Environment

Ecological Succession – Primary & Secondary Succession

FUNCTIONS OF ECOSYSTEM

  • The function of an ecosystem is a broad, vast and complete dynamic system. It can be studied under the following three heads.
    • Energy flow
    • Nutrient cycling (biogeochemical cycles)
    • Ecological succession or ecosystem development

We have already discussed about the Energy Flow (Food Chain & Food Web and Ecological Pyramids) and Nutrient Cycling (Biogeochemical Cycles – Carbon Cycle, Nitrogen Cycle, Water Cycle, Sulphur Cycle, Phosphorus Cycle). Here, we will discuss about the Ecological Succession in detail.

ECOLOGICAL SUCCESSION

  • The natural process of replacement of one vegetation community in a given habitat by the other vegetation community, is called succession.
  • The process by which communities of plant and animal species in an area are replaced or changed into another over a period of time is known as Ecological Succession.
  • Ecological Succession may also occur when the conditions of an environment suddenly and drastically change. A forest fires, wind storms, and human activities like agriculture all greatly alter the conditions of an environment.
  • Changes apparently move toward a more stable and mature condition, to an optimum for a specific environment. This end product in an area is traditionally called the ecological climax, with plants and animals forming a climax community—a stable, self-sustaining, and symbiotically functioning community with balanced birth, growth, and death.
  • Succession is a universal process of directional change in vegetation, on an ecological time scale.
  • Succession occurs due to large scale changes or destruction (natural or manmade).
  • The process involves a progressive series of changes with one community replacing another until a stable, mature, climax community develops.

Ecological Succession, Stages of Ecological Succession, Primary Succession, Secondary Succession, Difference between Primary and Secondary Succession, Notes on environment and Ecology,

STAGES OF ECOLOGICAL SUCCESSION

  • Ecological Succession proceeds through various stages, starting from Pioneer Community to Climax stage. Each such stage is called sere or seral community.
  • As seral community is an intermediate stage found in ecological succession in an ecosystem advancing towards its climax community.
  • As seral community is an intermediate stage found in ecological succession in an ecosystem advancing towards its climax community.
  • The first plant to colonise an area is called the pioneer community.
  • The final stage of succession is called the climax community.
  • A climax community is stable, mature, more complex and long-lasting.
  • Succession is characterised by the following: 
    • increased productivity,
    • the shift of nutrients from the reservoirs,
    • increased diversity of organisms, and
    • gradual increase in the complexity of food webs.

Primary Succession

    • Primary succession takes place an over where no community has existed previously.
    • Such areas include rock outcrops, newly formed deltas and sand dunes, emerging Volcano Islands and lava flows, glacial moraines (muddy area exposed by a retreating glacier), etc.
    • Often the first organisms to take hold are algae, fungi and simple plants such as lichens and mosses. Over time a thin layer of soil builds up so that more advanced plants, such as grasses and ferns, can take root. Along with the successful colonisation of plants come animals, insects, birds and small invertebrates.

Ecological Succession, Stages of Ecological Succession, Primary Succession, Secondary Succession, Difference between Primary and Secondary Succession, Notes on environment and Ecology,

Pioneer Community
      • It is a group of organisms that invade a new area in the process of Ecological Succession. In primary succession on a terrestrial site, the new site is first colonised by a few pioneer species that are often microbes, lichens and mosses.
      • The pioneers over a few generations alter the habitat conditions by their growth and development and through their death and decay leave patches of organic matter in which small animals can live.
      • The organic matter produced by these pioneer species produce organic acids during decomposition that dissolve and carve the substratum releasing nutrients to the substratum.
      • Organic debris accumulates in pockets and crevices, providing soil in which seeds can become lodged and grow.
      • The new conditions may be conducive to the establishment of additional organisms that may subsequently arrive at the site.
      • As the community of organisms continues to develop, it becomes more diverse, and competition increases, but at the same time, new niche opportunities develop.
      • The pioneer species disappear as the habitat conditions change and invasion of new species progresses, leading to the replacement of the preceding community.
Climax community
      • The culminating stage in the succession is the establishment of a stable community in the area, which is known as the climax community.
      • Climax communities are relatively stable and can vary widely in a given region.
      • Some of the features of the climax community are:
        • The vegetation of this region is tolerant to the environmental conditions.
        • The species diversity is large and the food chains of these species are complex.
        • It is a balanced ecosystem.
        • There is also equilibrium between the nutrients taken in from the soil and the return of the nutrients to the soil by litter fall.
        • The individual organisms in the climax ecosystem are replaced by other organisms of the same kind. Thus it maintains species equilibrium.

Secondary Succession

    • Secondary succession is the sequential development of biotic communities after the complete or partial destruction of the existing community.
    • Most ecological changes occur as secondary succession.
    • A mature or intermediate community may be destroyed by natural events such as floods, droughts, fires, or storms or by human interventions such as deforestation, agriculture, overgrazing, etc.

Ecological Succession, Stages of Ecological Succession, Primary Succession, Secondary Succession, Difference between Primary and Secondary Succession, Notes on environment and Ecology,

    • This abandoned land is first invaded by hardy species of grasses that can survive in bare, sun-baked soil.
    • These grasses may be soon joined by tall grasses and herbaceous plants. These dominate the ecosystem for some years along with mice, rabbits, insects and seed-eating birds.
    • Eventually, some trees come up in this area, seeds of which may be brought by wind or animals.
    • And over the years, a forest community develops. Thus, an abandoned land over a period becomes dominated by trees and is transformed into a forest.
    • Secondary succession is gradual, always moving toward the climax community. It occurs when an area that previously had an ecological community, which is so disturbed or changed that the original community was destroyed and a new community moves in.
    • It starts from previously built-up substrata with already existing living matter. This type of succession starts in a given area where the conditions for life are favourable because of the fact that the area was occupied earlier by well-developed community.

 

Difference between Primary and Secondary Succession

Properties

Primary Succession

Secondary Succession

Definition

It is the kind of ecological succession, which occurs or start from the barren, uninhabited and unoccupied areas, such as the newly formed pond, rock, dunes, etc.

Such kind of succession, which occurs in the area where there was the existence of life previously but got abandoned due to natural disturbances, such as flood, tsunami, earthquake, etc.

Occurs

In areas which are lifeless or barren.

In areas which were previously inhabited or recently uncovered

Time to complete

Around 1000 years or more

Around 50 – 200 years

Soil

There is the absence of soil at the starting of the process, and the condition is not suitable for sustaining life.

The soil is present, along with some
organisms.

Humus

Humus is absent in the starting as there is no soil

Presence of Humus due to the previous occupants and their decomposition

Seral community

There are many intermediary seral communities

Few intermediary seral communities when compared to the primary succession

Pioneer Community

It is present and comes from outside.

It gets develops from the migrants and previous occupants.

Environment

An unfavourable environment in the starting

Since beginning the environment is
favourable

Examples

Bare rock, ponds, desert, etc.

The area affected by natural calamities, covered under deforestation, etc.

 

Other Prominent Types of Ecological Succession

Autogenic and Allogenic Succession

    • When succession is brought about by living inhabitants of that community itself, the process is called autogenic succession, while change brought about by outside forces is known as allogenic succession.
    • Autogenic succession is driven by the biotic components of an ecosystem.
    • Allogenic succession is driven by the abiotic components (fire, flood) of the ecosystem.

Autotrophic and Heterotrophic succession

    • Succession in which, initially the green plants are much greater in quantity is known as autotrophic succession; and the ones in which the heterotrophs are greater in quantity is known as heterotrophic succession.
    • Succession would occur faster in area existing in the middle of the large continent because seeds of plants belonging to the different seres would reach much faster.

Primary and secondary in water

Succession in Plants
        • Succession that occurs on land (dry areas) where moisture content is low for e.g. on a bare rock is known as xerarch.
        • Succession that takes place in a water body, like ponds or lake is called hydrarch.
        • Both hydrarch and xerarch successions lead to medium water conditions (mesic) – neither too dry (xeric) nor too wet (hydric).
        • With time the xerophytic habitat gets converted into a mesophyte (plat needing only a moderate amount of water).
Succession in Water
        • In primary succession in water, the pioneers are the small phytoplankton, and they are replaced with time by free-floating angiosperms, then by rooted hydrophytes, sedges, grasses and finally the trees.
        • The climax again would be a forest. With time the water body is converted into land.
        • Another important fact is to understand that all succession whether taking place in water or on land, proceeds to a similar climax community – the mesic.

 

So, this was all about the Ecological Succession – Stages of Ecological Succession and Primary and Secondary Succession. 

In the Next Post (Click Here), we will start a new Topic of Biomes and Types of Biomes/Ecosystems. Till than, if you liked the notes than share it and comment below.

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