Wednesday, February 1, 2012

Davidson Professor Leads Study Documenting Python Damage to Native Species in Everglades

Precipitous declines in formerly common mammals in Everglades National
Park have been linked to the presence of invasive Burmese pythons,
according to a study by Davidson Associate Professor of Biology
Michael Dorcas and colleagues published today in the Proceedings of
the National Academy of Sciences.

The study, the first to document the ecological impacts of this
invasive species, strongly supports that animal communities in this
1.5-million-acre park have been markedly altered by the introduction
of pythons within 11 years of their establishment as an invasive
species. Mid-sized mammals are the most dramatically affected, but
some Everglades pythons are as large as16 feet long, and their prey
have included animals as large as deer and alligators.

"The magnitude of these declines underscores the apparent incredible
density of pythons in Everglades National Park and justifies the
argument for more intensive investigation into their ecological
effects, as well as the development of effective control methods,"
said Dorcas, lead author of the study and author of the book 2010 book
Invasive Pythons in the United States.

He continued, "Such severe declines in easily seen mammals bode poorly
for the many species of conservation concern that are more difficult
to sample but that may also bevulnerable to python predation."

The most severe declines, including a nearly complete disappearance of
raccoons, rabbits and opossums, have occurred in the remote
southernmost regions of the park, where pythons have been established
the longest. In this area, populations of raccoons dropped 99.3
percent, opossums 98.9 percent and bobcats 87.5 percent. Marsh and
cottontail rabbits, as well as foxes, were not seen at all.

The researchers collected their information via repeated systematic
night-time road surveys within the park, counting both live and road-
killed animals. Over the period of the study, researchers traveled a
total of nearly 39,000 miles from 2003 to 2011 and compared their
findings with similar surveys conducted in 1996 and 1997 along the
same roadways before pythons were recognized as established in
Everglades National Park.

The authors also conducted surveys in ecologically similar areas north
of the park where pythons have not yet been discovered. In those
areas, mammal abundances were similar to those in the park before
pythons proliferated. At sites where pythons have only recently been
documented, however, mammal populations were reduced, though not to
the dramatic extent observed within the park where pythons are well

"Pythons are wreaking havoc on one of America's most beautiful,
treasured and naturally bountifulecosystems," said U.S. Geological
Survey director Marcia McNutt. "Right now, the only hope to help halt
further python invasion into new areas is swift, decisive and
deliberate human action."

The authors suggested that one reason for such dramatic declines in
such a short time is that these prey species are "naïve" – that is,
they not used to being preyed upon by pythons since such large snakes
have not previously existed in that ecosystem.

"It took 30 years for the brown treesnake to be implicated in the
nearly complete disappearance of mammals and birds on Guam; it has
apparently taken only 11years since pythons were recognized as being
established in the Everglades for researchers to implicate pythons in
the same kind of severe mammal declines," said Robert Reed, a USGS
scientist and co-author of the paper. "It is possible that other
mammal species, including at-risk ones, have declined as well because
of python predation, but at this time, the status of those species is

Another coauthor of the study was John Willson '02, a research
scientist at Virginia Tech University who has worked with Dorcas on
several studies and co-authored the book Invasive Pythons in the
United States.

Willson commented, "Our research adds to the increasing evidence that
predators, whether native or exotic, exert major influence on the
structure of animal communities. The effects of declining mammal
populations on the overall Everglades ecosystem, which extends well
beyond the national park boundaries, are likely profound, but are
probably complex and difficult to predict. Studies examining such
effects are sorely needed to more fully understand the impacts pythons
are having on one of our most unique and valued national parks."

On January 23 the U.S. Fish and Wildlife Service published a rule in
the Federal Register that will ban the importation and interstate
transportation of four non-native constrictor snakes that threaten
the Everglades, including the Burmese python. These snakes are being
listed as injurious species under the Lacey Act.

In addition to Dorcas and Willson, authors of the study are Robert N.
Reed, USGS; Ray W. Snow, NPS; Michael R. Rochford, University of
Florida; Melissa A. Miller, Auburn University; Walter E. Meshaka, Jr.,
State Museum of Pennsylvania; Paul T. Andreadis, Denison University;
Frank J. Mazzotti, University of Florida; Christina M. Romagosa,
Auburn University; and Kristen M. Hart, USGS.

Davidson is a highly selective independent liberal arts college for
1,900 students located 20 minutes north of Charlotte in Davidson, N.C.
Since its establishment in 1837 by Presbyterians, the college has
graduated 23 Rhodes Scholars and is consistently regarded as one of
the top liberal artscolleges in the country. Through The Davidson
Trust, the college became the first liberal arts institution in the
nation to replace loans with grants in all financial aid packages,
giving all students the opportunity to graduate debt-free. Davidson
competes in NCAA athletics at the Division I level, and a longstanding
Honor Code is central to student life at the college.