White on White

Full text

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n at u r a l h i s t o ry June 2014
T
he largest gypsum dune field on
Earth—covering 275 square
miles—undulates across the Tularo-
sa Basin in south central New Mex-
ico. Approximately 40 percent of
the field falls within the protected
area of the White Sands National
Monument in Otero County. The
unusual feature started forming
about 8,000 years ago, when water
evaporated from the surface of large
lakes near the southwestern bound-
ary of the current dune field, and
gypsum crystallized out of solution.
Over time, weathering degraded
the crystals to sand-size particles,
and winds, predominately from
the southwest, blew the gypsum
sand from the now-dry lake bed
onto the dune field, which can rise
as high as sixty feet. The blowing
sand moves the dune crests from
the southwest to the northeast as
much as twenty-nine feet per year,
covering and uncovering plants and
soils as they move.
Plants respond to the harsh con-
ditions of shifting pure gypsum
soils in several ways. They add
stem length rapidly to accommo-
date encroaching dunes; they send
out rhizomes (lateral roots) so new
shoots can sprout up sixty feet away
from the original plant; and they
further bolster their root systems to
avoid being taken over by a passing
dune. Many animals have adapted to
life in the white dunes by evolving
modified coloration. Such White
Sands species and subspecies as the
southwestern fence lizard (Scelopo-
rus cowlesi) and the endemic bleached
earless lizard (Holbrookia maculata
ruthveni) are paler than closely re-
lated populations that live outside
the gypsum dunes. Animals that are
naturally white or pale in color else-
where may reside at White Sands to
take advantage of the pale substrate.
A lycosid, or wolf, spider maintains
production of its natural darker pig-
ments, but secretes a waxy substance
to appear white.
Before 2006, almost nothing was
known about the invertebrate fauna
in White Sands, or in Carlsbad Cav-
erns National Park, another protected
area of the northern Chihuahuan
Desert about 190 miles from White
Sands. As a result, the United States
National Park Service invited me to
conduct a ten-year study of the lepi-
doptera in the dunes of the Monu-
ment and within Carlsbad Caverns
National Park. A primary purpose of
the study was to survey the moths in
various habitats within Carlsbad and
White Sands, and to describe new
species discovered during the study.
White on White
An invertebrate inventory of White Sands National Monument
By Eric H. Metzler
S
ince the study began, in January
2007, we have recorded more
than 600 species of moths, includ-
ing 26 species new to science. The
first, Protogygia whitesandsensis, was
discovered in February 2007. The
most recent was found
last year. The moths
have been collected
and recorded using
black-light traps along
a less-than-two-mile
transect in the south-
eastern corner of the
dunes of the Monu-
ment. The number
of endemic species of
moths at White Sands,
when compared to all
of North America, is
the highest for a single
location. Given the
small study area and
the early stages of the
study, these numbers
seem impressive.
About 50 percent
of the new moth species are white
or display washed-out colors. No
quantifiable data exists to explain
the high incidence of paleness, just
a working hypothesis that it of-
fers protection to those species that
are more apt to be on the white
sand during the day when they
are not flying. Most moths fly at
night when color doesn’t matter.
Diet could also be a factor, since all
moths start out as caterpillars, and
99 percent of caterpillars eat only
plants. Thanks to the unique soil
chemistry of gypsum compared to
other nearby soils, the same spe-
cies of plants inside and outside the
dunes have different chemical sig-
natures and different endophytes, or
resident microbes.
Halfway through the study, I am
continuing to detect, classify, and
give names to new species. Descrip-
tions of species from units of the
National Park Service
are important be-
cause names facilitate
the cataloging and
protecting of vulner-
able species and the
communication of
information about
their significance.
The information
gives the Park Service
a baseline from which
to measure the effects
of changes in climate,
air pollution, water
tables, and a host of
other variables. Fig-
uring out why white
moths are white,
however, will have
to be the task of an
ongoing investigation. In the mean-
time, back to the field, where surely
more new moth species await.
Eric H. MEtzlEr lives in Alamogordo,
New Mexico, and is an adjunct curator in the
Department of Entomology at Michigan State
University.
FIELD NOTES
New species of pale moths blend into the gypsum crystals of sand.
Black-light traps collect moths and other
insects in the southeastern corner of White
Sands National Monument.
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n at u r a l h i s t o ry June 2014