Think plant-animal interactions are more “intense” in the tropics? In particular, think that herbivory levels are higher in the tropics, and that plant chemical defenses against herbivory are stronger there? Think again. Writing in the new issue of Ideas in Ecology and Evolution (open access), Angela Moles shows that those are zombie ideas which survive because of sheer dogmatism. Only 37% of papers find the expected higher herbivory at low latitudes, and the meta-analytic effect size is not significantly different from zero (Moles et al. 2011). And plant chemical defenses actually are stronger on average at high latitudes (Moles et al. 2011). But papers finding the expected pattern are cited several times more often than other papers–even if you restrict attention to papers by the same lead authors, published in the same journals! There are even cases where sloppy peer review allowed authors to claim support for this zombie idea despite being flat out contradicted by their own data. For instance, if your data say, with P=0.23 or P=0.85,
that there’s fail to reject the null hypothesis of no relationship between herbivory and latitude, you should not be claiming that “we found support for the hypothesis that plants suffer greater herbivore pressure at low latitudes”! (especially not in PNAS!)
Peer review is supposed to be the scientific literature’s defense against errors. But if the reviewers are in the grip of the same zombie ideas as authors, then far from eradicating zombie ideas peer review actually reinforces them.
I’ve also been wondering if our respect for “classic” papers and “textbook examples” isn’t the problem here. Just because a paper is a “classic”, meaning it was the first to suggest an idea, or is highly cited, or was especially well-conducted, or was especially cleverly done or clear, doesn’t make it representative or typical. When it comes to evaluating purportedly-general empirical patterns like latitudinal gradients in herbivory and plant defense, we ought to care much more about what’s typical, and much less about what “classic” papers say.
Kudos to Angela Moles for fighting the good fight. But if my own experience is any guide, she’s got an uphill battle ahead of her. Hope this post will help a bit.
UPDATE: And as noted in the comments, if a recent AREES review (Schemske et al. 2009) reinforces the zombie idea, you’re really in for an uphill battle! Angela’s IEE paper discusses why Schemske et al. 2009 shouldn’t be relied on.
HT Jarrod Cusens, via Twitter.