Monday, November 18, 2013

An Unstoppable Anaconda Invasion in Florida? What Slate Got Wrong.

Photo By Dave Lonsdale, Wikimedia
    Last week Slate ran a piece in their Wild Things blog entitled, “Green Anacondas in the Everglades: The Largest Snake in the World has Invaded the United States.” Obviously the sensational headline caught my attention as did the subtitle, which refers to this invasion as "unstoppable." However, after reading the actual article I realized that it was basically just a smattering of anecdotes. That makes for a fun story and some interesting conversations, but unfortunately it is too easy to interpret the article as news. Let me be clear: There is virtually no evidence that a population of anacondas exists in Florida.

    Curiously, Slate does not mention that the two individuals that provided the bulk of their anaconda information are affiliated with the Skunk Ape Museum in Ochopee, Florida (the facility is instead described as a “roadside zoo” or the “Trail Lakes Campground”). The Skunk Ape, if you’re not familiar, is the South Florida equivalent of Bigfoot. For what it’s worth, the official website of the Skunk Ape Museum unequivocally states that there are between 7-9 Skunk Apes living in the EvergladesNow, just because someone believes that there is a population of Skunk Apes living in the Everglades does not mean that we can or should discount everything they say, but it does indicate that they probably have different standards than most people when deciding what is circumstantial evidence and what is proof when it comes to determining whether an animal population exists.

    If you give the article a careful read, the entire premise that there is a breeding population of Green Anacondas (Eunectes murinus) in the Everglades boils down to: 1) ten years ago a juvenile Green Anaconda was found in the Everglades; the snake didn’t eat anything and died, 2) another Green Anaconda was later found in the region and finally, 3) lots of people around the Everglades have seen large snakes they did not identify but that possibly could have been Green Anacondas.

    I don't know about you, but this does not convince me that anacondas have invaded South Florida.

    The worst (and incredibly ironic) part of the article is that it repeatedly suggests that the well-publicized concern about the Burmese Python in Florida is largely a result of media-hype while the real problem (i.e., Green Anacondas) is overlooked. The fact that there is a large, reproducing population of Burmese Pythons in Florida is well-documented: thousands have been found including everything from juveniles to giant adults with 87 eggs inside. This population has been the subject of several large and ongoing research projects that have produced numerous scientific papers. For example, a recent paper in the Proceedings of the National Academy of Sciences described how mammal populations have crashed as the Burmese Python population expanded (and presumably, as they ate many of the mammals). 

    On the other hand, documentation of the Green Anaconda "invasion" basically consists entirely of the majorly hyped-up Slate article, which hints that the snakes can get as wide as hula-hoops (they can’t) and probably eat people.

    The irony boggled my mind. Because I only have very little first-hand experience with large invasive snakes, I contacted some of my friends and colleagues that study these Florida reptiles for their perspectives on the article. Unfortunately, I can’t repeat most of their reactions here (this is a family-friendly blog after all). But, fortunately Dr. J.D. Willson did provide a printable response. J.D. is an Assistant Professor at the University of Arkansas and has authored numerous articles about Burmese Pythons in Florida. Notably, he is also co-author of the new book, Invasive Pythons in the United States: Ecology of an Introduced Predator. I figured he could set the record straight.

J.D. replied, “Although there certainly has been a strong dose of sensationalism about the Burmese Python issue from the media, our research suggests that the problem is severe and should be considered a major threat to the Everglades. Over the past decade, Burmese Pythons have spread over an area of at least 4,000 square miles and including all of Everglades National Park and Big Cypress National Preserve. They also appear to have wiped out mammals such as rabbits, raccoons, and bobcats in the heart of the Everglades National Park. Over 2,000 of these snakes have been captured and our research shows that this is just a tiny fraction of the overall population…"

On the other hand…

“…We currently have no reason to suspect that anacondas are established in South Florida. This species certainly is kept in captivity and apparently escaped or released pets have been found. However, the small number of individuals that have been found were far apart and there has been no evidence of reproduction or of a ‘hotspot’ where sightings are concentrated.”

Photo By Trisha M Shears, Wikimedia
    Is it possible that there is a population of Green Anacondas prowling through the isolated marshes of the Everglades? Yes. When the author notes that even big snakes can effectively evade detection in the Everglades, he is completely correct. In addition, Burmese Pythons were already firmly established in Florida before there was indisputable proof that they represented a reproducing population. But there is really no compelling reason to think there is a Green Anaconda population in the Everglades; a grand total of four Green Anacondas have ever been confirmed in Florida, this despite a large-scale reporting and monitoring system that was recently put in place to track the presence of large invasive snakes there. If we use four animals as evidence of a population, for consistency we then also have to believe that just about every other exotic animal ever found in the state also represents an established population, with the possible exception of Skunk Apes.

    But what about all the large snakes people have reported seeing in the Everglades? This phenomenon is not unique to that region. Anyone that has spent any time answering snake questions knows that in general, people are not very good at identifying snakes and tend to exaggerate both their size and their potential to inflict bodily harm.

    Before closing, I want to address two specific points from the original article. First, the juvenile anaconda that was captured in the Everglades did not eat and later died. Is this compelling evidence that it was a wild snake and therefore that anacondas are breeding in the Everglades?

    Anyone that has experience with captive snakes knows that some are picky eaters, perhaps especially when said snake is an exotic species from a faraway land with unique habitats (like, for example, the Amazon). If we are to believe that a snake that did not eat is evidence that it is wild, should we then also believe that the only other individual Green Anaconda captured in the Everglades and mentioned in the article is actually an escaped captive because it did eat?

    Second, the original article argues that the Burmese Python invasion is no big deal compared to an invasion of Green Anacondas because fire ants kill pythons but not anacondas. Laboratory studies have confirmed that fire ants (i.e., Solenopsis invicta) are capable of penetrating reptile eggs, including those of Burmese Pythons. In addition, some have suggested that egg-laying reptiles are more susceptible to being killed by fire-ants than are reptiles that give birth to live young. Fire ants have even been implicated in the declines of some snakes in the southeastern United States, like Southern Hognosed Snakes (Heterodon simus) and Kingsnakes (Lampropeltis getula). But, these are just ideas. There is no evidence that fire ants are influencing the population growth of any reptile.

    To say with confidence that fire ants are limiting the population growth of Burmese Pythons we would need to have some kind of idea regarding how many young Burmese Pythons are being produced and how many are being killed by fire ants and this information is not available to us. The article notes that a single captive Burmese Python and her eggs were killed by fire ants and this is interesting. But, it does not suggest that the wild population is being affected at all. To put it another way, a paper published in 1989 identified 10 confirmed cases of fire ants killing human beings in Florida (and there surely have been more cases since that publication). I don’t think anyone would take that information and then suggest that fire ants are limiting human population growth.

    The possibility of Green Anacondas secretly prowling and reproducing throughout the Everglades is a fun topic to discuss around the campfire. But, it doesn’t stand up to scientific scrutiny. I wish Slate had made that clear.

Update 1/6/14: Slate has given me the opportunity to write more about how biologists differentiate exotic and invasive species, with a focus on large predatory reptiles, check it out!

You can follow me on Twitter and/or subscribe to this blog by e-mail.

Some Relevant Scientific Papers:

Diffie, S., Miller, J, & Murray, K. (2010). Laboratory Observations of Red Imported Fire Ant (Hymenoptera: Formicidae) Predation on Reptilian and Avian Eggs Journal of Herpetology (44), 294-296 DOI: 10.1670/08-282.1

Dorcas ME, Willson JD, Reed RN, Snow RW, Rochford MR, Miller MA, Meshaka WE Jr, Andreadis PT, Mazzotti FJ, Romagosa CM, & Hart KM (2012). Severe mammal declines coincide with proliferation of invasive Burmese pythons in Everglades National Park. Proceedings of the National Academy of Sciences of the United States of America, 109 (7), 2418-22 PMID: 22308381

Rhoades RB, Stafford CT, & James FK Jr. (1989). Survey of fatal anaphylactic reactions to imported fire ant stings J Allergy Clin Immunol., 84, 159-162 DOI: 10.1016/0091-6749(88)90373-9

No comments: