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Many philosophers, when they turn to biological questions, abandon in favor of captious logomachy the quest for epistemological or ontological enlightenment that, at least in the layman's view, ought to govern their discourse. Grene's argument (1979) forms an unusually flagrant example of this practice. Throughout, she seems unduly obsessed with my use of 'idealism,' as if I had used this term in a vacuum. Grene observes that "such terms as 'idealism' and 'materialism' are so vague that almost anything can be done with t h e m except, one would have thought, to treat such philosophies as those of Democritus." I agree. Where did I mention Democritus? My paper is largely devoted to elucidating the sense in which I claim 'idealism' and other philosophical movements operated in the evolution of ecology, with copious examples from the literature, and my success at least in being understood is witnessed by the number of eminent ecologists whose contributions to this volume, whether in agreement or disagreement with mine, do not manifest difficulty in understanding my arguments or terminology. Perhaps Grene's admittedly sketchy knowledge of the ecological literature causes her difficulty; I had assumed that most of my examples would be known to ecologists and would conjure up in their minds the appropriate sorts of work and governing worldviews. Grene also misses the sense in which I asserted that essentialist thinking in ecology has, by the nature of its essentials, produced deterministic models of population and community structure and function. Again, my examples from the literature include both the essentials and the modelling traditions associated with their study. Two areas of particular concern to Grene in my ecological discussion would also be transparent to one familiar with the literature, though in one instance (Cain's "Species are facts . . . " tirade) I presented sufficient explanatory material that prior expertise ought not Synthese 43 (1980) 79-93. 0039-785718010431-0079$01.50. Copyright © 1980by D. Reidel Publishing Co., Dordrecht, Holland, and Boston, U.S.A.
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to have been necessary. To repeat, Cain, in 1947, was rebelling against the essentialist doctrine of the ideal association which had dominated ecology from Clements' time, and was contrasting the association, of which a concrete example could not even be adduced, with an entity, the species, which at that time was felt to be sufficiently well-defined that one could easily find specific examples in nature, and could fruitfully attempt to describe and to understand their workings. Even today, I would claim, in spite of Raven's recent (1976) attack on the evolutionary species concept, that single-species population ecology from Andrewartha and Birch (1954) through Clark et al. (1967) to the present has served at least animal ecology well, to the point of allowing sufficient prediction for meaningful biological control programs. Grene also objects to my suggestions that Levins' work is in the spirit of Clements as opposed to that of Gleason, and that Levins and Watt are on the same side of this issue. I feel that Levins' models (1968a, 1975), in which the dynamics and even geographic distributions of an individual species are governed by its interactions with the other species in an a priori community of interest, are very much in the spirit of Clements as opposed to that of Gleason; they certainly are not individualistic! And the salient difference, from this perspective, of Watt's models (1968) from those of Levins is that Watt prefers difference equations and computer simulations, Levins differential equations and analytic solutions. Of course these are generally viewed as different traditions (Levins 1968b), but I attempted to show in my paper that their shared assumptions are more important than their differences. Finally, Grene excoriates me, unfairly, I feel, for my discussion of the Darwinian revolution and neo-Darwinian synthesis, in two particulars. My metaphor of the synthesis's sounding "the death knell for Newtonian cause-and-effect determinism in biology" was not meant to imply that causal thinking was thus destroyed, only that billiardball precision in the predictions of transmission genetics was forever precluded. I believe I made it very clear that genetic environmental causality, with predictive (though probabilistic) rules, is very much alive. In fact, the sentence preceding that to which Grene objects is, "The major thrust now, as stated above, is to determine the rules
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(doubtless also probabilistic) by which the genotype and enivronment interact to produce a phenotype." Grene also asks, "Why is the observation of particulate inheritance 'material' while the notion of blending inheritance is necessarily 'ideal'?" I cannot answer that question; certainly I never said such a thing. I said "this belief [in blending inheritance] is readily traced to Darwin's attachment to essentialist, typological thought (Ghiselin 1969)." On p. 161 of the cited reference is a discussion of how Darwin's essentialism hindered his ability to elaborate a particulate theory of inheritance. Although I find the contribution of Levins and Lewontin (1979) thoughtful, provocative, and illuminating, I nevertheless disagree with several of their contentions and also feel that they have occasionally attributed to me viewpoints which I did not intend to espouse. By briefly outlining those areas of difference, and clarifying those of my ideas which were not interpreted as I would have expected, perhaps I can aid in the dialectic discussion which all of us feel would be fruitful for ecology at this time. At the outset, Levins and Lewontin (p. 48) suggest that my attempts to escape the Scylla of the superorganism have led me to the Charybdis of "obscurantist stochasticity and indeterminism." I certainly did not wish to propose ultimate agnosticism regarding the structure and function of collections of biological organisms. Rather, I had hoped to suggest that study of populations as populations had proven useful in many situations in the past, that such study had been largely superseded by a holistic focus on communities without adequate demonstration that cited community traits were truly emergent properties rather than epiphenomena of the component populations, that this supersession was due to several forces, none of which relate to a demonstration that communities a r e emergent entities and some of which stretch back to antiquity, and that study of populations can allow predictive ecological statements but that the predictions must be probabilistic rather than deterministic. Levins and Lewontin feel that I was led astray by confusing reductionism with materialism, idealism with abstraction, and statistics with stochasticity. Their greatest effort to enlighten me is with respect to the first putative confusion, that of reductionism with
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materialism, and in this they are at particular pains to correct my focus on populations to the exclusion of communities. Since I had not intended to urge a dogmatic reductionism I was surprised to be viewed as its apostle. On rereading my contribution I find that I had imparted to it an unduly Manichaean cast, doubtless because I felt myself beleaguered by an overwhelming army of community theorists (cf. my original citations). For this, I apologize. My intent was to suggest that the most parsimonious tenable hypothesis about community level attributes, that they are primarily epiphenomena of component population attributes, had never been sufficiently tested and that where it had (e.g., succession) it had not been falsified. Levins and Lewontin's discussion, however, is so rife with unsupported ex cathedra statements about the behavior of both ecological communities and ecologists that it is far from convincing me that my view is in error. I will list a few, with counter-examples: 1. On p. 49, they claim that reductionists put aside "the reciprocal phenomenon, the reaction and evolution of the environment in response to the species." I would argue that no one, least of all 'population-reductionsts' (among whom I would classify myself), has put aside changes in the physical environment caused by species. The classical explanation, for example, of what drives succession is that each stage changes the physical environment in some way (light, chemistry, etc.) that renders it inimical to that stage, but favorable to the species of another stage. The only change for a populationreductionist would be to emphasize that the physical changes are wrought by individual species, rather than by the community acting as a whole. Drury and Nisbet (1973) exemplify this view. 2. On pp. 49-50, they state that a prey and a predator will approach an equilibrium of numbers by a spiral path in the two dimensional space whose axes are the abundances of the two species. This path is completely unambiguous in the sense that given the location of a point in two dimensional space at one instant of time, a unique vector of change can be established predicting its position at the next instant.
What prey and what predator? Except for laboratory experiments with micro-organisms I know of no prey and predator which approach such an equilbrium of numbers, nor am I aware of any simple
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two-species predator-prey model which has successfully predicted the abundances of both species in a feld setting. Krebs (1978, p. 261) goes even further: "No one has yet found a classical predator-prey oscillation in field populations." Further, I claim that the most commonly observed predator-prey trajectories in 2-space, aside from 'chaotic' ones whose causal mechanisms we are unable to determine from the trajectories themselves (May 1974, Oster 1975, Poole 1977, Beddington et al. 1975), are not equilbria of numbers but approximate cycles of either the stable limit or neutral variety (May 1973). And further that there is little evidence that the few cycles which even approach regularity and are observed in the field are actually governed by the dynamics of the two-species interaction. For at least one oft-cited example (the lynx and hare data), it seems very likely that the hare population cycles independently of that of the lynx, and that when lynx are present their population fluctuations are entrained to those of the hare (Krebs 1978); on islands with no lynx, the hare population cycles just as on the mainland (Keith 1963). 3. On p. 50, they assert that "no new objects of study arise at the community level" in the large-scale computer models of systems ecology. This surely must be news to the systems modellers, who are busy predicting herbivore biomass and energy content (Garfinkel 1962, Patten 1965), community biomass and respiration (Van Dyne 1969), understory biomass and organic layer mass (Odum et al. 1975), ecosystem power flow (Odum 1971), and total community photosynthesis and CO2 flux (Miller et al. 1976). 4. On p. 5I we find that "there is no clear stopping place [with respect to appropriate levels of focus] in the reductionist program." Clear to whom? To me a clear stopping place is a level whose study reveals causal mechanisms for most phenomena at that level, and for which the phenomena of higher levels for the most part are shown to be epiphenomena, with respect to both prediction and causation. I cite many references in my paper plus this note to support my contention that the population level bids fair to satisfy this criterion based on the evidence so far. But should subsequent data falsify this proposition, one will be able to look for a clear stopping place at the level of individual or community.
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5. Levins and Lewontin base their claim that the ecological community is a meaningful whole on its having distinct dynamics (p. 53). This is a statement of belief, not fact; they cite no references, only a plausible scenario of the dynamics of a hypothetical ensemble of species. In fact, as I have noted above, this claim is a testable hypothesis, at least for each putative community, and I have cited evidence from several studies which falsifies it. I do not wish to be dogmatic here, and I readily concede the points that we are dealing in generalities, that different communities may have very different dynamic organizations, and that there may well be communities for which we must study community-level properties as well as those of component populations. But I reject the notion that we can state for any community a priori that a population approach will be insufficient, I object to a scenario based not on data but on intuition, and I particularly object to the presentation of such a scenario as a general truth, or as the necessary framework on which to build a useful and causal ecological model. 6. They add (p. 53) that their scenario of community dynamics renders insignificant the question which I consider to be of great importance-whether communities exist as discrete entities or are abstracted from a continuum of variation. I did not intend this to be the question of great importance. I did depict how this question was critical in the historical development of an alternative to the Clementsian paradigm; each of Gleason's three 1947 converts viewed this as a critical question. As for what I take to be the question of great importance, it is not whether communities are discrete, but rather is two-fold: First, are they sufficiently discrete (sufficiently low migration rates) that it is possible to study them as individual entities rather than as collections of transients? And second, even if they are sufficiently discrete, do they have important emergent properties? For most collections which we conveniently denote as 'communities,' there are not nearly sufficient field data to answer the first question Simberloff 1976a). I have already addressed the second. 7. Levins and Lewontin claim (p. 55) that "the notion of multiple alternative steady states of communities is a natural consequence of the recognition of biological complexity," and adduce the mutual
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exclusion of Solenopsis geminata and Pheidole megacephala ants as an example. If one is willing to accept the degenerate case of two mutually exclusive species as compelling evidence that multiple alternative steady states are an important community trait, I suppose I would have to concur. After all, Park's classic experiments can be construed as consistent with that view; Levins and Lewontin (p. 70) take exactly this tack. I would note, however, that for neither the ant nor the beetle example has the dynamic model with multiple domains of attraction been produced, and further that, should such a model be produced, it is not clear why it would be in principle more testable than the Neyman et al. (1956) stochastic model which Levins and Lewontin view as untestable. They do not explain here exactly what they mean by 'testable,' but if they mean with respect to the underlying causal forces, I eagerly await the experimental protocol involving "small perturbations in the initial age distribution within species, or in the initial actual fecundities of the samples of the beetles in each vial," which could conceivably be enacted and which could in principle falsify the multiple-stable-state hypothesis. I would also observe that much of the data in the literature purporting to show competitively produced mutually exclusive ranges is statistically flawed, and when properly examined show such mutual exclusion to be consistent with a random colonization model (Connor and Simberloff 1979, Simberloff and Connor 1979). Finally, it seems to me that if a few two-species systems constitute the most compelling field evidence available to support the notion that multiple alternative steady states are a salient feature in the organization of nature, one might be pardoned for viewing this notion with skepticism. And the notion would then seem doubly odd as an argument that my reductionist prescription for community ecology is too extreme. 8. Levins and Lewontin (p. 55) assert that there are important community properties which are many-to-one transformations of the properties of constituent populations, which are "interesting objects of study regardless of how they are eventually explained," and which permit communities to be seen as similar despite species substitutions. Interesting to whom, and for what reasons? Since Levins and Lewontin (p. 51) seem to agree with me that material causes are
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the ultimate objects of our investigations, of what interest would these properties be if they should eventually be explained as adventitious rather than emergent? Levins and Lewontin cite Lane (1975) to the effect that some community measures which are manyto-one functions of the species in zooplankton communities persist over time, differ systematically among lakes, and change with eutrophication. Lane (1978) adds that these community measures represent macroscopic, presumably emergent, properties since they "(i) vary less than the original [component population] variables, (ii) are characteristic of a type of community, [and] (iii) vary among different types of communities so that their consistency is not a mathematical artifact." Makarewicz and Likens (1975, 1978), examining Lane's conclusions plus their own data, come to a very different conclusion; they believe the planktonic data are best interpreted as consistent with Gleason's individualistic concept of species association. They found what they interpret as evidence of community structure, but they feel that most of this structure is explained through an understanding of the individual species. The only result which they claim as clearly not epiphenomenal is that the "niche centers have evolved toward dispersion in relation to complex gradients of depth, time, and food . . . . " I cite this limnological example (Levins and Lewontin's only reference for this aspect of community properties) at some length to demonstrate that there is informed dissent from their views among primary workers in the field. Although it is clear that my sympathies are more with Makarewicz and Likens than with Lane in this matter, I would suggest that both sides have failed to test conclusively the parsimonious hypothesis that the species act as individual species. Lane has yet to show that random assemblages of species, subject to various constraints on species distributions and lake species diversity (cf. Connor and Simberloff 1979), do not produce patterns identical to those which she takes as evidence for emergent community structure. Some of her community measures, for example, are logarithmic, so one would expect them to "vary less than the original variables [such as species abundances] "even for random sets of species. And that these community measures "are characteristic of a type of com-
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munity" could be due to the species found in that type of community, functioning as individual species. Makarewicz and Likens, though claiming overdispersion, have not demonstrated it statistically. In their Fig. 2 (1978), for example, three sets of zooplankton species are located in two-dimensional depth × time niche space. If one combines the sets and circumscribes them in a rectangular subset of the space (thus eliminating depth × time combinations which no species appears able to use), leaves the axes scaled as in the figure, and performs a nearest-neighbor analysis of the locations of the niches' centroids (whether or not corrected for the niches' finite sizes as in Simberloff 1979a), one finds that the niches are no more dispersed than a random set would be, with a standard normal variate of .76, P >- .275, 1-tailed. 9. Levins and Lewontin (p. 57) allude to an "empiricist refusal to group, generalize, and abstract" which "reduces science to collecting if not specimens then examples." Which empiricists? If they intend to include me in this category, I object that I am perfectly willing to group, generalize, and abstract. But I suggest that we must do this primarily at the population level to detect and to demonstrate material causes. Reichenbach (1966, p. 75) defines 'empiricism' as the view "that sense observation is the primary source and the ultimate judge of knowledge, and that it is self-deception to believe the human mind to have direct access to any kind of truth other than that of empty logical relations," and suggests (p. 202) that all modern biology is primarily empiricist. Popper (1968, p. 324) asserts, "It can safely be said that empiricism, in some form or other, although perhaps in a modest and modified form, is the only interpretation of scientific method which can be taken seriously in our day." Surely Levins and Lewontin are not claiming that most modern scientists refuse to group, generalize, and abstract? Even the founders of British empiricism were quite willing to classify and abstract, although the specific classifications and abstractions of, e.g., Bacon may seem peculiar and of little value today. 10. Levins and Lewontin deduce, as a rule of community structure and function, that "the more strongly the feeding preferences of species overlap, the less uniform will be their relative abundances, and the greater the fluctuations over time." I know of no spectrum of
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communities for which this has been demonstrated; they cite no evidence. Although a rigorous test of this hypothesis would require data on several communities differing primarily in the degree of food overlap of their component species and I have no such data at hand, I can think of two extensive field studies on single communities which would be very unlikely to support such a generalization. Holmes and Pitelka (1968) examined four widely sympatric, congeneric sandpiper species, found them to have broadly overlapping insectivorous diets (and not to be greatly separated in other obvious ways), and found rather equably distributed abundances and no striking temporal fluctuations. McGowan and Walker (1979) discovered enormous feeding (and other) overlap among species of copepods in the central north Pacific gyre, coupled with highly equable abundances. 11. Another community-level deduction presented, without empirical evidence, as a rule of nature is that "populations which are preyed upon by a specialist will be buffered against changes arising elsewhere in the system and will respond through their age distribution more than through total numbers." Once again, I am skeptical that many data exist which bear on this statement taken as a hypothesis. One excellent counter-example would be the work of Askew (1975 and references therein) and H. Cornell (pers. comm.) on the community consisting of gall-making cynipid wasps on oaks, plus their attendant parasitoids, hyperparasites, etc. Among the parasites are many which are host-specific and others which are polyphagous, and some cynipid species are therefore primarily preyed upon by specialists, others by generalists. Although both abundance and life history data exist, no pattern of either sort claimed by Levins and Lewontin (certain populations buffered; certain populations responding more through age structure than through numbers) has been observed. 12. Levins and Lewontin suggest (p. 59) that one consequence of the individualistic concept of species association would be that "a species is most abundant where the physical environment is closest to its physiologically optimum conditions." They cite two field studies in which this pattern was not observed and point out that there are others known for which species interactions prevent given species
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from being most abundant where the physical conditions would have been optimal. This point is well taken, and I would occasionally agree with their further suggestion that either other species, or a physicalenvironment X other-species interaction, may be critical in determining abundances and ranges. I would argue, however, that the appropriate procedure in each instance is first to test the most parsimonious hypothesis, that species are individually distributed according to their interactions with their physical surroundings, and that only upon falsification of this hypothesis ought one to move on to more complex ones. Further, I would observe that, with respect to geographic range, the individualistic hypothesis is statistically falsifiable in a variety of ways (Pielou 1975a, b, Underwood 1978a, b, Simberloff 1978, 1979b), whereas the falsification of a physicalenvironment X other-species interaction hypothesis would be problematic at best. Finally, I would note the long tradition of successful research demonstrating physical determination of species' abundances and ranges (Krebs 1978, ch. 6-8). 13. Finally, Levins and Lewontin (p. 66) admonish us that "where particular techniques are unsatisfactory, the remedy is likely to be not a retreat from complexity to reductionist strategies but a further enrichment of the theory of complex systems." Which particular techniques are unsatisfactory? For what purposes, and with respect to what organisms? And for all the reasons stated in my original contribution plus this note, I cannot accept the proposition that "further enrichment of the theory of complex systems" is nearly as likely to assist ecology as is thoughtful reductionism. As for my "confusion between idealism and abstraction," I did not intend my original contribution to imply "that abstractions are a form of idealism and that the materialism in science necessarily overthrows abstraction and replaces them (sic) with some sort of 'real' entities . . . " (Levins and Lewontin, p. 66), so they are right to infer (p. 66) that "[I] cannot really mean that all abstractions are to be eliminated." Nor did I ever say this. I endorse their view that "abstraction becomes destructive when the abstract becomes reified and when the historical process of abstraction has been forgotten so that the abstract descriptions are taken for descriptions of the actual objects" (p. 67).
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Parts III and IV of my contribution attempted to depict how this reification is precisely what dominated ecology through the first half of this century, and that at least two important current ecological approaches tend to do the same thing. With respect to "confusion between statistical and stochastic," never did I conclude "that stochastic models are in essential contradiction to predictive models." In fact, I cited several stochastic models whose predictive performance was impressive (especially on p. 24, but also the Tribolium and succession models) and lamented that such models had not received their due attention among ecologists. My phrase "Newtonian cause-and-effect" can be read in either the narrow or wide sense; I meant the narrow. I had intended, by the adjective "Newtonian," to convey the notion of deterministic, billiard-ball, precise mechanics. I certainly did not intend to inveigh against causality, nor to endorse astrology. Since Grene also took my phrase as an argument against causality, it is clear that I was not sufficiently precise; mea culpa. Finally, I must confess to both imprecise terminology and some superficial thinking with respect to the relationships among statistics, idealism, and materialism. Levins and Lewontin convince me that statistics, particularly in the social sciences but also in biology, has at least as frequently served idealism as it has materialism, and I am indebted to them for this explication. I would, however, defend one of my phrases plus my ecological leanings against an interpretation that I fear may be unfairly placed upon them by Levins and Lewontin. First, Levins and Lewontin assert that "statistics does not take 'noise' as its object of study, but on the contrary consists largely of techniques for reducing, discounting, or separating ' n o i s e ' . . . . " This strikes me as unnecessarily contentious. I concede 'noise' to be insufficiently defined and unfortunately value-laden, but I feel that it is clear from context that I meant 'variation' and that I was contrasting statistics to ideal mathematics (which does not recognize the variation as variation or as worthy of study). If statistics does not study 'noise' or variation it is not likely to effect a reduction or separation of it. Secondly, I do not believe that, in my contribution or in my ecological work generally, I have been guilty of attempting to
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use either analysis of variance or regression to separate out and to reify main effects, to treat the main effects as main causes, and to discount the causal i m p o r t a n c e of interactions of variables. M y m e t h a p h o r that noise to the physicist m a y be music to the ecologist is m e a n t to c o n v e y the sense that the frequent scatters of points in ecological regression analysis do not represent error or pathology of any sort, but rather m a y result in completely causal fashion f r o m the welter of forces acting on populations in nature; these forces m a y interact in myriad important ways. Lastly, I would defend myself, at least, f r o m the blanket charge against biologists' use of correlation analysis (p. 74). M y disclaimers that correlation should not be c o n f u s e d with causation are n o t disingenuous, and I believe I have gone further than m o s t (e.g., Simberloff 1976b, Connor and Simberloff 1978) to recognize and to publicize the pitfalls of correlation and to e x p e r i m e n t rather than to correlate w h e r e v e r possible in seeking causation. I take this opportunity to call attention to an interesting article b y Egerton (1973) on the relationship b e t w e e n popular notions of a balance of nature and superorganismic ecological constructs, tracing the f o r m e r b a c k to antiquity. Florida S t a t e U n i v e r s i t y
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