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ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
1
Paper : 12 Principles of Ecology
Module : 20 Community: Community characteristics, types of biodiversity, diversity
index, abundance, species richness, vertical and horizontal stratification: Part IV
Development Team
Paper Coordinator: Prof. D.K. Singh Department of Zoology, University of Delhi
Principal Investigator: Prof. Neeta Sehgal Department of Zoology, University of Delhi
Content Writer: Dr. Haren Ram Chiary and Dr. Kapinder Kirori Mal College, University of Delhi Content Reviewer: Prof. K.S. Rao Department of Botany, University of Delhi
Co-Principal Investigator: Prof. D.K. Singh Department of Zoology, University of Delhi
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
2
Contents
1. Learning Objective
2. Introduction
3. History of study of succession
4. Ecological succession and types: Primary and secondary succession
5. Stages of Primary and secondary succession
6. Process of succession in Hydrosere
7. Process of succession in Lithosere
8. Theories of climax community
9. Summary
Description of Module
Subject Name ZOOLOGY
Paper Name Zool 12, Principles of Ecology
Module Name/Title Community
Module Id M20, Community characteristics, types of biodiversity, diversity index,
abundance, species richness, vertical and horizontal stratification : Part-IV
Keywords Succession, Primary succession, secondary succession, Sera, Climax
community, Hydrosere, Lithosere, theories of climax community
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
3
1. Learning Outcomes
After studying this module, you shall be able to
• Understand the meaning of succession and the history of study of succession.
• Briefly study the types of succession
• Learn about the general pattern of Primary and secondary succession
• Evaluate different stages of Hydrosere succession and Lithosere succession
• Understand different theories of Climax community
2. Introduction
More or less but communities are regularly changing over time and thus, are dynamic
entities. Each community has its own developmental history with its particular prevailing
environment and time. The source of studying the growth and development of ecological
community can be a barren area. The development of the community initiates on arrival of
the propagules or their parent organisms to the area of study. Out of all the immigrating
organisms or popagules only few of them survives, grow and gets established at the new site.
The first developmental stage of the community is called as the pioneering community
which is made up of those few successfully survived and established organisms or their
propagules. As more and more new species immigrates to this site the competition for the
resources becomes more intense between them. Due to the activities of the survived species
and physiography and constant change in the climatic conditions, the prevailing environment
conditions keeps on changing. The nature works on the principle of “survival of the fittest”
and thus, supports only those organisms which adapts and fits best to the changing
environment conditions. Until the community becomes incomplete accordance with the
environment and become a relatively stable community, the process of development and
change in community continues. The changes occurring during the entire process of
community development is ordered and highly directional. This highly directional and
sequences changes in the community are called as succession.
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
4
3. History of the Study of Succession
Europeans have already described the coastal dunes related succession when, in 1899, Henry
Cowles’s got inspired from this study and started his study on sand dunes along Lake
Michigan. He defined the laws essential to the changing patterns of the community and
influenced many ecologists of new generation. He viewed plant communities and
documented that these communities differ in the underlying physical environment and
species composition and are dynamic in nature. The plant communities in sand dunes were
studied at different ages in order to reflect the pattern of changes in the community over time.
Since then, many other ecologists along with Cowles studied the succession process by using
the chrono-sequence approach. This temporal approach to study succession process is
difficult to follow for centuries or decades and thus replaced by another approach that uses
spatial differences between communities to infer the occurrence of succession. Spatial
differences means locations of different ages are compared to understand the process of
succession. Sere is defined as the stage in the succession sequence. Ecologists identified
animals as the factors that affect the rate and direction of succession along with different
patterns of succession. All the taxonomical groups such as rodents, fish, protozoans and
insects and all type of ecosystems such as marine or aquatic etc are being investigated to
study succession.
4. Ecological succession and types: Primary and secondary succession
In ecology, the community structure evolves over time and the process of this progress is
termed as Ecological Succession. Over a period of time, the replacement of one population or
community by another is called as succession. The sequence of change in the type of
community sequentially relates different community types and describes the landform or soil
or total site succession and vegetation succession.
Ecological succession is majorly categorized into primary and secondary succession. Based
on the association between individual with their biotic and abiotic factors, ecologists
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
5
suggested two types of succession process (a) primary and (b) secondary succession.
Primary Succession: The establishment of a community in an area never been habituated by
organisms or where no prior existence of life is evidenced. The presence of complete lifeless
empty area may be because of greater natural disasters such as lava flow, sand dunes or via
glacier newly introduced rocks etc. Over a period of time few living organisms manage to
sustain life in these empty areas and with continuous succession variety of life-forms begins
to grow in the area. Secondary succession: The more common type of succession is
secondary succession where the existed life forms of community are partially destroyed by
small scale disturbances, for example forest wildfire. For a period of time, with remaining
nutrients in environment the area remains empty but gradually life begins to reappear and
communities changes over time.
In both type of succession the sizes, intensities and frequency of change in species vary
within communities while altering the area or habitat leading to mixture of species exploiting
the prevailing conditions of community. The species evolved life histories in a partially
predictable sequential way and leads to gradual progressive changes in species composing the
community. Initially in the unfavourable environmental conditions of this disturbed habitat
only few species from the surrounding areas invade and then they modify the habitat by
alterations such as soil component compositions, amount of sunlight or shades on grounds
etc. The first community established in an originally completely lifeless land is called Pioneer
community and the plants and animals are called Pioneer plants or animals. After these
successive changes in habitat environment a stable community is achieved termed as Climax
dominated by few prominent species. The community with this stable state of equilibrium is
termed as Climax Community. Thus, Climax community is characterized by stable
environment conditions limiting any further admission of other species in the community. At
each successive community the replacing species are more complex. Other than climax
community other communities at the time of succession undergo small scale environmental
disturbances thereby offering species diversity with equal probability of each species to
become dominant.
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
6
5. Stages of Ecological succession
A process of ecological changes where established communities are replaced by more
evolved natural communities is called as succession. Depending on the type of area over
which succession has to take place mainly two types of succession occurred: primary and
secondary succession.
1. Primary succession
When completely lifeless bare area starts succession it is called as Primary succession.
2. Secondary succession
When succession starts from an area which has been once occupied by vegetation but become
vegetation free due to some disturbances, the mechanism called as denudation or secondary
succession. The disturbances can be because of strong winds, fire, rains and cultivation.
The stages of ecological process of primary succession includes following stages:
1. Nudation
Nudation is a stage occurred when greater disturbances leads to formation of a bare land
uninhabited by any plant or animal species. The disturbing factors can be biotic (because of
human activities) or abiotic like climatic (fire, hails, glaciations etc) or topographic (wind
action, soil erosion etc.). This uninhabited land can sustain only autotrophic species
consuming inorganic substrates and offering a new environmental condition for inhabitation
of newer species. For instance, rocks are breakdown to soil with the help of acidic substance
secretion by lichens. These lichens act as a Pioneer species in the community.
2. Migration or Invasion
Migration is a two way direction movement or mechanism of dispersal and a group
characteristic feature of population. The reproductive propagules such as spores, seeds etc.
migrate for the species establishment into a new area. Non-native organisms called invasive
species enter from the neighbouring environment and spread widely in a community. These
invasive species are responsible for community disturbances and thus are threat to the stable
ecosystem but in the succession process they aid in altering the environmental conditions
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
7
such as soil composition, function and texture. R-Strategists with high fecundity rate and high
dispersal rate are the first colonizers.
3. Ecesis
On the basis of soil composition the initial establishment of community is called
colonization. The initial community proliferates abundantly. Allogenic mechanisms of
succession are those which are completely driven by the abiotic factors i.e. environment
mediated and completely regulate the ecesis process. Ecesis happens when different pioneer
species are sustained after dispersal in an area, they have different germination, growth and
reproduction rates and that’s why the pioneer species take much longer time and gradual
replacement of other species. By the establishment of these pioneer species the texture and
composition of soil changes which leads to germination of seeds already present there but
were not able to germinate.
4. Aggregation
The established species in the area increases in population and this increase in population
density is called as Aggregation. As an example in most successions of plant community
small herbs is been replaced by shrubs and further inhabitants are supported by this as a
source of food.
5. Competition
As a result of aggregation, few pioneer and initial species got established and increase in
population which further leads to enhanced intraspecific and interspecific competition among
the species. This stage of competition is for the resource utilization like shelter, nutrients,
water etc. Plants and animal species both exhibit the stage of competition and leads to either
competitive exclusion where no two species utilizing same resources can coexist or resource
partitioning where two competing species share their part of resources and can coexist.
6. Reaction
The established species in the habitat modify the environmental conditions subsequently
leads to gradual replacement of older species by newer ones as the conditions are now
become unfavourable for the survival of older species. This type of succession include
Autogenic mechanism driven by the biotic factors in which existing species themselves
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
8
modify the environmental conditions offering harsh conditions for their own survival. Pioneer
colonizers facilitate the colonization of mature K-selected species.
7. Stabilization
The mechanism of climax community colonization is termed as stabilization. Climax
community is a final sate of equilibrium, stable, self-perpetuating and mature stage of
succession. The entire community is now been supported by the altered abiotic factors
(chemical and physical conditions). Climax community generally made up of K-selected
species adapts according to the area of succession and are well established until any further
external disturbances. The structure, composition and energy flow is very much specific for
climax community and thus represent a well-adapted steady state of equilibrium.
The general pattern of ecological succession occurring in a community is depicted in figure 1.
The process of secondary succession is almost similar to primary succession except some
steps. Also, as secondary succession starts from an initial state already enriched in soil
nutrients and the process occurs at much faster rate than primary succession. The limiting
factor in secondary succession is the disturbances. Both type of succession resulted into
stable and steady state of ecological equilibrium called Climax community.
Figure 1: General patterns of sequential succession
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
9
Different types of succession in Plants
1. Halosere: If the plants succession starts from saline water or salty soil this is called
Halosere.
2. Hydrosere: Hydrarch is when succession of plants starts from aquatic environment and
the subsequent changes in the vegetation is called Hydrosere or Hyrarch.
3. Xeroarch or Xerosere: When the vegetation starts from a dry land, the process of
succession is called as Xerosere or Xeroarch. The two types of xeroarch are:
a. Lithosere: Succession when begins from the rock surfaces.
b. Psammosere: It is the succession that occurs on sandy habitat.
4. Serule: If succession starts from decaying woods, tree barks etc is called as serule. It
includes microorganism’s succession such as fungi or bacteria. All sere ends into mesic
community irrespective of succession types.
6. Process of succession in Hydrosere
When succession of vegetation starts from a water body such as pond it is called as hydarch
or hydrosere. The Stages in Hydrosere/ Hydarch are briefly (fig.2) described below:
1. Plankton stages
The pioneer community consists of cysted spores which germinate first in the new lakes or
ponds. Spores are dispersed there uninhabited places by dispersal agents such as animals or
wind. Population of phytoplanktons includes phytoflagellates, autotrophic diatoms,
cyanobacteria etc. which can withstand the harsh conditions and are regulated/ controlled by
zooplanktons. When these phytoplanktons are dead, they decay into organic substances and
after mixing with silt forms soft mud at the base of the water body.
2. Rooted submerged stage
Utricularis, Hydrilla, Vallisneric etc are the rooted submerged hydrophytes which grows on
the soft mud at the water body bottom when these hydrophytes are dead, their organic matter
along with the sand and silt leads to deposition of extra soil layer at the top of the soft mud
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
10
and this give gradual rise to bottom level of water body eg. ponds. All the decaying matter is
a good source of human for nest successive vegetation.
3. Rooted floating stage
Trapa, Nymphea, Nelumbo, Monochoria etc are the leaved, floating and anchored
hydrophytes which invade this area and make it mineral and organic matter enriched. After
these anchored plants, Lemna, Azolla, Eichornia, Pistia etc are the new free floating
hydrophytes. The decaying matter of these plants will make the water level shallow.
4. Reed swamp stage
Hydrophytes like Sagittaria, Typha, Scripus etc replaces the rooted and free floating stage of
succession and are called as amphibious stage. These plants used transpiration mechanism for
large amount of water loss and are a source of huge amount of organic waste. These waste
materials of organic matter settle down at the ponds bottom and make the environment
unfavourable for these amphibious plant growth and development.
5. Sedge meadow stage
This stage is mainly habituated by hydrophytes like Juncus, Sedge (Carex), Diochanthium
and herbs such as Polygonum, Caitha etc. This stage of succession is also called as “marsh
meadow stage”. These vegetations have a characteristic rhizomatous system which forms a
mat like covering and this develop a mesic condition which is unsuitable for their own
growth.
6. Wood land stage
Shrubby plants like Cephlanthus, Cornus etc invades at the periphery of area. These shrubby
plants can tolerate water logged situation and bright sunlight. Later other invading plants also
grow there such as Alnus, Populus etc. The soil build up, amount of minerals increases and
further falling of these trees into the ponds leads to enhanced soil formation which further
favours next seral community colonization.
7. Forest stage
Forest stage is dependent on climatic conditions and leads to climax community (fig.4). For
instance, tropical rain forest within heavy rainfall areas, tropical deciduous forest in moderate
rainfall habitats etc are the forest stages.
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
11
Figure 2: The Stages in Hydrosere/ Hydarch
6. Process of succession in Lithosere
Another example of succession can be studies by understanding the succession occurring in
the dry land. The succession initiating from the dry land is called as Xeroarch. Xeroarch or
Xerosere is further categorized into Lithosere, defined as the succession sequence which
begins from the rock surfaces (fig.3). The succession sequence in the growth and
development of lithosere community includes following stages:
1. Lichen stage
The pioneer community is composed of lichens species such as Rinodina, Rhizocarpon and
Lacanorma. This stage is also called as Crustose and the species of this stage can tolerate
desiccation. Lichens grow on rock surfaces by secreting acidic substrate which will corrode
the rocks and produce minerals and gaps within the rocks. These gaps are filled with organic
matter and soil particles as a result of wind action and initiate formation of soil. This initial
formation of soil in depressions of rocks supports the growth of lichens called foliose lichens
such as Physcia, Parmelia etc.
These newly invaded foliose lichens aggregate more soil particles as well as water leading to
formation of thin soil layer on rocks.
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
12
2. Moss stage
Grimmia and Polytrichum are the moss which invades in an area due to the thin layer of soil
on rock surfaces. After some time, these mosses will accumulate more soil particles, water
and organic matter and leads to colonization of moisture loving mosses such as Bryum,
Hypnum etc. and thus called as moss stage of succession.
3. Herb stage
Moss when decomposed into organic matters forming a mat over fragmented rock and
provide a substratum for the seed germination of annual grasses such as Aristicla, Eleusin,
Poa etc. The death and decay of these grasses leads to replacement of the vegetation by
perennial grasses such as Heteropogon, Cymbopogon etc. Invasion of small animals were
also encounters at his stage of succession.
4. Shrub stage
Colonization of shrub such as Zizyphus, Caparis and Rhus are favourable of rock weathering
and mineralization. Shrubs are larger than herbs in size with deep root penetration and
further leading to soil formation via rock weathering.
5. Forest stage
The environmental is now favourable for the colonization of hard and stunted trees requiring
sunlight for growth. Mesophytic type of vegetation is supported by the environmental factors
and thus leads to an equilibrium, stable and steady state of succession between biotic
community and environment. For example, coniferous forests in temperate region etc are the
climax community (fig.4).
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
13
Figure 3: The Stages in Xerosere/ Lithosere
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
14
Figure 4: Successional stages involved in the succession of Hydrosere and Xerosere/or
Lithosere, both resulting into much stable Climax forest community.
8. Theories of Climax Community
The succession of community structure attains a stable and final equilibrium state called
Climax Community suggested by Shimwell (1971) and Clements (1936). This stable
community is in accordance with the predicting biotic and physically environment and is self-
perpetuating. Birth rate, death rate and growth process induce structural changes in climax
community. The following are the four theories of climax community:
1. Mono-climax theory
In 1936, Clements suggested the mono-climax theory of succession according to which all
communities of different regions to reach climax community. He believed that climate is a
determining functional factor of climax and vegetation is solely influenced by the climatic
conditions of the community. This climate based theory termed various stages of succession
process as sub-climax, dis-, post- and pre-climax with stabilized climax as last stage of
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
15
community. Other than climate controlled community, exceptional cases of edaphic (soil),
topographic and biotic factors influencing communities are also discussed under this theory.
2. Poly-climax theory
In 1939, Tansley proposed Poly-climax theory which was supported by Daubenmire (1966).
According to this theory in an area the climax community may have varied type of vegetation
and these are called as climaxes. These climaxes are influenced not only by the climate rather
by the activities of animals, soil nutrients and moisture etc. Unlike mono-climax theory,
climate is one factor among all other influencing factors regulating the stability and structure
of climax community and allows multiple climaxes and thus called as poly-climax theory.
In 1994, Kreb suggested that it is the time dependent relative stability measurements which
differentiate between the two theories. The factors influencing climax varies with geological
time scale and ecological time scale such as climate. Thus different vegetation develops to
reach different climax leading to a continuous succession. Therefore, the mono-climax theory
and poly-climax theory mainly differ on understanding the functional factor which is
responsible for establishing the steady state climax community.
3. Climax-pattern theory
In 1953, Whittaker proposed climax pattern hypothesis. The climax pattern theory of
succession holds that the existing ecological community is affected by the entire pattern of
environmental factors. The environmental factors influencing the community can be climate
site, activity of animals (biotic), soil, species genetic structure, plant and animal species,
dispersal, wind and fire etc. This theory emphasizes on the total environmental conditions
regulating the pattern of population constituting the climax community. There is no single
functional factor influencing the climax community and thus, there is no mono- or poly-
climax.
Unlike mono-climax hypothesis resulting into one climatic climax in an area and several
climaxes in poly-climax theory, the climate pattern theory allow continuous inseparable
climax types under the influence of gradually changing gradient of environmental conditions.
4. Climax as Vegetation
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
16
In 1954, Egler hypothesized in a broad sense that the whole pattern of vegetation represents
the climaxes. He favours the vegetation study of an area as by the careful observation of the
vegetation we can predict the community conditions.
Thus from these entire hypothesis we can conclude that the ultimate goal of succession is to
achieve a stable form of community structure called climax. The climax community can be
disturbed and incompletely stable. The vegetation of an area is totally controlled by the
existing climatic conditions but the broad climatic zones leads to many climax populations
under the influence of animal activities, topographic and soil compositions.
Figure 5: Flow chart depicting different theories of Climax community.
7. Summary
Communities are regularly changing or dynamic entities. The development of the community
initiates on arrival of the propagules or their parent organisms to the area of study. The first
developmental stage of the community is called as the pioneering community which is made
up of those few successfully survived and established organisms or their propagules. The
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
17
nature supports only those organisms which adapts and fits best to the changing environment
conditions. The changes occurring during the entire process of community development is
ordered and highly directional. Until the community becomes in complete accordance with
the environment and become a relatively stable community, the process of development and
change in community continues. This highly directional and sequences changes in the
community are called as succession. Many ecologists along with Cowles studied the
succession process by using the chrono-sequence approach. This temporal approach is later
replaced by another approach that uses spatial differences between communities. Spatial
differences means locations of different ages are compared to understand the process of
succession. Sere is defined as the stage in the succession sequence.
Based on the association between individual with their biotic and abiotic factors, ecologists
suggested two types of succession process (a) primary and (b) secondary succession.
Primary Succession: The establishment of a community in an area never been habituated by
organisms or where no prior existence of life is evidenced. The more common type of
succession is secondary succession where the existed life forms of community are partially
destroyed by small scale disturbances, for example forest wildfire. Initially in the
unfavourable environmental conditions of this disturbed habitat only few species from the
surrounding areas invade and then they modify the habitat by alterations such as soil
component compositions, amount of sunlight or shades on grounds etc. The first community
established in an originally completely lifeless land is called Pioneer community and the
plants and animals are called Pioneer plants or animals. After these successive changes in
habitat environment a stable community is achieved termed as Climax dominated by few
prominent species. The community with this stable state of equilibrium is termed as Climax
Community. Thus, Climax community is characterized by stable environment conditions
limiting any further admission of other species in the community. The stages of ecological
process of primary succession includes following stages: Nudation, Migration or invasion,
ecesis, aggregation, competition, reaction and stabilization. The process of secondary
succession is almost similar to primary succession except some steps. The limiting factor in
secondary succession is the disturbances. Both type of succession resulted into stable and
ZOOLOGY
Principles of Ecology
Community: Community characteristics, types of biodiversity,
diversity index, abundance, species richness, vertical and horizontal
stratification: Part IV
18
steady state of ecological equilibrium called Climax community. Halosere, Hydrosere,
Xeroarch or Xerosere (Lithosere and Psammosere) and Serule are the different types of
ecological succession occurring in plant communities. The Stages in Hydrosere/ Hydarch
succession includes initial plankton stages followed by secondary stages like rooted
submerged stage, rooted floating stage, reed swamp stage, sedge meadow stage, wood land
stage and forest stage ultimately leading to climax community. The succession initiating from
the dry land is called as Xeroarch. Xeroarch or Xerosere is further categorized into Lithosere,
defined as the succession sequence which begins from the rock surfaces. The succession
sequence in the growth and development of lithosere community includes stages such as
lichen stage, moss stage, herb stage, shrubs stage and forest stage. Birth rate, death rate and
growth process induce structural changes in climax community. The following are the four
theories of climax community: Mono-climax theory, Poly-climax theory, climax pattern
theory and climax as vegetation theory.