Balance of nature

An ecosystem is located in the ecological balance when his condition did not change without externally applied disturbances. The concept of ecological balance has become problematic as a technical term and is no longer employed with the meanings that fell to him in its definition and implementation. Usually the term is used today outside of science and almost always with evaluative connotations.

System -theoretical description of the equilibrium

Systems theory can be an ecological balance described as follows: All possible states which can adopt the ecosystem, one can represented by a phase space, imagine. The dimensions of this space, the individual parameters which are necessary for the description of the system. Each state, the system can take any, can therefore be represented by a point in the state space. Since the space has as many dimensions as its complete description is required, it has many dimensions and is therefore not clearly represented. A change in the state (for example, increase or decrease of a kind) forms a track in the phase space ( a trajectory ) that leads from the initial state via the intermediate stages as the new final state. At equilibrium, the system as described above is if it does not leave a point of the state space. Fluctuate around an equilibrium state around it would be if the current phase of a regular or longer-term development cycle is well trained ( periodic orbit ). In the corresponding mathematical terminology called " ecological balance " then under undisturbed system dynamics (ie without additional effects from the outside ) " positively invariant " compact subset of the state space of an ecosystem. Not related to the system itself, but on the constituent individuals, there is a dynamic equilibrium, as it maintains only by constant flow of energy and materials to its stable state.

In the mathematical description of possible equilibrium points that can be stable or unstable. Although an unstable equilibrium point is considered on its constant, but comes at the slightest disturbance in another over ( in a graph it would on top of a " potential hill " balance ). With " ecological balance " are usually only stable equilibrium points meant ( they correspond to a " potential trough ").

Explanation of the modern, dynamic conception

System theoretical explanations

Investigative approaches to equilibrium come from two complementary sources:

• Empirical studies of populations and ecosystems with observation of the temporal dynamics. Considering the size population investigated species can (rarely ) more or less unchanged determine conditions for an extended period of time. More frequently, the populations of more or less extensive changes, which may indicate a mean value after a long observation period, around which the fluctuation occurs. In some cases, the population size is not only random but cyclical fluctuations, ie it passes through a certain period length repeating the same conditions. In other cases, the population size, however, can move in the long term, it can drop to zero, ie the population dies out (local). In the case of permanent changes to the system under consideration is different at the end of the observation period significantly from that at the beginning. This is not the case, it is stable over time.
• Empirical work on the ecological balance can also be based on functional ecosystem parameters. Thus, the temporal consistency of the built-up of an ecosystem biomass, the net primary production or its biologically regulated energy sales can give an indication of the existence of an equilibrium state. If the center of gravity of the system description given to the phenomena of mass and energy balance, one can speak of an ecological balance in these cases, even if the individual Polulationen not remain constant.

• Mathematical models of systems with multiple species. To better understand the intricate natural connections sought the theoretical ecology, map the behavior of the system in mathematical models. Input size of the models are population models of the species concerned with factors such as growth rate, mortality rate, carrying capacity of the habitat (how many individuals could total up to live there? ). Do the species one another, for example, by predator-prey relationships or competition, the fluctuations of the various species are coupled together. The behavior of the model is only of the values ​​of the respective factors ( input values ​​) in response. Models can be very simple with only a few factors or sophisticated with numerous sizes considered. Furthermore, it is possible to simulate random environmental fluctuations due to the introduction of random variables. Many models are based on systems of differential equations, which are based on the logistic equation, according to the inventors, so-called Lotka -Volterra models.
• If it is possible to simulate the empirically observed state of an ecosystem by a model, you have come to the understanding of the relationships in more detail. If this fails (although sufficient data are available), reveals a deficiency in the scientific theoretical models of the system. It is desirable for a better knowledge to make the models used as easy as possible.

If one tries to simple models of interacting species to construct that is intended to reflect the natural conditions in order to solve the problem of stability, observed the following one:

• Very simple models show constant population sizes, resulting from the initial parameters. If we choose different initial conditions, there is a different, also stable condition. This is called " neutral stable " models. A corresponding behavior of natural ecosystems is not observed. It is obviously not realistic pictures of reality
• More realistic models show highly fluctuating population sizes. Finally, one of the lines crossing the zero line, that is, the nature dies out. Through the extinction of all types, the system eventually collapses. Although in principle only once, there is nothing that behave as natural systems, shows the sheer fact that the biosphere still exists that this obviously can not be a sufficient explanation.
• Further adjustment is obtained through model, in which several types may coexist in certain parameter ranges. It shows: Within the range of values ​​that enables coexistence, aspire Popuationsgrößen a particular combination of values ​​, ie a given population size. In other cases, not a single value is reached, but the values ​​vary continuously around an average value. Outside the stable parameter range ( that is, if one of the types is too frequently or too infrequently ) the variations are randomly, which inevitably leads to breakdown of the system (see above). Within the "stable" range of values ​​strive all original combinations of values ​​, regardless of their initial values ​​, ie a value to it. In the phase diagram of this value corresponds to a certain point (or a cyclic oscillation of: a circle). Mathematicians call such a point an attractor of the system.
• In more complex systems, it can be observed that there may be different for different attractors regions of the state space. This means that with certain initial conditions, the system reaches a constant value combination, and then no longer be changed. For other initial conditions, the same system of another combination of values ​​tends to. For natural systems, this would mean: There are the same species with the same environmental factors acting more " stable " states.
• If models with multiple attractors represent reality true, this means that a system can be observed in a constant state, which it will strive again for deviations. Since in reality the environmental factors will never be completely stable, real systems would more or less around this equilibrium state (which corresponds to an attractor ) fluctuate. In addition, this state systems would strive again for interference. This property is referred to as resilience in natural systems (see below). But: If the fluctuations or disturbances too large, the system falls into the sphere of another attractor. One would observe a directional change to a new state of equilibrium towards. Because of strong disturbance, the system may miss the stable range of values ​​at all, ie collapse.

Observations of natural ecosystems have numerous circumstantial evidence geliefer that the mentioned model concepts may be applied to natural systems. In particular, systems with multiple equilibria in nature have been detected directly .. It is an active field of ecological research, to be published to the ongoing further work.

So what you referred to as ecological balance is characterized in that the development of the system is not leading out on its own from a fixed point or an orbit. In these cases, the paced point set of the state space is called the invariant.

A property which belongs to some equilibria, is stability. There are several different types of stability of ecological systems. It is helpful, for example, the following classification, which focuses on the composition of the " structure types ":

• Stability spoken to an ecosystem whose species composition remains unchanged at external disturbances substantially.
• Cyclicality causes induced fluctuations in species composition are run through completely and quickly by regular changing of environmental conditions.
• Elasticity exists when catastrophic stress situations, but they are typical of the location, can be compensated.
• Resilience is the ability, after major species shifts by a succession of other ecosystems (succession ) to return to the initial state.

However, a focus on certain forms of temporal invariance of the species is not mandatory for a definition of stability. Likewise, functional ecosystem parameters (eg, net primary production, energy expenditure ) can be used.

Examples of the modern conception

The former, static conception " of harmony, order and balance " in ecosystems is now considered outdated. In the example of a mehrschürigen meadow on medium ( mesotrophem ) Soil is a human -influenced ecosystems, which can be called cyclically stable. The cyclic disturbance is the mowing, which engages in the short term, the system, but it is produced by the regular interventions a long-term stable state. As soon as the management is omitted - ie is not mowed, shrubs spread out and eventually enters a bush encroachment. This succession finally ends in a forest. It thus enters a shift to a different ecosystem one that can be just as stable.

During the period of transition the ecosystem is out of balance. The concept of stability is not reasonably applicable at this time. However, this does not automatically mean that stocks in the imbalance automatically " less valuable " would be. It should be noted here, among other things, that insights into the " worthiness " of system states can in principle be derived not only from scientific data ( see below).

Other than under the static conception of ecological balance certain disorders can even strengthen the resilience of an ecosystem, so that the adaptability of ecosystems can be actively constructed. So to prevent the long term the outbreak of large, uncontrolled wildfires, covering also the crown area of ​​the regular, targeted Place of smaller, localized fires in the undergrowth of certain forest ecosystems. An example of a non- Resilient system condition would be an over-fertilized lake, which can " upset " in a hot summer. As a result, it can come in such a polytrophic lake sapropel formation and a permanent shortage of oxygen, which usually has a strong decline in biodiversity result. The disorder overwhelms the self-organizing capacity of the lake, in the sense that the return to the previous state is very slow.

Period, the reference state, local purchase

Depending on the viewing scale (days, years, centuries, geological eras ), there are different results for what can be considered "stable " or " balanced ". The long-term, related to a larger space equilibrium of a so-called climax community may be influenced by different cyclical dynamics on a smaller scale. This recent studies show the development of virgin forests that extend from the so-called mosaic - cycle concept. In particular for species that colonize pioneer sites, the extinction of local populations, the re-establishment is a natural process, just as in other locations (eg at the Little Ringed Plover ). The question of stability or the balance of the population depends here also depend on which spatial reference is selected.

Some ecosystems need to achieve a stable state for centuries; here can be always defined sense the ecological balance even after a dynamic conception often not. This is because that relevant environmental influences faster (and unpredictable ) change as the ecosystem can respond. One example is the forest ecosystems of the temperate zone. These take many centuries to return after a strong disturbance in an initial state "back". Even without human influence, however, is to be expected in such periods of climate change, which are strong enough to change the direction of succession ( cf. Little Ice Age ). The requirement for an " undisturbed system dynamics " here is largely a definitional fiction, which is empirically not to meet.

Into account the anthropogenic influence

It is controversial whether and at what level human impacts on ecosystems are to be regarded as a fault.

Evaluation and application in conservation

Terms such as " stability " or " balance " often contain a normative significance: imbalances are considered by many people as threatening rather than a " harmonious " balance. What is meant with " fault" of the ecological balance, is therefore usually meant implicitly that an intervention to restore the balance was necessary.

In the scientific debate about desirable stability properties or desirable ecosystem dynamics is the argument of the " ecological balance " is no longer used. When a newly adopted system state is less productive or has a lower biodiversity, it may be less desirable according to a subjective view. The subject of nature and species protection issues was therefore often been the preservation of a certain state: A particular plant community or species should - be obtained - preferably at the same place and in a similar number. However there are in recent times reinforced trends that move away from such a rather conservative nature protection concept. This may on the one hand be to accept the change through a process protection as part of natural processes. On the other hand, can actively pursue the protection of biodiversity and aesthetic as well as cultural and historical specificity of the landscape a landscape conservation approach with targeted habitat management.

• The beginning of the 19th century, especially in Central Europe spreading cataloging of vegetation in hierarchical units (plant sociology) has probably reinforced the thinking in static categories. This now mostly as worthy of protection prestigious units (eg Genisto pilosae - Callunetum = hair broom heath ) at that time were quite typical landscape elements, however, were based on a partially unsustainable use manner ( in the example the hair broom Gentiles are substitute communities for over-exploited oak forest communities ), while today's landscape is dominated by plant communities, since the (agricultural ) use manner has changed greatly over 100 years ago.
• Spreads a species becomes extinct, because the living conditions are better for them, and if this is spreading ( also ) at the expense of other target species of conservation, species protection and / or hunting, quickly creates the requirement that the preservation of the ecological balance stopped the spread or should be done. reversed.

In both cases, upon close scrutiny not readily clear why just meant to represent the former and current situation of the need to retain optimum state of " ecological balance ".

• Bezzel brings as an example of the high forest, which perform certain functions as protection forest or timber resource or a landscape impressed: " Too much ungulates disrupts this requirement corresponding forest. You do not want to wait for deer or chamois destroyed by overuse of the young plant their own habitat, so they are forced to disappear by lack of resources and the forest gets its chance in a long time periods spanning cycle. Whether such an intention, the question amounts often, a particular developmental ( successional ) stage stop, as " biological balance " is described properly be doubted emphatically. " Constant relations or structures " would be the more appropriate term. "

For the preservation of certain communities or a certain status of biodiversity, the argument of " ecological balance " is therefore not suitable even if it would be a fundamentally empirical and normative duty term. For many target species of conservation management measures are common, representing a disturbance of naturally occurring successional processes and thus a disturbance of itself naturally -adjusting " equilibrium " (eg for pioneer species, the early or middle stages of succession as a habitat need as natterjack toad, woodlark and red-backed shrike ).