Ecosystem development follows a series of stages. The overall development is denoted succession:
Start of the succession (pioneer stage, boundary growth after J0rgensen and Fath, exploitation function after Holling): In this initial state, an input of low-entropy (high exergy; for this concept see Eco-Exergy as an Ecosystem Health Indicator and Exergy) energy into the system starts the sere. The developmental potential depends on the genetic information that is available in the seed bank or by lateral inputs. The connectivity (see Connectance and Connectivity) between the elements and the self-regulation are low, leakiness is high, and the sum of potential developmental opportunities (developmental uncertainty) is high. The system has a very high adaptability and flexibility.
Fast growth (pioneer stage, structural growth after J0rgensen and Fath, exploitation function after Holling): Pioneer stages can also be characterized by a high and rapid increase of biomass, correlated with an increase of the numbers and sizes of the ecosystem components. The biomass forms a physical structure that is able to capture the incoming high-exergy-containing solar radiation. To provide for the growing number of participants, the energy throughflow increases as well as exergy degradation which is necessary for the maintenance of the components. Connectivity is still low, and therefore external inputs can modify the system easily: the adaptability is high. The ecosystem is dominated by r-strategists, which can utilize the increasing input of high-exergy solar radiation for fast growth.
Fast development (middle succession, network growth after J0rgensen and Fath, conservation function after Holling): After initial structure has been established, the successful actors start funneling energy and matter into their own physiology. The connectivity of the system increases by additional structural, energetic, and material interrelations, and cycling mechanisms. The single species become more and more dependent on each other, uncertainty decreases, and the role of self-regulating processes grows, reinforcing the prevailing structure. Adaptability is reduced. r-strategists are still dominant but are gradually replaced by ^-strategists in this phase of development.
Maturity (information growth after J0rgensen and Fath, conservation function after Holling): In this stage, a qualitative growth in system behavior takes place, changing from exploitative patterns to more conservative patterns with high efficiencies of energy and matter processing. r-selected species, which easily adapt to external variability, have been replaced by the variability-controlling ^-strategists, which are more effective in their use of the incoming energy. The niche structure is enhanced widely, and loss is reduced. The information content of the system increases continuously. Most of the captured exergy is used for the maintenance of the system; but as the information grows the system is getting more effective and uses less exergy for maintenance. It implies that we get an energetic surplus which can be used for adaptation processes. Sensitivities versus external perturbations have become high, while the system's buffer capacities may be smaller compared with the former stages of the development. These items result in a rise of the system's vulnerability. Adaptability has reached minimum values. Most nutrients are in form of organic matter either in living or dead organisms. It means that the amount of inorganic nutrients is low which reduces the possibilities to test new sexual recombinations of genes or mutations.
Breakdown (release function after Holling, creative destruction after Schumpeter): Due to the 'brittleness' of the mature stages, their structure may break down very rapidly. Accumulated resources are released, internal control and organization mechanisms are broken, and positive feedbacks provoke the decay of the mature system. Uncertainty rises enormously, hierarchies are broken, and chaotic behavior may sometimes occur. There are only extremely weak interactions between the system components: nutrients are lost and cycling webs are disconnected. Adaptability and resilience have been exceeded. Most of nutrients will now be in the form of inorganic matter giving new possibilities to sexual recombinations and mutations. The breakdown opens for a renewal process.
Reorganization: During this short period the structural and functional resources can be arranged to favor in new directions, new species can occur and become successful, and - in spite of the inherited memory (e.g., seed bank of the old system and neighboring influences) - unpredictable developmental traits are possible. There are weak controls, and innovation, novelty, and change can lead to an optimized adaptation on a higher level.
Reset: A new ecosystem succession starts.
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