In 1987, Robert Ricklefs published a paper in Science, making a strong case for the role of “regional processes” in influencing species diversity in biological communities. Twenty-nine years after the paper was published, I asked Robert Ricklefs about his motivated to write this paper, the impact it has had on the field, and where he stands, currently, on what he said in the paper.
(Questions sent by email on 15 August 2016; responses received on 19 September 2016)
Citation: Ricklefs, R. E. (1987). Community diversity: relative roles of local and regional processes. Science 235: 167-171.
Hari Sridhar: For the first two decades of your research career, your primary research interest seems to have been the evolution of avian life histories. This 1987 paper is one of your first on the topic of large-scale patterns in biodiversity. What triggered your interest in the latter at this point in your career?
Robert Ricklefs: I had been interested in community ecology since beginning my graduate studies with Robert MacArthur in 1963. Community ecology was caught up in a new wave of excitement at that time, and was the primary emphasis of MacArthur’s students, including Martin Cody and Michael Rosenzweig. Mathematical modeling of ecological communities, including the development of community matrices to examine community stability was an important development of this period. Life history evolution also generated broad interest at the time, particularly owing to the work of David Lack and the controversy over ideas about reproductive restraint espoused by V. C. Wynne-Edwards and Alexander Skutch, among others.
HS: What was your motivation to write up this particular paper?
RR: The emphasis of community ecology during the 1970s and 1980s on mathematical modeling and experimental approaches naturally limited the perspective of many ecologists to local assemblages and short time frames. Although MacArthur is well known for his work in biogeography, he believed that one could develop an understanding of community ecology only by investigating spatially and temporally local systems. History was unique and unpredictable. Of course, many biologists, particularly those with an interest in the evolutionary relationships within, and diversity of, particular groups of organisms, took for granted that history and geography were important. Yet, their perspective was largely ignored by community ecologists at the time. Thus, many of these biologists welcomed the Science paper, but with the thought that “Well, we knew this all along.”
HS: How long did the writing of this paper take? Where did you do most of the writing?
RR: I wrote the paper 30 years ago, and some details of the circumstances have faded. Certainly the manuscript was produced in my office at the University of Pennsylvania, and probably relatively quickly. I had been teaching ecology for some years and had written a textbook on the subject, so the manuscript probably was written fairly quickly.
HS: In the paper you thank “R. Burton, H.V. Cornell, J. Diamond, R. Karban, R.T. Paine, S.L. Pimm, J. Roughgarden and N. Stoyan for comments”. Can you tell us a little more about how you knew these people at that time, and how they helped?
RR: These people were a combination of professional colleagues (Cornell, Diamond, Paine, Pimm, Roughgarden [with whom I had spent a sabbatical]), department members (Burton), and former (Karban) and current (Stoyan) students, to whom I had sent drafts of the manuscript. Their comments were very helpful in providing as much balance as possible in a paper that grew out of a strong point of view. Several of the reviewers objected that too little credit was given to others who had expressed similar ideas. Yet, the large number of citations to the paper over the last 30 years suggest that a similar ‘sign-post’ paper was lacking.
HS: Did this paper have a relatively easy ride through peer-review? Was Science the first journal to which this paper was submitted? Would you remember in what ways the final published paper was different from the first submitted draft?
RR: A manuscript on a topic of my choice was solicited by Dr. Ruth Patrick at the Academy of Natural Sciences in Philadelphia and a member of the Science editorial board. Ruth was a wonderful mentor and promoted the careers of a number of young scientists in many ways. This certainly provided me a unique opportunity.
HS: How was the paper received when it was published?
RR: The paper was welcomed by many biologists with similar views. Communication then wasn’t what it is now, and so I was glad to get a few letters from colleagues.
HS: This paper has been cited over 1800 times. At the time when you wrote it, did you already feel that this would have a big impact? Do you know what this paper mostly gets cited for?
RR: Of course, I thought the paper was important at the time, and that it represented a departure from the direction of much of community ecology. It was probably the clearest and most prominently published (and most conveniently citable) statement that history and geography matter in ecology.
HS: What kind of an impact did this paper have on your career, and on the future course of your research?
RR: The strong and mostly positive response to the paper certainly encouraged me to pursue further work on the historical and geographic contexts of ecological communities, although I continued to work on avian life histories. The paper directly led to my collaboration with Dolph Schluter on an edited book on the geographic and historic contexts of ecological communities and patterns of species richness, published by the University of Chicago Press in 1993. The response to the paper also encouraged me to pursue my interests in taxon cycles of West Indian birds, basically an historical/geographical hypothesis, in collaboration with Eldredge Bermingham, whom I met in 1989.
HS: Towards the end of the paper you highlight four steps that need to be taken to “regain a historical perspective and use it to resolve the major issues of community ecology”:
- paying attention to developments in biogeography, paleontology, systematics, and evolutionary biology.
- studying the historical development of community ecology and reevaluating the conclusions of influential investigators.
- rigorously examining the hypothesis of local equilibrium by putting community convergence and the independence of local and regional diversity to the test.
- assimilating data on geographical distribution, habitat selection, and taxonomic status into the phenomenology of the community concept.
Twenty-nine years after this paper was published, how well do you think community ecology has fared in each of these aspects?
RR: There is no question that community ecology now fully embraces the large-scale temporal and geographic contexts of species distributions and local assemblages of species, and it is a more exciting field because of this. These contexts have largely stimulated current interest in global datasets of species distributions and functional traits, and have helped to further integrate evolution, biogeography, and ecology. Hypotheses concerning community development and maintenance are difficult to test, as we have seen in the case of Steve Hubbell’s neutral theory of communities, but community ecology remains a vibrant and important (and optimistic) area of ecological research.
HS: You say “The scales of population processes leading to local exclusion of species, and those of the evolutionary and biogeographical processes that promote species richness, remain to be determined”. How much progress have we made in understanding the scales over which these different processes operate?
RR: The predominant view at present seems to be that large-scale processes are felt locally. Integrating across scales has proven difficult, although phylogenetic analyses of local assemblages and species traits and distributions are providing new insights into the history and geographic context of local ecological communities. It is an exciting time!
HS: In the Conclusion to your paper, you indicate certain approaches that will be useful in understanding historical and regional causes in variation in species richness: “comparative studies, statistical analyses of patterns, and “natural experiments””. How well do you think these approaches have been used in addressing this issue? Have there been other approaches that you didn’t anticipate in this paper, that have helped in addressing this question?
RR: The paper was written just as molecular phylogenetic analyses and phylogeography were becoming generally available. This has changed everything in the sense that one can now visualize something of the history and geography of species assemblages. New statistical tools are very powerful; large, global datasets have become available; approaches such as species distribution modeling, combined with genomic and gene expression analyses, have helped us to understand the geography of species. I am very optimistic.
HS: Have you ever read the paper after it was published? When you read it now what strikes you the most about it, especially in comparison to the papers you write today?
RR: I had not read the paper for many years, until recently in the context of responding to these questions. The paper reads as though it was written as a critique (it was!) on the predominant direction of ecology at the time. As mentioned above, these views were shared by many biologists, particularly those with a deep interest in the evolution and distribution of species in a particular taxon, including systematists, taxonomists, and biogeographers, who felt disenfranchised to some extent by ecologists. Most of what I have published is predominantly empirical or, in a few cases, theoretical. I have written few papers, like the 1987 Science paper, of a critical nature, although some of my papers in Ecology Letters (2004, 2015) and The American Naturalist (2008, 2012) have a similar feeling of addressing broader issues in community ecology.
HS: Among all the papers you have written, would you consider this one of your favorites?
RR: It is certainly one of the most important in the sense of its impact on the field and in clarifying, to myself, my thinking about community ecology. It has been gratifying to the extent that community ecology has encompassed the points of view expressed in the paper, although I believe this would have happened in any event. Thus, the paper was perhaps more a chronicle of changes ongoing in community ecology at the time.
HS: What would you tell a student who is about to read this paper today? What should he or she takeaway from this paper written twenty-nine years ago?
RR: I emphasize to students that historic papers can help us to understand the development of ideas and approaches in a discipline. Our ideas don’t arrive out of the blue, but rather develop over time through observation and inspiration. It is unfortunate that the early literature in ecology is becoming (inevitably) more remote to present-day students. Understanding how ideas (including bad ones) have developed in the past within a discipline, as recorded in the classic literature, provides a context for the development of new directions.