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closeContradiction Claim Is Contradicted By Ecology
Posted by herpdude1 on 14 Aug 2008 at 19:24 GMT
There are a number of significant shortcomings to this article and its conclusions. I have attempted to condense the major issues for the sake of brevity. Hopefully, the maligned USGS authors will rebut this article more fully.
(1) The “imminent” threat of giant snakes invading neighborhoods throughout the nation is descriptive text used by the authors of this article and not conclusions made by the USGS. The authors exaggerate the “alarmist” nature of the USGS report that they cite.
(2) The authors confuse several discrete locations within the geography of south Florida. “Extreme southern Florida” is undefined by the authors, but local use would generally place it as “south of Lake Okeechobee to Florida Bay” and, within the scope of this article, west of the Kissimmee River. This area would be smaller than the historic Everglades, but larger than Everglades National Park. Big Cypress National Preserve is not part of the Everglades, although it is lumped into the “Everglades Ecoregion” as part of the Everglades restoration project. Thus the authors place the “restricted area” of pythons at somewhere between 500,000 to 2,000,000 hectares. However, the latter figure would have to be considered the minimum area, since numerous snakes of variable age classes have been detected far outside of “the confines of Everglades National Park” on both of Florida's coasts.
(3) The authors’ own map [Fig. 2] shows “suitable habitat” extending up the Gulf coast of Florida to Tampa Bay, which is well beyond “extreme southern Florida.” It should also be noted that the Indian River Lagoon system on the eastern coast of Florida is more similar to the state’s subtropical southern tip than is the Tampa Bay region, yet this area is left out by the authors’ model. Ecologically speaking, their ecological niche model would not hold up under simple groundtruthing of Florida’s ecology, as measured by a visit, for example, to Merritt Island National Wildlife Refuge.
(4) The authors are also confused about the ecology of the Everglades and peninsular Florida. They state, “The Everglades form an ecosystem …a subtropical marshland. The rest of the peninsula is composed of xeric highlands and mesic subtropical lowlands. The proposed expansion of the python … would require an expansion of the actual tropical [sic] marshland habitat comprising most of the Everglades.” Florida’s climate ranges from tropical (Florida Keys only) to temperate (the “Panhandle”). The subtropical portion of the peninsula encompasses the Everglades to Disney World (more or less). Various descriptions of Florida’s natural systems identify anywhere from a dozen to over sixty natural communities, which are split or grouped into “ecosystems” depending upon which defining criteria are used. In any case, to indentify peninsular Florida as comprised of three ecosystems is to repeat a mistake last seen over forty years ago. “Xeric highlands” represent three percent (or less) of the state’s natural areas. “Mesic subtropical lowlands” … I don’t even know what that means, but it sounds like perfectly suitable habitat for a large number of boid species.
In short, despite their finely crafted model, the authors don’t have a clue what they are talking about.
Ruark Cleary
Herpetologist
Florida native
RE: Contradiction Claim Is Contradicted By Ecology
RAPyron replied to herpdude1 on 14 Aug 2008 at 21:05 GMT
I appreciate the input, but I feel that there are a number of clarifications that need to be made:
a) The original title of the USGS paper is "What Parts of the U.S. Mainland Are Climatically Suitable for Invasive Alien Pythons Spreading from Everglades National Park?"
The abstract opens with the sentences "The Burmese Python (Python molurus bivittatus) is now well established in southern Florida and spreading northward. The factors likely to limit this spread are unknown, but presumably include climate or are correlated with climate." A northern spread is clearly indicated by the authors. The alarmist claims are evident in the media and interviews with the USGS.
b) We would consider extreme southern Florida to indeed be the area south of Lake Okeechobee. This is smaller than the historical Everglades and larger than the current boundaries of the National Park. There is some margin of error involved in ecological niche modeling, with the land area south of Lake Okeechobee well within that margin. The main indications of this model are that suitable habitat for the pythons occurs primarily in south Florida, generally in the area south of Lake Okeechobee. This is very different from the 22-32 states predicted as suitable by the USGS model. Equivocating over the details of a small amount of land area around the Everglades is meaningless in light of this.
As for Tampa Bay region, the same concept holds. Some variability in the models is expected, while the largest areas of suitable habitat are confined to the Everglades. As for the assertions about the Indian River lagoon system, the author seems to think that maps were drawn based on personal notions of ecology, which is incorrect. A very small amount of land area in the Tampa Bay region is predicted as suitable by the statistically generated niche models based on the known localities of the Burmese python in their native habitat, while the Indian River lagoon system is not. This is not premised on any putative ecological similarity that we suggested for the model. In a similar vein, claims about the apparent suitability of MINWR have no weight in this context.
With regard to the ecological subdivisions of Florida, these assertions are relatively meaningless. The Everglades are a unique ecosystem not found elsewhere in Florida, and are primarily predicted to be the only ecologically suitable areas in Florida for the Burmese python. The definition of ecosystems elsewhere in Florida has little bearing on their ecological suitability, as these models are, again, not based on any input regarding the environmental composition of the world beyond the climatological data contained in the 19 BIOCLIM variables. Regardless of how regions of Florida are classified, only a small area in southern Florida, primarily in the Everglades, is predicted to be ecologically suitable based on our models.
With reference to the conclusion of the author’s comments, we feel that such a statement is not of a particularly scholarly tone, nor is it really likely to foster open discussion on the topic.
RE: RE: Contradiction Claim Is Contradicted By Ecology
herpdude1 replied to RAPyron on 21 Aug 2008 at 21:01 GMT
The USGS and PLoS articles represent dueling models that lead to disparate conclusions. This might appear to be a simple case of statistical validity. However, the larger issue underlying these articles has broader implications; therefore, a closer scrutiny of the ecological validity of this particular niche model is warranted.
I am under no illusion that the PLoS authors have any personal knowledge of Florida’s ecosystems. The ecological niche model is only a mathematical representation of “suitable habitat” based upon climatological data. Contrary to the author’s response above, an understanding of Florida’s unique ecological subdivisions is far from meaningless when examining the zoogeography of an invasive species. In the simplest terms, the Big Cypress Swamp is NOT the Everglades. Yet the ecological niche model lumps these two systems together. Under that broad-brush approach, a much larger area of similar “suitable habitat” is encompassed, which this model fails to recognize. If the ecological model is not consistent with ecological reality, then the value of any conclusions drawn from the model is suspect.
{As a personal challenge, I would ask the PLoS authors (or other modelers) to apply the ecological niche model to two tropical lizards, the Cuban anole (Anolis sagrei) and the Mediterranean gecko (Hemidactylus turcicus). Based upon climatological data, the U.S. range of these two species should be quite restricted. It would be instructional to compare the modeled results with the known range of these two lizards.}
Climate is not the only factor that determines whether an invasive species has the potential to establish itself in a novel environment. Other factors such as propagule pressure, presence/absence of competitors/diseases, availability of resources, environmental physiology, adaptability/genetic plasticity, and anthropogenic forces must also be taken into account. Granted, the PLoS authors were responding to the USGS’s rough-hewn climate model. But the absolute nature of their conclusions gives the impression that the “python issue” has been resolved. Not that this was their intent, but this is how the media is interpreting their article. By failing to clarify that their model is only one piece of a much larger puzzle, the PLoS authors impart more weight to their conclusions than is justified.
I will admit to the possibility that the PLoS authors are unaware of the pending decision on listing the Burmese python as an injurious species under the Lacey Act. The review actually encompasses a number of large boids, including the boa constrictor and an anaconda species, both of which have been found in the Everglades region. The PLoS authors mention the likely relevance of models to policy decisions. They also reference the media hype surrounding the python issue, which they are also now a part of, whether intentionally or not. This removes them from the realm of scholarly discussion and places them as just players in the politicized issue of invasive species regulation. That, of itself, is enough to remove the likelihood of fostering any open discussion.
Ruark Cleary
Invasion Biologist