The USA has more
than 160 invasive species of vertebrates (Witmer et al., 2007). Rarely do you
see people complaining about feral horses, starlings, or bullfrogs. But, the level
of emotion involved in discussing invasive giant snakes during 2010 rivals rhetoric directed at the reintroduction of wolves to Yellowstone
National Park. Giant snakes and wolves are both apex predators capable of
killing humans and their domesticated species as well as a reminder that humans
are not on the top of the food chain.
The
USGS’ report on invasive giant constricting snakes by Reed and Rodda was
released in October of 2009. Rotella et al. (2010) studied the public reaction
to the release on the Internet, using news stories based on the report for one
month. They analyzed the news items in terms of key points and interpretational
errors. Key points of the original publication were identified by consensus and
then tallied through critical reading of the news items. Errors in the news
items were categorized as: factual errors, exaggerations, conclusions beyond
the data, and political.
Rotella
and colleagues results revealed 26 unique news stories produced by 11
syndicated news agencies, and 15 blog posts, newsletters, or as items released
by net forums for special interest groups. The articles had a mean word count
of 621 (the original report was 302 pages). The team identified the key points
as: threat to humans, invasion range, effects of climate change, risk
assessment, pet release, removal/capture, reproduction/growth, rights of pet
owners, biology in the native habitat, and extinction risk for competing
species. The key points mentioned most frequently in the news items were:
threat to humans, snake removal/capture, reproduction/growth, and pet release.
Nineteen of the 26 news items (73%) had errors. The most frequent errors were
exaggerations (13 items), unsubstantiated conclusions (11 items), and factual
errors (10 items). Two of the news items included parodies based on the
original publication.
Other criticism
of the report comes from David and Tracy Barker (2010a, b), who run VPI, a
python breeding facility in Texas. They argue for less regulation on the
captive snake breeding industry and criticize the report on a variety of levels
which range from style and grammar to methodology and conclusions drawn from
the study.
|
Python bivittatus, JCM |
Some of the
problem with the USGS report and its critics rests in the lack of knowledge and
confusion concerning the systematics of the Python
molurus complex. It is now relatively clear that the Indian Python, P. molurus is a peninsular Indian
species, while the Burmese Python (P.
bivittatus) is a Myanmar- Indochinese species. They undoubtedly shared a
common ancestor, and are thus morphologically similar, but are in all
likelihood distinct species (despite the fact they can reproduce with each
other). See Jacobs et al. 2009. The failure to recognize this in the USGS report
is understandable give the morphological similarity of the species and the fact
that large snakes are poorly studied in their native countries. Much of the
literature on these species is a tangled mess that results from writers
reworking what others have previously said about the natural history of large
snakes. Murphy and Henderson (1997) attempted to unravel part of this by using
direct quotes from earlier literature, but even this was only partially successful.
Biological field work for western researchers is virtually impossible in
countries like Myanmar (Burma). Therefore, advancing knowledge about these
snakes is left to observation of captive specimens and the few field studies
that do get done within the snake's natural distribution.
Predicting the
future is always difficult. The climate modeling work done by Pyron et al, (2008) suggests that pythons won’t be able to
expand their distribution much beyond what it is today during the course of
this century. And, the study done by Dorcas et al. (2010) would seem to support
this – although nobody is talking about sample size. The special interests have
latched on to this study in an attempt to find support for their view point.
The well documented ecological disaster brought about by the
Brown Treesnake in Guam is certainly a wake-up call to prevent invasive snakes
from eating their way through the native fauna of southern Florida or any other place
they might survive and thrive.
As for giant snakes surviving and spreading –natural
selection will be finding those individuals that can withstand cold temperatures
(assuming a small percentage can - it may be only a fraction of 1%). Those individuals will be leaving more
offspring in the next generation, so as time goes on it seem probable that the Florida
populations of Python bivittatus and Python sebae, as well as the Boa constrictor will be adapting to cold
snaps. Any reduction in the Florida giant snake populations due to die off from
cold weather in southern Florida is at best temporary and offers only a short reprieve
to the native vertebrate fauna.
From my perspective the government should be working to minimize
invasive species and protect the native fauna - an important natural resource. Perhaps the snake breeding
industry should be working on developing designer snake morphs that self-destruct
when they escape or are released from captivity. Or, perhaps more realistically
sterile designer snake morphs should be produced. So, escapees and released pets at least cannot
reproduce.
As for the
danger of snakes to humans, in the USA, it pales in comparison to deaths from
auto accidents or firearms. In the United States there are more than 250
million privately owned firearms and that the number increases by about 4
million per year. The CDC estimates 75,000 annual human deaths from firearms. Therefore,
outrage or even loud concern about snakes that kill less than a dozen people
per year seems a bit over the top. Not that the loss of human life should not be a concern, only that statically being killed and or eaten by a giant snake in the USA is a non-issue.
Literature
Barker, D. G.
and T. M. Barker. 2010a. A critique of the analysis used to predict the climate
space of the Burmese Python in the United Snakes by Rodda et al. (2008, 2009)
and Reed and Rodda (2009). Bulletin of
the Chicago Herpetological Society 45(6):97-106.
Barker, D. G.
and T. M. Barker. 2010b. The Tympanum. Bulletin
of the Chicago Herpetological Society 45(9):144-149. Bulletin of the Chicago Herpetological Society 45(12):97-106.
Barker, D. G.
and T. M. Barker. 2010c. A review of: Dorcas, M. E., J. D. Willson, and J. WE.
Gibbons. 2010. Can Invasive Burmese Pythons Inhabit Temperate Regions of the
Southeastern United States? Biological Invasions. Online at
doi10.107/s10530-010-9869-6. Bulletin of
the Chicago Herpetological Society 45(12):187-189..
Beschta, R. L.,
and Ripple, W. J. 2009. Large predators and trophic cascades in terrestrial
ecosystems of the western United States. Biological
Conservation 142, 2009: 2401-2414.
Jacobs, H. J., M. Auliya and W. Böhme. 2009. Zur Taxonomie des Dunklen
Tigerpythons, Python molurus bivittatus KUHL, 1820, speziell der
Population von Sulawesi. Sauria,
Berlin, 2009, 31 (3): 5–16.
Murphy, J. C.
and R. W. Henderson. 1997. Tales of
Giant Snakes. Krieger Publishing, Malabar, Florida.
Pyron,
R. A., F. T. Burbrink, and T. J. Guiher. 2008. Claims of potential expansion
throughout the U.S. by invasive python species are contradicted by ecological
niche models. PLoS ONE 3:e2931
[doi:10.1371/journal.pone.0002931]
Reed,
R. N. and G. H. Rodda. 2009. Giant
constrictors: biological and management profiles and an establishment risk
assessment for nine large species of pythons, anacondas, and the boa
constrictor: U.S. Geological Survey Open-File Report 2009-1202, Washington,
D.C., USA.
Rotella,
A. R., R. A. Connelly, M. D. Marsh, C. C. Wessel, J. W. Murphy, L. L. Canton,
and J. O. Luken. 2010. Snake Invasion: Evaluation
of an Online News Frenzy. Bulletin
of the Ecological Society of America 91:438–441.
[doi:10.1890/0012-9623-91.4.438]
Witmer, G. W. et al. 2007. Management of invasive
vertebrates in the United States, An Overview. USDA National Wildlife Research Center Symposia. 12 pages. http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1055&context=nwrcinvasive
Labels: alien species, opinion, snakes