Ecological succession

 

Ecological succession

 

What is ecological succession? Explain various kinds of succession.

“ Ecological succession may be defined as on orderly and progressive replacement of one community by another community until reaching stable community occupies in that area”.

Or

“Successive replacement of same habitat by different communities over a period of time in particular area is called ecological succession.”

Ecological succession is a sequential process of community development which result in formation of climax community in the environment. The succession gives us an idea that never stand still everywhere, it is continuous process of changes.

According to the habitat there are various kinds of succession, which are as follows.

Hydrach:  Succession begins in water habitat like pond, marshes, etc is called hydrach.  Various stages of development of hydrach constitutes hydrosere. 

Xerach: when succession began in dry land (and deserts, sand dunes, salt deserts, rock deserts etc.) are termed as xerach.  Various stages of development of xerach are called xerosere. 

When succession started on bare area, is called as lithosere.  When succession started from sand is called psamosere.  But when succession began on the region or inter habitat between water and sand it is termed as mesorch. 

Kinds of succession:   Ecological succession may be

•         Primary succession

•         Secondary succession

•         Autotrophic succession

•         Heterotrophic succession

Primary succession:

When succession proceeds from bare area i.e. area devoid of organism or an area which has not been changed by organism, then it is termed as primary succession.

 

Secondary succession:

If succession stared on  the area previously having community and has organically rich soil, then it is termed as secondary succession. 

3.  Autotrophic succession: it is characterized by early and continuous dominance of autotrophic organisms like green plants.  Autotrophic succession began in pre-dominantly on inorganic environment.   The green plants converting inorganic components into organic matter in substratum.

4. Heterotrophic succession.  It is characterized by an early dominance of heterotrophic organisms like, bacteria, fungi, protozoan, and animals.  Heterotrophic succession  begins in predominantly organic environment.  The  heterotrophic organisms e.g. bacteria, actinomycetes, fungi, converting organic components into inorganic matter declining energy.

What is ecological succession? Explain the requirements of succession?

Or

What is ecological succession? Explain the process of ecological succession?

“ Ecological succession may be defined as on orderly and progressive replacement of one community by another community until reaching stable community occupies in that area”.

Or

“Successive replacement of same habitat by different communities over a period of time in particular area is called ecological succession.”

Ecological succession is a sequential process of community development which result in formation of climax community in the environment. The succession gives us an idea that never stand still everywhere, it is continuous process of changes.

General process of ecological succession.

Complete process of primary autotrophic ecological succession involves following steps which are followed one another.

•         Nudation

•         Invasion

•         Ecesis

•         Aggregation

•         Reaction

•         Stabilization

 

Requirements of succession

Succession involves following phases:-

Nudation: Succession begins with the development of a bare area, called Nudation (disturbance). Nudation may be caused due to  several reasons such as volcanic eruption, flood, erosion (physiographic, climatic and biotic agents).

Invasion: (Entry or arrival) invasion is arrival or entry of reproductive bodies of various organisms from some other area is called invasion. It refers to arrival or migration of propagules. Thus entry of organism is called as invasion.

Ecesis: if conditions are favorable some of the migrant get germinate in new area and starts to reproduce.  Thus, it involves establishment and initial growth of migrant is called ecesis.  Generally plant community are the pioneer.

Aggregation: increase in number of individuals of invaded species.  As vegetation became well established, grew, and spread, various species began to compete. Increased population leads to competition for space, light, water, soil etc.   competition results in decrease in number.  The competition between members of same community or same species is called intra-specific competition. If competition between individuals of different species is called inter-specific competition.

Reaction: The competing organism modifies the environmental factors such as, soil, moisture, temperature, gases, etc. the changed conditions become unfavorable for the pioneer, but better suited for new comer (Invader).   During this phase autogenic changes affect the habitat resulting in replacement of one community by another.  Thus, the pioneer community are replace by another community through sequence of new invasions.

Stabilization: Sequential replacement results at last in stabilization of community, called climax community. Which, is the final stage of ecological succession.  It is not affected by environmental changes.  Hence, it remain stable for long period. 

On the margin of climax community another stable communities are develops called as Pro-climax community.  Some time strip of community of higher life form within the climax community are develops called as post climax community. 

 

Write short Note?

Concept of climax community.  Or

Theory of climax community.

“ Ecological succession may be defined as on orderly and progressive replacement of one community by another community until reaching stable community or climax community occupies in that area”.

On the margin of climax community another stable communities are develops called as Pro-climax community.  Some time strip of community of higher life form within the climax community are develops called as post climax community. 

There are two prominent theories have been concerned with climax community are as follows.

•         Mono-climax

•         Poly-climax

 

•         Mono-climax: this theory was advance by Patrick Clement.  According to this theory there is only one climax community in an climatic area.  The another communities which  are present in addition  to climatic community are regarded as sub-ordinate communities.  The term pro-climax and post-climax are used to define sub-ordinate community. 

•         Poly-climax: This theory was advanced by Whitaker.  According to this theory, numbers of climax community are present in an climatic area.  The pro-climax and post-climax communities are nothing but the  different climax communities

Ex.    1.      Hydrach      2.       Xerach.      

Hydrach

“ Ecological succession may be defined as on orderly and progressive replacement of one community by another community until reaching stable community or climax community occupies in that area”.

Hydrach:  Succession begins in water habitat like pond, marshes, etc is called hydrach.  Various stages of development of hydrach constitutes hydrosere.

 

Following are the various stages of development of hydrach (Hydroseres)

•         Phytoplankton stage:

•         Submerged stage

•         Floating stage

•         Reed swamp stage

•         Sedge-meadow stage Or Marginal stage

•         Woodland stage

•         Climax stage

 

Phytoplankton stage:

Unicellular floating algal plants such as diatoms are pioneer species of a bare water body, such as a pond. Their spores are carried by air to the pond.

The phytoplankton are followed by zooplankton.They settle down to the bottom of the pond after death, and decay into humus that mixes with silt and clay particles brought into the basin by runoff water and wave action and form soil. As soil build up, the pond becomes shallower and further environmental changes.

Submerged stage

As the water body becomes shallower, more submerged rooted species are able to become established due to increasing light penetration in the shallower water. This is suitable for growth of rooted submerged species such as Myriophyllum, Vallisneria, Elodea, Hydrilla, and Ceratophyllum. These plants root themselves in mud. Once submerged species colonize the successional changes are more rapid and are mainly autogenic as organic matter accumulates. Inorganic sediment is still entering the pond or lake and is trapped more quickly by the net of plant roots and rhizomes growing on the pond floor. The pond becomes sufficiently shallow (2-5ft) for floating species and less suitable for rooted submerged plants.

Floating stage

The floating plants are rooted in the mud, but some or all their leaves float on the surface of the water. These include species like Nymphaea, Nelumbo Potamogeton and Echornia lilly. The large and broad leaves of floating plants shade the water surface and conditions become unsuitable for growth of submerged species which start disappearing. The plants decay to form organic mud which makes the pond more shallow yet (1-3 ft).

Reed swamp stage

The pond is now invaded by emergent plants such as Phragmites (reed-grasses), Typha (cattail), and Zizania (wild rice) to form a reed-swamp (in North American usage, this habitat is called a marsh). These plants have creeping rhizomes which knit the mud together to produce large quantities of leaf litter. This litter is resistant to decay and reed peat builds up, accelerating the autogenic change. The surface of the pond is converted into water-saturated marshy land.

Sedge-meadow stage Or Marginal stage

Successive decreases in water level and changes in substratum help members of Cyperaceae and Graminae such as Carex, Juncus to establish themselves. They form a mat of vegetation extending towards the centre of the pond. The above water leaves transpire water to lower the water level further and add additional leaf litter to the soil. Eventually the sedge peat accumulates above the water level and soil is no longer totally waterlogged. The habitat becomes suitable for invasion of herbs which grow luxuriantly and bring further changes to the environment. Mesic conditions develop and marshy vegetation begins to disappear.

Woodland stage

The soil now remains drier for most of the year and becomes suitable for development of wet woodland. It is invaded by shrubs and trees such as Salix (willow), Alnus (alders), and Populus. These plants react upon the habitat by producing shade, lower the water table still further by transpiration, build up the soil, and lead to the accumulation of humus with associated microorganisms. This type of wet woodland is also known as carr.

Climax stage

Finally a self perpetuating climax community develops. It may be a forest (if the climate is humid), grassland (if sub-humid environment), or a desert in arid and semi-arid conditions.  A forest is characterized by presence of herbs, shrubs, mosses, shade-loving plants and trees including decomposers.

The overall changes taking place during development of successional communities are building up of substratum, shallowing of water, addition of humus and minerals, soil building and aeration of soil. As the water body fills in with sediment, the area of open water decreases and the vegetation types moves inwards as the water becomes shallower. Many of the above mentioned communities can be seen growing together in a water body. The center is occupied by floating and submerged plants with reeds nearer the shores.

 

 

 

 

 

 

What is xerach? Explain various stages of xerach?

 “ Ecological succession may be defined as on orderly and progressive replacement of one community by another community until reaching stable community occupies in that area”.

Or

“Successive replacement of same habitat by different communities over a period of time in particular area is called ecological succession.”

Xerach: when succession began in dry land (and deserts, sand dunes, salt deserts, rock deserts etc.) are termed as xerach.  Various stages of development of xerach are called xerosere. 

When succession started on bare area, is called as lithosere.  When succession started from sand is called psamosere.  But when succession began on the region or inter habitat between water and sand it is termed as mesorch.

Various stages of development of xerach are as follows

•         Crustose lichen stage (Pioneer stage)

•         Foliose and fruticose lichen stage

•         Moss stage

•         Herb stage

•         Shrub stage

•         Tree stage or Forest stage.

Crustose lichen stage (Pioneer stage)

The rock having extreme xeric  condition. The  water and nutrients are extremely deficient and there is direct exposure to sun, wind and extreme hot temperature. In such condition crustose lichens enters in such area and become pioneer.  The thalli of crustose lichens can adhere to the surface of rock and absorb moisture from atmosphere; & colonize the bare surfaces of rocks first. The porpagules of these lichens are brought by air from the surrounding areas.  These lichens produce acids which modifies the properties of the rock leads to formation of  thin film of soil.When these lichens die their thalli are decomposed to add humus. This promotes soil building and the environment becomes suitable for growth of foliose and fruticose type of lichens.

Foliose and fruticose lichen stage

Foliose lichens have leaf-like thalli, while the fruticose lichens are like small bushes. They are attached to the substratum at one point only, They can absorb and retain more water and are able to accumulate more dust particles. Their dead remains are decomposed to humus which mixes with soil particles and help building substratum and improving soil moisture contents further. This layer of soil is formed get filled in to the depressions in the rocks and crevices. It opens avenues (entry) for the growth of xerophytic mosses.

Moss stage

When sufficient amount of soil accumulate in the crevices and depression in the rock in which  mosses begins to appear xerophytic mosses such as black mosses, hair mosses, pristed mosses, etc. Their rhizoids penetrate soil among the crevices, secrete acids and modifies the rocks leads to formation of mat of soil. The bodies of mosses are rich in organic and inorganic compounds. When these die they add these compounds to the soil, increasing the fertility of the soil, greater water holding capacity.  

The changing environment become suitable for the growth of herb plants. 

Herb stage

By the death of mosses the mat of soil is developed on which the germination of seeds of various xerophytic herds is take place.  Herbaceous weeds, mostly annuals such as asters, evening primroses and milk weeds, invade the rock. Their roots penetrate deep down, secrete acids and enhance the process of weathering. Leaf litter and death of herbs add humus to the soil. Shading of soil results in decrease in evaporation and there is a slight increase in temperature.

Xeric conditions begin to change and biennial and perennial herbs and xeric grasses such as Aristida, Festuca, and Poa, begin to inhabit. These climatic conditions favor growth of bacterial and fungal populations, resulting in increase in decomposition activity.

Shrub stage

On the soil which is prepared by lichens, mosses and herb there is appearance of xerophytic shrub is take place. The shrub make conditions unfavorable for herb and shadow them.  Due to this herbs unable to compete with shrubs. The shrub also check evaporation of water from soil and retard wind movement. Once a few bushes have become established, birds invade the area and help disperse scrub seeds. The soil formation continues and its moisture content increases. The environment becomes mesic (moderately moist).

Tree stage or Forest stage or Climax stage. 

The kind of tree species inhabiting the area depends upon the nature of the soil. First species of the tree  are relatively xeric and  have stunted growth. As weathering process continues the soil deepness increases.  Due to this trees grows in number and height and become stable. Leaf litter and decaying roots weather the soil further and add humus to it making the habitat more favorable for growth to trees.  Xeric conditions are replaced by mesophyttic trees which ultimately, develop in to forest or climax stage  in future.