At the March 25 edition of the free Tuesday noon science lectures at
the Smithsonian Tropical Research Institute’s Tupper Auditorium
in Ancon, biologist Richard Condit spoke of studies he and five other
researchers have been been conducting about the ranges of tree species
in Central Panama. His talk was appreciated by a good dry season crowd,
but mostly composed of other scientists, with few members of the general
public, who are always welcome at these lectures, in attendance.
From the start, Condit noted the possibility of inaccuracies in his
data. The work, he said, “relies on the accurate identification
of a lot of species,” and though great care is taken, “that
doesn’t mean that there are any misidentifications.” And in
fact, there are some trees that were encountered that were not identified,
and even more that were only classified as to genus or family without
narrowing the label down to species.
Taxonomy, the classification of nature’s living things, is in the
early stages of a great revolution wrought by DNA analysis. In the study
of tree species ranges, for example, Condit said that “sometimes
people lump a local endemic into a larger species.” Moreover, in
the vast literature of biology a species that may appear to be new to
a scientist who encounters it may in fact have been noted and given
a Latin name in an obscure study. In the database of 1,162 tree species
that Condit and his associates have compiled, “for about 300 we
don’t have Latin names.” But with the use of new technologies
“there might be genetic ways” to achieve more precise identification.
The researcher also noted that the small group of people working on
the project is insufficient to identify every tree in all of Central
Panama’s forests or to do anything remotely close to that. They
had to study 88 relatively small plots, asymetrically distributed in
and around Fort Sherman, the Upper Chagres area, Santa Rita Ridge, the
park system around the Panama Canal and Cerro Campana. Thus they took
a sampling from which many things may be learned, but one that any pollster
who strays from politics or marketing to ponder neotropical trees would
have to say is not random. Just how far from random is a constant concern
for Condit, who tries to keep an open mind about unintended biases that
may be inherent in the selection of forest areas to be surveyed.
With all of these limitations duly noted, but also with the wealth of
decades of observations by many scientists on tree distribution in a
50-hectare plot on Barro Colorado Island and the aid of various computer
models, Condit got down to his findings and what they might mean.
Some trees are found in patches, while others are less so and some not
at all. This, Condit thinks, has much to do with the way seeds are dispersed
and how far from the parent plant new seedlings tend to grow. Species
that are propagated by heavy seeds that simply fall to the ground and
sprout, for example, are likely to exist in patches for more generations
than plants with light seeds that are carried by the wind or which are
propagated by animals.
“Circular patches indicate recent invasion,” Condit concluded,
noting that even species with seeds that don’t stray far tend to
thrive in more favorable soil, moisture, light or other conditions over
time, creating asymetrical dispersal patterns after several generations.
Still, he noted, “the patchiness never seems to go away with some
species, although they move around.”
In general, Condit has found that there is a greater diversity of trees
in the forested areas that receive more rainfall. “Half the species
are restricted to wet forest areas only.” To learn more about the
processes that promote the differences in diversity, he said that he’d
like to see soil moisture data collected at the end of March at all
of the study sites over several years.
Some tree species don’t appear to be as sensitive to moisture,
but follow outcroppings of specific rock strata. Others prefer certain
altitudes.
There are widespead species that more readily adapt to different ecological
niches. “Widespread species in Panama tend to be widespread all
over the world,” Condit noted, adding that “it appears that
if a species is really widespread, it has been around a long time.”
Most of the canal area species are found in Costa Rica, and some range
as far away as the southern United States or northern Argentina.
On the other hand, nearly one-third of the trees in Condit’s database
are classified as “rare” for the purposes of his study, because
they were found at only one of the 88 sites. At the site where they
were encountered, there may be many specimens, but it seems that abundance
in one place does not indicate a wide range.
Despite the rarity of so many species in Condit’s sampling, only
15 were identified as endemic to central Panama. “We’re losing
endemic species but it’s not because they’re going extinct
but because they’re being collected better,” he noted.
