ANIMAL ECOLOGY TO-DAY MONOGRAPHIAE BIOLOGICAE EDITORES F. S. BODENHEIMER W. W. WEISBACH Jerusalem Den Haag VOL. VI Springer-Science+Business Media, B.V. 1958 ANIMAL ECOLOGY TO-DAY BY F. S. BODENHEIMER Professor Emeritus of Zoology Hebrew University of Jerusalem Springer-Science+Business Media, B.V. 1958 Dedicated to four great pioneers of animal ecology VICTOR SHELFORD - Urbana RICHARD HESSE - Berlin A. ]. NICHOLSON - Canberra P. A. ERRINGTON- Ames Copyright 1958 by Springer Science+Business Media Dordrecht Originally published by Uitgeverij Dr. W. Junk, Den Haag in 1958. Softcover reprint ofthe hardcover lst edition 1958 Zuid-Nederlandsche Drukkerij N.Y. - 's-Hertogenbosch ISBN 978-94-017-5845-1 ISBN 978-94-017-6310-3 (eBook) DOI 10.1007/978-94-017-6310-3 CONTENTS Chapter page I. Physiological and Ecological Life-Tables 12 Life-intensity and longevity, ecological and physiological life-ex pectation, age structure of populations, ecological ages II. The Life-History and its Ecological Interpretation 40 Physical ecology, life cycles of some lady-beetles, climograms, bonitation of Ceratitis, sense ecology and behaviour III. First Approach to an Analysis of some Animal Popula- tions . . . . . . . . . . . . . . . . . . . . . . 67 Drosophila, aphids, Schistocerca, epidemiology of malaria, voles in Israel, muskrats in Iowa IV. Animal Populations in Equilibrium . . . . . . . . . 112 The case for biotic equilibrium and for weather control, the the orems of VoLTERRA and of NICHOLSON, climatic control, biotic balance, biological control, equilibrium V. Is the Animal Community a Dynamic or merely a Descriptive Conception? . . . . . . . . . . . . . 164 Some definitions, animal communities in sea and on land, superor ganism or empirical combination VI. The Interaction of Environment and of Heredity within the Organism . . . . . . . . . . . . . . . . . . 202 Heredity, population genetics, diapause, sex-determination, geo graphical variation, adaptation VII. WhyHuman Ecology . . . . . . . . . . . . . . . 237 Human fertility, environmentalism in sociology and geography, erosion and similar effects of human activity in forestry, sea fishery, and husbandry INTRODUCTION "Everyone who writes a textbook on any branch of experimental science must set down as many wrong statements as right; he cannot carry out most experiments himself, he must rely on the testimony of others and often take probability for truth. Thus a compendium is a monument of the time when the facts were collected and it must be renewed and rewritten again and again. But while fresh discoveries are accepted and a few chapters improved, others perpetrate misleading experiments and erroneous deductions." from The Theory of Colour, by GoETHE. A colleague1 stated recently in an ecological analysis that he had studied some parts of the population problem intensively and that therefore his findings were based on definite facts; others had been studied by him relatively little, so that on these he offered suggestive ideas based on insufficient evidence; and still others he had barely studied so that he gave in these cases unbased theories. This is a good and sincere statement which should serve to introduce all treatises on the theory of animal populations. Despite the apparently great diversity of opinions in modern population theory, the contrasting views stem mainly from very similar situations. Every one of us who has devoted a lifetime of research on animal populations, has by necessity, because of the limitations of the human mind, proceeded in one way. We all studied one aspect thoroughly, found this special approach fertile, and continued to follow this promising path. This limitation of perspecti ve however has blinded us to greater or lesser degree to other colours or perspectives of nature's picture. We have all, at least during early development, overemphasized one aspect and neglected many others. Once this difficulty is fully recognised, the time has come for an attempt to synthesize all the serious work in our field without any false compromise. We have endeavoured to give here a tentative synthesis, lacking perfection as it may still be, in the hope that we have nonetheless demonstrated that it is both possible and feasible. All different approaches can be united in the study of a population as a whole, thus merely complementing one another. The situation is similar to that described for philosophy by A. J. AYER2, who stated: "I maintain that there is nothing in the nature of philosophy to warrant the existence of conflicting philoso phical "schools". And I attempt to substantiate this by providing a definite solution of the problems which have been the chief sources of controversy between philosophers in the past." Many ways have been ventured by nature to solve the problem of "natural balance", and it is for the common good that almost every path has been trodden, often to the end, with eager stubbornness. Every one of these attempts has caught one corner of the truth, without which we would be unable to comprehend the whole. 8 This book is not written against anyone or against any theory. Everybody has the right to build up his philosophy according to his own experience and suiting his own temperament. We accord due respect to every idea of a serious worker, and have permitted our selves merely that same liberty to build our own philosophy based on our life experiences, principally in the acquisition of facts and prin ciples of animal ecology, as revealed by others as well as ourselves. It is not our intention to convince the reader or produce a "sole truth" of animal ecology. Nature moves in many directions and makes use of all possible roads to the solution of a problem. A good illustration of this point is the climbing of a tree-trunk-spirally by a woodpecker, straight by a squirrel. We present the views of an individual who tried hard to rid himself of prejudices, to learn what seemed to him to be important. The synthesis gained may be of interest to others still seeking their way through the embarrassing multiplicity of natural phenomena. This book is not sophisticated. Its purpose is to be a "common sense" book, with the background of prolonged experience. This combination should be the aim of every young worker in animal ecology. Even if his predilections lead him from autecology to some kind of "biocoenotics" as the basis of his ecological research, he should neglect neither common sense nor experience. In our science, as in every science "All roads lead to Rome" as long as these funda mentals are safeguarded. Between the "Problems of Animal Ecology" (1938, now long out of print) and the present "Animal Ecology To-day" lies a world of experience - ecological facts, the shape of the problems and a maturation in the author's experience. Thus the "Animal Ecology To-day" is practically a new book. We consider the two greatest steps in ecological progress, both connected with the names of A. j. NICHOLSON and P. A. ERRINGTON, to be: (1) The first puts numeric changes of population in the centre of all research; and (2) The second is the principle of compensation. These steps have altered our outlook on animal ecology more than anything else. We may here add another principle, now developing: The difference between homology and analogy must be much more stressed than hitherto. We often considered casual, accidental, non structural parallels and coincidences as causally significant, whereas they actually are merely cases of analogy. As stated above, the principal aim of ecological research is to explore the fluctuation of populations and their (homologous) causes; that of the environment is never an aim in itself, only that of the population. A factor causing high mortality in early youth may be numerically insignificant and have no influence on the size 9 of the reproducing population, as compensatory factors will pro bably replace most or all of this early mortality at later stages. We were thus certainly inaccurate in stating in the "Problems" that all factors are destructive in direct proportion to the percentage per stage destroyed by each. The population flow is much less dependent on any single factor or group of factors at any stage of development, as any part of the population killed by one factor is interchangeable and replaceable by many other factors (density-dependent as well as density-independent ones). The important population base remains the number of reproducing and breeding adults at the season of reproduction, where such a season exists. All losses of the other ages are oflittle importance as they are either pre-or post-reproduc tive. Thus, we may distinguish between two regular fluctuations within every population in time. The one is the regular and steady decimation of the pre- and post-reproductive ages in every gener ation, but the real fluctuations which count are the annual changes in numbers of the population in the reproductive age from one reproducing season to the next one. Ever-increasing importance is ascribed to the organism itself. True, it is an inseparable part of the ecoworld, meaning that it is an integral part of its own (so-called) environment, reacting to it in behaviour and physiology, but never a passive object to the environmental changes. It also influences its own "environment" as by its reactions it actively participates in all actions, re-actions and co-actions of its ecoworld. In the meantime the problems of "synecology" become more and more formal descriptions which are useful schemata of the human mind but which scarcely enter the problems of dynamic ecology, so far mainly restricted to intraspecific population problems. We are now as remote from any decisive conclusion as before, but the continuous rearrangement of our thought leads to what we believe an ever clearer comprehension of the problems of animal ecology. It is dubious whether more could be achieved in principle even in the future of ecology or in that of any other science3. We believe the real solutions of any problem, exceeding mere descrip tion and its coordination, are beyond the grasp of the human mind. Many problems analysed in this book were new twenty-five years ago, when the "Problems" were conceived. We hope that this book takes full account of the advances of ecology during this period. The main problems treated are: The contrast between physiological and ecological longevity still seems one of the best introductions to the problems of animal ecology. The correlations between longevity and life-intensity offer important suggestions from the borderland of physiology and ecology. The ecological interpretation of the life-history of the individual has passed its preliminary stages and becomes an increasingly 10 valuable instrument of prognosis. The analysis of population growth has been studied in the "Problems" by means of Drosophila. Here we give the story of the long road of errors in the theory of density as a decisive population factor, interesting in that as much can be learned from errors as from truth. Some sections analyse the ecolo gicallifehistory of a few other common animals such as Schistocerca greg aria, aphids, the epidemiology of malaria, of Microtus guentheri, outbreaks of the desert locust and of muskrats in Iowa. The problem of so-called biological equilibrium, whose solution has been attempted from many different angles, is now ripe for real synthesis doing justice to them all, provided that nonambiguous definitions are given of basic concepts. Animal communities are generally treated in the same sense as classical plant sociology treats its associations. Our analysis clearly shows that the belief in a supraorganismic integration of life communities is based on intuition - which may be true or not, but is certainly not proven by induction. They remain, in our regions at least, valuable statistical units for description and somehow even for classification. The interaction of environment and heredity is one of the central problems of general biology. We here try to demonstrate the need for close cooperation of genetics and ecology in population dynamics, diapause, sex-determination, geographical variation, and adaptation. It is most improbable that any one of these phenomena may be understood alone, without realising the background of the other. We wish to stress here that phenotype and genotype are not the expression of heredity vs. environment, but that both have a genetical background which is manifested on different ecological backgrounds. It would be misunderstanding the author's intention were this chapter to be taken as a strict support of the Lamarckian theory. All experimental proof is on the side of Mendelism, but all experience together is still far from being con clusive to the exclusion of any other solution. We merely plead for an unprejudiced approach to the problem, but we wish to make it clear that the writer believes that Lamarckism is one ofthe solutions of evolution, that we personally do not believe in any kind of super organismic biocoenotics etc. We think everyone has the right to his own concept of truth. Negation of this freedom of opinion means negation of science. We have added a chapter, "Why Human Ecology?" We intended originally to deal with that problem in a special book but we doubt whether our life-span would suffice for this task. The implications of consistent neglect of our own ecological problems may involve us in future catastrophes far greater than those menacing us in the shape of the H-bomb. These problems should be to-day very much more in the centre of ecological discussion. The human future is at stake. We have omitted here all the problems connected with the spiritual