Cybernetics

A M Makarieva, Petersburg Nuclear Physics Institute, St. Petersburg, Russia © 2008 Elsevier B.V. All rights reserved.

Introduction Control Processes in Ecological Systems

Solar Energy and Information Further Reading

Stores and Fluxes of Information in the Natural Biota and Civilization

Introduction

The word 'cybernetics' originates from the Greek word for 'steersman'. Cybernetics can be broadly defined as a field of knowledge seeking to offer a general mathematical approach to the study of complex systems irrespective of their nature (e.g., artificial or living). In this context, under complex systems, one understands the systems composed of elements exchanging energy, matter, and information with one another and with the environment, that is, systems where various control (feedback) processes operate (Figure 1).

To give a simple example, stability of a system quantity x over time t can be described as dx/dt =—kx, where parameter k can, in general, depend on both x and t. If the value of k is positive, any disturbance ax = x — x0 of the initial value x0 of this parameter will exponentially diminish with time, returning the system to the initial state, ax = exp(—kt). At negative k, any slight perturbation will exponentially amplify, destabilizing the system. Such formal description does not depend on the nature of either parameter x or the positive or negative feedback processes in the system that are responsible, respectively, for the system's instability or stability (homeostasis).

Established in the 1940s and the 1950s with works of Norbert Wiener, William Ashby, and others, the notion of cybernetics became well-known in the 1970s and the 1980s, the time marked with intensive research and large expectations associated with the idea of creating artificial intelligence. Cybernetics studies in life sciences can be exemplified by the models of organic evolution like the Eigen's hypercycle; there is much modeling research in the fields of neurophysiology and sociobiology.

While generality of a scientific approach is obviously an important scientific merit, the overall success of the approach is determined by its concrete applications within particular fields. Ecology, the science of interactions among

Figure 1 Natural terrestrial ecosystem represented as a cybernetic system. The division into blocks is made on the basis of the trophic level and body size l (cm) of the organisms. Feedback loops between the system's blocks are exemplified by the fluxes of organic carbon (solid arrows) coming in and out of each block and fluxes of inorganic carbon (dotted arrows) coming out of the heterotrophic blocks into the autotrophic one. For heterotrophic blocks dM/dt = Pin - Pout - R, where M is the store of organic carbon in live biomass within the block, Pin is the incoming organic carbon, Pout is the organic carbon produced within the block and transferred to the next trophic level, and R is respiration (decomposition of organic carbon). 'Carnivores' indicate vertebrate-feeding heterotrophs, 'insectivores' indicate invertebrate-feeding heterotrophs. Numbers near solid arrows indicate the flux magnitude in terms of the percentage of ecosystem net primary productivity (100%). Numerical data of Gorshkov VG (1995) Physical and Biological Bases of Life Stability. Berlin: Springer; Makarieva AM, Gorshkov VG, and Li B-L(2004) Body size, energy consumption and allometric scaling: Anew dimension in the diversity-stability debate. Ecological Complexity 1: 139-175.

Figure 1 Natural terrestrial ecosystem represented as a cybernetic system. The division into blocks is made on the basis of the trophic level and body size l (cm) of the organisms. Feedback loops between the system's blocks are exemplified by the fluxes of organic carbon (solid arrows) coming in and out of each block and fluxes of inorganic carbon (dotted arrows) coming out of the heterotrophic blocks into the autotrophic one. For heterotrophic blocks dM/dt = Pin - Pout - R, where M is the store of organic carbon in live biomass within the block, Pin is the incoming organic carbon, Pout is the organic carbon produced within the block and transferred to the next trophic level, and R is respiration (decomposition of organic carbon). 'Carnivores' indicate vertebrate-feeding heterotrophs, 'insectivores' indicate invertebrate-feeding heterotrophs. Numbers near solid arrows indicate the flux magnitude in terms of the percentage of ecosystem net primary productivity (100%). Numerical data of Gorshkov VG (1995) Physical and Biological Bases of Life Stability. Berlin: Springer; Makarieva AM, Gorshkov VG, and Li B-L(2004) Body size, energy consumption and allometric scaling: Anew dimension in the diversity-stability debate. Ecological Complexity 1: 139-175.

organisms and between the organisms and their environment features high complexity and has the problem of homeostasis versus change at its very heart. To apply the cybernetics approach in ecology, it is important to establish the correspondence between the major notions of cybernetics like information exchange, communication, control processes, etc., and measurable characteristics of the organism, ecosystem, and biosphere. This article describes the essential aspects of ecological cybernetics. Among the subsequent sections, the first section discusses the origin of information fluxes in the biosphere. In the second section, information stores and exchange fluxes within the biosphere, on the one hand, and within the modern civilization, on the other hand, are described and compared. The third section discusses control processes operating at the biota-environment interface, which allow life to persist on Earth for practically infinite time periods of the order of billion years, thus maintaining homeostasis of the living matter.

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