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Frequently asked questions:
Q.1. Define Succession?
Ans. The orderly progression of a vegetation community, through
a series of developmental stages, reaching equilibrium in a
climax community.
Q.2. What is the difference between Primary and Secondary
Succession?
Ans. Primary Succession: It occurs in areas where no community
has existed before. It begins on sand dunes, volacanic islands,
lava flows etc. It may take about 1000 years to reach the
climax community.
Secondary Succession: It occurs in area where a community
had existed before. It begins on the area devasted by fire,
earthquake or forest cleared by man. It takes a shorter time
about 50-300 years to reach climax community.
Q.3. What is Allogenic Succesion?
Ans. When the replacement of one community is brought about
largely due to forces other than the effects of communities
itself on the environment, the succession is called allogenic
succession.
Q.4. What are the main causes of Succession?
Ans. There are three main causes of Succession;
a. Initial or Initiating causes: These are climatic as well as biotic in nature. The climatic causes include factors such as
erosion and deposits, wind, fire, etc., which are caused by
lightening or volcanic activity. The biotic causes include various activities of organisms like grazing, cutting, clearing,
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cultivation, harvesting, deforestation etc. All these causes
produce the bare areas or destroy the existing populations
in an area and the process is called as nudation.
b. Ecesis or Continuing causes: These include processes such
as migration, ecesis, aggregation, competition, reaction,
etc., which induce successive waves of populations as a
result of changes, chiefly in the edaphic (soil) features of
the area.
c. Stabilizing causes: These include factors such as climate
of the area which result in the stabilization of the community.
Q.5. What is Nudation?
Ans. It is the development of a bare site uninhabited by any
organisms. The process is usually caused by disturbances.
These factors can be either topographic (soil erosion, wind
action etc); climatic (hails, storm, glaciations, fire etc.); or
biotic (human activities). The area thus formed can sustain
only autotrophic organisms which can utilize inorganic
substrates. The environmental conditions are set up for the
inhabitation of new species. For example, secretion of acidic
substances by lichen species helps in breakdown of rocks
into soil. Q.6. What is a Hydrosere and what are the different stages taking
place in a Hydrosere?
Ans. It is a type of succession taking place in an aquatic
environment such as ponds, pools, lakes, etc. In a virgin
pond, hydrosere starts with a colonization of phytoplanktons
and finally reaches a climax forest stage. The different stages
of succession are as follows;
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a. Phytoplankton stage
b. Rooted submerged stage
c. Floating stage
d. Reed-Swamp stage
e. Sedge-meadow stage
f. Woodland stage and
g. Climax stage.
Q.7. Define the term Invasion?
Ans. Successful establishment of non-native species which
spread widely in an area migrated from some other area is
called as invasion.
Q.8. How will you differentiate between Autotrophic and
Heterotrophic succession?
Ans. Autotrophic succession: It is characterized by early and
continued dominance of autotrophic organisms such as green
plants. It begins in predominantly inorganic environments
and the energy flow is maintained indefinitely. There is
gradual increase in the organic matter content supported
by energy flow. Such a succession characterized by gradual
increase in the organic matter content of the environment is
called autotrophic successsion.
Heterotrophic succession: It is characterized by early
dominance of heterotrophic organisms such as bacteria,
actinomycetes, fungi and animals. It begins in a medium
which is rich in organic matter such as small areas of rivers,
streams; these are polluted heavily with sewage or in small
pools receiving leaf litter in large quantities.
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Q.9. Define a Climax community?
Ans. The final and stable stage of ecological succession is called
as Climax community. At this stage, there is a complete
harmony between the plant community and the environment
of the habitat. There is a perfect interaction among different
groups of organisms including bacteria, fungi and other
microorganisms.
Q.10. Define Retrogressive and Cyclic succession?
Ans. Retrogressive succession: It means a return to simpler and
less dense or even impoverished form of community from an
advanced or climax community. In most cases, the causes
are allogenic, i.e., forces from outside the ecosystem become
severe and demanding.
Cyclic succession: Cyclic refers to repeated occurrence
of certain stages of succession whenever there is an open
condition created within a large community.
Q.11. Define Ecesis?
Ans. This is the initial establishment of plant community. This
is dependent on the soil structure. The stage is also called
as ‘colonization’. In this stage, the early colonizing species
proliferate abundantly through germination, growth, and
reproduction. Ecesis is due to allogenic mechanisms alone.
This is the stage at which the pioneer species survive the
dispersal mechanisms.
Q.12. What do you understand by Polyclimax theory?
Ans. This theory considers that the climax vegetation of region
consists of not just one type but a mosaic of vegetational
climaxes controlled by soil moisture, soil nutrients,
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topography, slope exposure, fire and animal activity. The
advocates of polyclimax theory preferred to call each stable
community as a climax and described them with a prefix
as edaphic climax, topographic climax, biotic climax and
fire climax. This theory argues that climate is only one of
the several characters. As there are several environmental
factors, many climax communities are established.
Q.13. Give some examples of the pioneer species involved in the
Rooted-submerged stage of Hydrosere?
Ans. Some of the examples of the pioneer species include
Elodea, Hydrilla, Potamogeton, Myriophyllum, Vallisneria,
Ceratophyllum, Utricularia, Chara.
Q.14. What is a Xerosere and write a short note on the Crustoselichen stage?
Ans. Xerosere is defined as a succession which begins in dry
habitat like rocks or dry sand and reaches a climax.
Crustose-lichen stage: The first stage of xerosere is crustoselichen stage. The soil is absent for the complete penetration
of roots. Main pioneer species include Blue-green algae
and lichens. However in cooler climates, crustose lichens
like Rhizocarpon, Rinodina and Lecanora are the common
pioneers. They produce acids which bring about weathering of
rocks. The dead organic matter of algae and lichens become
mixed with the small particles of rocks to form a thin layer
of moist soil on the rocks. The soils formed by weathering
of the organic matter make the substratum suitable for the
growth of foliose lichens.
Q.15. What is the role of Competetion in the process of succession?
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Ans. Due to aggregation of a large number of individuals of
the species at the limited place, there develops competition
(i.e., interspecific and intraspecific competiyion) for space
and resources such as food, water etc. between the
individuals. Competition is found in both plants as well as
animal species. The process leads to sharing of resources
(resource partitioning) or competitive exclusion. Q.16. What are pioneer species?
Ans. Pioneer species are those first species that colonize
places where previously there were no living beings, like,
for example, algae that colonize bare rocks. In general,
pioneer species are autotrophs or those that maintain
harmonious ecological interaction with autotrophic beings
(like autotrophic bacteria, herbaceous plants, lichens).