As promised, here’s what I found when I looked up citation data for various classic papers in ecology (and a couple in evolution):
Citations of all of these papers (with one exception) are increasing roughly exponentially over time, as expected given the exponential growth in the number of ecology & evolution papers being published, and being indexed in Web of Science. But these data have lots of other interesting features. Here are some that jumped out at me:
- Being a zombie is no obstacle to being well-cited, apparently. Connell 1978 is the paper that coined the term “intermediate disturbance hypothesis”. That idea, of course, has long since been refuted, theoretically and empirically. Which has not stopped Connell 1978 from being by far the most-cited paper of the ones I looked at! It has been since shortly after it was published, and the gap has only grown over time (especially since the mid-90s–why the sudden jump in citation rate of Connell 1978 at that time?) I’d looked at the numbers for Connell 1978 before for an old post. I figured that other classic papers of similar vintage would be cited at similar rates–and I was very wrong! Looking at these data makes it clear just how hard it’s going to be to kill off the zombie idea of the intermediate disturbance hypothesis. One might wonder whether it would be easier to kill off non-zombie ideas like coevolution or trophic cascades! 😉 Seriously, it just staggers me how often Connell 1978 is cited compared to every other paper on this list. Indeed, I wonder if it’s not the single most-cited paper in all of ecology these days. It surely has to be at least close, right? How many ecology papers, no matter when they were published, can possibly have been cited 200+ times/year in recent years?
- UPDATE: A hypothesis regarding the mid-90s revival of the IDH. I just had a thought regarding the mid-90s revival of interest in the IDH. I wonder if it wasn’t due at least in part to the work of someone I’ve known since grad school: Steward Pickett, a great guy and a very influential ecologist (doing a very different “style” of work than what I do). Steward co-authored some widely-read books on landscape ecology and ecosystem ecology in the late 80s and mid-90s: Ecological Heterogeneity in 1989, and Ecological Understanding in 1994. As I recall (and I am going by memory here), these books placed a lot of emphasis on the importance of disturbance. Again going by memory, these books also placed a lot of emphasis on synthesis and unification as opposed to criticism (Steward has a paper arguing that “critical” habits of mind are not conducive to “synthetic” thought), on empirical case studies and illustrative examples as opposed to systematic review, and on verbal models as opposed to mathematical models. Not sure how you’d test the hypothesis that Steward’s work is responsible for the mid-90s revival in interest in the IDH, but it at least seems like a plausible hypothesis. I’ll try to keep thinking about other things from the late 80s or early 90s that might be responsible for the IDH revival.
If a classic is never cited, is it still a classic? I have papers that have been cited more often than May 1975, the paper that introduced the idea of chaos into ecology (and other fields; May didn’t discover chaos but I don’t think the possibility was widely recognized until his paper). May 1975 has only been cited 32 times! That’s far less than any other paper on this list. I was shocked that the number is that low. I assume May 1975 is not cited much because he didn’t actually discover chaos, and so now that people know about the idea they don’t feel any need to cite him for first pointing it out? Or maybe the basic idea of “chaos” is just considered part of general background knowledge by those who work on it, so that nobody feels the need to cite anyone as the source of the idea, or for early work on the idea, or etc.? Much as nobody cites Darwin or Wallace when discussing evolution by natural selection?
- UPDATE: My memory sucks. I came up with this list of papers from memory. Which means the list is only as good as my memory. Which is a problem because my memory sucks. As Chris Klausmeier points out, May 1976 and May 1974 get the “chaos” cites, not May 1975! My bad. Consider this a reminder, if one was needed, that you get the background research you pay for on this blog.
- Which classic to cite? Commenting on the previous post, Dan Gruner made a very good point. Paine 1969 coined the term “keystone predation”–but Paine 1966 is the paper reporting the classic experiment demonstrating what Paine later called keystone predation. So if you’re writing a paper on keystone predation, you might well cite Paine 1966 instead of Paine 1969. Similarly, HSS 1960 is the source for the concept of trophic cascades–but Paine 1980 coined the term “trophic cascades”. So if you’re writing a paper on trophic cascades, maybe you cite Paine 1980 instead of HSS 1960. And many people working on stability and complexity cite May’s 1973 monograph rather than his 1972 paper. Obviously, it’s impossible to tell from the data I presented how much effect such “competition for citations” has had on the citation patterns of the papers examined. Paine 1969 and May 1972 are indeed two of the less-cited classics I looked at–but on the other hand, HSS 1960 is one of the more-cited ones. (UPDATE: And, as noted in the comments and the update above, May 1974 and 1976 get all the “chaos” citations, not May 1975!)
- Man, optimal foraging was big in the late 70s and early 80s! MacArthur and Pianka 1966 was cited something like 50 times/year back then, a massive rate given the much smaller number of papers being published in those days. Stephens and Krebs reviewed the optimal foraging literature up through the mid-80s in a classic 1987 book. But by that point perhaps the low-hanging fruit had already been picked and people’s interests were shifting to other topics. Citations of MacArthur and Pianka 1966 actually declined from the late 80s until the mid 90s…
- Everything old is new again? …but citations of MacArthur and Pianka 1966 have picked up since the mid-90s, to the point where these days they’re cited much more often than a number of other classic papers. Not sure why that is. Has there been a big revival of interest in foraging theory, or optimization theory more generally, that I’ve just missed? Are they getting cited in lots of papers on “adaptive dynamics” or “eco-evolutionary dynamics”?
- Classics catch lifts on bandwagons and controversies. See the spike in citations of MacArthur and Levins 1967 (“limiting similarity”) in the late 70s and early 80s? That’s presumably because of the “null model wars“, the big fight over the prevalence of interspecific competition and how to test for it. And notice the jump in the citation rate of MacArthur and Levins starting around 2005, so that by 2012 it was being cited at the second-highest rate of the papers on this list? 2005 is about when the ongoing bandwagons in phylogenetic community ecology and “trait-based” ecology really took off. Both of those bandwagons are based in significant part on the idea of “limiting similarity”. Too bad that’s a zombie idea. And see the spike in the early 1990s in citations of Hairston, Smith, and Slobodkin 1960? That’s the signal of the brief-but-intense fight over “top down vs. bottom up” effects. Finally, after a long period in which Price 1970 was cited only by a few group- and kin-selection aficionados, interest revived following publication of a major paper by Steven Frank in 1997 in Evolution. Conversely, apparently there’s never been a major bandwagon or controversy associated with keystone predation (Paine 1969), deforestation and nutrient cycling (Likens et al. 1970), the stability-complexity relationship (May 1972), or coevolution (Ehrlich and Raven 1964). Citations of those papers seem to be growing steadily over time, with no obvious temporal fluctuations.
- So, did you guess right? As I said above, I knew that Connell 1978 had been cited a lot, but I thought some of the other classics on this list, especially MacArthur and Levins 1967, would be cited as much or more. And while I knew that there’d been a recent surge of interest in the Price equation, I’d have guessed that Price 1970 would still be the least-cited paper on this list. Not bad guesses, but they’re both wrong. Which puts me in good company. The poll results were widely split, as you’d expect. Overall, folks guessed pretty well, but only a minority guessed right on each question. Connell 1978 was the most popular guess for “most cited” (16% of guesses), and two of the less-cited papers (Price 1970 and Likens et al. 1970) were the least popular guess for “most cited”. On the other hand, the 11% of you who guessed May 1975 for “most cited” clearly have no psychic powers. 😉 For “least cited”, Price 1970 was by far the most popular guess (34% of guesses), with Likens et al. 1970 a clear second choice (17%). As I said, good guesses, but wrong. Only 6% of you correctly guessed May 1975. And as for the 4% of you who guessed Connell 1978 for “least cited”, I assume you guessed that more in hope than in expectation. 😉
So, did anyone get them both right?
Thanks for playing everyone!