Complex Population Dynamics: A Theoretical/Empirical Synthesis

  • Peter Turchin
Princeton University Press: 2003. 456 pp. $75, £52 (hbk); $29.95, £19.95 (pbk)

People have been fascinated and puzzled for centuries by the profound variations from one year to the next in the abundance of lemmings and populations of hares and lynxes. The archbishop of Uppsala, for example, wrote about the phenomenon as long ago as the fifteenth century. And hunters and other rural people such as the Sami of northern Scandinavia have their own theories to explain the burgeoning populations of lemmings, for instance, in some years. But it was the Oxford zoologist Charles Elton who built the scientific platform for the modern study of population cycles with a 1924 publication in the British Journal of Experimental Biology. That paper and his 1942 book Voles, Mice and Lemmings have been key references ever since.

Much of this work has focused on vertebrates of the north, but similar phenomena have been observed for species in other regions, such as the larch budmoth found in the Alps. The scientific literature on population cycles is vast and has to some extent been characterized by heated debates. So a book that aims to synthesize this rather chaotic field and make it more accessible to outsiders is to be welcomed.

Complex Population Dynamics, written by Russian-born ecologist Peter Turchin, is split into three parts: theory, data and finally a series of six case studies. The theory part provides an excellent synthesis of the work by Turchin and colleagues, but specialists on population cycles may find that it does not cover the literature as fully as they might like in a book with ambitions of providing a synthesis of the field. I preferred the second part of the book, which covers both phenomenological (time series-based) and mechanistic modelling — the latter more fully than the former.

The section on case examples is good for the systems that Turchin has worked on himself, but is rather shallow for some of the other systems described, a good exception being the chapter on grouse. However, I think that this book contributes profoundly to the literature, in particular with its emphasis on integrating statistical analysis, theoretical modelling and experiments, rather than relying solely on experimental work. I fully agree with Turchin's conclusion that ecological investigations of population cycles and similar phenomena should start with statistical data analysis, aimed at describing the patterns to be explained, and end with experimental work to discriminate between alternative mechanistic explanations. In this respect the book may have a huge impact on the field, not necessarily because everybody agrees with Turchin's conclusions, but because he provides examples of what a research programme ought to look like.

Turchin's book covers many of the same elements as Population Cycles (Oxford University Press), which was published last year. Edited by Alan Berryman, who contributed an opening chapter and a postscript, Population Cycles comprises seven chapters written by specialists in the field, each considering an example of a population cycle. These chapters, although somewhat variable both in form and quality, display great enthusiasm in attempting to understand why some species and populations exhibit extensive population cycles whereas others do not. A concluding chapter is written by ecologists Xavier Lambin, Charley Krebs, Robert Moss and Nigel Yoccoz, who favour the experimental approach over statistical data analysis. Together with the postscript by Berryman, this provides a good balance regarding methodological approaches — a balance that I am convinced is needed if we are to find the solution to the cycle puzzle.

Both of these books show that the study of population cycles is a stimulating field, with much data and several plausible hypotheses needing to be tested by specifically designed and well-planned experiments. Although both books will provide active scientists in the field with much to think about — and to disagree with — I would not recommend either of them as textbooks, as they both seem too biased or narrow to serve a general educational purpose.

They both express rather similar perspectives, for instance in emphasizing feedback interactions between different trophic levels (between plant and herbivore, predator and prey, and parasite and host). But do such trophic interactions provide a general explanation of population cycles? In my view, much more work (involving all elements of the research programme advocated by Turchin) is needed to settle this question.

Turchin claims that ecology has become a mature science, but I think it is still maturing, and as such is all the more exciting to work in — it is during the maturing stages of any life cycle that the interesting developments happen. I am quite sure that Elton and the group around him in the Bureau of Animal Population, which he set up at Oxford University, would have agreed and been happy about the development of what they started three-quarters of a century ago.