Friday, February 10, 2012

Thinking Critically about Science in the News

Your grammar is making you fat, and giant, invasive snakes have eaten everything in the Everglades . . . or not.

A couple interesting stories in the news have started my skeptical radar ringing. I love surprising and counter-intuitive science discoveries, but some are just too hard to swallow.

The first of the two news pieces I read today that made me go "hmmm" is about Yale researcher M. Keith Chen who has written a paper that suggests that some languages tend to weaken the connection we feel to future events. This makes speakers of English and Spanish, for example, less concerned about the long term effects of their behavior than speakers of languages like Mandarin Chinese. According to Chen, this helps explain why we English and Spanish speakers are fat, save less, and smoke more than speakers of Mandarin.

I might have bought the connection to obesity and spend thriftiness, but according to Wikipedia the Chinese are the heaviest smokers in the world, with the prevalence among men at about 60%, while only about 20% of Americans smoke. What's more, smoking in the US has fallen dramatically since 1965 when 42% of us smoked, even though most of us have spoken English and/or Spanish the whole time.

Chen's paper is packed with technical jargon, so I can't say I've plodded through the whole thing just yet. But it also hasn't been published by a reputable journal. It's too bad that it's already gotten so much press, because I'd bet it will never make it past the peer review process. Only time will tell, provided I can pay attention that long.

The other paper that has me in a tiff has indeed been published in a scientific journal, but it happens to be a journal that seems to put out a lot of pretty dicey stuff - the Proceedings of the National Academy of Science (PNAS). According to an article in the Washington Post, the authors claim that non-native pythons and anacondas are decimating the small animal population in the Everglades. The problem is this, predators as a rule CAN'T devastate prey populations because as soon as prey populations fall, predators starve to death and the prey populations rebound.

Invasive animals don't typically wipe out the things they eat. The ebb and flow of predator and prey populations is described by the well known Lotka-Volterra equation, which makes it clear that any reduction in prey animal numbers is going to be relatively manageable and temporary, as snakes first gorge and then die off.

Invasive species are, however, a serious threat to OTHER things that eat the things they eat. That is, anacondas and pythons are more likely to out-compete, and potentially devastate, the native alligator population, than to wipe out the rabbits, raccoons, opposums and bobcats that they compete for.

Of course, I'm no expert on either of these topics. It's just that my inner skeptic tells me that both papers seem suspiciously designed to grab headlines with shocking and dubious claims.

I'd promise to keep an eye on the stories to see if they hold up over time, but my English proficiency is making it hard to think of doing anything besides eating, drinking, and blowing all my money on exotic, carnivorous pets that will eventually grow to be longer than my house. Que sera sera.


  1. Dear Buzz,

    The second part of this post on articles that got you in a tiff ended up getting me in a tiff. While you are right that the Lotka-Volterra equations won't lead to extinction, they are only valid for very simple single-predator-prey systems in a constant environment. I am not an expert in ecology, though my brother is a marine biologist. However, it should be pretty clear that many ecosystems are much more complex than the idealized Lotka-Volterra model. The simplest case I can think of that would fall outside the this model would be a system with a primary and secondary prey source, so a decline in one prey population would not necessarily lead to a decline in predator population (discussed in more detail here: Also, many ecosystems are already changing and under pressure from other factors, such as human development. It's not hard to imagine that the introduction of a new predator could push already threatened populations below the minimum level needed to sustain themselves.

    A cursory google search will bring up plenty of articles on predator-driven extinction, such as "Avian Extinction and Mammalian Introductions on Oceanic Islands" by Tim Blackburn et al, Science 305, 1955-1958, (2004), which specifically deals with introduced species. While I am not an expert qualified to judge the validity of the PNAS paper you mention, your reasoning for dismissing it was sloppy and rather disrespectful to the whole field of ecology and wildlife management. I don't mean to fly off the handle and generally enjoy Physics Buzz quite a bit, but I am particularly troubled and upset when scientists in fields like physics make sloppy or uninformed statements marginalizing environmental issues. Especially since such statements can be used as cover by groups opposed to environmental regulations to cast false doubt on legitimate research done by hardworking, dedicated scientists in the field.

  2. Thanks for the comment.

    You're correct that the simplest Lotka-Volterra equation is probably to meager to address many real world situations, but the picture these researchers present is very simple: all small mammals seem to be disappearing from the Everglades in regions that they say correlate with rising populations of non-native constrictors. So there are two entities at play: predatory snakes and warm-blooded prey. If only some of the species were decimated, then I'd agree with you. For the sort of example you give in your link, the snakes would have to subsist on something else when they run out of prey. The PNAS paper doesn't document any secondary prey population in their survey that would fit the bill - they seem to have eaten everything. With food now so scarce, how on earth can the snakes survive?

    The other thing that surprises me is that they didn't count (or at least didn't record) constrictors in their survey of road kill and sightings. If the place is crawling (sorry) with boas and anacondas, shouldn't at least a few get run over from time to time? They claim that there's a correlation between invasive snakes and mammal population decline, but they don't seem to have the data to prove that, only anecdotal evidence that there are lots of snakes (I don't know how to evaluate what a "lot" of snakes is, I need numbers) in areas where there are few mammals. Even if they had documented the correlation, they'd still have work to do to prove that the snakes are the actual cause of the declining mammal numbers.

    In any case, there's something fishy about the paper. Pointing that out hardly marginalizes the environmental issue. If the decline in mammals is due to something else, like pollution or development, it's important to know that. (Both of those things are potentially able to wipe out entire animal populations, BTW, unlike normal predator-prey interactions.) If the researchers are wrong, as I suspect, we'd better get on the stick to find the real culprit. If they're correct, good for them - lets go to work killing the snakes and restoring the ecological balance. First, however, I'd like to see them make their case in a journal that's a bit more reliable than PNAS.

  3. Hi Buzz,

    Thanks for responding to my comment. I agree that identifying a correlation between more pythons and less animals is only a first step and organizing a Simpson's-style Whacking Day hunt for pythons in the everglades would be a bit premature. There is certainly a need for more followup research and studies.
    However, I want to contest at two points you made in your comment. In the abstract, they specifically mention that they are concerned about "species of conservation concern" as opposed to the common species such as raccoons. In this case I think the multi-prey model is appropriate, since the pythons could kill off the last few members of these rare species before the drop in common prey species would be enough to drop the python numbers.

    They do attempt to roughly quantify 'a lot' of pythons in fig. 2 where the plot the number of pythons removed (by park rangers, I assume). I don't know how to go from this to an actual number of pythons in the everglades, but I think this figure at least shows a growing (possibly leveling off) population of pythons in the everglades. It would be better to have more reliable population numbers, and I would hope that this paper will spur other groups to conduct further studies. The population declines the identify in this paper seem rather dramatic, and while an "OMG Snakes in the Everglades!" article in the washington post was maybe a bit over done, I do think these researchers identified a potential cause that deserves serious attention.

  4. I agree, more research would be good, and would potentially satisfy my skepticism. I'm willing to admit that my skeptical radar is not always as well calibrated as I would like. So I could be wrong about both of these papers. The headlines just seemed too tabloidy to me, which puts me on edge.

    In any case, I hate seeing invasive species screwing up ecosystems, so I hope we take care of it before too much harm is done - to predators or prey in the Everglades.