DOCSLIB.ORG

16 Biodiversity and the Balance of Nature

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
16 Biodiversity and the Balance of Nature 16 Biodiversity and the Balance of Nature S.L. Pimm 16.1 What Biodiversity Is Good for As we destroy biological diversity, what else are we doing to the environ­ ment, what is being changed, and how will those changes affect us? One part of the answers to these questions is provided by Lawton and Brown's consideration of redundancy (Chap. 12). Part of what the environment does for us involves "ecosystem services" - the movement of energy and nutrients through the air, water, and land, and through the food chains (Ehrlich, Foreword). Just how much biological diversity we need to keep the movement at approximately natural levels is a question of critical im­ portance. Nonetheless, it is not a question that is commonly asked. A major synthesis of theories on the dynamics of nutrient cycling (DeAngelis 1991) devotes little space to the consequences of changes in the numbers of species per trophic level: It is the number of trophic levels that receives the atten­ tion. One might well conclude that, over broad limits, ecosystem services will continue to be provided, so long as there are some plants, some animals, some decomposers, and so on. Lawton and Brown conclude that numerous species are redundant. One cannot be confident about this conclusion, for the evidence one way or another is still very limited. Even if it were correct, it would not provide a complete answer to the questions of the value of biological diversity. The conclusion only deals with the average movement of material; ecologists have long recognised that diversity may be important in determining the variability and persistence of ecological processes and their resistance to external changes. Following the loss of diversity, one often hears ideas such as: the loss threatens ecological integrity; the environment becomes more fragile as diversity decreases; ecosystems have some capacity to resist change or to recover from it, that is, there is some balance of nature or stability, and this balance is affected by the loss of diversity. So what do all these terms mean and what scientific principles do they encompass? One illustration of these concerns involves the fisheries in the Great Lakes of North America. For over a century and a half, these lakes have been subjected to pollution, intense fishing, the loss of several native species, E.-D. Schulze et al. (eds.), Biodiversity and Ecosystem Function © Springer-Verlag Berlin Heidelberg 1994 348 S.L. Pimm and the deliberate and accidental introduction of other fish species. For example, the Lake Erie fishery between 1920 and 1950 was dominated by blue pike (33% of the yield by weight), lake herring (14%), and yellow perch (15%); by 1979-1983 the first two species had been lost, and rainbow smelt accounted for 56% of the yield (Loftus et al. 1987). In contrast, the average total landings increased slightly (about 30%). Similar figures are noted for the other lakes. Simply, the secondary productivity of these ecosystems has changed remarkable little during a period when the com­ position changed greatly. Considerable experience with the lakes and their fisheries (see the papers in Christie and Spangler 1987) reveals that there is no comfort in the similarity of the total yields. In part, this is because the blue pike are worth much more per kilogram than rainbow smelt. (In reality, the species do matter; we cannot reduce all ecology to flows of nutrients.) More important is the sense that the ecosystems in the lakes no longer function in the same way as they did in the past. It is not always clear what these changes in function are, but they are of considerable concern. They involve the internal dynamics of the lakes and they are independent of such summary statistics as overall yield. So just what is diversity good for? It seems to have something to do with what we call stability. Ecological stability has a history, and I want to review it briefly to set the context of what follows. 16.2 A History of Ecological Stability In his 1958 book, The Ecology of Invasions by Animals and Plants, Elton wrote: I will now try and set out some of the evidence that the balance of relatively simple communities of plants and animals is more easily upset than that of richer ones; that [the balance] is more subject to destructive oscillations in populations, especially of animals, and more vulnerable to invasions.... For if this can be shown to be anywhere near the truth, it will have to be admitted that there is something very dangerous about handling cultivated land as we handle it now, and [it will be] even more dangerous if we continue down the present road of 'simplification for efficiency'. Elton then discuses the evidence for his assertion that simple communities are less stable than complex ones. His first evidence comes from "mathe­ matical speculation about population dynamics." Simple models of a pred­ ator and its prey or a single host and its parasite have population densities that "fluctuate in numbers considerably." Such fluctuations would mean that in simple communities, populations would "never have constant population levels, but would be subject to periodic 'outbreaks' of each species". Elton's second line of evidence was from laboratory experiments that made the Biodiversity and the Balance of Nature 349 same point. The third piece of evidence is that the natural habitats on small islands seem to be much more vulnerable to invading species than those of continents. His fourth argument was that "invasions and pest oubreaks most often occur on cultivated or planted land - that is, habitats and communities very much simplified by man". His fifth argument was similar. Insect out­ breaks, Elton claimed, were a feature of simple temperate forests but not of complex tropical forests. His sixth argument seems to recapitulate the earlier ones: insect pests are more likely to invade and become a nuisance in orchards, especially following spraying designed to eliminate the pests. Elton's arguments have received extensive discussion. The models and the laboratory experiments available to Elton looked only at simple systems: Models of, or experiments with, complex systems were not available as a control. The data on invasions were compelling, but comparative studies of population fluctuations were nonexistent. Moreover, Elton discussed a range of very different phenomena: population variability, the potential abundance of a species, the rate at which a pest species might increase in numbers after the removal of its predators, how readily communities may be invaded, and the extent of damage the invading species cause. Yet this range is perhaps the most remarkable part of Elton's argument. Ecologists should be thinking about different kinds of stability: population variability, population recovery, ease of invasion, and consequences of invasion. All are ways of characterizing population and community changes to facilitate comparisons. Moreover, Elton considers a factor called "complexity" that should determine "stability" and the importance of their interdependence. Notice something else: the effect of humans is to destroy stability, and with the loss of stability comes the loss of species, and so less complexity. Systems that are less complex are less stable, more likely to lose species, and so on. 16.2.1 Controversy The relationships between stability and complexity have generated a large literature (Pimm 1982, 1984). Controversy arose because of the many meanings of "stability" and "complexity" (Pimm 1984). Elton and more recent theoretical and empirical ecologists have used the word "stability" to mean at least five different things (Pimm 1984, 1991b). Theoreticians have considered stability in its strict mathematical sense, where systems are either stable or not. So given May's (1974) argument that what we observe most often in nature will be stable systems, the theoretical results make predictions about the kind of communities we observe and those that we do not. The other four definitions of stability do permit comparisons of dif­ ferent existing systems, however, and these were the concerns of empirical ecologists. 350 S.L. Pimm 1.2 1.0 E .;:::J 0.8 .c 0.6 ::J 0'" 0.4 Q) E 0.2 o... -c: 0.0 f----;:=---=---=:a==.---.Ik-~tr_.....,.r___...-...._- 0 :;:; -0.2 III .~ -0.4 0 -0.6 0 2 4 6 8 10 Time (t) 140 40000 .c l/I 120 ::l 30000 III .c ::l t- iii Cl Q. C 100 ::l 0 al C/) 20000 "0 "0 80 ?: ?: 0; ·iii c c .. .. 10000 Q Q 60 40 0 10 20 Year (starting 1960 for Song Thrush, 1890 for Bupalus) Fig. 16.1. Above, Two model populations returning to equilibrium density (set at zero) from the same initial displacement at +0.5. One population (open triangles) is much less resilient than the other (closed triangles) and returns more slowly to equilibrium. Below, Extent of year-to-year variabilities for different species: song thrush (open squares) in English farmlands (units of density relative to 100 in 1966) and the moth Bupalus (solid circles) in German forests (numbers per hectare of forest floor) To complicate matters further, different studies looked at "stabilities" at different levels of ecological organization. Theoretical studies of whether interacting sets of species will be stable consider whether the densities of all those species return to equilibrium or not. To ask how long a community persists before it is invaded is to ask how long the community composition lasts. Such a discussion ignores fluctuations in the abundance of species and looks only at the species list itself. In contrast, McNaughton (1977; Chap. 17) placed his emphasis on how much the total biomass changed and not on which species were involved in the changes. Therefore, we can discuss the stability of populations, community composition, or community biomass.
Load more

Recommended publications
  • Restoring Nature :Perspectives from the Social Sciences and Humanities / Paul H
    FVUR NC-4902-2 3.23 AVAILABLE RESTORING NATURE .._._ Perspectives from the Social Sciences _i_._aaQ_ and Humanities g_• _o ot_ _._.__._ ° _° _,._ • "_ EDITED BY PAUL H. GOBSTER AND R. BRUCE HULL ISLANDPRESS Washington, D.C. • Covelo, California Copyright © 2000 by Island Press All rights reserved under International and Pan-American Copyright Conventions. No part of this book may be reproduced in any form or by any means without permission in writing from the publisher: Island Press, 1718 Connecticut Avenue, N.W.., Suite 300, Washington, DC 20009. ISLAND PRESS is a trademark of The Center for Resource Economics. No copyright claim is made in work by the following employees of the federal government: Susan C. Barro, Carol Raish, and Herbert W.. Schroeder. Grateful acknowledgment is made for permission to include the poem "Volunteer Revegetation Saturday"© 1999 by Cindy Goulder. Published by permission of the poet. Library of Congress Cataloging-in-Publication Data Restoring nature :perspectives from the social sciences and humanities / Paul H. Gobster and R. Bruce Hull, editors. p. cm. Includes bibliographical references and index. ISBN 1-55963-767-6 (cloth :alk. paper) --ISBN 1-55963-768-4 (pbk: : alk. paper) 1. Environmental sciences--Philosophy. 2. Restoration ecology. 3. Environmental management. I. Gobster, Paul H. II. Hull, R. Bruce. GE300 .R47 2000 363.7---dc21 00-009375 Printed on recycled, acid-free paper {_ Manufactured in the United States of America 10987654321 CONTENTS Acknowledgments xiii Introduction: Restoring Nature: Human Actions, Interactions, and Reactions 1 Paul H. Gobster PART1.PHILOSOPHYAND RATIONALEOF RESTORATION 1.
    [Show full text]
  • Is Ecological Succession Predictable?
    Is ecological succession predictable? Commissioned by Prof. dr. P. Opdam; Kennisbasis Thema 1. Project Ecosystem Predictability, Projectnr. 232317. 2 Alterra-Report 1277 Is ecological succession predictable? Theory and applications Koen Kramer Bert Brinkman Loek Kuiters Piet Verdonschot Alterra-Report 1277 Alterra, Wageningen, 2005 ABSTRACT Koen Kramer, Bert Brinkman, Loek Kuiters, Piet Verdonschot, 2005. Is ecological succession predictable? Theory and applications. Wageningen, Alterra, Alterra-Report 1277. 80 blz.; 6 figs.; 0 tables.; 197 refs. A literature study is presented on the predictability of ecological succession. Both equilibrium and nonequilibrium theories are discussed in relation to competition between, and co-existence of species. The consequences for conservation management are outlined and a research agenda is proposed focusing on a nonequilibrium view of ecosystem functioning. Applications are presented for freshwater-; marine-; dune- and forest ecosystems. Keywords: conservation management; competition; species co-existence; disturbance; ecological succession; equilibrium; nonequilibrium ISSN 1566-7197 This report can be ordered by paying € 15,- to bank account number 36 70 54 612 by name of Alterra Wageningen, IBAN number NL 83 RABO 036 70 54 612, Swift number RABO2u nl. Please refer to Alterra-Report 1277. This amount is including tax (where applicable) and handling costs. © 2005 Alterra P.O. Box 47; 6700 AA Wageningen; The Netherlands Phone: + 31 317 474700; fax: +31 317 419000; e-mail: [email protected] No part of this publication may be reproduced or published in any form or by any means, or stored in a database or retrieval system without the written permission of Alterra. Alterra assumes no liability for any losses resulting from the use of the research results or recommendations in this report.
    [Show full text]
  • The Science of the Struggle for Existence on the Foundations of Ecology
    P1: FpQ CY239/Cooper-FM 0 52180432 9 July 29, 2003 15:6 The Science of the Struggle for Existence On the Foundations of Ecology GREGORY J. COOPER Washington and Lee University v P1: FpQ CY239/Cooper-FM 0 52180432 9 July 29, 2003 15:6 published by the press syndicate of the university of cambridge The Pitt Building, Trumpington Street, Cambridge, United Kingdom cambridge university press The Edinburgh Building, Cambridge CB2 2RU, UK 40 West 20th Street, New York, NY 10011-4211, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia Ruiz de Alarcon´ 13, 28014 Madrid, Spain Dock House, The Waterfront, Cape Town 8001, South Africa http://www.cambridge.org c Gregory J. Cooper 2003 This book is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2003 Printed in the United Kingdom at the University Press, Cambridge Typeface Times Roman 10.25/13 pt. System LATEX 2 [TB] A catalog record for this book is available from the British Library. Library of Congress Cataloging in Publication data Cooper, Gregory John. The science of the struggle for existence : on the foundations of ecology / by Gregory Cooper. p. cm – (Cambridge studies in philosophy and biology) Includes bibliographical references (p. ). ISBN 0-521-80432-9 1. Ecology – Philosophy. I. Title. II. Series. QH540.5.C66 2003 577–dc21 2002041441 ISBN 0 521 80432 9 hardback vi P1: FpQ CY239/Cooper-FM 0 52180432
    [Show full text]
  • Metaphor and Equilibrium in Population Ecology
    Biology and Philosophy 16: 463–479, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands. The “Balance of Nature” Metaphor and Equilibrium in Population Ecology KIM CUDDINGTON Department of Ecology and Evolutionary Biology University of Connecticut 75 N. Eagleville Rd., U-43 Storrs, CT 06269-3043, U.S.A. [email protected] Abstract. I claim that the “balance of nature” metaphor is shorthand for a paradigmatic view of nature as a beneficent force. I trace the historical origins of this concept and demonstrate that it operates today in the discipline of population ecology. Although it might be suspected that this metaphor is a pre-theoretic description of the more precisely defined notion of equi- librium, I demonstrate that “balance of nature” has constricted the meaning of mathematical equilibrium in population ecology. As well as influencing the meaning of equilibrium, the metaphor has also loaded the mathematical term with values. Environmentalists and critics use this conflation of meaning and value to their advantage. This interplay between the “balance of nature” and equilibrium fits an interactionist interpretation of the role of metaphor in science. However, it seems the interaction is asymmetric, and the “balance of nature” metaphor has had a larger influence on mathematical equilibrium than vice versa. This disproportionate influence suggests that the metaphor was and continues to be a constitutive part of ecological theories. Key words: ecology, equilibrium, language, metaphor, science Introduction The “balance of nature” metaphor has influenced the development and continued practice of ecology. This metaphor has been used to invoke ideas such as a divinely determined stability, orderliness and predictability in natural systems.
    [Show full text]
  • Predators: the Balance of Nature”
    THE BALANCE OF NATURE PREDATORS Chewonki’s Balance of Nature presentation explores the adaptations and features of predators and looks at why predators are often feared and persecuted by people throughout the world. Using a slide show and various activities, we will examine the important function predators play in the natural world. We will discuss these animals’ crucial role in the food chain and identify predator-prey relationships in different habitats. Students will closely observe a few of Maine’s predators, including a mounted coyote, as well as several live non-releasable predatory animals from around the world. This program is designed for grades 3 and up and can compliment classes in biology, environmental issues or Maine studies, or be successfully integrated into any curriculum area, such as language arts, math, social studies or art. Equipment and Room Requirements • Classroom or multi-purpose room space is fine. • Students should sit at desks or in seats to easily view slides and displays. • Presentations can be done at a single location or in individual classrooms if 15 minutes is allowed between presentations. • The maximum group size is 30. • Teachers must be present in the room during the program. • Please have students wear name tags provided in packet. Note: Permits are required for most of the specimens (living and stuffed) that are used in Chewonki Traveling Natural History Programs and students are reminded of the legal limitations of private collections. All of our living animals are non-releasable because of injuries or were captive raised before arriving at Chewonki. No animals have been harmed or taken specifically for use in Chewonki programs.
    [Show full text]
  • The Present Status of the Competitive Exclusion Principle
    TREE vol. 1, no. I, July 7986 could be expected to rise periodically some other nuclear power stations 6 Bumazyan, A./. f1975)At. Energi. 39, (particularly during the spring snow are beinq built much nearer to these 167-172 melting) for many years. cities than the Chernobyl station to 7 Mednik, LG., Tikhomirov, F.A., It is very likely that the Soviet Kiev. The Chernobvl disaster will Prokhorov, V.M. and Karaban, P.T. (1981) Ekologiya, no. 1,4C-45 Union, after some initial reluctance, affect future plans, and will certainly 8 Molchanova, I.V., and Karavaeva, E.N. will eventually adopt the same atti- make a serious impact on the nuclear (1981) Ekologiya, no. 5,86-88 tude towards nuclear power stations generating strategy in many other 9 Molchanova, I.V., Karavaeva, E.N., as was adopted by the United States countries as well. Chebotina. M.Ya., and Kulikov, N.V. after the long public enquiry into the (1982) Ekologiya, no. 2.4-g accident at Three Mile Island in 1979. 10 Buyanov, N.I. (1981) Ekologiya, no. 3, As well as ending the propaganda of Acknowledgements 66-70 the almost absolute safety of nuclear The author is grateful to Geoffrey R. 11 Nifontova, M.G., and Kulikov, N.V. Banks for reading the manuscript and for power plants and labelling them as (1981) Ekologiya, no. 6,94-96 comments and editorial assistance. 12 Kulikov, N.V. 11981) Ekologiya, no. 4, ‘potentially dangerous’, the US gov- 5-11 ernment also recommended that 13 Vennikov, V.A. (1975) In new nuclear power plants be located References Methodological Aspects of Study of in areas remote from concentrations 1 Medvedev, Z.A.
    [Show full text]
  • Invasive Species and Natural Function in Ecology
    Invasive Species and Natural Function in Ecology Christopher Hunter Lean1 Abstract If ecological systems are functionally organised, they can possess functions or malfunctions. Natural function would provide justification for conservationists to act for the protection of current ecological arrangements and control the presence of populations that create ecosystem malfunctions. Invasive species are often thought to be malfunctional for ecosystems, so functional arrangement would provide an objective reason for their control. Unfortunately for this prospect, I argue no theory of function, which can support such normative conclusions, can be applied to large scale ecosystems. Instead ecological systems have causal structure, with small clusters of populations achieving functional arrangement. This, however, does not leave us without reason to control invasive species. We can look at the causal arrangement of ecological systems for populations that support ecological features that we should preserve. Populations that play a causal role in reducing biodiversity should be controlled, because biodiversity is a good all prudent agents should want to preserve. 1. Department of Philosophy, University of Sydney, A14 Quadrangle, 2006, Australia. For correspondence please send enquiries to [email protected]. 1 ‘Your heart has great value to your body. No one would argue that point. Does a mosquito population have similar value to a marsh?’ John Kricher, The Balance of Nature: Ecology’s Enduring Myth, p .19 1. Introduction There has been a persistent hope that populations in ecological systems have natural normativity, just as organs do in a body. Lungs, hearts, and kidneys have a relatively uncontroversial interpretation as possessing functions and malfunctions, these are normative in the sense that there is something they should be doing.
    [Show full text]
  • Ecosystem Learning Sheet Solution 4 1. Why Are Nutrient Cycles In
    Ecosystem Learning Sheet Solution 4 1. Why are nutrient cycles in nature called biogeochemical cycles? A1. Nutrient cycles in nature are called biogeochemical cycles because the elements move cyclically from the environment to living organisms and back to the environment. 2. State the function of a reservoir in a nutrient cycle. A2. The function of a reservoir in a nutrient cycle: It meets the deficit which occurs due to the imbalances in the state of influx and efflux of nutrients. Carbon cycle: Thus, they pass the carbon compounds along the food chain. Most of the carbon these animals consume however is exhaled as carbon dioxide. 3. Outline salient features of carbon cycling in an ecosystem. A3. Salient features of carbon cycling are as follows 1. Carbon cycling occurs through atmosphere, ocean and through the living and dead organisms. 2. Most of the carbon is fixed by plants during the process of photosynthesis and returns to the atmosphere in the form of CO2 during respiration. 3. Burning of wood, forest fire and combustion of organic matter, fossil fuel, and volcanic activity are some other sources of releasing CO2 in the atmosphere. An outline of C‐cycle is depicted in the figure given below: 4. Explain the phosphorus cycle A4. Weathering. Since the main source of phosphorus is found in rocks, the first step of the phosphorus cycle involves the extraction of phosphorus from the rocks by weathering. Absorption by Plants and Animals. Return to the Environment via Decomposition. 5. The nutrients are never lost in the ecosystem but are recycled back in time and again the cycles continue indefinitely Answer the following questions on the basis of above information.
    [Show full text]
  • Food Chain Checkers
    3FTPVSDFTGPS5FBDIFST Lesson Plans and Activities for the Classroom www.windows2universe.org food chain checkers Summary Students play a game that models dynamics of a simple food chain, then they improve the model by making their own Materials rules that better account for the ways that food chains work. (For each group of four) Source Windows to the Universe activity by Lisa Gardiner • Checkerboard Grade Level 5-9 • 24 Diatom game pieces • 24 Copepod game pieces Time 15 minutes prep time • 24 Herring game pieces One or two 50-minute class periods • 24 Whale game pieces Student • Students will learn that food chains connect organisms • Food Chain Checkers Learning within an ecosystem. worksheets for each student Outcomes • Students will learn that food availability can cause (double-sided) changes in population size. • Optional Graphing • Students will learn that the size of populations in a bal- Populations over Time anced ecosystem stay somewhat constant over time. worksheet for each student • Students will learn that models can be used to represent (double-sided) the natural world and that improvements to models al- • Colored pencils for optional low us to more accurately represent natural conditions. graphing activity National • 5-8 Content Standard C: Populations and Ecosystems Standards • 9-12 Content Standard C: Interdependence of Organisms • Benchmarks: 5A/5 and 5E/2 Preparation: 1. Copy and cut apart game pieces from the template (last page). You will need two copies of the template for each group of students. 2. Copy Food Chain Checkers worksheet (pages 4 and 5) and, if you wish, the optional Graphing Populations over Time worksheet (pages 6 and 7) for a more quantitative activity.
    [Show full text]
  • Flow Learning "Joseph Cornell
    Flow Learning "Joseph Cornell Awake Enthusiasm (Stage 1) / Focus Attention (Stage 2) Direct Experience (Stage 3) Share Inspiration (Stage 4) Notes on Flow Learning – Joseph Cornell Five tenets of becoming a good nature instructor Joseph Cornell suggests in his book, Sharing Nature with Children that there are five tenets for teachers and guides: 1. Teach less, and share more. 2. Be receptive. 3. Focus the child's attention without delay. 4. Look and experience first; talk later. 5. A sense of joy should permeate the experience. Explanations of the Flow Learning Model 1. Awaken Enthusiasm - Children learn if the subject matter is meaningful, useful, fun, or in some way engages their emotions. Time spent in creating an atmosphere of curiosity, amusement, or personal interest is invaluable because once students' enthusiasm is engaged, their energy can be focused on the upcoming lesson or experience. 2. Focus Attention - Some students' minds can be compared to a team of wild horses running out of control. Without concentration no true learning can take place. The activities in this stage challenge the players in fun and creative ways. To successfully meet these "challenges" the players have to concentrate on one of their physical senses. In doing so, they become more calm, observant and receptive to their surroundings. 3. Direct Experience - Once students' interest and energy is awakened and focused, the stage is set for deeply experiencing nature. These absorbing, experiential activities have a dramatic impact that involves people directly with nature. These games help us discover a deep, inner sense of belonging and understanding. If people are to develop a love and concern for the earth, they need these direct experiences; otherwise, their knowing remains remote and theoretical and never touches them deeply.
    [Show full text]
  • PATTERN and the BALANCE of NATURE 31 Leigh Van Valen
    PATTERNAND THE BALANCEOF NATURE 31 Leigh Van Valen Department of Biology University of Chlcago Chicago, Illinols 60637 @.!: SomemaJor ecological patterns indicate that the herbivore trophic l-evel (as defined) is regulaEed ln the Long run by food. Three Levels of fac- tors of population control" must be clearly dlstlnguished and have different evolutionary consequences. The remarkably regular evo1utlon of mammaLlan body size on isLands needs study. A consideration gf various possibllities does not cLearLy resolve the Enigma of Balance: Hori can it be that some species regulated even uLti.mateLy by food do not perlodically greatly re- duce their food supply by overeating? J Introduction The subjeet of thls paper ls one that is easy to gl-oss over. It has a remarkable propensity for encouraging superficial thought, and so is often regarded as trivial. Yet it is one of the most important well-deflned prob- lems in ecology. It has unexpectedly deep roots, and their ramlfications underly apparently quite unrelated matters. Many anslrers seem pLausible until they are put lnto a broader context. My argument is necessarlly con- voluted and branched; most of the notes are an integral part of the argu- ment but are separated for ease of readlng. I have found the problem lntel- Lectually more difficuLt than any other I have considered, including that of the preceding paper (Van Valen, 1"973b). Tn their well-known paper' Hairston, Smith and Slobodkin (1950i = HSS) proposed, among other points, that in terrestrial communities the dominant herbivores are predator-limited while dominant predators are food-limlted. Murdoch (1966) and Ehrlich and Birch (L967) criticized HSS; most of thelr arguments were adequately met by Slobodkin, Smith, and Haireton (L967; = SSH).
    [Show full text]
  • Bill Williams River National Wildlife Refuge Environmental Education Programs
    Bill Williams River National Wildlife Refuge Environmental Education Programs Create an Animal (Amazingly Astounding & Astonishingly Awesome Animal Adaptations) Students will become aware of the different adaptations that animals have in order to survive in the desert Students will create their own animal based on physical and behavioral adaptations The Hidden World of Camouflage Students will learn about the many ways predator and prey animals use camouflage to survive Seed Olympics Students will learn about the journey of a seed, pollination and the lifecycle of plants Using a variety of materials, students will develop a seed dispersal device based on the propulsion technique and compete in the “Seed Olympics” Myth Making: The Night Sky and the Secret Lives of Stars Students will learn of the importance of myth, story and legend on other cultures to explain natural phenomena as they develop an understanding of a star’s lifecycle and the stories behind the most well-known constellations Students will build their own constellation star hero You Animal: Desert animals and their role in the web of life Students will learn about some of the animals native to the Mohave Desert and the differences between herbivores, carnivores, omnivores and insectivores as well as how to identify them by their teeth Students will identify how consumers, producers and decomposers form food chains and webs Going Batty! All about the bats of Arizona and beyond Students will develop an understanding of echolocation, bat physiology, and their contribution
    [Show full text]