (when a single species begins to diverge into two). We
can only hope that those fuzzy moments in the evolutionary history
of a species are rare, and we deal with them as best we can.