Peter Abrams has retired (I think; he’s been easing into it for a couple of years and so I’m not sure if he’s officially 100% retired just yet). I don’t know Peter very well personally–we’ve chatted a number of times, and reviewed each others’ papers–but I do know his work quite well. Indeed, I still have two filing cabinets full of paper reprints, which I began accumulating when I started grad school and didn’t stop accumulating until a couple of years ago. They’re organized by author. I have so many Peter Abrams reprints that I need two file folders to hold them all; he’s the only author for whom that’s true. So by that measure of “impact”, Peter Abrams has had more impact on me than any other ecologist. And given how carefully I read many of those papers (filling the margins with notes), and how I developed into someone who (I think!) approaches ecology in much the same way as Peter does, it’s fair to say he’s had as much impact on me–by any measure–as any ecologist. So I thought it appropriate to mark his retirement with an appreciation. Hopefully, folks who knew Peter better than I did will chime in in the comments.
Peter Abrams was one of the world’s leading theoretical ecologists. His publication record is outstanding. He has something north of 150 papers I believe, many first-authored (often sole-authored) and mostly in leading journals. His interests centered on fundamental issues in population and community dynamics, which he preferred to explore using simple differential equation models of small numbers of species (what Bob Holt calls “food web modules”). Often, he would work on the boundary of analytical tractability, so his papers often combined analytical results for simple limiting cases with numerical simulations of more complex, analytically-intractable cases.
Peter was probably ecology’s greatest contrarian. He loved pushing back against the conventional wisdom. No one was better than Peter at exposing how much of what ecologists think they know is based on fragile conceptual foundations, unrecognized implicit assumptions, overgeneralization from special cases, and selective focus on certain possibilities to the exclusion of other, equally-plausible possibilities. Many of his earliest papers attack the idea of “limiting similarity”, the notion that there is some absolute limit to how similar coexisting competitors can possibly be. Peter returned to this idea often in his later work. Other early work showed that predator-prey coevolution often does not take the form of an “arms race”. Peter showed how coevolution of competing species doesn’t necessarily lead to character displacement, and in fact can to lead to character convergence. I’ve done a bit of work building on this idea of character convergence, and I think it would be a great hypothesis for some ambitious student to try to test empirically (it’d be a hard experiment, but if it worked it would be a Science paper) Peter wrote a nice review back in the mid-90s of all the reasons why species diversity might not peak at intermediate productivity levels. He did a bunch of modeling work on adaptive foraging in patchy habitats, showing that we typically don’t expect adaptive foragers to exhibit an ideal free distribution. He identified circumstances in which increasing density-independent mortality can actually increase population size, and circumstances in which species that share resources or predators can act as mutualists rather than competitors. He showed how extinctions brought on by gradual directional environmental change often will involve sudden crashes from high population size, rather than being preceded by gradual declines to low population size. Occasionally, I do think his contrarianism went too far. Some of Peter’s papers come off as just introducing arbitrary complications, purely for the sake of showing that the world is complicated. But those are the exceptions. Overall, I think ecology would be much better off if we had more contrarians like Peter. (I should emphasize that I have no idea if Peter sees himself as a contrarian. All I can say is that’s the impression his papers give me, which I admit may say as much about me as a reader as it does about Peter as an author).
Peter was a theoretician’s theoretician–he was very precise, and very alert to how imprecision in how we define our terms can lead us astray. In the ’80s he pointed out just how tricky it is to define what we mean by “competition”, for instance because species can negatively affect one another at an individual level without necessarily reducing one another’s population sizes. He has a very thoughtful paper about how to individuate and count “limiting factors”, which is something you have to do in order to properly interpret and test the competitive exclusion principle (the number of species coexisting at equilibrium can’t exceed the number of limiting factors). That paper suggests that Hutchinson’s “paradox of the plankton” (how do so many species of algae coexist on only a few limiting factors?) is actually a non-paradox, and only looks paradoxical because we’re not distinguishing and counting “limiting factors” properly. He thought hard about the definition of “indirect effects”, and how to distinguish between different kinds of indirect effects. That work revealed serious problems with standard experimental designs used to tease apart “density-mediated” and “trait-mediated” indirect effects. And he almost single-handedly exposed the conceptual flaws in the once-trendy idea of “ratio-dependent” functional responses (in which the feeding rate of an individual predator depends on the ratio of predator abundance to prey abundance).
But it would be a mistake to think that all Peter Abrams did was just criticize the work of others or point out that the world is complicated (important as both those activities are). He was a pioneer of “eco-evolutionary dynamics”, from long before that term existed. Some of his very first papers, from the late ’70s and early ’80s, are about the consequences of adaptive foraging for coexistence and food web stability. And in 1993 he derived the canonical equation of “adaptive dynamics”, an approximation to quantitative genetics which makes modeling eco-evolutionary dynamics much more tractable than it otherwise would be (others derived the same equation independently around the same time, via other arguments). The population- and community-level consequences of behavioral and evolutionary adaptation is a key theme running through much of Peter’s work. Peter also did a lot of work on the behavior of fluctuating, nonlinear systems. And he made important contributions in areas I know less well, like modeling life history evolution and sexual selection.
It’s probably the fate of the contrarian to be underappreciated, especially if he’s also a theoretician. And while Peter certainly was very well-known and well-cited, he didn’t win a lot of the battles he fought, at least not in the minds of non-theoreticians. Unfortunately, ecologists today still mostly believe in limiting similarity (that’s the basis for much of “phylogenetic community ecology”, for instance), they mostly believe that competition always selects for character displacement, they mostly believe that high density-independent mortality rates prevent competitive exclusion, they mostly believe that the diversity-productivity relationship must be humped…But if Peter’s influence wasn’t widespread except among theoreticians and the more theoretically-minded empiricists, well, I think that’s just a measure of how rare it is for any one person to have really wide influence over an entire field. Especially if that person is trying to push back against established ideas.
Peter wasn’t just a prolific author, he was an extraordinarily active reviewer. A couple of years ago he told me that he refused to do more than one review per week! His example is one to keep in mind next time you’re tempted to turn down a review request because you’re “too busy”. And as someone who’s been reviewed by Peter, let me tell you, he was not one to just toss off sloppy reviews! Peter was as thorough and rigorous as any reviewer I’ve ever encountered in all my years as an author and editor. He knew the literature back-to-front, and always let you know if he thought you were reinventing the wheel or putting old wine in new bottles. I can’t say I always agreed with his reviews, but they always made my papers much better.
As I said, while Peter’s work is hardly unknown, I do think it’s underappreciated. But it’s never too late for that to change. So if you’re looking for something to read, Peter’s retirement is as good an excuse as any to dig into his “back catalog”. You’ll be well-rewarded.