Laws, like sausages, cease to inspire respect in proportion as we know how they are made. - John Godfrey Saxe
Sometimes I feel the same way about media coverage. It seems the more I know about a story the less I feel the coverage is accurate and the more sensational a story is the less accurate they seem to be. The recent plethora of stories about pythons consuming prey in the Everglades is a prime example. Stories about large snakes feed directly into an archetypal fear that humans have of snakes, and stories about a feeding frenzy of snakes wiping out wildlife fuels a feeding frenzy of media coverage that wipes out the truth. With great certainty, I predict that the media will make the jump to pythons eating people. Any bets?
This is a story that I do know something about as I am one of the co-authors. The title of the paper ("Severe mammal declines coincide with proliferation of invasive Burmese pythons in Everglades National Park"), published in the Proceedings of the National Academy of Sciences, suggests that the occurrence of pythons is coincident with a dramatic decline in mammal populations. We were careful not to say "caused" because we don't know that. With few exceptions, you would get that impression from the media coverage that hoards of rampaging snakes were vacuuming up mammals in the Everglades. We don't know that and we could be making the right prediction for the wrong reasons.
Let me correct two common misconceptions first. This study was not done by the National Academy of Sciences as many stories reported; it was published in the Proceedings of the National Academy of Sciences -- big difference. Likewise this was not a nine-year study in that we did not start this study nine years ago. We started this study 1-2 years ago and collected information that was available over a nine-year period (2003-2011) and compared it to similar data collected earlier (1993-1999). And sure enough a very dramatic pattern did exist. I liken what we did to a grand jury investigation. We amassed the available evidence and asked if it was sufficient to demonstrate that a crime had occurred (mammal populations had declined) and to suggest that pythons could be responsible (they had motive, means, and opportunity). An indictment was handed down. That does not mean the pythons are guilty. It does mean we need to go to trial. According to English law the accused should be considered innocent until proven guilty. In science terms we call this a null hypothesis, or a statement of no effect. Of course none of this sells newspapers, draws viewers to a television station, or causes hits on a website.
What do we do now? We go to trial. In scientific terms, we design a study that evaluates the presence of pythons with the absence of mammals in relation to differences and changes in habitat, hydrology, and other biological components. This study should be a high priority for funding as it critically tests the hypothesis that the presence of pythons is related to the absence of mammals while also quantifying habitats and hydrology. This is important because pythons might not be guilty. If not pythons, what could be causing the decline in mammals?
I have been thinking about this python-mammal pattern since we assembled the paper and I have been gathering more information. Quite honestly I am seeing other potential patterns emerge. Now let me step back for a moment and comment that it is clear than many people think that a publication is the final complete word on a subject. Not so; many times publications are the first word on a subject and their purpose is to stimulate thinking. I often tell my students that it is okay to be wrong and that in fact you learn more when you are wrong than when you are right. That is also one of the most important reasons that we consider pythons innocent and that we take them to trial. Because, what happens if we are wrong and something else caused mammal populations to decline? We do not want the real guilty party to remain free.
If we use the period 2000-2002 as the dividing point and ask what other biological responses occurred in the Everglades system before and after that time period, we see that fish communities have changed, location and success of Roseate spoonbill nesting colonies have changed, alligators have gotten skinnier, and the number of young snail kites fledged from nests has plummeted. Are pythons responsible for all of these coincident biological changes? Have other events occurred that could explain these biological changes? Hopefully more science and a better understanding of what is happening to wildlife in the Everglades will emerge from this discussion. Because if it is not pythons (and it might not be), something else is wrong in an ecosystem that we are spending billions of dollars to restore and we need to know what that is.