NEET Biology Notes Organisms and Ecosystem-Ecological Pyramids
Ecological pyramids are the graphical representations of the trophic structure and functions at successive trophic levels of an ecosystem, which may be shown in terms of their number, biomass or energy content. The concept of pyramid was proposed by Charles Elton (1927). So, they are also known as Eltonian pyramids.
There are three types of pyramids below in figure :
Ecological succession is a natural process by which different groups or communities colonise the same area over a period of time in a definite sequence. It is the developmental stages of community are known as serai stages.
Climax community is the final terminal community that can maintain itself more or less indefinitely in equilibrium with the prevailing environment and the stage as climax. The initial stage of the community of the area until climax is reached is known as pioneer stage or pioneer community.
Succession is of various types :
- Primary succession takes places where no life existed before. It is comparatively slow as suitable soil has to be formed.
- Secondary succession takes place in a region, where life existed in the past, but got destroyed completely, it is comparatively faster as some soil or sediment is already present.
- Autotrophic succession that begins in a predominantly inorganic environment and characterised by early and continued dominance.
- Heterotrophic succession occurs in special and rare case, where the environment is predominantly organic..
- Autogenic succession is resulting from the changes brought about by the organisms themselves.
- Allogenic succession is resulting from the changes brought about by factors external to the community.
Succession of Plants
Based on the nature of habitat, succession of plants can be grouped into two categories
Hydrarch succession occurs in water bodies and xerarch succession takes place in dry or xeric conditions (bare rocks). The species that invade a bare area are called pioneer species. Primary succession is a very slow process that make thousands of years for the establishment of climax community.
In secondary succession, the type of pioneer species depends on the following :
- Condition of soil
- Availability of water
- Environmental conditions
- Seeds/other propagules present
Ecosystems are the base for a wide range of economic, environmental and aesthetic goods and services. The products of ecosystem processes are named as ecosystem services.
The following services are provided by an ecosystem, e.g. a healthy forest ecosystem.
- Purify air by releasing oxygen
- Purify water
- Mitigate droughts and floods
- Pollinate crops
- Cycle nutrients
- Provide storage site for carbon
- Provide aesthetic, cultural and spiritual values
The value of services of biodiversity is difficult to determine. Robert Constanza et. al., have tried to put price tags on nature’s life-support services. Scientists have estimated this price to be 33 trillion US dollars a year, while our global gross production is only 18 trillion US dollar