Grass land Ecosystem | Community, Succession and its Process in Hydrosere

BIOLOGY | BOTANY
UNIT TEN : BIOTA AND THEIR ENVIRONMENT
ECOSYSTEM
CLASS : 11

Grass Land Ecosystem 

Community 

The aggregation or assembles of living organisms having mutual relationship among themselves and to their environment is called community. Assembles of plants is called plant community and the assemblage of animals is called animal community. 

Characters of community 

• Different types of species are found in the community. This is called species diversity 
• Some of the species are found to be dominant. This may be either due to number of individual of that species or due to the size of the body. Usually only one species is found dominant in a community. This is called species dominant. 
• The size of the community varies from very small to very large. The example of very small community is microorganisms found in the gut and the example of very large community is the forest community. 
• The community is changeable. One community can be replaced by another community in due coarse of time. This process is called succession. 

Succession 

Series of changes in a community in due course of time is called succession. This process is gradual and continuous. This process does not stop unless a stable community is formed. There are two types of succession 

Primary succession: The succession which starts from bare area where there was no life existed previously is called primary succession. 

Secondary succession: The succession which starts from bare area which had occupied by some community before is secondary succession. 

Causes of succession 

• The environmental change 
• The changes in nutrition, organic matters and characters of the soil cause succession. The succession due to above factor is called autogenic succession. 
• The natural disasters like flood deposition of soil erosion etc also cause succession which is called allogenic succession 

Process of succession 

Nudation: the process of development of new species on bare areas is called nudation 

Invasion: the establishment of new species on bare areas is called invasion, it includes followingthree steps. 

Migration: seed, spores or propagules migrate on bare area through air water and animals. 

Ecesis: seed, spores or propagulaes germinate. Some of them become capable for successful growth and they get established. This process is called ecesis. 

Aggregation: The established species reproduce and number is increase to form large population. This process is called aggregation. 

Competition 

The large number of individuals competes for water food and space. This is called competition. The competition may be intra or inter species. They also react with the environment. Due to their activities, some modification occurs in the environment, which becomes suitable for new invaders or species, which is called reaction. 

Stabilization: 

After reaction, the community becomes more or less stable for long time, which is called climax. These different stages of the successions are called sere. 

Process of succession in Hydrosere 

The process of succession occurring in water mass like ponds, pools, and lakes is known as hydrosere. In the pond, the microorganisms ie phytoplanktons (Bacteria, cyanobacteria, algae) are pioneers to be invade in the early pond water. They are consumed by zooplanktons like protozoans or smaller fishes, which after their death increase the organic content in the pond. The organic content are decomposed by decomposers like fungi, bacteria and the nutrients released. The released nutrients help in the growth of rooted hydrophytes like Hydrilla, Chara etc. and the submerged animals. Their dead bodies are also decomposed by microbes to release nutrients. In due course, of time water depth of pond reduced and at the margin rooted floating plants like Nympaea, Nelumbo and animals like insects larvae grow. Gradually the pond depth further decreases and concentration of nutrients increases which develop freely floating plants like Azolla Salvinia etc. Gradually dead bodies also increase. The pond becomes swampy and the rooted plants like Typha, Rumex are developed. 

If the water level further decrease the growth of amphibious species is unfavorable and they are replace by plant like Juncus, Cyperus of graminae family. These plants are again replaced by mesic communities As the soil become further drier then soil favors the growth of trees like Alnus and the woodland community appears. Finally, tree community is replaced by forest, which is the climax stage.