Prof. Bai-Lian (Larry) Li is mathematical and theoretical ecologist and director of the Ecological Modeling Lab at the University of New Mexico Department of Biology. His main research interest is ecological modeling and systems theory, and recent work has emphasized ecological scaling, spatio-temporal modeling techniques, energetic and thermodynamic foundations of ecological dynamics, and application of nonlinear dynamics and complex systems theories to multiple scale ecology. This article is excerpted largely from "Why is the holistic approach becoming so important in landscape ecology?" as it appeared in the journal Landscape and Urban Planning 50(1-3):27-41, Elsevier.
Patricia (Patty) Sprott is editor of this Newsletter who strives to understand as much of the subject matter as possible. When considering this article, Patty turned to Larry again and again for clarification on this difficult material, producing this conversation.
Landscape ecology is a way of thinking about the evolution and dynamics of heterogeneous landscapes. The core of landscape ecology is viewed as the body of knowledge or facts about ecological space, spatial heterogeneity, and scaling.
Traditionally, landscape ecology has resorted to reductionism, borrowing models from other sciences because it has not formulated its own basic theories. In the reductionism tradition, landscape ecology studies have been dominated by taking things apart and individually characterizing various attributes of spatial patterns.
But shortfalls in reductionism are increasingly apparent. In terms of how biomolecules work, for example, reductionism has been used successfully to examine the components, but not the complex interactions between the components. Biology has spent decades trying to be like traditional physics, if only to utilize its basic theory of trying to understand complicated systems by understanding each part at its most basic level. Now biologists have found that its time to put it all back together, and there is no mechanism for doing this.
Herein lies the problem: Studies in landscape ecology generally do not address the intrinsic causality and underlying dynamics of the pattern. Therefore, they cannot explain why patterns change with biotic and abiotic conditions. Some of the field's most fundamental questions cannot be answered, as there are no mechanisms, no underlying theories for addressing them through this traditional reductionism approach. In other words, now that we have taken everything apart and have defined and described all the pieces, how to we reassemble them into a working whole? To do this, Larry Li proposes a ‘holistic-mechanistic' approach.
Larry: Here, I propose a non-linear physics-based holistic approach--an ‘operationable' holistic approach (something we can actually use), which I will call holistic-mechanistic, which defines a system-level or global property of ecological systems by using non-equilibrium thermodynamics of self-organization, synergetics, as well as other systems approaches.
Patty: So you are borrowing theories from non-equilibrium thermodynamics of self-organization, and synergetics, and adding some theories of your own, to form new methods for studying landscape ecology (Landscape ecology 101).
Landscape Ecology 101Here is a quick primer in the basic theories discussed in this article -- Ilya Prigogine (b. Jan. 25, 1917, Moscow, Russia: Nobel Prize for Chemistry in 1977 for contributions to non-equilibrium thermodynamics) applied the second law of thermodynamics to complex systems, including living organisms. The second law states that physical systems tend to slide spontaneously and irreversibly toward a state of disorder (a.k.a. ‘entropy'). The second law does not, however, explain how complex systems could have arisen spontaneously from less ordered states and have maintained themselves in defiance of the tendency toward entropy. Prigogine argued that as long as systems receive energy and matter from an external source, nonlinear systems (or dissipative structures, as he called them) could go through periods of instability and then self-organization, resulting in more complex systems whose characteristics cannot be predicted except as statistical probabilities. Prigogine's work was influential in a wide variety of fields, from physical chemistry to biology, and was fundamental to the new disciplines of chaos theory and complexity theory. ‘Self-organization' is the process by which systems of many components tend to reach a particular state with no external interference. Self-organizing behavior is the spontaneous formation of well-organized structures, patterns, or behaviors, from random initial conditions. In nature, there is a universal tendency for spontaneous self-organization. Self-organizing structures can only be maintained by a constant flux of energy through them, and are therefore not in equilibrium. The most interesting behavior is found in the transition between order and chaos -- edge of chaos -- and classified as a kind of organized complexity. This behavior -- many parts working together to achieve some order -- is also known as synergetics [Haken, 1977]. |
Patty: O.k. so ‘mechanistic' means mechanically determined and refers to Prigogine's theory of non-linear systems -- and ‘holistic' means relating to or concerned with wholes or with complete systems rather than with the analysis of, treatment of, or dissection into parts and refers directly to the "many parts working together to achieve some order" part of Haken's synergetics theory... How do these fit together?
Larry: The term ‘ecosystem' refers to a holistic and integrative ecological concept that combines living organisms and their physical environment into a structural and functional, interacting entity (Tansley, 1935). Within this entity, the notion ‘system' implies an irreducible complex of elements and subsystems in which the parts are interacting and producing a very special behavior, which can only be assigned to the total system -- as a whole. These systems dynamics have to be analyzed as very specific qualities where the whole is more than the sum of parts.
Whenever the interrelations between ‘parts' and ‘wholes' are discussed in ecology, the central object of interest is the ecosystem with its hierarchical connections between superior and inferior spatio-temporal levels of organization.
The systems-level itself comprises features that are not predictable from the subsystem levels if these parts are observed in isolation. Such additional hierarchical qualities are nominated as emergent properties. They characterize specific systems levels; therefore, if such a level has to be described, the corresponding emergent properties should be included in any case.
If one considers subsystems of a grand complex landscape system, then one should also consider the connectivity among the subsystems. That the whole is more than the sum of the parts is the central theme for all holistic approaches.
Thermodynamics is concerned with the laws governing the macroscopic properties of systems subject to thermal change (e.g. energy, temperature, pressure, entropy). In Erwin Schrodinger's book What is Life? He discusses the metabolism of a living body in terms of entropy production and entropy flow (Schrodinger, 1944). If an organism is in a steady state, its entropy remains constant over time, and, therefore, dS=0. As a result, the entropy production diS is compensated by the entropy flow diS+deS=0, or deS= -- diS<0. Life is associated with entropy production and, therefore, with irreversible processes.
Patty: Wait a minute -- are equations really necessary? Can't you just use English?
Larry: Basically, No. Equations are the language of mathematics. If an equation could be explained in English, there would be no need for the equations. The ‘proof' must have an equation -- there is some abstraction that the language of math represents. Mathematic proof is fundamentally different than physical proof. For example: In a field study, the researcher sees no black rabbits. Therefore, the statement "all rabbits in this field during this study were white" is true. But physical proof cannot guarantee the future as can math proof, which can describe what has been as well as what will be. See, math can prove the future and so in general mathematical equations cannot be reduced to natural language.
Anyway, in equilibrium thermodynamics, the second law (i.e. the law of free energy decrease and entropy production) enables stable states to be distinguished in a definite way: in a stable state the free energy has at least a local minimum, and the entropy, at least a local maximum. In the theory of open systems, the second law of thermodynamics is no longer of help, since in non-equilibrium stationary states the free energy need not have a minimum, nor the entropy a maximum.
Near-equilibrium laws of nature are universal, but when they are far from equilibrium, they become mechanism-dependent (Prigogine, 1977). Considering ecological landscapes under constant influence of stresses and disturbances, the systems definitely are in a state far from thermal equilibrium. However, current energetic and thermodynamic perspectives of ecosystem theories are all based on non-equilibrium, but linear thermodynamics. We have to rethink some of the fundamental assumptions of physical laws for complex ecological systems accordingly.
On the basis of a holistic systems view and Prigogine and Haken's theories discussed above, a synergetic theory of ecological landscape systems can be formed-a combination of holistic and mechanistic approach -- together.
Now I propose four basic principles on which to build landscape ecology.
- Landscape wholeness and hierarchy (or ‘holarchy') principle - much of the above discussion already focused on the principle. A holarchically (rather than hierarchically) integrated system is not a passive system, committed to the status quo. It is a dynamic and adaptive entity, reflecting in its own functioning the patterns of change over all levels of the system. It seems to me that the term holarchy may be more suitable here.
- Landscape antagonism principle -- there is an antagonistic action between endogenic (originating inside the landscape) and exogenic (origninating outside the landscape) processes. Atagnoistic processes roughly balance each other in landscape development.
- Landscape instability or multistability principle -- dissipative systems can reach conditions in which the stochastic fluctuations lead to an intrinsic instability: this is at the root of the principle. The mechanistic reason for the operation of the instability principle lies in the frequent existence of a positive feedback mechanism.
- Landscape selection principle -- those landscape forms or types are selected by geophysical-chemical, biological and climatic processes which are thermodynamically the most stable ones at near or far-from equilibrium. The natural forms and configurations in a landscape are primarily those that are most stable under their own weight. All processes within the landscape are of irreversible type, thus producing entropy. The above four principles usually will work together. Non-equilibrium, nonlinear physics is integral to our holistic mechanistic approach. Several examples showing how such a holistic approach can help us to get a better understanding of landscape systems and their dynamics are available in the article from which this conversation is derived (Li, 2000).
Patty: The "examples" are replete with sophisticated equations so I have spared our Newsletter readers the chore of flipping quickly past them.
Larry: Yes, well... Finally, we must ask: What makes a good theoretical model? If a model can be formally constructed from a body of existing theories with the addition of any necessary new development, if the theory takes into account the dominant processes operating, and if the theories are at the scale of interest, then the new theory should be as fundamental as that from which it is derived. Unfortunately, most of our existing models in landscape ecology have only an informal link to an accepted body of theory. I believe that theoretical concepts from the basic sciences (such as physics and chemistry) and mathematics should provide foundational principles for guiding the development of theories about landscape dynamics. What I have tried to demonstrate here are the criteria I used in this holistic theoretic framework/approach, that is, an explicit mathematical physical basis, simplicity, generality, richness and the potential for scaling-up and down. This, I believe, should be our ultimate goal in developing holistic or theoretical landscape ecology.
References
Haken, H. [1977]. Synergetics. Springer-Verlag. Normile, D., 1999. Exploring the systems of life. Science 284, 80-81.
Prigogine, I., 1997. The End of Certainty: Time, Chaos, and the new Laws of Nature. The Free Press, New York, 228 pp.
Schrodinger, E., 1944. What is Life? Cambridge University Press. Cambridge, 90 pp.
Tansley, A.G., 1935. The use and abuse of vegetational concepts and terms. Ecology 16, 284-307.