Change in ecosystem properties during succession

CHANGES IN ECOSYSTEM PROPERTIES  DURING SUCCESSION

In the ecosystem, changes occur during the successional stages.  These changes may be progressive or retrogressive but successional changes are always progressive during the succession.  Here are the following type of changes that occur.

Fluctuation changes

When the random changes are taking place in the ecosystem then they are known as fluctuation changes.  These changes occur due to the response of climate and is also known as adaptability.  These changes may be regular and cyclic type as well as the changes may be irregular.  Fluctuation occurs at large level, local level or at a smaller area.  Generally, ecosystem is the complex system so if one factor is changed then it causes the sequential changes and the changes in the environment cannot be easily predicted, while the fluctuation changes within the community can be expected.  So, if one species is affected then it shows a log series of changes.  These changes may be in kinds of species, dominance penology and in growth rate.

Directional changes

These are the real successional changes.  Although these are known as non-cyclic changes, but the changes are taking place in an ordered sequence and due to directional changes, the community becomes more complex, which is known as progression and changes from more to less complex community is known as retrogression.  If the succession occurs due to changing the factors plant then they are known as antigenic changes but if the changes are created by any outside (or external) factor, then they are known as allogentic changes.  Generally succession is a progressive development, which takes place from simple to complex community.  During succession many factors change like diversity, stability, productivity, self-maintenance and soil maturity.  These are positive directional changes like in hydrosere succession the sequential step are

            i.          Phytoplankton stage                        v.         Marsh meadow stage

            ii.         Free floating stage                           vi.        Herb stage

            iii.        Submerged stage                            vii.       Shrub stage

            iv.        Reed swamp stage                          viii.      Climax stage

           

In this stage, climax stage is the most stable stage and these changes are continuous changes.  If any stage is interpreted, then nature of all community changes.  Some directional changes may be deflected like formation of savanna from tropical rain forest through forest and shrub stage.  Some ecologist considered the retrogressive changes as successional changes, which is induced by changes in climate, grazing, browsing, trampling, soil erosion, repeated flooding etc.

Rate of Change

In the different communities, rate of changes is differing.  It is dependent on the factors causing the succession like the xerosere lichen stage can be seen hundreds of year.  In the areas like arctic and alpine zone, the rate of change is very less, because climate is complex there.  So there community shows stability in the primary stage.  But if the rate of disturbances is higher, then rate of change in community will also be higher.  During the development stages the trends of changes are as follows:

Table 1.1: Community Energetic

Ecosystem attributes	Developmental stages	Mature stages
i.  Gross production/community      Respiration (P/R ratio) ii.  Gross production/standing      crop biomass (P/B ratio) iii.  Biomass supported/Unit      energy flow (B/E ratio) iv.  Net community production v.  Food chain      grazing      detritous	Greater or less than 1 High Low High Linear, predominantly predominantly	Approaches 1 Low High Low Web like

Table 1.2: Community Structure

vi.  Total organic matter vii. Inorganic nutrients viii. Species diversity -       variety component ix.  Species diversity      equability component x.  Biochemical diversity xi.  Stratification and spatial       heterogeneity

Small Extra biotic Low Low Low Poorly organized

Large Intra biotic High High High Well developed & organized

Table 1.3: Life history

xii.  Niche specialization xiii.  Size of organism xiv.  Life cycles

Broad Small Short, simple

Narrow Large Large, complex

Table 1.4: Nutrient Cycling

xv.  Mineral cycles xvi.  Nutrient exchange rate between        organism and Environment xvii. Role of detritus in        nutrient regeneration

Open Rapid Unimportant

Closed Slow Important

Table 1.5: Selection Pressure

xviii.  Growth form xix.   Production

For rapid growth (r-selection) Quantity

For feedback control (k-selection) Quality

Table 1.6: Overall Homeostasis

xx.  Internal symbiosis xxi.  Nutrient conservation xxii.  Stability xxiii. Entropy xxiv. Information

Undeveloped Poor Poor High Low

Developed Good Good Low High