Ecology Ecosystem Ecology
by
J.C. Moore
  • LAST MODIFIED: 28 August 2018
  • DOI: 10.1093/obo/9780199830060-0202

Introduction

Ecosystem ecology is a branch of study and thinking within the ecological sciences that focuses on the ecosystem—a dynamic network of interactions of organisms and their environment—and the importance of these interactions to the organisms and earth system processes. The discipline represents one of two different epistemological approaches within ecology that emerged in the 20th century: a species-centric community-based approach, and a process-centric ecosystem-based approach. Both approaches study the ways in which species interact among themselves and their environment, share a common language, and share a common set of principles. The community-based approach focuses on how species’ distributions and abundances are shaped by their resource needs and tolerances to environmental conditions, and by their interactions with other species. The ecosystem-based approach represents a significant departure in that it considers both the resource needs and tolerances of species and their interactions with other species, but also factors in the contributions that species make to earth system processes (e.g., biogeochemical cycles, climate). The two perspectives are not as mutually exclusive as the phrasing of the approaches suggests, but rather offer different approaches to how we view the environment and communities and the factors that regulate them. In the 21st century, modern ecosystem science includes the influences that humans have as part of ecological communities and as drivers of change in ecological communities. This linkage within the ecosystem perspective of biology affecting the physical environment, and the recent developments that include the social and human dimensions, has positioned the approach as a critical one in understanding the relationship among global processes and the services that ecosystems provide to human well-being that is embodied in the emerging science of sustainability.

General Overview

Ecosystem ecology is a relatively young discipline. Golley 1993 and Coleman 2010 provide excellent reviews of the history of ecosystem science and firsthand accounts of the field’s development. Elements of the foundations of the science go back centuries, but they began to coalesce in the late 19th and early 20th centuries. During the early part of the 20th century, there was a rapid shift from what was considered traditional ecology to what is now recognized as modern ecosystem thinking. The field was formalized in the late 20th century after World War II. Contemporary ecosystem thought has further evolved, and the field now embraces the importance of social and human dimensions. Golley 1993 focuses on the historical development of the field in general, but prior to the establishment and development of the social-ecological perspective. Coleman 2010 traces the development of the field by focusing on the large international and national initiatives that were initiated in response to the International Geophysical Year (1957–1958).

  • Coleman, D. C. 2010. Big ecology: The emergence of ecosystem science. Berkeley: Univ. of California Press.

    DOI: 10.1525/california/9780520264755.001.0001Save Citation »Export Citation »E-mail Citation »

    An easy-to-read accounting of the developments in ecosystem ecology during the latter half of the 20th century. The book is written from a participant’s perspective, providing insights into the advances in ecosystem science and the large-scale initiatives that were undertaken.

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    • Golley, F. B. 1993. A history of the ecosystem concept in ecology. New Haven, CT: Yale Univ. Press.

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      An interesting and thorough description of the history of the ecosystem concept as it developed during the 20th century.

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      Foundational Works

      Tansley 1935 first coined the term ecosystem, defined as the fundamental units of nature formed by the coupling of the interactions among organisms and the physical factors within the environment. The ecosystem concept can be traced back to Möbius 1877 and the idea of biocenosis of communities, the work of Clements 1916 on plant succession, and the contributions of Lotka 1924 and Elton 1927 (both cited under Ecosystem Models) on population growth, biogeochemical cycles, and community development and structure. Möbius coined the term biocenosis to represent a description of the interactions among organisms living in a specific habitat or biotope. Clements took this view a step further by viewing mature communities as entities in and among themselves, possessing the capacity to reproduce their parts and the ecological succession leading to their development as a form of ontogeny akin to the developmental stages of an individual species. Elton applied the law of thermodynamics to ecological systems, leading to the modern concepts of a food chain and food web, defining them not only in terms of the species that were present, but also of the matter and energy contained within them, as illustrated in his concepts of the pyramids of numbers and biomass, respectively. Tansley’s definition in essence melded the concepts of biocenosis and biotope, and the idea that ecosystems were natural entities shaped by Eltonian principles rather than the Clementian notion of the “superorganism” organization and development.

      • Clements, F. E. 1916. Plant succession: An analysis of the development of vegetation. Carnegie Institute of Washington Publication 242. Washington, DC: Carnegie Institution of Washington.

        DOI: 10.5962/bhl.title.56234Save Citation »Export Citation »E-mail Citation »

        Foundational publication wherein Clements defines a community as a superorganism and the process of succession and community development as a deterministic process that leads to a climax community. The ideas that are presented are dated, but they provide an important context from which the ecosystem perspective emerged.

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        • Möbius, Karl. 1877. Die Auster und die Austernwirtschaft. Berlin: Verlag von Wiegandt, Hemple & Parey.

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          Introduces the concept of biocenosis, or the biological community—organisms living together in a defined habitat. The English translation, The Oyster and Oyster Farming, is available in the U.S. Commission Fish and Fisheries Report, 1880: 683–7510.

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          • Tansley, A. G. 1935. The use and abuse of vegetational terms and concepts. Ecology 16.3: 284–307.

            DOI: 10.2307/1930070Save Citation »Export Citation »E-mail Citation »

            The paper that provides the first modern definition of the ecosystem. Tansley stresses that the ecosystem consists of both living and nonliving (organic and inorganic) components. The ecosystem is presented as a fundamental concept of nature wherein organisms and inorganic components exist in a “relatively stable dynamic equilibrium.”

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            Systems Theory and Information Theory

            Ecosystem ecology has been heavily influenced by the ideas that emerged from information theory, hierarchy theory, cybernetics, and complexity theory (see Tansley 1935 [cited under Foundational Works], Simon 1962, Odum 1969, Allen and Starr 1982, and Waldrop 1992). Tansley rejected the extreme nature of the superorganism concept pushed by Clements (discussed above), but embraced the hierarchical systems thinking that it embodied. In fact, in defining the ecosystem, Tansley referred to them as forming “one category of the multitudinous physical systems of the universe, which range from the universe as a whole down to the atom” (Tansley 1935, p. 299, cited under Foundational Works). Hutchinson 1948 (and other ecologists of the time) became interested in the field of cybernetics, the science of control and communication (Wiener 1948). The term cybernetics was derived from the Greek word kubernetes, meaning steersman or governor, from the radical kuberman, meaning to steer or govern. The concept relies on the flow of information among constituents to control processes within an organized system, and on the notion that the system is in homeostasis or strives toward it. The ideas presented in Odum 1969 generated intense debates over the entire concept of the ecosystem and its purported cybernetic properties. Engelberg and Boyarsky 1979 argued that elements within ecosystems, like predator-prey interactions, are cybernetic, but that ecosystems as a whole are not, because the requisite stability, homeostasis, and feedbacks are endpoints or outcomes of interactions rather than goals by design. Patten and Odum 1981 and McNaughton and Coughenour 1981 countered this reasoning and made the case that an ecosystem is a cybernetic system in that ecosystems possesses coordination, regulation, communication, and control through the information flow embedded in trophic interactions (see Lindeman 1942, cited under Development of Modern Ecosystem Thinking, and Hairston, et al. 1960) among species and their interactions with the abiotic environment. While elements of cybernetic organization are apparent, O’Neill, et al. 1986 makes a poignant case that the concept is incomplete in that it relies on homeostasis and does a poor job in explaining the reaction of systems to stress and instability. Ecosystems might possess cybernetic properties, but the concept does not represent the fundament organizing principle that shapes and guides them. In its place, O’Neill, et al. 1986 applies the concept of hierarchical organization to ecosystems. Parallel to these developments was the advance of complexity science and the concept of the complex adaptive system, covered in Waldrop 1992 and Levin 1998. Complex adaptive systems possess hierarchical organization of subsystems of self-similar interacting components, possess the capacity to adapt and evolve (read coevolve with its environment), and shun the notion of homeostasis, as they often operate far from equilibrium conditions. While not fully accepted by the community, the perspectives embodied in complex adaptive thinking provide a means of advancing ecosystem ecology, particularly when the social and human dimensions are considered.

            • Allen, T. F. H., and T. B. Starr. 1982. Hierarchy theory: Perspectives for ecological complexity. Chicago: Univ. of Chicago Press.

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              The book presents the basic concepts of hierarchical organization and connections between structure, function, and dynamics as they relate to ecological systems. The importance of temporal and spatial scales and their relationships of structure to function and dynamics are discussed.

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              • Engelberg, J. and L. L. Boyarsky. 1979. The noncybernetic nature of ecosystems. American Naturalist 114:317–324.

                DOI: 10.1086/283480Save Citation »Export Citation »E-mail Citation »

                The authors argue that cybernetic systems possess information networks, feedback loops, and stability. Given these criteria, ecosystems are not true cybernetic systems given that ecosystem components are not connected by an information network. True cybernetic systems in their view “lies in the existence of a communication network that connects all parts of the system.” This interpretation of what constitutes a cybernetic systems was criticized by several authors as being too narrow.

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                • Hairston, N. G., F. E. Smith, and L. B. Slobodkin. 1960. Community structure, population control and distribution. American Naturalist 94:89–98.

                  DOI: 10.1086/282146Save Citation »Export Citation »E-mail Citation »

                  A classic paper that addresses the many concepts of the relationships among community structure, functional aspects of ecosystems, and their dynamics. In many ways this is a companion read to Hutchinson 1959, cited under Development of Modern Ecosystem Thinking.

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                  • Hutchinson, G. E. 1948. Circular causal systems in ecology. Annals of the New York Academy of Sciences 50:221–246.

                    DOI: 10.1111/j.1749-6632.1948.tb39854.xSave Citation »Export Citation »E-mail Citation »

                    An important paper that lays out the framework for what became the model ecosystem approach.

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                    • Levin, S. A. 1998. Ecosystems and the biosphere as complex adaptive systems. Ecosystems 1:431–436.

                      DOI: 10.1007/s100219900037Save Citation »Export Citation »E-mail Citation »

                      An important paper that defines an ecosystem as a complex adaptive system. The paper explicitly links ecology and evolution, by asserting that evolution shapes ecosystem properties. The paper makes a compelling case that by studying the structural, functional, and dynamic properties of ecosystems, we might anticipate changes to ecosystems and the consequences of these changes to human well-being.

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                      • McNaughton, S. J., and M. B. Coughenour. 1981. The cybernetic nature of ecosystems. American Naturalist 117:985–990.

                        DOI: 10.1086/283782Save Citation »Export Citation »E-mail Citation »

                        A commentary on the arguments made by Engelberg and Boyarsky 1979 that rebuffs the claim that an ecosystem is not a cybernetic system. The paper, along with the companion paper Patten and Odum 1981, highlights the depth of the debate on the nature of ecosystem structure and control.

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                        • Odum, E. P. 1969. The strategy of ecosystem development. Science 164:262–279.

                          DOI: 10.1126/science.164.3877.262Save Citation »Export Citation »E-mail Citation »

                          A summary of ecosystem structural, functional, and dynamic properties for early and late successional properties. Odum offers the comparison as a basis for general ecosystem science theory.

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                          • O’Neill, R. V., D. L. DeAngelis, J. B. Waide, and T. F. H. Allen. 1986. A hierarchical concept of ecosystems. Princeton, NJ: Princeton Univ. Press.

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                            An excellent presentation and argument defining the ecosystem concept based on the tenets of hierarchy theory.

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                            • Patten, B., and E. P. Odum. 1981. The cybernetic nature of ecosystems. American Naturalist 118:886–895.

                              DOI: 10.1086/283881Save Citation »Export Citation »E-mail Citation »

                              A commentary on the arguments made by Engelberg and Boyarsky 1979 hat rebuffs the claim that an ecosystem is not a cybernetic system. The paper, along with the companion paper McNaughton and Coughenour 1981 highlights the depth of the debate on the nature of ecosystem structure and control.

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                              • Simon, H. A. 1962. The architecture of complexity. Proceedings of the American Philosophical Society 106:467–482.

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                                A lengthy but interesting read on the nature of complex systems. The paper lays the foundation for hierarchy theory.

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                                • Waldrop, M. M. 1992. Complexity: The emerging science at the edge of order and chaos. New York: Simon & Schuster.

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                                  The book covers the fundamentals of complexity and complex adaptive systems.

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                                  • Wiener, N. 1948. Cybernetics. New York: Wiley.

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                                    A foundational and transformative work on the developing field of cybernetics that emerged from information theory.

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                                    Ecosystem Models

                                    Ecosystem ecology has embraced models and mathematics as a means to develop and test theory, to integrate multiple components, to catalogue interactions, and to generate predictions. The development of the field coincided with advances in information theory and modern computing. May 1973 categorized models used in ecology as being arranged along a continuum bounded by purely strategic models designed to test general theory and tactical models designed to describe phenomena (read ecosystem processes) or systems in detail. The models used in ecosystem ecology span this continuum, embracing both modeling strategies, but tended early on to follow the tactical model using energetic and biogeochemical approaches. The earliest representations can be traced to predator-prey systems based on differential equations designed to study their dynamics, and to food chains and food webs designed to illustrate the cycling of matter, as presented in Lotka 1924 and Elton 1927. Currencies used to parameterize the models included population sizes and biomass. Lindeman 1942 (cited under Development of Modern Ecosystem Thinking) provided a comprehensive description of the ecosystem in energetic terms that established a new framework to study systems that formalized the study of energy and material flow (see Odum 1953, under Formalizing Ecosystem Ecology as a Discipline) and introduced the concept of the trophic level. MacArthur 1955 and DeAngelis 1975 melded traditional equation-based models to the concepts of energy flow to study food web dynamics—see Moore and de Ruiter 2012 for an overview. Parton, et al. 1987 developed a general process-oriented model (CENTURY) to describe the cycling of soil organic matter in terrestrial systems (see also Parton, et al. 2015). Rastetter, et al. 2003 explores these approaches, which are used extensively to study ecosystems and ecosystem processes, and are often used with or to develop elements of spatial models and climate models, over a range of spatial and temporal scales.

                                    • DeAngelis, D. L. 1975. Stability and connectance in food web models. Ecology 56:238–243.

                                      DOI: 10.2307/1935318Save Citation »Export Citation »E-mail Citation »

                                      An early fusion of the ecosystem and community ecological approaches applied to food webs. Energetic properties of organisms and their positions in the trophic structure are considered.

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                                      • Elton, C. S. 1927. Animal ecology. Chicago: Univ. of Chicago Press.

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                                        This classic text provides the foundation of many general ecological and ecosystem concepts. Republished in 2001.

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                                        • Lotka, A. J. 1924. Elements of physical biology. Baltimore: Williams &Wilkins.

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                                          A foundational work in mathematical biology and ecology that melds basic population biology and biogeochemistry. An unabridged republication of the work by Dover Publications appeared in 1956 under the title Elements of Mathematical Biology.

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                                          • MacArthur, R. 1955. Fluctuations of animal populations and a measure of community stability. Ecology 36.3: 533–536.

                                            DOI: 10.2307/1929601Save Citation »Export Citation »E-mail Citation »

                                            An early treatment of the relationship between population dynamics and stability. The concepts of community organization as multiple pathways of trophic interactions and redundancy of pathways are presented.

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                                            • May, R. M. 1973. Stability and complexity of model ecosystems. Princeton, NJ: Princeton Univ. Press.

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                                              Covers fundamental approaches to modeling ecosystems. The book is clearly written and provides a solid foundation on the use of differential and difference equations to model simple ecological communities.

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                                              • Moore, J. C., and P. C. de Ruiter. 2012. Energetic food webs: An analysis of real and model ecosystems. Oxford: Oxford Univ. Press.

                                                DOI: 10.1093/acprof:oso/9780198566182.001.0001Save Citation »Export Citation »E-mail Citation »

                                                The book uses both the community-based and ecosystem-based approaches to study the relationship between food webs’ structure, biogeochemistry (functional aspects), and dynamics.

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                                                • Parton, W. J., S. J. Del Grosso, A. F. Plante, E. C. Adair, and S. M. Lutz. 2015. Modeling the dynamics of soil organic matter and nutrient cycling. In Soil microbiology, ecology and biochemistry. 4th ed. Edited by E. A. Paul, 505–538. San Diego, CA: Academic Press.

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                                                  This chapter provides an overview of soil organic matter models.

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                                                  • Parton, W. J., D. S. Schimel, C. V. Cole, and D. S. Ojima. 1987. Analysis of factors controlling soil organic matter levels in Great Plains grasslands. Soil Science Society of America Journal 51:1173–1179.

                                                    DOI: 10.2136/sssaj1987.03615995005100050015xSave Citation »Export Citation »E-mail Citation »

                                                    An early description of the CENTURY model and its application. This is one of the most widely used models to study soil organic matter dynamics. A number of variants of the model have since been developed (see Parton, et al. 2015)

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                                                    • Rastetter, E. B., J. D. Aber, D. P. C. Peters, D. S. Ojima, and I. Burke. 2003. Using mechanistic models to scale ecological processes across space and time. BioScience 53:68–76.

                                                      DOI: 10.1641/0006-3568(2003)053[0068:UMMTSE]2.0.CO;2Save Citation »Export Citation »E-mail Citation »

                                                      Explores the value of using models and empirical data collected over different temporal and spatial scales to understand ecosystem processes across space and time. The paper is part of a special feature on the US Long Term Ecological Research (LTER) Network.

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                                                      Development of Modern Ecosystem Thinking

                                                      Slobodkin 1993 credits the ecologist G. Evelyn Hutchinson with having had a major impact on the development of ecology through his work and that of his students by transforming ecology from a description science to a predictive science. Hutchinson championed the use of mathematics and quantifying observations to answer basic questions and test hypotheses. He balanced the need to understand organisms in the ways that early naturalists studied them with a holistic approach that included biogeochemical cycling and exchanges with the geophysical world typically studied in earth systems science (see Hutchinson 1948, cited under Systems Theory and Information Theory). Hutchinson pioneered the field, describing the physical and chemical conditions of lakes, elemental cycling, and the dynamics of plankton, as explained in Hutchinson 1941. Raymond L. Lindeman, a student of Hutchinson, produced a seminal paper (Lindeman 1942) that epitomized this new synthesis and perspective by representing ecosystems in terms of species interactions in the context of the abiotic environment, and by quantifying not only the biomasses of the species, but also the flows among species. His description of the food web of the Cedar Creek Bog defined groups of species interactions in energetic terms, and included detritus (“ooze”), microbes, and nutrients as direct inflows and outflows in ways that encapsulated the ecosystem concept and ecosystem practice.

                                                      • Hutchinson, G. E. 1941. Limnological studies in Connecticut, IV: The mechanisms of intermediary metabolism in stratified lakes. Ecological Monographs 11:22–60.

                                                        DOI: 10.2307/1948456Save Citation »Export Citation »E-mail Citation »

                                                        One of a series of papers providing a glimpse of the detailed approach taken by Hutchinson and his colleagues and students, linking the geophysical and biological realms of freshwater lakes. The approaches presented in these papers represent the basis of modern ecosystem ecology and, more specifically, limnology.

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                                                        • Hutchinson, G. E. 1959. Homage to Santa Rosalia, or why are there so many kinds of animals. American Naturalist 93:145–159.

                                                          DOI: 10.1086/282070Save Citation »Export Citation »E-mail Citation »

                                                          A published version of an address to the Society of the American Naturalists, wherein a variety of then contemporary issues in ecology were first clearly articulated. The paper is a must-read for students of the ecological sciences.

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                                                          • Lindeman, R. L. 1942. The trophic-dynamic aspect of ecology. Ecology 23:399–418.

                                                            DOI: 10.2307/1930126Save Citation »Export Citation »E-mail Citation »

                                                            A seminal paper in ecosystem ecology that proposes an energetics view of ecological interactions. The work is empirically based and theoretical, providing a detailed description of a system to convey abstract ideas. The work was one of the first to integrate living and dead organic material, and one of the first to explicitly include detritus, or “ooze.”

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                                                            • Slobodkin, L. B. 1993. An appreciation: George Evelyn Hutchinson. Journal of Animal Ecology 62:390–394.

                                                              DOI: 10.2307/5370Save Citation »Export Citation »E-mail Citation »

                                                              A tribute to the life of G. Evelyn Hutchinson, written by a former student. The paper provides a summary of not only the contributions that Hutchinson made to the field of ecology and the ecosystem concept, but also the important developments in thinking that were taking place at the time.

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                                                              Formalizing Ecosystem Ecology as a Discipline

                                                              Odum 1953 was one of the first textbooks published in ecology (it was written by Eugene P. Odum with the help of his brother Howard T. Odum). The book presented and formalized a holistic approach to studying organisms in their environment, drawing on natural history, earth system science, and ecological energetics (i.e., the study of energy flow). It represented a departure from previous works and marked a beginning of the formalization of the ecosystem approach in ecology, and of ecology as a discipline. The ecosystem approach was well aligned and suited to address the scope and vision of several large international and national initiatives that emerged from the International Geophysical Year (1957–1958), which is discussed below under Large Initiatives. Odum 1969 presented a “strategy of ecosystem development,” wherein characteristics of ecosystems during their developmental and mature stages were compared. The ideas are more phenomenological than explanatory, in that they do not ascribe explicit mechanisms to this development. The paper takes a holistic approach by positioning the ecosystem, not the species that compose it, at the center of the discussion. While a contemporary set of ideas from the community-based ecology approach in MacArthur and Wilson 1967 explained observed patterns of species diversity based on random rates of colonization and extinction of individual species that are influenced by physical geography (proximity and size of islands to mainlands), Odum 1969 does not clearly spell out the mechanisms that lead to the changes underlying the contrasts between developing and mature communities. Unlike the ideas presented in MacArthur and Wilson 1967, Odum 1969 does not assume that process operate in an equal manner at random on species or other components of the system. Odum 1969 embraces the coevolution between species and feedbacks between organisms and abiotic factors (inorganic nutrients), to bring an ecosystem and its components and processes in balance. An ecosystem possesses cybernetic properties engrained in the genetic makeup of the constituent species and governed by the first and second laws of thermodynamics and the conservation of matter.

                                                              • MacArthur, R. M., and E. O. Wilson. 1967. The theory of island biogeography. Princeton, NJ: Princeton Univ. Press.

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                                                                An outstanding example of the power of the scientific method and how theory emerges from years of empirical observation and experimentation.

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                                                                • Odum, E. P. 1953. Fundamentals of ecology. Philadelphia: Saunders.

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                                                                  A classic textbook of ecosystem ecology. The book fully embraced the ecosystem approach and was a standard ecology text for several decades, with the fifth edition, coauthored by Gary Barrett, appearing in 2005 (Belmont, CA, Thompson Books).

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                                                                  • Odum, E. P. 1969. The strategy of ecosystem development. Science 164:262–279.

                                                                    DOI: 10.1126/science.164.3877.262Save Citation »Export Citation »E-mail Citation »

                                                                    A summary of ecosystem structural, functional, and dynamic properties for early and late successional properties. Odum offers the comparison as a basis for general ecosystem science theory.

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                                                                    Ecosystem Frameworks

                                                                    Ecologists define and study complex ecosystems using a framework that considers the inextricable linkages between structural, functional, and dynamic characteristics of ecosystems. Odum 1969 (cited under Formalizing Ecosystem Ecology as a Discipline) used this framework, if not directly, in a tabular model of succession, as the twenty-four ecosystem attributions that are listed could be described as structural, functional, or dynamic. Paine 1980 made this distinction in a categorization of food web types, and Moore and de Ruiter 2012 (cited under Ecosystem Models) did so in a treatment of food webs. Adaptions of system components and the idea of ecosystems as being complex adaptive systems have also been proposed in Levin 1998 (cited under Systems Theory and Information Theory) and Levin 2002. Key elements of the framework to consider include (1) the boundary conditions (structural components) that define an ecosystem; (2) the biodiversity (structural and functional components)—the species and the interactions among species and the biogeophysical components of the ecosystem; (3) the processes (functional attributes) that emerge from the interactions among species within the ecosystems; and (4) the dynamic properties (dynamic components) of ecosystems and the consequences of dynamics on the structural and functional components of the system.

                                                                    • Levin, S. A. 2002. Complex adaptive systems: Exploring the known, the unknown and the unknowable. Bulletin of the American Mathematical Society 40:3–19.

                                                                      DOI: 10.1090/S0273-0979-02-00965-5Save Citation »Export Citation »E-mail Citation »

                                                                      One of a series of papers by Levin that discusses complex adaptive systems; the paper focuses on mathematical challenges.

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                                                                      • Paine, R. T. 1980. Food webs: Linkage, interaction strength and community infrastructure. Journal of Animal Ecology 49:667–685.

                                                                        DOI: 10.2307/4220Save Citation »Export Citation »E-mail Citation »

                                                                        The paper makes a distinction between different types of food web descriptions, the information that is used in the different descriptions, and the strengths and limitations of each type of description. The paper is an early example of the use of the structural, functional, and dynamics framework to describe ecological communities.

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                                                                        Boundaries

                                                                        The different variations of the definition of ecosystem ecology all include the study of organisms and their interactions within their physical environment. Within ecosystem ecology, defining their boundaries can be a challenge, as they are dependent on the spatial and temporal scale of interest and on the questions being asked. Post, et al. 2007 provides a review and overview of the structural and functional criteria that are used to establish the boundaries of an ecosystem. At the global scale, the earth can be viewed as an ecosystem, open to energy and largely closed to matter. At smaller scales, ecosystems are open to both energy and matter, and are defined in terms of terrestrial and aquatic features, dominant vegetation types, assemblages of organisms, climate, geologic history, biogeography, soil types, or habitat characterizations. For terrestrial ecosystems, the commonly used life zone (Holdridge 1947) and biome (Whittaker 1975) concepts of characterizing ecological communities are based on climate (temperature and precipitation) and the dominant vegetation types. Turner and Gardner 2015 argues that landscapes—expanses of land and water—have also served as boundaries for ecosystems, or collections of ecosystems. Ellis and Ramankutty 2008 introduces the idea that urban centers should now be classified as anthropogenic biomes. At finer scales, biomes are often subdivided into smaller units of study. Freshwater and marine ecosystems are often subdivided into littoral, pelagic, and benthic zones. Coleman, et al. 2004 notes that soils are subdivided along the litter layer, lower soil horizons, or the region around roots (the rhizosphere).

                                                                        • Coleman, D. C., D. Crossley Jr., and P. F. Hendrix. 2004. Fundamentals of soil ecology. 2d ed. Amsterdam: Elsevier Academic Press.

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                                                                          An excellent text on soil biology and ecology, and on ecosystem structure and function.

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                                                                          • Ellis, E. C., and N. Ramankutty. 2008. Putting people in the map: Anthropogenic biomes of the world. Frontiers in Ecology and the Environment 6:439–447.

                                                                            DOI: 10.1890/070062Save Citation »Export Citation »E-mail Citation »

                                                                            The authors introduce the concept of anthropogenic biomes—a characterization of terrestrial biomes based on global patterns of sustained, direct human interaction with ecosystems. An important paper in the ongoing evolution of social ecology.

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                                                                            • Holdridge, L. R. 1947. Determination of world plant formation from simple climate data. Science 105:367–368.

                                                                              DOI: 10.1126/science.105.2727.367Save Citation »Export Citation »E-mail Citation »

                                                                              The paper that established the concept of life zones to categorize ecosystems.

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                                                                              • Post, D. M., M. W. Doyle, J. L. Sabo, and J. C. Finlay. 2007. The problem of boundaries in defining ecosystems: A potential landmine in uniting geomorphology and ecology. Geomorphology 89.1–2: 111–126.

                                                                                DOI: 10.1016/j.geomorph.2006.07.014Save Citation »Export Citation »E-mail Citation »

                                                                                An excellent review of the criteria used, and their scale-dependent nature, to define the boundaries of ecosystems.

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                                                                                • Turner, M. G., and R. H. Gardner. 2015. Landscape ecology in theory and practice. New York: Springer-Verlag.

                                                                                  DOI: 10.1007/978-1-4939-2794-4Save Citation »Export Citation »E-mail Citation »

                                                                                  A modern and thorough treatment of the field of landscape ecology from the ecosystem perspective. This is an important advancement, as it incorporates current social-ecological thinking.

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                                                                                  • Whittaker, R. H. 1975. Communities and ecosystems. 2d ed. New York: MacMillan.

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                                                                                    A compilation of the biomes of the world.

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                                                                                    Biodiversity

                                                                                    Biodiversity refers to more than the number of species, as it characterizes the variation and variety of life at the genetic, species, and ecosystem levels. These characterizations are important because they provide a framework from which to study the relationships between ecosystem structure, function, and dynamics. Cleland 2011 and Moore 2013 provide reviews of the criteria that ecosystem ecologists have used to study biodiversity. For certain questions and scales, individual species are used, but often systems are described in terms of species grouped into larger units. The schemes used have ranged from ones of convenience, which are usually based on a broad taxonomic category, to ones that have adopted strict criteria such as resource use or functional traits that may include organisms from different taxonomic groupings. Naeem, et al. 1994 and Norberg, et al. 2001 are important papers on the relationship between ecosystem biodiversity and ecosystem function. Loreau, et al. 2002 provides an excellent compilation on the relationship between diversity and function. Tilman and Downing 1994 takes this idea further by demonstrating that, for plant communities, diversity, function (as measured by productivity), and stability (as measured by recovery from drought) are interrelated, and arguing that biodiversity is important in maintaining stable rates of productivity in ecosystems. McCann 2000 reviews the relationship between the biodiversity of an ecosystem and its dynamic stability. Hoeksema, et al. 2010 presents a comprehensive meta-analysis on the impact of mycorrhizal fungi on plant growth, local biodiversity, and ecosystem function. Levin 1998 (cited under Systems Theory and Information Theory) argues that the biodiversity of an ecosystem provides the means through which ecosystems evolve via the influence of natural selection on the constituent species. Hector and Bagchi 2007 makes the case that species contribute to a suite of ecosystem functions and ecosystem services (discussed below), giving rise to the concept of multifunctionality—the ability of an ecosystem to provide multiple functions and service. Multifunctionality approaches the relationships between biodiversity and function through a socio-ecological lens, as the priorities of stakeholders are taken into consideration, and as such provides a linkage between the functional aspects of ecosystems to biodiversity and ecosystem services (discussed below).

                                                                                    • Cleland, E. E. 2011. Biodiversity and ecosystem stability. Nature Education Knowledge 3:14.

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                                                                                      A nice summary of the criteria used to define ecosystem biodiversity and how the information can be used to study ecosystem function and dynamics.

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                                                                                      • Hector, A., and R. Bagchi. 2007. Biodiversity and ecosystem multifunctionality. Nature 448:188–190.

                                                                                        DOI: 10.1038/nature05947Save Citation »Export Citation »E-mail Citation »

                                                                                        An early treatment of the concept of multifunctionality. The paper provides a compelling case for studying the impacts of biodiversity on a host of ecosystem functions. The study found a strong positive saturating relationship between the number of ecosystem processes measured and the number of species (read biodiversity) of the systems.

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                                                                                        • Hoeksema, J. D., V. B. Chaudhary, C. A. Gerhing, et al. 2010. A meta-analysis of context-dependency in plant response to inoculation with mycorrhizal fungi. Ecology Letters 13:394–407.

                                                                                          DOI: 10.1111/j.1461-0248.2009.01430.xSave Citation »Export Citation »E-mail Citation »

                                                                                          A thorough and interesting meta-analysis of field and laboratory studies on the effects of N additions to mycorrhizal associations. This demonstrates the importance of mycorrhizae to the biodiversity and function of ecosystems.

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                                                                                          • Loreau, M., S. Naeem, and P. Inchausti, eds. 2002. Biodiversity and ecosystem functioning: Synthesis and perspectives. Oxford: Oxford Univ. Press.

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                                                                                            An excellent compilation of papers that address different aspects of the relationship between biodiversity and ecosystem function.

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                                                                                            • McCann, K. S. 2000. The diversity-stability debate. Nature 405:228–233.

                                                                                              DOI: 10.1038/35012234Save Citation »Export Citation »E-mail Citation »

                                                                                              An excellent review of the diversity-stability debate.

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                                                                                              • Moore, J. C. 2013. Biodiversity, taxonomic verses functional. In Encyclopedia of biodiversity. 2d ed. Vol. 1. Edited by S. Levin, 648–656. Amsterdam: Elsevier.

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                                                                                                A review of different ways to categorize biodiversity to ecosystem processes.

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                                                                                                • Naeem, S., L. J. Thompson, S. P. Lawler, J. H. Lawton, and R. M. Woodfin. 1994. Declining biodiversity can alter the performance of ecosystems. Nature 368:734–737.

                                                                                                  DOI: 10.1038/368734a0Save Citation »Export Citation »E-mail Citation »

                                                                                                  A seminal paper which proposed that ecosystem function was inextricably interrelated to biodiversity.

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                                                                                                  • Norberg, J., D. P. Swaney, J. Dushoff, J. Lin, R. Casagrandi, and S. A. Levin. 2001. Phenotypic diversity and ecosystem functioning in changing environments: A theoretical framework. Proceedings of the National Academy of Sciences 98:11376–11381.

                                                                                                    DOI: 10.1073/pnas.171315998Save Citation »Export Citation »E-mail Citation »

                                                                                                    The authors present a framework that suggests that phenotypic variance within functional groups (groups of species) is linearly related to their ability to respond to environmental change. This is a departure for earlier work that focused in individual species.

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                                                                                                    • Tilman, D., and J. A. Downing. 1994. Biodiversity and stability in grasslands. Nature 367:363–365.

                                                                                                      DOI: 10.1038/367363a0Save Citation »Export Citation »E-mail Citation »

                                                                                                      A seminal paper demonstrating the interrelationship among ecosystem structure, function, and dynamics.

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                                                                                                      Ecosystem Processes

                                                                                                      Ecosystem processes represent both structural and functional aspects of ecosystems. The textbooks Odum 1953 and Chapin, et al. 2011 (among others) provide detailed accounts of fundamental ecosystem processes—production, decomposition, mineralization, immobilization—within the context of biogeochemical cycles. Ecosystem processes encompass the transformation and flow of materials and energy from and among biotic and abiotic pools. Biotic pools can be living or nonliving, represented by organisms and their by-products (e.g., corpses, unconsumed prey and leavings, feces). Abiotic components include but are not limited to the atmosphere, bodies and expanses of liquid and frozen water, and the chemical and physical components of soils and water. A biogeochemical cycle describes the pathway that a chemical substance uses to move through the biotic and abiotic components of the earth system. There are several biogeochemical cycles that are of interest to ecosystem scientists, but the primary cycles are the carbon cycle, nitrogen cycle, phosphorous cycle, sulfur cycle, and water cycle. Hutchinson 1948 provides the foundational account of the relationship of biogeochemical cycles to the ecosystem concept. Ecosystem processes can be discussed in the simplest terms of the input and output of energy of driving immobilization (the transformation of substance from an inorganic form to an organic form) and mineralization (the transformation of a substance from an organic form to an inorganic form, as represented in the familiar chemical equilibrium representation of photosynthesis and respiration 6CO2 + 6H20 Ö C6H12O6 + 6O2. Biogeochemical cycles do not operate in isolation and are often interrelated and dependent on one another, due in part to the finite (read limiting) nature of resources, thermodynamic constraints, and the coupled dependency of cycles (ecological stoichiometry). Much of the work that followed tended to be descriptive in nature, studying the factors that regulate production and decomposition and cataloguing the sources and sinks of key moieties, experimental treatments studying the consequences of altering the abundances of nutrients on plant growth and ecosystem process, or studies designed to understand regulators of biogeochemical cycles within ecosystems. Contemporary treatments of biogeochemical cycles cover much of the earlier work by including detailed synopses of their descriptions and the factors that regulate them, how they interact with one another, how human activity has affected them, and how changes in the cycles affect the structural, functional, and dynamic properties of ecosystems. Schlesinger and Bernhardt 2013 is a thorough and basic stand-alone text on biogeochemical cycles, their interactions, and the effects of humans on them. Chapin, et al. 2011 provides an in-depth account of ecosystem processes and the dominant biogeochemical cycles. Sterner and Elser 2002 presents a comprehensive treatment of ecological stoichiometry—the coupled dependency of biogeochemical cycles and energetics on organisms and ecosystems.

                                                                                                      • Chapin, S. F., III, P. A. Matson, and P. M. Vitousek. 2011. Principles of terrestrial ecosystem ecology. 2d ed. New York: Springer.

                                                                                                        DOI: 10.1007/978-1-4419-9504-9Save Citation »Export Citation »E-mail Citation »

                                                                                                        This general text in ecosystem ecology provides excellent overviews of the major biogeochemical cycles, how human activity alters them, and the consequences of these alterations on ecosystems and ecosystem services.

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                                                                                                        • Hutchinson, G. E. 1948. Circular causal systems in ecology. Annals of the New York Academy of Sciences 50:221–246.

                                                                                                          DOI: 10.1111/j.1749-6632.1948.tb39854.xSave Citation »Export Citation »E-mail Citation »

                                                                                                          An important paper that lays out the framework for what became the model ecosystem approach.

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                                                                                                          • Odum, E. P. 1953. Fundamentals of ecology. Philadelphia: Saunders.

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                                                                                                            A classic textbook of ecosystem ecology. The book fully embraced the ecosystem approach and was a standard ecology text for several decades, with the fifth edition, coauthored by Gary Barrett, appearing in 2005 (Belmont, CA: Thompson Books).

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                                                                                                            • Schlesinger, W. H., and E. S. Bernhardt. 2013. Biogeochemistry: An analysis of global change. 3d ed. Amsterdam: Academic Press.

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                                                                                                              A comprehensive and contemporary treatment of the field of biogeochemistry. The book provides descriptive information on the structure and regulation of biogeochemical cycles and the consequences of human activity on them.

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                                                                                                              • Sterner, R. W., and J. J. Elser. 2002. Ecological stoichiometry: The biology of elements from molecules to the biosphere. Princeton, NJ: Princeton Univ. Press.

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                                                                                                                An important text on ecological stoichiometry—the study of the effects of the relationship between energy and elements—and how it is affected by interactions and processes in ecosystems.

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                                                                                                                Ecosystem Dynamics

                                                                                                                Ecosystem dynamics refers to the changes in both structure and processes that ecosystems undergo in space and time. Early works often referred to an ecosystem being in balance, equilibrium, or at homeostasis in terms of its structure and processes (e.g., the ratio of production to respiration being equal in natural systems), while at the same time recognizing that ecosystems change through time (e.g., succession). Holling 1973 explores how the concept of ecosystem resilience was defined in terms of the ability of deviations in the structural and functional characteristics following a disturbance to return to its original homeostasis. Current views see ecosystem homeostasis as one of many states, embracing the idea of ecosystems in a state of non-equilibrium, and that the spatial and temporal dynamics that ecosystems undergo are important to their persistence. Hastings 2001, Hastings 2004, and Hastings 2010 argue that the nature of short-term transient dynamics in the structural and functional aspects of the ecosystem following a disturbance may be as or more important to its persistence that the long-term asymptotic behavior. Traditional concepts of resilience and return-times are deconstructed into component concepts of reactivity (the maximum rate of growth of a deviation from homeostasis following a disturbance) and amplification envelope (the magnitude of the deviation among others). Recent research has focused on looking for signals in the long-term dynamics of ecosystems that might help foretell a transition, tipping point, or change in their structural and functional aspects. May 1976 demonstrated that the dynamic state of a system can change abruptly if underlying conditions change. Levin 1999 (cited under Ecosystem Services) argued that many ecosystems are near or at the edge of abrupt change. Predicting these changes in advance has been difficult. In some cases, explored in Scheffer and Carpenter 2003 and Carpenter and Brock 2010, changes in the magnitude and variation of key ecosystem components over time serve as predictors of change, while in others the changes occur without warning, as argued in Hastings and Wysham 2010.

                                                                                                                • Carpenter, S. R., and W. A. Brock. 2010. Early warnings of regime shifts in spatial dynamics using the discrete Fourier transform. Ecosphere 1:1–15.

                                                                                                                  DOI: 10.1890/ES10-00016.1Save Citation »Export Citation »E-mail Citation »

                                                                                                                  The paper reports that there are signals in the time-series.

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                                                                                                                  • Hastings, A. 2001. Transient dynamics and persistence of ecological systems. Ecology Letters 4:215–220.

                                                                                                                    DOI: 10.1046/j.1461-0248.2001.00220.xSave Citation »Export Citation »E-mail Citation »

                                                                                                                    An early paper that focused on the importance of the transient dynamics leading to ecosystem persistence, as opposed to asymptotically stable dynamics.

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                                                                                                                    • Hastings, A. 2004. Transients: The key to long-term ecological understanding? Trends in Ecology and Evolution 19:39–45.

                                                                                                                      DOI: 10.1016/j.tree.2003.09.007Save Citation »Export Citation »E-mail Citation »

                                                                                                                      The paper points out that theory focuses on stable equilibria and long-term asymptotic behavior, while most empirical data focuses on short-term transient behavior that is more in line with ecological timescales. This mismatch between theory and empiricism may lead to an incomplete understanding of how ecological systems persist.

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                                                                                                                      • Hastings, A. 2010. Timescales, dynamics, and ecological understanding. Ecology 91:3471–3480.

                                                                                                                        DOI: 10.1890/10-0776.1Save Citation »Export Citation »E-mail Citation »

                                                                                                                        The paper is the published perspective of the lecture given by the author as the recipient of the Robert MacArthur Award from the Ecological Society of America. Hastings argues that the dynamics of ecological populations can best be explained as transient responses to exogenous influences.

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                                                                                                                        • Hastings, A., and D. B. Wysham. 2010. Regime shifts in ecological systems can occur with no warning. Ecology Letters 13:464–472.

                                                                                                                          DOI: 10.1111/j.1461-0248.2010.01439.xSave Citation »Export Citation »E-mail Citation »

                                                                                                                          The paper makes the argument that regime shifts can happen without warning. The paper is model-based. A central point is that empirical evidence from long-term monitoring represents one possible trajectory that a system may undertake.

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                                                                                                                          • Holling, C. S. 1973. Resilience and stability of ecological systems. Annual Review of Ecology and Systematics 4:1–23.

                                                                                                                            DOI: 10.1146/annurev.es.04.110173.000245Save Citation »Export Citation »E-mail Citation »

                                                                                                                            A classic paper that frames the concepts of resilience and stability in terms of system behaviors. The paper shows how the two are related yet yield different perspectives on how ecosystems respond to disturbance and persist through time.

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                                                                                                                            • May, R. M. 1976. Simple mathematical models with very complicated dynamics. Nature 261:459–467.

                                                                                                                              DOI: 10.1038/261459a0Save Citation »Export Citation »E-mail Citation »

                                                                                                                              An important paper that illustrates the potential of abrupt changes in population dynamics with changes in underlying conditions. May demonstrates how population dynamics can transition from equilibrium to chaos using a simple difference equation, in this case by varying the intrinsic rate of increase of the population. This paper opened up a discussion on the possibility that ecological systems may possess alternative stable states.

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                                                                                                                              • Scheffer, M., and S. R. Carpenter. 2003. Catastrophic regime shifts in ecosystems: Linking theory to observations. Trends in Ecology and Evolution 18:648–656.

                                                                                                                                DOI: 10.1016/j.tree.2003.09.002Save Citation »Export Citation »E-mail Citation »

                                                                                                                                The paper explores ways to link the theoretical existence of alternative stable states to empirical time series data to explain ecological regime shifts. The authors stress that the best approaches would combine field observations, experiments, and modeling.

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                                                                                                                                Modern Theory and Practice

                                                                                                                                Ecosystem ecology has undergone major transformations over the past couple of decades. The theoretical basis of the science and how it is practiced has been consistently challenged both from within and from outside the community. O’Neill 2001 is a poignant address delivered by the author upon receiving the MacArthur Award at the annual meeting of the Ecological Society of America in 2000. He appears to have challenged basic tenets of ecosystem science altogether, citing the lack of a coherent theoretical underpinning. This seeming rebuke was more of a pivot away from the cybernetic leanings of earlier thinking to more of a principle-based approach. This address had been preceded by several calls to invoke theory in ecosystem studies, if not in ecology writ large (Levin 1989). Carpenter 1998 advocated the use of observations in space and time, experiments, and theory, the latter being conspicuously absent or given short shrift. The debate is ongoing. Knapp and D’Avanzo 2010 provides a review of principles that form the basis ecosystem ecology from a teaching perspective. In a special issue commemorating the twenty-year anniversary of the establishment of the journal Ecosystems, Cottingham, et al. 2017 revisits this debate, reminding the field that theory needs to be the foundation of ecosystem ecology.

                                                                                                                                • Carpenter, S. R. 1998. The need for large-scale experiments to assess and predict the response of ecosystems to perturbation. In Successes, limitations, and frontiers in ecosystem science. Edited by M. L. Pace and P. M. Groffman, 287–312. New York: Springer.

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                                                                                                                                  The author makes the case that large-scale experiments that use multiple lines of inference are necessary to understand how ecosystems function and to study ecosystem responses to disturbance. The metaphor of a table with legs representing theory, observations in space, observations in time, and experiments is used to represent the multiple lines of inference.

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                                                                                                                                  • Cottingham, K. L., S. B. Fey, K. J. Fritschie, and J. V. Trout-Haney. 2017. Advancing ecosystem science by promoting greater use of theory and multiple research approaches in graduate education. Ecosystems 20:267–273.

                                                                                                                                    DOI: 10.1007/s10021-016-0070-3Save Citation »Export Citation »E-mail Citation »

                                                                                                                                    A well-written account and review of the role of theory in shaping ecosystem science, and of the different modalities of practice within the field. The authors stress the need to integrate theory into practice.

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                                                                                                                                    • Knapp, A. K., and C. D’Avanzo. 2010. Teaching with principles: Toward more effective pedagogy in ecology. Ecosphere 1:1–10.

                                                                                                                                      DOI: 10.1890/ES10-00013.1Save Citation »Export Citation »E-mail Citation »

                                                                                                                                      An excellent paper that reviews key ecological principles and aligns them with innovative instructional strategies.

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                                                                                                                                      • Levin, S. A. 1989. Challenges in the development of a theory of community and ecosystem structure and function. In Perspectives in ecological theory. Edited by J. Roughgarden, R. M. May, and S. A. Levin, 242–255. Princeton, NJ: Princeton Univ. Press.

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                                                                                                                                        This paper reviews mathematical models that are used to study environmental disturbance on ecosystem processes, such as productivity, nutrient cycling, and succession. The author addresses the need to couple biological and physical factors and components that are operating on different spatial and temporal scales.

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                                                                                                                                        • O’Neill, R. V. 2001. Is it time to bury the ecosystem concept? (with full military honors, of course!). Ecology 82:3275–3284.

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                                                                                                                                          The paper is a summary of O’Neill’s address to the Ecological Society of America on the occasion of his receiving the Robert MacArthur Award. The paper is an honest assessment of the state of ecosystem science at the end of the 20th century. O’Neill offers a series of tenets that could strengthen the field.

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                                                                                                                                          Social and Human Dimensions

                                                                                                                                          Ecosystem ecology has evolved as a discipline to include human interactions, and it now serves as a foundational discipline for the modern development of urban ecology, elements of landscape ecology (see Clark 2010 for an overview), and sustainability science. The discipline has long influenced natural resource management and agriculture, as practitioners have adopted basic ecosystem principles into the management of forest, rangeland, and agricultural settings. The major evolution in the science has been in how humans and their actions are positioned within the discipline, as the epistemological perspective of the social sciences worked its way into ecosystem ecology. Early studies either studied ecological interactions in urban centers or human-dominated landscapes, or they explicitly incorporated humans into studies, much like any other organism. Pelt 1977 advocated fundamental changes in the relationship between humans and urban centers that incorporated ecological principles to better human well-being. Coughenour, et al. 1985 presented an analysis of the energy flows within an arid tropical ecosystem that included the Ngisonyoka pastoralists in the Turkana region of Kenya as being an integral component of the system. The study presented one of the first detailed accounts of human energy utilization from an ecosystem perspective; the key feature was that humans were treated as other organisms engaged in trophic interactions, responding to environmental conditions and affecting the local environment. The system was described as being maintenance-oriented rather than production-oriented, with the energy utilization of Ngisonyoka being “consistent with the ecological patterns that promote rather than diminish stability under stress.” Other approaches catalogued the impacts of humans on ecosystem structure and function. Vitousek, et al. 1997 was the lead paper in a special issue of the journal Science titled Human-Dominated Ecosystems that catalogued the extent to which humans affect ecosystem structure and function on a global scale. Humans have affected ecosystems and ecosystem processes to the point that the idea that natural ecosystems—those without human influence—exist should be challenged and questioned, as presented in Matson, et al. 1997. These papers, including Pickett, et al. 1997 and Collins, et al. 2010, represent the forbearers of a shift in the science to formally include a social or human dimension (read social-ecological perspective), to the point that ecosystem ecology and the services that ecosystems provide now form a basis of modern sustainability science, as it represents the ecology and environment in the triple bottom line of ecology, economy, and social sustainability, and provides the systems approach to study the complexity of sustainability.

                                                                                                                                          • Collins, S. L., S. R. Carpenter, S. M. Swinton, et al. 2010. An integrated conceptual framework for long-term social-ecological research. Frontiers of Ecology and the Environment 9:351–357.

                                                                                                                                            DOI: 10.1890/100068Save Citation »Export Citation »E-mail Citation »

                                                                                                                                            The paper advocates the use of the Press-Pulse Dynamics concept from ecosystem ecology as a framework to study social-ecological systems.

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                                                                                                                                            • Clark, W. R. 2010. Principles of landscape ecology. Nature Education Knowledge 3:34.

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                                                                                                                                              An overview of the development of landscape ecology and its theoretical underpinnings.

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                                                                                                                                              • Coughenour, M. B., J. E. Ellis, D. M. Swift, et al. 1985. Energy extraction and use in a nomadic pastoral ecosystem. Science 230:619–625.

                                                                                                                                                DOI: 10.1126/science.230.4726.619Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                An excellent application of the ecosystem perspective to a human population and its interactions with the environment.

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                                                                                                                                                • Matson, P. A., W. J. Parton, A. G. Power, and M. J. Swift. 1997. Agricultural intensification and ecosystem properties. Science 277:504–509.

                                                                                                                                                  DOI: 10.1126/science.277.5325.504Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                  The paper documents the extent of agricultural intensification and its impact on biotic interactions and resource allocation. The authors advocate the adoption of ecologically based management strategies.

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                                                                                                                                                  • Pelt, J. M. 1977. L’homme re-naturé. Paris: Editions du Seuil.

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                                                                                                                                                    Pelt’s volume (The re-naturalized human) presents a rethinking of the relationship between humans and urban centers. Largely viewed as a precursor to modern urban ecology.

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                                                                                                                                                    • Pickett, S. T. A., W. R. Burch Jr., S. E. Dalton, T. W. Foresman, J. M. Grove, and R. A. Rowntree. 1997. A conceptual framework for the study of human ecosystems in urban areas. Urban Ecosystems 1:185–199.

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                                                                                                                                                      The paper proposes a framework for studying the role of humans in ecosystems. The authors stress that the ecosystem concept can serve as the basis, but that specific social attributes of humans and their institutions such as learning must be added.

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                                                                                                                                                      • Vitousek, P. M., H. A. Mooney, J. Lubchenco, and J. M. Melillo. 1997. Human domination of earth’s ecosystems. Science 277:494–499.

                                                                                                                                                        DOI: 10.1126/science.277.5325.494Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                        A comprehensive synthesis of the impact that humans are having on the earth’s ecosystems. The paper represents an important tipping point in thinking by clearing showing the global extent of human impacts.

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                                                                                                                                                        Ecosystem Services

                                                                                                                                                        Human activities have altered ecosystems on a global scale. Vitousek, et al. 1997 (cited under Social and Human Dimensions) and Levin 1999 provide accounts of the scope and consequences of human activity in terms of their impacts on ecosystem structure, function, and dynamics, and on human well-being. These works and others led to the concept of ecosystem services, or the benefits that people obtain from ecosystems. The concept formalizes how aspects of ecosystem structure, function, and dynamics affect human well-being and is central to the conceptual framework of Millennium Ecosystem Assessment 2005. The publication of the Millennial Ecosystem Assessment (MEA) provided a richer framework to study human impacts on a global scale. Within the MEA framework, ecosystem services include foundational supporting services (e.g., primary production, nutrient cycling, evolution, spatial structure, and soil formation), provisioning services (e.g., food, water, fiber, fuel, biochemical, genetic resources), regulating services (e.g., climate regulation, water regulation, water purification, pollination, and disease), and cultural services (e.g., spiritual and religious, recreation, ecotourism, cultural heritage, aesthetic, recreation, and education).

                                                                                                                                                        • Levin, S. A. 1999. Fragile dominion: Complexity and the commons. Cambridge, MA: Perseus.

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                                                                                                                                                          An important book that defines an ecosystem as a complex adaptive system. The book makes a compelling case that by studying the structural, functional, and dynamic properties of ecosystems we might anticipate changes to ecosystems and the consequences of these changes to human well-being.

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                                                                                                                                                          • Millennium Ecosystem Assessment. 2005. Ecosystems and human well-being: Synthesis. Washington, DC: Island Press.

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                                                                                                                                                            One of a series of volumes produced as part of the Millennium Ecosystem Assessment. This volume defines and summarizes the concept of ecosystem services. This volume and the companion volumes are excellent resources.

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                                                                                                                                                            Human Impacts and Global Change

                                                                                                                                                            Ecosystem science and the ecosystem approach are central to current research on human impacts on the environment and global change. For example, the concept of ecosystem boundaries has shifted from its initial roots, as discussed above, to include thresholds or limits in which human activity can operate without adversely affecting both the ecosystem and human well-being. For example, Rockström, et al. 2009 formulates a series of planetary boundaries that human activities could putatively operate within, based on the structural, functional, and dynamic attributes of ecosystems. The boundaries are based on climate change, ocean acidification, stratospheric ozone depletion, the nitrogen cycle, the phosphorus cycle, global freshwater use, land system change, the rate of biodiversity loss, atmospheric loading, and chemical pollution. Among these, human activities have exceeded the proposed boundary levels for safe operating space for climate change, the nitrogen cycle, and the rate of biodiversity loss. A follow-up study, Steffen, et al. 2015, extends the work by identifying two core boundaries—climate change and biosphere integrity. Extensive work has been done on the impacts of humans on land use and land use intensification on biodiversity and ecosystem function (Allan, et al. 2015; Ceballos, et al. 2017), soils (Bradford, et al. 2014; Smith, et al. 2016), and biogeochemical cycles (Galloway, et al. 2003). There are numerous papers, books, and reports that cover specific biogeochemical cycles and the environmental consequences of altering them. Galloway, et al. 2003 provides a comprehensive synthesis and framework on the effects of anthropogenic loading of nitrogen from numerous sources on ecosystems. Carpenter, et al. 1998 and Schindler and Vallentyne 2008 provide excellent reviews of the sources and consequences of nutrient loading—eutrophication—to freshwater systems. Dybas 2005 covers the growing concern over the hypoxic areas in marine and large lake systems known as dead zones, caused by nutrient pollution. Baron, et al. 2013 summarizes several studies on the regional effects of anthropogenic reactive nitrogen and climate change on alpine and sub-alpine aquatic systems. Caldeira and Wickett 2003 provide a detailed accounting of the extent of and effect of elevated atmospheric CO2 concentrations on ocean pH. The Intergovernmental Panel on Climate Change (IPCC) produced three reports and a synthesis report (Bernstein, et al. 2008) on the consequences of greenhouse gases on ecosystems structure and function, along with a series of mitigation and adaptation strategies.

                                                                                                                                                            Large Initiatives

                                                                                                                                                            The ecosystem perspective has served as the basis for several large national and international initiatives, outlined in Aronova, et al. 2010 and Coleman 2010. The International Geophysical Year (1957–1958) provided the impetus for a new way of conducting ecological science—collaborative big data–driven science. The ecosystem approach seemed well suited to lead these efforts. A partial listing of the programs within the United States includes the International Geophysical Year (IGY, 1957–1958), The International Biological Program (IBP, 1964–1974), the US Long Term Ecological Research Program (LTER, 1980–present), and the National Ecological Observatory Network (NEON, 2008–present). These large initiatives have had a profound effect on the development of ecosystem ecology, and they reflect the development, challenges, and benefits of ecosystem ecology. Coleman 2010 provides an overview of the history of these initiatives, while Aronova, et al. 2010 provides an overview of the impact of these program on science writ large. C.H. 1975 provided a synopsis of a report by the National Academy of Sciences on the IBP, the findings of which were mixed. Among the participants, the report noted that the IBP “validated the interdisciplinary team approach to the study of ecosystems as well as the use of systems analysis and mathematical modeling, which they say, has turned ecology from a descriptive science into one with predictive capabilities that will aid policy-makers in making sophisticated decisions on resource management.” Among nonparticipants, the report noted that many felt that “the biome studies have accumulated masses of data while failing to establish chains of cause and effect that could lead to deeper understanding of how ecosystems work.” Boffey 1976 questioned the cost of the IBP. Hobbie, et al. 2000 is the lead paper in a special issue of BioScience that highlights the science of the NSF LTER program. The long-term perspective and the distributed nature of the sites within diverse regions and biomes has produced a significant advance in ecosystem ecology, particularly in our understanding of how ecosystem processes respond to change at different locations and at different spatial scale, and of how processes that operate over decadal time steps may drive or interact with local conditions. Mervis 2015 provides a critical assessment of the development and launch of the NEON network, “a continental-scale observatory that would monitor environmental change into a concrete plan.”

                                                                                                                                                            • Aronova, E., K. S. Baker, and N. Oreskes. 2010. Big science and big data in biology: From the International Geophysical Year through the International Biological Program to the Long Term Ecological Research (LTER) Network, 1957–present. Historical Studies in Natural Science 40:183–224.

                                                                                                                                                              DOI: 10.1525/hsns.2010.40.2.183Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                              The paper follows the development of ecosystem ecology in the era of big science and big data—defined as the synoptic collection of observational data on a global geographic scale.

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                                                                                                                                                              • Boffey, P. M. 1976. International Biological Program: Was it worth the cost and effort? Science 193:866–868.

                                                                                                                                                                DOI: 10.1126/science.193.4256.866Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                A critical assessment of the International Biological Program.

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                                                                                                                                                                • C.H. 1975. NAS report on International Biological Program. Science 187:663.

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                                                                                                                                                                  A candid assessment by the National Academy of Sciences of the successes and perceived failure of the International Biological Program.

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                                                                                                                                                                  • Coleman, D. C. 2010. Big ecology: The emergence of ecosystem science. Berkeley: Univ. of California Press.

                                                                                                                                                                    DOI: 10.1525/california/9780520264755.001.0001Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                    An easy-to-read account of the developments that took place in ecosystem ecology during the latter half of the 20th century. The book is written from a participant’s perspective, providing insights into the advances in ecosystem science and the large-scale initiatives that were undertaken.

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                                                                                                                                                                    • Hobbie, J. E., S. R. Carpenter, N. B. Grimm, J. R. Gosz, and T. R. Seastedt. 2000. Scientific accomplishments of the Long Term Ecological Research Program: An introduction. BioScience 53:21–32.

                                                                                                                                                                      DOI: 10.1641/0006-3568(2003)053[0021:TULTER]2.0.CO;2Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                      Lead paper of a special issue of BioScience that highlights the rational and importance of the NSF Long Term Ecological Research Program. The companion papers touch on many of the aspects of ecosystem ecology discussed above.

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                                                                                                                                                                      • Mervis, J. 2015. Ecology’s tough climb. Science 349:1436–1441.

                                                                                                                                                                        DOI: 10.1126/science.349.6255.1436Save Citation »Export Citation »E-mail Citation »

                                                                                                                                                                        A candid assessment of the launch of the National Ecological Observatory Network. The conclusions drawn are similar in many respects to those made about the International Biological Program.

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