Three earlier reviews of my recent book Marine Parasitology and one review of my book Nonequilibrium Ecology are mentioned in the relevant posts (NE, MP). They were the only ones available until a few days ago. A second one for Nonequilibrium Ecology has now been published in Ecology 88, No.5, 1338-1339.
The reviewer concludes that
“………………. Nonequilibrium ecology is a useful book providing much food for thoughtâ€”even for ecologists considering selection and competition as factors of prime importance (like myself), it is healthy to be confronted with arguments and evidence to the contrary.”
However, he draws attention to a number of “deficiencies”, on which I comment in the following. Some of the reviewer’s statements are plainly wrong or misleading. I address these points in the order in which they are discussed in the review.
1) The reviewer writes that I view the terms equilibrium thinking and competition thinking as almost synonymous. There has been much debate on the meaning and definition of equilibrium and nonequilibrium, and I have given not an exhaustive, but a fairly comprehensive historical review of the concepts in the book, which makes it clear that there are very wide differences of opinion on this. It is obvious from the discussion in Chapter 1 of the book and from the various examples given, that I do not view equilibrium and competition thinking as being almost synonymous, even though many authors consider density dependence (usually thought to be due to competition) as a major characteristic of equilibrium.
In this context, according to the reviewer,”Viewed this way, empirical studies showing that populations are kept at equilibrium by predation pressure are viewed as evidence against equilibrium ecology. Conversely, limit-cycle oscillations and other complex behavior are subsumed under the heading “equilibrium dynamics”… This also is incorrect. On pages 13-15 and elsewhere I discuss examples in detail, which show that predation and parasitism may regulate host populations, leading to apparent equilibrium.
2) The reviewer further accuses me of placing too much emphasis on marine parasites, a “bias” which I supposedly “justify” by my own expertise and by the fact that parasites represent probably the largest component of the Earth’s fauna and should therefore not be ignored when determining the mainstream of ecological thought. He writes that even hard-core competition biologists will readily agree that parasites are often more strongly limited by their hosts than by their conspecifics, and that host-parasite interactions have an inherent tendency for exhibiting nonequilibrium behavior. He further claims that “Although they are of obvious ecological relevance, host-parasite systems just do not form the arena for the discussion on the relative importance of competition.”
I believe that these comments by the reviewer are misleading. Chapters 7-9 deal with detailed examples, of these, four sections with 19 pages are on marine parasites, one with 3 1/2 pages is on ectoparasitic insects (plant herbivores), seven sections with 47 pages deal with other groups. The two large chapters on interspecific competition make only some reference to parasites, and other chapters even less. Further, the comment that I justify my “bias” towards marine parasites by my expertise in the field, applies only to the autoecological example in Chapter 10, where I use Aspidogastrea, and one of them a freshwater species, and give as ONE reason the fact that I have done much work on them. The ratio parasites/free-living species discussed corresponds roughly to what one finds in nature. Importantly, contrary to the reviewerâ€™s statement, in almost all cases I do not analyse host parasite interactions, but interactions between species in parasite communities. Furthermore, why should hard-core competition ecologists a priori agree that parasites tend towards nonequilibrium? Should one not analyse the data first, as done in my book? Moreover, the section on “Larval trematodes in snails” (pp.131-134) clearly shows that parasite communities, like free- living ones, may be strongly structured by interspecific competition. Indeed, many parasite ecologists believe in the great importance of competition in structuring communities. But importantly, as stated in the Introduction to my book, a majority of authors are prejudiced towards equilibrium assumptions because they select systems in which equilibrium is expected. The whole idea of the book is to remedy this situation by using examples from groups where equilibrium may be expected, and others from groups where it is not expected. As it turns out, there really are significant differences in equilibrium/nonequilibrium between groups, and this is explained in chapter 11 (Fig. 11.1).
3). The reviewer objects to some of my theoretical statements, foremost to my statement in the legend to Fig.1.3 that “x never reaches carrying capacity” in the bifurcation diagram of the discrete-time logistic growth model. Different interpretations are possible and I do not wish to comment on this further, except to state that two reviewers and the journal editor, all of whom have considerable experience in chaos theory, accepted my interpretation in a paper on chaos (Rohde and Rohde 2001 : Fuzzy chaos: reduced chaos in the combined dynamics of several independently chaotic populations. American Naturalist, 158, 553-55). Whichever interpretation one uses, it does not affect the validity of the conclusions (at which I have arrived in several earlier papers not using the bifurcation diagram in Fig. 1.2), i.e., that large oscillations in population density can occur even when conditions are constant, and that equilibrium may be established well below the saturation level.
The reviewer further criticizes me for applying the packing rules of Ritchie and Olff to fish parasites. He believes “that there is no reason to assume that the parasite fauna satisfies the assumptions of the model which was built for competing herbivores in a fractal landscape”. Within the context of the packing rules, I do not write that “that competition for limiting resources has not been important in evolution” (as stated by the reviewer), but much more cautiously that “these negative results support the view” (also shown by various other tests) “that parasites of marine fish do not live in saturated structured communities, but rather in assemblages not significantly structured by interspecific competition”. Ritchie and Olff did apply their packing rules not only to herbivores in a fractal landscape, as implied by the reviewer, but to plants as well. There is no a priori reason that they should not apply to parasites, whose “landscape”, because of their small size, may not appear patchy and fractal to us, but may in fact be so for many of them. It is important here to realize that parasites living in the same microhabitat may differ vastly in size! The packing rules provide an excellent model to test for competition in a fractal landscape for any group of plants and animals. One should not make any a priori assumptions. What is the point in testing if the answer has to be known in advance? Furthermore, Ritchie and Olff clearly were after something universally applicable. They write: “Spatial scaling laws provide potentially unifying first principles that may explain many important patterns of species diversity” and ” Packing rules yield a theory of species diversity”. Even if variability of the resource density and R(w) as an independent biological property are included in the model, there is no reason to assume that it is not applicable to parasites.- Most importantly, I am convinced the reviewer agrees with me that one should never base conclusions on a single model. Concerning the data analysed using the packing rules of Ritchie and Orff, they were also analysed using a variety of other methods, and they all led to the same conclusion: fish parasites live in communities largely unstructured by interspecific competition.
Finally, the reviewer criticises me for stating that the metabolic theory of ecology does not rely on equilibrium assumptions. In fact, the theory (as developed by the time when the book was submitted, and I do not believe now) “does not rely on equilibrium assumptions”, a belief which is shared by the one of the chief architects of the theory whom I contacted (see also Allen, A.P. and Gillooly, J.F. 2007. The mechanistic basis of the metabolic theory of ecology, Oikos in press). This does not mean that the theory does not make certain predictions on when equilibrium and nonequilibrium conditions may arise, but this is something quite different from “relying” on equilibrium assumptions.
Some appendices and Errata of the book are available at: