The document discusses community dynamics, emphasizing cyclic and non-cyclic replacement changes in ecological communities. Cyclic succession involves a recurring pattern of species dominance, while non-cyclic (or directional) succession represents a continuous, one-directional species replacement leading to a climax community. Examples include plant communities affected by fires and specific species replacements in distinct environments.

1. COMMUNITY DYNAMICS CHARACTERISTICS- CYCLIC AND NON-
CYCLIC REPLACEMENT CHANGES
SUBMITTED TO, SUBMITTED BY
DR. AGHIL SOORYA KRISHNAPRIYA M
DEPARTMENT OF BOTANY ROLL NO: 10
ST.TERESA’S COLLEGE II M.Sc BOTANY
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2. COMMUNITY DYNAMICS
 Communities are complex systems characterized by community structure (number and size of populations
and their interactions) and community dynamics (how members and their interactions change over time).
 Understanding community structure and dynamics allow us to minimize impacts on ecosystem and manage
ecological communities we benefit from.
 Changes in community structure and composition over time, often following environmental disturbances
such as earthquakes, volcanoes, storms, fires and climate change is called Community Dynamics.
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3. Community dynamics cont…
 Communities with a relatively constant number of species are said to be at equilibrium.
 Equilibrium is dynamic with species identities and relationships changing over time.
 But it maintains relatively constant numbers.
 Following a disturbance, communities may or may not return to equilibrium state.
 Succession- sequential appearance and disappearance of species in a community over time after a severe
disturbance.
 In Primary Succession, newly exposed or newly formed rock is colonized by living organisms.
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4. Community dynamics cont…
 In Secondary Succession, a part of ecosystem is disturbed and remnants of previous community remains.
 In both cases, there is a sequential change in species until a more-or-less permanent community develops.
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5. CYCLIC REPLACEMENT CHANGES
 Cyclic replacement changes involves a series of vegetation and habitat changes through which community
maintains and regenerates itself.
 It is also a pattern of vegetation change in which small number of species tend to replace each other over
time unless there is large-scale disturbance.
 It is one of several types of ecological succession and is a concept of community ecology.
 Cyclic succession refers to processes not initiated by wholesale exogenous disturbances or long term
physical changes in environment.
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6. Cyclic replacement changes cont…
 Cyclic mode of succession was proposed by British ecologist Alexander Watt in 1947 in his seminal paper
on vegetation patterns in grass, heath and bog communities.
 He described plant community as a regenerating entity.
 He explains that community can either be in an upgrade phase toward late successional shrubs or downward
phase toward grasses.
 These phases occur in a predictable cycle.
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7. Cyclic replacement changes cont…
 Cyclic model of succession can be explained in a transition matrix.
 The three states in the cyclic model are open substrate (usually a bare patch of land), Species A dominance
and Species B dominance.
 It explains that Species A and Species B are not autosuccessional- they do not facilitate their own growth.
 Species A will either facilitate succession of Species B or be eliminated (through mortality) such that patch
occupied becomes open substrate.
 Species B will either facilitate succession of Species A or be eliminated.
 Open substrate can remain open or become occupied by either Species A or B.
 This results in cyclic scheme of species dominance.
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8. Cyclic replacement changes cont…
 Cyclic succession usually involves a series of stages, with different dominating at each stage.
 These stages often occur due to disturbances or environmental changes.
a) Pioneer species:
 Cyclic succession often begins with pioneer species, which are first to colonize a disturbed or barren
environment.
 These species are adapted to harsh conditions.
b) Intermediate species:
 As environment stabilizes, intermediate species with different ecological characteristics may replace pioneer
species. This lead to increased biodiversity.
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9. Cyclic replacement changes cont…
c) Climax species:
 Eventually, a stable and mature community dominated by climax species may develop.
 These species are well suited to prevailing environmental conditions and are typically more competitive.
d) Disturbance and Reversal:
 Cyclic succession may not always lead to a climax community.
 Disturbances or changes in environmental conditions can restart the cycle, returning community to earlier
stages.
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10. Cyclic replacement changes cont…
Example 1: Calluna vulgaris
 When Calluna dies in a patch, Cladonia sylvatica grows and become dominant on dead stems of Calluna
stems, if protection is provided.
 Disintegration of Cladonia and creation of bare patches of exposed soil follow this and is the termination of
downgrade series.
 Upgrade series is initiated on bare patches with appearance and subsequent occupation of Arctostaphylos
uva-ursi.
 This stage is subsequently invaded by Calluna, which becomes dominant again completing upgrade series.
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12. Cyclic replacement changes cont…
Example 2: Two species plant community in Sonoran Desert.
 Creosote bush (Larrea tridentata)- cholla cactus (Opuntia leptocaulis) replacement cycles from plants to
people.
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14. Cyclic replacement changes cont…
Example 3: Repeated fire cycles of coastal chaparral ecosystem in California
 This type of ecosystem has a climax community of shrub-sized deciduous and evergreen vegetation.
 Fires are major source of disturbance in this ecosystem.
 Fires come through in cycles of between 10 and 15 years or sometimes longer.
 Plants and animals must be adapted to long periods of dryness and mild, winter time precipitation.
 When fires occur, plant life can recover relatively rapidly and return to similar climax community in less
than several years.
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16. NON-CYCLIC REPLACEMENT CHANGES
 Also known as directional succession.
 It involves a continuous and one-way sequence of species replacement within a community.
 This type of succession occurs when a community transitions through a series of distinct stages, each
characterised by different dominant species.
 Community ultimately reaches a climax state in which species composition remains relatively stable, as long
as environmental conditions remain constant.
 They are often observed in environments with more gradual or continuous changes, such as changes in soil
conditions or climate.
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17. Non-cyclic replacement changes cont…
 As environmental conditions shifts, species that are better adapted to new conditions gradually replaces
previous dominant species.
 This process continues until a climax community is reached where species composition is relatively stable.
Eg: If a field is left abandoned, it may undergo directional succession from grasses to shrubs and eventually to
trees over course of many years as soil and environmental conditions change.
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18. reference
1) Dash. M. C. (2001). Fundamentals of Ecology. Tata McGraw-Hill Education.
2) Mishra, D. D. (2008). Fundamental Concepts in Environmental Studies. S. Chand & Company Pvt Ltd.
3) Sharma, P. D., & Sharma, P. D. (2012). Ecology and Environment. Rastogi Publications.
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19. THANK YOU
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