The National Academy of Science often publishes some really bad studies. Two years ago, the journal of this organization published a paper entitled “Severe Mammal Declines Coincide with the Proliferation of Burmese Pythons in Everglades National Park.” This study was authored by Michael Dorcas, an herpetologist from Davidson College, along with a long list of other scientists. I’m always leery of studies with a long list of contributing scientists. I suspect the lead authors of these studies do most of the work, and misleadingly include many co-authors. With minimal input, the many co-authors lend legitimacy to a study in exchange for getting the publishing credit that is so important for their academic careers.
Michael Dorcas. This scientist authored a really bad study of Burmese pythons that led him to conclude they were wiping out mammal populations in the Everglades National Park. His study was debunked by the Florida Fish and Wildlife Conservation Commission. Nevertheless, the media took his ridiculous conclusions as gospel. Not a single journalist questioned this terrible amateurish study.
I read Dr. Dorcas’s study and knew the results didn’t fit within ecological reality. He went back to records of road-killed animals in Everglades National Park during the 1990’s before the population of Burmese pythons had become significant and compared them with the number of road side sightings of these same species 10 years later. He concluded that the populations of raccoons, possums, bobcats, and marsh rabbits had been decimated and in some cases had been reduced by 100%. This doesn’t make any sense ecologically. If the population of prey declines in abundance, than the population of predators declines as well because there is nothing for the predators to eat. Burmese pythons couldn’t decimate mammal populations without eventually succombing to starvation themselves. So the results of Dr. Dorcas’s study were unbelievably ridiculous. Nevertheless, every news media outlet picked up this alarmist nonsense and not a single journalist questioned the credibility of such an absurd conclusion. This demonstrates the ignorance of basic ecology among the average layperson. I mentioned my logical objections to this study’s findings on my blog about a year ago but thought I was a lone voice in the wilderness. However, I discovered someone from The Florida Fish and Wildlife Conservation agrees with me. They found the following flaws in Dr. Dorcas’s study.
1. The survey for road-killed animals (Dr. Dorcas’s data from the 1990’s) didn’t include critical information–how many observers, the number of miles driven, the number of days the survey was done, and the procedures used to avoid double counting. In other words this data is anecdotal and useless.
2. The year of the pre-python survey was a high water year when more animals were forced to take refuge on the high ground where the road exists. This explains why more animals were counted during the survey than during later drought years. Road-side surveys yield dubious data. Dr. Dorcas should have used live trapping to get an accurate count of mammal populations.
3. There is no actual data on python densities.
4. The timing of the python population increase and the supposed decline in mammal populations is not documented. Scientists can’t explain how python populations could increase following prey population declines (my point exactly).
5. There is no mention in Dr. Dorcas’s study of coyotes. Coyotes recently re-colonized south Florida and may play a role in the decline of mammal populations there.
6. The differences in prey density inside and outside Everglades National Park are likely due to differences in habitat, not the presence of pythons. Everglades National Park is actually very poor wildlife habitat. More wildlife lives outside the park than inside. With very few exceptions most of the best wildlife habitat left in the world is occupied by humans. We give animals the wastelands that are too expensive to commercially develop and call them national parks.
Burmese python killed by alligator. Burmese pythons are beneficial additions to Florida’s ecology, despite what alarmist environmentalists claim. South Florida’s ecology was in desperate need of a large predator.
Contrary to the claims of alarmist environmentalists, Burmese pythons are a beneficial addition to South Florida’s ecosystem. During the Pleistocene in this region there were 5 species of big cats plus dire wolves, bears, and alligators. Now, there are just alligators and pythons. (Very few Florida panthers live in Everglades National Park. Most occur on cattle ranches located well north of the park.) Without the presence of large predators, the populations of smaller predators such as raccoons and possums increased. These predators eat reptile eggs and put a big dent in the population of 17 endangered and threatened species of reptiles, including rare sea turtles. Pythons help control the numbers of raccoons and possums, helping increase the nesting success of endangered reptiles. Pythons are beneficial for twice as many endangered species than ones they might prey upon.
Scientists’ estimates of Burmese pythons populations in Florida are not based on scientific data. They are wild guesses bordering on fantasy. The oft-cited number of 30,000-150,000 is a wild overstimate. Over the past 12 years, 2000 pythons have been removed from Everglades National Park. That’s less than 200 per year–nowhere near what one would expect, if there were 30,000 large snakes slithering inside the park. Last year, there was a python round up. For a month 1500 snake hunters looked for Burmese pythons to kill. They netted just 50. This is strong evidence Burmese pythons are not even close to being as abundant as researchers claim.
Dorcas, Michael; et. al.
“Severe Mammal Declines Coincide with Proliferation of Invasive Burmese Pythons in Everglades National Park”
PNAS December 2011
“Commentary on Mammal Declines in Everglades National Park”
Florida Fish and Wildlife Conservation Commission report 2012