A community is a complex group of individuals interacting and sharing an environment. Communities can be characterized by their structure (the types and numbers of species present) and dynamics (how communities change over time).

2. Definition
Community characteristics – diversity, stratification,
dominance, structure, periodicity, fluctuations,
stability, interdependence, interactions and
succession.
Biotic community – salient features, types.
Concept of biocoenosis.
Community concept, types and hypotheses.
Community succession.
Important species(Foundation, keystone, invasive)
and concepts (ecotone, edge effect, Niche).
summary

3. Definition -1
• Communities are assemblages of large number of species
that occur together in space and time and all interact
directly or indirectly with each other.
Definition -2
• A community is defined as groups of different organisms
living together in a particular space
Definition -3
• A biotic community comprises plants and animals present in a
particular area.
• E.g. microbial community, plant community, animal
community

5. 
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plants and animals belonging to different
taxonomic groups are present in a
community.
The abundance of populations and
number of species varies greatly in a
community.
Species richness = no. of species in a
community.
Species evenness = the distribution of
individuals among the species.
Species diversity is the product of richness
and evenness.

6. All communities have a physical
structure and biological pattern.
 Stratification is a layering or series of
separations that differently distributes the
organisms occurring in an ecosystem.
 Stratifications can be described in terms
of separations between organisms in
space (vertical or horizontal) or
 In terms of separations between
organisms in time (periodicity).


7. An ecosystem can be stratified in space
either vertically (layers) or horizontally
(concentric circles).
 Stratification of terrestrial communities
reflects the life forms of plants.
 Stratification results in economy of space
and per unit area of the land surface.
 Organisms in a community display daily,
lunar, seasonal or irregular patterns that
separate them in time.


8. Tropical
rain forest
Coniferous
forest
Deciduous
forest
Thorn
forest
Thorn
scrub
Tall-grass Short-grass
prairie
prairie
Desert
scrub

9. All the organisms in a community are not
equally important in determining the nature
of that community.
Only a few species generally exert the
major controlling influence on the
community due to their size, number or
activities.
These groups largely control the energy
flow, which are known as ecological
dominants.
In pasture grass and cattle are ecological
dominants.

10. A community is a composite biotic unit.
The individual populations of different
species depend on each other and on
the abiotic environment for their food,
shelter and reproduction.
A community consists of mainly 3 groups.
Producers= autotrophic organisms
Consumers= herbivores and carnivores
Decomposers= microbes

11. 
The rhythmic changes occur in the
activities of organisms.
1. Seasonal periodicity – temperature, rainfall
and photoperiod determine the
reproductive cycle of its inhabitants.
2. Dial periodicity – animals of terrestrial
community active during the day and
inactive during night.

12. Even within permanent and stable
community, fluctuations in species
abundance and numbers occur due to
the interplay of biotic potential and
environmental resistance.
 It may be regular or cyclic.
 E.g. host-parasite or predator- prey


13. 
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Community stability is the degree of
fluctuations in the size of the populations
comprising the community.
Environmental stability is the fluctuations in the
abiotic factors of the ecosystem.
Both the types of stability are closely related.
The structure of community has a major role in
determining the degree of environmental
variability.
For e.g. the organisms of a forest floor is
protected from winds, evaporation and
temperature variations by the thick forest
canopy.

14. A community is a self-sustained unit.
 The interdependence among different
species of a community is found for
food, reproduction and protection.
 Most communities are interdependent,
or share a mutual responsibility for group
survival.


15. 
Competition occurs when organisms of the same
or different species attempt to use an ecological
resource(water, nutrients, light, food or space) in
the same place at same time.

Predator –prey interactions

Symbiosis-
different species rely on each other :3 kinds.
– Mutualism- both partners benefit.
– Commensalism- one partner benefits and the other is
unaffected.
– Parasitism- One benefits the other is harmed.

16. 
Trophic structures are the feeding relationships
within communities i.e. who's eating whom

The first trophic level is made up of the primary
producers, the organisms that obtain the
energy from inorganic sources.

Primary producers are photosynthetic
organisms; more generally, primary producers
are autotrophs (i.e., they fix CO2)

Consumers are the heterotrophs, i.e., organisms
that obtain their carbon from other organisms.

17. It is the development of a community.
 It is a directional change in the community structure as a function of
time.
 There two fundamental types of succession: primary and secondary.
Primary succession is the series of community changes which occur
on an entirely new habitat.
 Secondary succession is the series of community changes which
take place on a previously colonized, but disturbed or damaged
habitat.


18. 
There is a balanced assemblage of
autotrophic plants and heterotrophic animals
in the trophic structure of a community.

19. A community is an aggregate of
organisms, which form a distinct ecological
unit.
2. The size of community unit may be large
(forest community) or small (community of
invertebrates).
3. Different community occurs in different
habitats.
4. The composition and character of a
community is an indicator of the type of
environment that is present.
1.

20. 5.The structure of a community is dependent on:
1) the number of species.2) the relative
number individuals in each species.
6.Species diversity indices give quantitative
expression of community structure.
7.Communities are constantly changing. The
replacement of one community by another is
called community succession. The final stage
in community succession is a climax
community.
On the whole a community is considered as a
highly integrated self-contained organic unit.

21. Minor
communities
Major
communities
• Are those communities more or less
dependent on neighboring
communities for energy.
• They are secondary aggregations within
a major community.
• Are those communities of sufficient size
and completeness of organization.
• They are relatively independent of
resources from adjacent communities.
• They receive only solar energy from the
sun.

22. A biocoenosis is a biotic community,
coined by Karl Mobius in 1877.
 This concept defines community as the
interacting organisms living together in a
habitat(biotope).

 Zoocoenosis refers to faunal community
 Phytocoenosis refers to floral community
 Microbiocoenosis refers to microbial
community.

23. Community concept is one of the most
important principles in Ecology.
 This concept defines community as
diverse organisms usually live together in
an orderly manner.
 Victor E. Shelford has defined “the
community as an assemblage of
populations living in a prescribed area or
physical habitat with a definite trophic
organization and metabolic pattern”.


24. 
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The individualistic hypothesis
was proposed by H.A.
Gleason( American
Ecologist),1917.
This hypothesis depicted a
community as a chance
assemblage of species found
in an area because they have
similar abiotic requirements.
In other words ―vegetation is
continuously variable in
response to a continuously
varying environment‖.

25. The interactive hypothesis was proposed
by F.E. Clements in 1916.
 According to him, each community is an
assemblage of closely linked species
having mandatory biotic interactions
that cause the community to function as
an integrated unit.


26. Communities are stable, integrated, and
orderly entities.
 a. Biologically they have a highlypredictable composition.
 b. The diversity and abundance of a
species in a particular community will be
the same before and after a disturbance.
 c. Communities develop by passing
through a series of predictable stages,
culminating in a stable climax community.


27. Communities are neither stable nor
predictable.
 a. Plant and animal communities are
ephemeral associations of species that
just happen to share similar climatic
requirements.
 b. It is largely a matter of chance
whether a similar community develops in
the same area after a disturbance
occurs.


28. The number of species
 The relative
abundance of those
species
 The types of species
 The number, types and
strength of interactions
among species (i.e.,
the structure of food
webs)


29.  1.Tropical
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rain forests
They found at equator.
Temperatures and rainfall are high and
variation is low.
Plants grow all year long.
High productivity, and high amounts of
aboveground biomass.
Highest amounts of BIODIVERSITY on Earth.
Extraordinary structural diversity.
A multilayered tree canopy is intermingled
with vines, epiphytes, shrubs and herbs.

30.  2.Temperate

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Forests
Precipitation is high and relatively constant
throughout the year.
This abundance of moisture allows trees to
dominate the landscape.
Plants experience a seasonal period of
dormancy.
Productivity higher than deserts or
grasslands, lower than tropical forests.
Biodiversity is moderate.

31.  3.
Grasslands
These areas are also called prairies or steppes.
 Precipitation conditions are quite dry.
 Temperatures are moderate but highly SEASONAL.
 Plant growth occurs in wet and warm months
 Grasslands can develop in forested regions if
recurring fires burn out
 Productivity is lower than in forests.
 Grassland soil is highly fertile.


32.  4.Deserts
Low annual precipitation
 Low productivity
 Individual plants are widely spaced due
to the intense competition for water.
 Desert species must cope with extreme
temperatures and aridity.


33. 
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Pond community –
there may be
populations of aquatic
plants, herbivorous
organisms, carnivores
and bacteria at the
bottom.
They are
interdependent for
food supplies and form
a specific group.

34. 
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Species diversity is a key feature of
biological communities.
Species diversity affects the stability and
productivity of communities.
A latitudinal gradient of species diversity
exists for many taxa.
Species diversity declines as latitude
increases.
High diversity in the tropics leads to high
productivity.
Diversity is positively correlated with stability.

35. Each community type experiences a
characteristic type, frequency, and
severity of disturbance. This is known as a
community’s disturbance regime.
 Disturbance patterns profoundly affect
the composition of communities.
 Examples—Fires in boreal forests and
tree falls in temperate and tropical
forests.


36. Definition
•Community succession is
defined as a gradual,
continuous and
unidirectional change in
the species composition of
a natural community over
a long time.

37. All ecosystems change over time
 There are two types of ecosystem changes

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Nondirectional directional changes-ReplacementFluctuations

Directional changes-Biogeographic change- Succession

All these types of changes may occur
simultaneously within a single ecosystem

38. Primary
Community
succession
succession
Secondary
succession
It takes place
in barren
areas
It takes place
in disturbed
areas

39. Early stages
Middle stages
Final stages
• Low biomass
• Low nutrient levels
• Low Species
diversity
• Short food chain
• High productivity
• Rich biomass
• Rich organic
nutrients
• More species
diversity
• Stable high biomass
• High organic
nutrients & low
productivity
• Complex food
chain
• High species
diversity
&competition

40. Pioneer
Community/
Sere /
intervening
First community
communities
Climax
community

41. Forest Succession
Pioneer
Comm.
Climax
Comm.

42. Increase in
Species composition
And species diversity
Increase in species density
And heterogeneity
Increase in
Organic nutrients
Metabolic stability in
Community metabolism

44. Foundation species are considered the
―base‖ of a community, having the
greatest influence on its overall structure.
 They are usually the primary producers:
 Foundation species may physically
modify the environment to produce and
maintain habitats that benefit the other
organisms that use them.
 E.g. the photosynthetic corals of the
coral reef.


45. 
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A species whose presence is key to
maintaining biodiversity within an ecosystem
and to upholding an ecological community’s
structure.
The species may be a strong interactor or a
weak interactor.
Strong interactors are fewer in number and
critical to the ecosystem function.
Elimination of a keystone species may result in
the loss of many other species in a community.
E.g. beavers of Canada, Bengal tiger of India,
African elephants.

46. Invasive species are non-indigenous
species whose introduction can cause
harm to the community and the
environment.
 Invasive species are often better
competitors than native species,
resulting in population explosions.
 These new species usually overtake the
native populations, driving them to
localized extinctions.


48. A niche is the role of an organism in a
community (Charles Elton 1927)- functional
niche = functional status of an organism in its
community.
 Joseph Grinnell (1917)referred niche as an
organism’s physical environment- spatial
niche
 Niche is a property of a biotic community.
 Niches includes all the physical, chemical
and biological conditions.
 The niche concept was formulated to study the
role of organisms in community.


49. An edge is where two or more different
vegetational communities meet. e.g. forestgrass land.
 An ecotone is where two or more
communities not only meet but also
intergrade.
 Edges result from abrupt changes in soil
type, topographic differences, geomorphic
differences and microclimatic changes.
 Ecotones arise from the blending of two or
more vegetational types.


50. A community is a complex group of
individuals interacting and sharing an
environment.
 Communities can be characterized by
their structure (the types and numbers of
species present) and dynamics (how
communities change over time).


51. 
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Dr. B. Victor is a highly experienced postgraduate
professor, retired from the reputed educational
institution - St. Xavier’ s College(Autonomous),
Palayamkottai, India-627001.
He was the dean of sciences, assistant controller of
examinations and coordinator several academic
research workshops.
He has more than 32 years of teaching and research
experience
He has taught a diversity of courses and published
45 research articles in reputed national and
international journals.
Send your comments to : bonfiliusvictor@gmail.com