Ecological balance

from Wikipedia, the free encyclopedia

An ecosystem is in ecological equilibrium if its condition does not change without external disturbances . The term ecological balance has become problematic as a technical term and is no longer used in the meaning that it was given when it was defined and introduced. Today the term is mostly used outside of science and almost always with judgmental connotations.

System theory description of equilibrium

In system theory , an ecological balance can be described as follows: All possible states that the ecosystem can assume can be imagined as represented by a phase space . The dimensions of this space form the individual parameters that are required to describe the system. Every state that the system can assume can be represented by a point in this state space. Since the room has as many dimensions as are necessary to fully describe it, it has a large number of dimensions and can therefore no longer be represented clearly. A change in the state (e.g. increase or decrease in a species) forms a path in phase space (a trajectory ) that leads from the original state through the intermediate stages to the new final state. The system described in this way is in equilibrium when it does not leave a point in the state space. It would fluctuate around a state of equilibrium if the current phase of a regular or long-term development cycle is well developed ( periodic orbit ). In the corresponding mathematical terminology, “ecological equilibrium” then describes a “positively invariant” compact subset of the state space of an ecosystem under undisturbed system dynamics (i.e. without additional external influences) . With reference not to the system itself, but to the constituent individuals, it is a steady state , since it can only maintain its stable state through the constant flow of energy and substances.

When describing possible equilibrium points mathematically , these can be stable or unstable. An unstable equilibrium point is constant in itself, but changes into another with the slightest disturbance (in a graphic representation it would balance on the top of a "mountain of potential"). “Ecological balance” usually only refers to stable points of balance (they correspond to a “potential trough”).

System theory explanations

Research approaches to equilibrium come from two complementary sources:

  • empirical studies of populations and ecosystems with observation of temporal dynamics.
    • If one looks at the population size of examined species, one can (rarely) determine more or less unchanged conditions over a longer period of time. More often, the populations show more or less extensive fluctuations, which after a long observation period can reveal a mean value around which the fluctuation occurs. In some cases the population size shows not only random but cyclical fluctuations; that is, it runs through the same states over and over again with a certain period length. In other cases, however, the population size can shift over the long term, it can fall to zero, i.e. i.e. the population is (locally) extinct. In the case of permanent changes, the system under consideration at the end of the observation period differs significantly from that at the beginning. If this is not the case, it is stable over time.
    • Empirical work on ecological balance can also be based on functional ecosystem parameters. The temporal constancy of the biomass built up by an ecosystem , its net primary production or its biologically regulated energy turnover can give an indication of the existence of a state of equilibrium. If the focus of the system description is placed on phenomena of the material and energy balance, one can even speak of an ecological balance in these cases if the individual populations do not remain constant.
  • mathematical models of systems of several types.
    • For a better understanding of the involved natural relationships, theoretical ecology tries to depict the behavior of the system in mathematical models. The input variables of the models are population models of the species involved with factors such as growth rate, mortality, and the carrying capacity of the habitat (how many individuals could live there at most?). Do the species interact, e.g. B. through predator-prey relationships or competition, the fluctuations of the different species are linked. The behavior of the model depends exclusively on the values ​​of the respective factors (the input values). Models can be extremely simple with just a few factors, or sophisticated with numerous sizes considered. It is also possible to simulate random environmental fluctuations by introducing random variables. Many models are based on systems of differential equations that are based on the logistic equation , so-called Lotka-Volterra models after the inventors.
    • If it is possible to simulate the empirically observed conditions of an ecosystem using a model, one has come closer to understanding the relationships. If this does not succeed (although sufficient data is available), there is a deficiency in the scientific model conception of the system. For better knowledge, it is worthwhile to make the models used as simple as possible.

If one tries to construct simple models of interacting species that are supposed to represent the natural conditions in order to solve the problem of stability, one observes the following:

  • very simple models show constant population sizes that result from the initial parameters. If one chooses other initial conditions, another, likewise stable, state results. This is called “neutral stable” models. A corresponding behavior of natural ecosystems is not observed. Obviously, they are not realistic representations of reality
  • somewhat more realistic models show strongly fluctuating population sizes. Eventually one of the lines crosses the zero line, i.e. i.e., the species is dying out. The system eventually collapses due to the extinction of all species. Although in principle nothing speaks against the fact that natural systems behave in this way, the sheer fact that the biosphere still exists shows that this obviously cannot yet be a sufficient explanation.
  • through further adaptation, models are obtained in which several types can coexist with one another in certain parameter ranges. It can be seen that within the range of values ​​that enables coexistence, the population sizes strive for a certain combination of values, i.e. H. a certain population size. In other cases, a single value is not achieved, but the values ​​fluctuate permanently around a mean value. Outside the stable parameter range (i.e. when one of the types becomes too frequent or too rare), the fluctuations become random, which inevitably leads to system breakdown (see above). Within the "stable" value range, all original value combinations, regardless of their initial values, strive towards one value. In the phase diagram, this value corresponds to a certain point (or for a cyclic oscillation: a circle). Mathematicians call such a point an attractor of the system.
  • In even more complex systems one can observe that there can be different attractors for different areas of the state space. This means: With certain initial conditions, the system achieves a constant combination of values ​​and then no longer changes. With different starting conditions, the same system strives for a different combination of values. For natural systems this would mean: There are several “stable” states for the same species with the same environmental factors.
  • If models with several attractors accurately represent reality, this means: A system can be observed in a constant state, which it will strive towards again in the event of deviations. Since in reality the environmental factors will never be completely stable, real systems would always fluctuate more or less strongly around this state of equilibrium (which corresponds to an attractor). In addition, systems would strive to return to this state in the event of a malfunction . This property is called resilience in natural systems (see below). But: If the fluctuations or disturbances become too large, the system comes under the influence of another attractor. One would now observe a directed change towards a new state of equilibrium. Due to strong disturbances, the system can miss the stable value range at all, i. H. to collapse.

Observations on natural ecosystems have provided numerous indications that the model concepts mentioned here are possibly applicable to natural systems. In particular, systems with multiple equilibria have already been demonstrated directly in nature. It is an active field of ecological research, on which further work is published continuously.

What is called ecological equilibrium is characterized by the fact that the development of the system does not by itself lead out of a fixed point or an orbit . In these cases the set of points in the state space is called invariant .

Stability, cyclicality, elasticity, resilience

In connection with the discussion on the equilibrium or stability of ecosystems, a distinction must be made between several terms, which, however, are sometimes used differently in the literature. The following structure is based on Heinz Ellenberg with a focus on vegetation:

  • Stability is attributed to an ecosystem whose species structure remains essentially unchanged in the event of external disturbances.
  • Cyclicality means that fluctuations in the species structure caused by regular changes in environmental conditions are completely and quickly run through.
  • Elasticity exists, even if catastrophic stress situations, which are typical for the location, can be compensated.
  • Resilience is the ability toreturn to the original species structurethrough a sequence of other ecosystems ( succession )after significant species shifts (e.g. from forest to herbaceous societies).

Elastic and resilient systems are at least temporarily unstable. There is not just one, but several equilibrium positions that are stable or unstable, that can be natural or man-made. A meadow can be understood as a stable, human-influenced ecosystem. If the mowing omitted or changed propagate perennials and finally enters a Verbuschung one. This succession eventually leads to a forest that can be just as stable. During the succession period, the ecosystem is not in equilibrium, and the concept of stability cannot be used meaningfully.

Use of the term "ecological balance"

The idea of ​​a balance in nature can be traced back to ancient times. In the 18th century, Carl von Linné found the idea of ​​equilibrium and striving towards an order predetermined by the Creator . With the discovery of evolution in the 19th century, there were counter-arguments, but the mathematical models for ecosystems that emerged at the beginning of the 20th century suggested a striving for equilibrium. Even then, some ecologists contradicted the theories of striving for a balance in nature. Nevertheless, the equilibrium theory with the so-called species-area relationship reached its climax in the 1960s: As the species communities were striving for equilibrium, historical effects, spatial heterogeneity or disturbances in ecosystems would play small to insignificant roles in the prediction of species numbers on a particular one Area too.

During the search for evidence or counter-arguments for this theory, it became clear that it is not the striving for equilibrium of organisms that determines the biodiversity of an area, but various system and species-immanent factors. A stability debate arose from the equilibrium debate. It was expected that a simple, species-poor system would fluctuate rather than a more complex, species-rich system. Productivity was later added to the scientific dispute. It became clear that z. For example, if the soil has a good nitrogen supply, the less productive species in grasslands are lost, but this does not necessarily go hand in hand with a decrease in productivity and stability of the biological system. Landscape ecologists found that ecosystems are generally subject to complex dynamics due to various systemic disturbances. In nature conservation, however, the idea of ​​balance and stability was maintained for a long time, until dynamic processes in process protection were finally recognized as a nature conservation goal.

The concept of "ecological balance" is considered out of date for justifications in nature conservation issues. However, the nature conservation discussion is still shaped by the idea of ​​an ecological balance that is damaged by human intervention. Problems in the use of the term "ecological balance" arise from several fuzziness:

  • The time span and spatial reference must be specified. Depending on the scale of observation (days, years, centuries, geological epochs), there are different results for what can be considered "in equilibrium". Mostly unspoken reference states are meant that result from a human interest in a certain state of the ecosystem. In nature conservation, the 19th century is often unspoken as the reference state. The abundance of species at that time, however, resulted from the extensive and almost extensive overuse of the soil. In general, a certain, single state cannot be assigned to nature as “correct”, since then all previous ones would be “wrong”. In the long term, nature is not static, but changing. These changes made possible the creation of biodiversity through evolution.
  • Consideration of the anthropogenic influence: In the cultural landscape, which is increasingly shaped by man, initially, on the one hand, areas characterized by high natural dynamics such as river meadows disappeared, on the other hand, new, human-influenced dynamic processes emerged (e.g. clearing of trees, arable farming, grassland management, opencast mining), which in turn ensured that biodiversity was maintained and even increased. The biodiversity that exists in Germany and has arisen through historical land use would only be unsustainable if human interference were not taken. The discussions in nature conservation therefore deal with the degree of process protection (not intervening) on ​​the one hand and active disturbances on the other. It is controversial whether and to what extent human influences on ecosystems are to be regarded as a disruption and what is the relationship between nature and humans. The subject of nature and species protection issues is often the preservation of a certain condition: a certain plant community or animal species should be preserved - if possible in the same place and in a similar number. The maintenance of a certain development stage of the vegetation with adapted animal species through constant human intervention on a defined area with suppression of the "naturally" occurring developments cannot plausibly be described with the justification of the maintenance of an "ecological balance".
  • Terms such as “stability” or “equilibrium” contain a normative meaning that suggests an objectively determinable target state of the ecosystem. When speaking of a disturbance of the ecological balance, it is usually implied that an intervention is necessary to restore the balance. But nature doesn't judge. Judgments and evaluations come from people. Which human perspective prevails depends on time.

Individual evidence

  1. ↑ on the history of concepts: FN Egerton: Changing concepts of balance of nature . In: Quarterly review of biology . tape 48 , 1973, pp. 322-350 , JSTOR : 2820544 ( jstor.org ).
  2. ↑ Kim Cuddington: The Balance of Nature metaphor in Population Ecology: Theory or Paradigm? Presentation by The Philosophy of Science Association on November 2, 2000, PSA 2000 Program , as of December 2010.
  3. ↑ It can be proven mathematically that there can be no other solutions besides the three listed
  4. ^ Carl Folke , Steve Carpenter, Brian Walker, Marten Scheffer, Thomas Elmqvist, Lance Gunderson, CS Holling: Regime Shifts, Resilience, and Biodiversity in Ecosystem Management . In: Annual Review of Ecology, Evolution, and Systematics . tape 35 , no. 1 , 2004, ISSN  1543-592X , p. 557-581 , doi : 10.1146 / annurev.ecolsys.35.021103.105711 ( annualreviews.org [accessed May 8, 2011]).
  5. ^ Robert M. May: Thresholds and breakpoints in ecosystems wih a multiplicity of stable states. In: Nature . Volume 269, 1977, pp. 471-477.
  6. ↑ CS Holling: Resilience and stability of ecological systems. In: Annual Review of Ecology and Systematics. Volume 4, 1973, pp. 1-23.
  7. ↑ Examples: a) Hartmut Dierschke ( Plant Sociology . Basics and Methods. Eugen Ulmer Verlag, Stuttgart 1994, ISBN 3-8001-2662-1 , p. 441 f.) Uses elasticity and resilience synonymously. b) Wolfgang Scherzinger ( nature conservation in the forest. Quality goals of dynamic forest development. Ulmer Verlag, Stuttgart 1996, p. 169) understands elasticity to mean "overcoming disturbances by restoring the initial stage (e.g. rapid regeneration on disaster areas)" and under resilience the "duration of the elasticity process". c) Otti Wilmanns ( Ecological Plant Sociology. Quelle & Meyer Verlag, Wiesbaden 1998, ISBN 3-494-02239-9 , p. 22) describes biocenoses as stable “if the population sizes of their species either under constant general conditions only change slightly and for a short time commute a mean value, i.e. show constancy; or if, in response to certain disturbances, they return elastically to the old state, that is, they have elasticity; or if only strong external influences lead to changes, i.e. there is resistance. "
  8. ^ A b Heinz Ellenberg : Vegetation of Central Europe with the Alps in an ecological, dynamic and historical perspective. 5th, heavily changed and improved edition. Ulmer, Stuttgart 1996, ISBN 3-8001-2696-6 , p. 110.
  9. ↑ Otti Wilmanns: Ecological Plant Sociology. Quelle & Meyer Verlag, Wiesbaden 1998, ISBN 3-494-02239-9 , p. 23.
  10. ↑ a b c d Andre Bönsel, Joachim Matthes: Process protection and disturbance biology . Nature conservation theses since the ecological paradigm shift from balance to imbalance in nature. In: Nature and Landscape. Tape. 82, No. 7, 2007, pp. 323-325.
  11. ↑ a b c Reinhard Piechoki: Landscape homeland wilderness. Protection of nature - but which one and why? Verlag CH Beck, Munich 2010, ISBN 978-3-406-54152-0 , pp. 18, 64f.
  12. ↑ a b Martin Gorke: Eigenwert der Natur. Ethical reasons and consequences. Hirzel-Verlag, 2010, ISBN 978-3-7776-2102-9 , p. 142 f.
  13. ↑ a b c Joseph Reichholf: The future of the species. New ecological surprises . CH Beck-Verlag, Munich 2005, ISBN 3-406-52786-8 , pp. 14, 17, 126, 148.
  14. ↑ a b Ludger Honnefelder: Which nature should we protect? In: GAIA Volume 2, No. 5, 1993, pp. 257, 261.
  15. ↑ Klaus Peter Rippe: To deal with animal immigrants. Ethics, animal killing and the control of invasive species. In: animal ethics. Volume 11, 2015, p. 58.
  16. ↑ G. Hartung, T. Kirchhoff: What nature do we need? Anthropological dimensions of dealing with nature. In: G. Hartung, T. Kirchhoff (Ed.): What nature do we need? Analysis of a basic anthropological problem of the 21st century. Verlag Karl Alber, Freiburg 2014, p. 23.
  17. ↑ Einhard Bezzel: Dear bad animal. The misunderstood creature. Artemis & Winkler Verlag, Munich 1992, ISBN 3-7608-1936-2 , pp. 160, 196 f.
  18. ↑ Wolfgang Scherzinger: Nature conservation in the forest. Quality goals of dynamic forest development. Ulmer Verlag, Stuttgart 1996, p. 175.