Download olabisi onabanjo university pls317: plant ecology

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OLABISI ONABANJO UNIVERSITY
PLS317: PLANT ECOLOGY
LECTURE: ECOLOGICAL SUCCESSION
CONTENTS
1.0 Introduction
2.0 Objectives
3.0 Main content
3.1 Fundamental concept
 Habitat
 Population
 Community
 Ecosystem
 Climax community
3.2 Types of Succession
3.2.1 Primary succession
3.2.2 Secondary succession
3.3 Derived succession
3.3.1 Autogenic
3.3.2 Allogenic
3.4 Clement’s theory of successional phases
3.5 Seral communities
4.0 Conclusion
5.0 Summary
6.0 References/further readings
7.0 Tutorial-marked quizzes
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Bup
OLABISI ONABANJO UNIVERSITY
PLS317: PLANT ECOLOGY
1.0 Introduction
Today’s lecture introduces to you the ecological succession concept under which we have the
various phases of forest development. You are going to learn the fundamental concept of ecological
succession. This lecture will benefit those of you going to major in environmental sciences, animal and
plant ecology, as well as those needing the knowledge in their field of study.
2.0 Objectives
At the end of this lecture, you will be able to:
 appreciate the need to be knowledgeable about ecology

have a clear idea of the concepts that operate in a given forest
 Identify types of succession
 Identify characteristics of the different successions
3.0
Main content
Succession is a process of ecological change involving the progressive replacement of earlier biotic
communities with others over time. It will interest you to know that succession usually begins with the
disturbance of a pre-existing ecosystem follow by recovery. In the absence of further disturbance,
succession attains a stable state called climax community. The climax community is determined by
climate, edaphic factors, and structure of local biotic
Therefore; ecological succession is the changing sequence of communities that live in an ecosystem
during a given time period. Pioneer species are those first species that colonize places where previously
there were no living beings (e.g. algae that colonize bare rocks, autotrophic bacteria, lichens and
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OLABISI ONABANJO UNIVERSITY
PLS317: PLANT ECOLOGY
bryophytes). The pioneer community is formed of species able to survive under hostile environments.
The presence of these species modifies the microenvironment generating changes in abiotic and biotic
factors of a particular ecosystem. Therefore they open the way to other species to establish in the place
by the creation of new potential ecological niches.
3.1
Fundamental concepts


Habitat : A place where organisms live e.g. a pond, tree, soils
Population: A group of individuals of the same species in a particular location.

Community: Two or more populations of species in a given area.

Ecosystem: A community interacting with the physical and chemical
environment of a particular area.
3.2
Types of successions
3.2.1 Primary succession occurs on bare surface (newly exposed rock, sand surface or newly formed
lake) that have not been previously modified by biological processes or occupied by a community.
3.2.2 Secondary succession occurs on surfaces that have been modified by mild biological
disturbances that do not totally remove the regenerative capacity of the local vegetation. Thus the
subsequent process of community development in an area from which original community was
removed by humans or animals activities and replaced by offsprings through regeneration by seeds,
above stem buds, underground stems of the original vegetation.
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OLABISI ONABANJO UNIVERSITY
PLS317: PLANT ECOLOGY
3.3 Derived successions
Seasonal and cyclic succession, unlike secondary succession, these types of vegetation changes are not
dependent on disturbance but are periodic changes arising from fluctuating or recurring events or
species interactions. These types of succession modified the climax community concept towards either
one of these dynamic states, autogenic or allogenic.
3.3.1
Autogenic succession can be brought by changes in the soil caused by the organisms there.
These changes include accumulation of organic matter in litter or humus layer, alteration of soil
nutrients, change in pH of soil by plants growing there. The structure of the plants themselves can also
alter the community. For example, when larger species like trees mature, they produce shade on to the
developing forest floor that tends to exclude light-requiring species. Shade-tolerant species will invade
the area (i.e. species interaction).
3.3.2
Allogenic succession is caused by external environmental influences and not by the vegetation.
For example soil changes due to erosion, leaching or the deposition of silt and clays can alter the
nutrient content and water relationships in the ecosystems (i.e. events). Although animals also play an
important role in allogenic changes as they are pollinators, seed dispersers and herbivores (i.e. species
interaction). Animals and insects can increase nutrient content of the soil in certain areas, or shift soil
about (as termites, ants, and moles do) creating patches in the habitat. This may create regeneration of
sites that favor certain species.
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OLABISI ONABANJO UNIVERSITY
PLS317: PLANT ECOLOGY
3.4 Clement’s theory of succession mechanism
 Nudation: Succession begins with the development of a bare sites caused by disturbance.
 Migration: propagules ( may be spores or seeds) arrival at the disturbed sites
 Ecesis: initial growth and establishment of vegetation at the disturbed sites
 Competition: established vegetation spread and various species compete for space, light and
nutrients.
 Reaction: During competition autogenic reactions cause changes that affect the habitat resulting
in replacement of one plant community by another.
 Stabilization: Reaction phase leads to stable development of a climax community.
3.4
Seral communities
A seral community is an intermediate stage found in an ecosystem advancing towards its climax
community i.e. a collection of seres making up the development of an area from non-vegetated surfaces
to a climax community. In many cases series of seral stage evolves until climax conditions are attained.
Depending on the substratum and climate, a seral community can be one of the following:
 Hydrosere (fresh water habitat)
 Lithosere (rocky habitat)
 Psammosere (sandy habitat)
 Xerosere (dry habitat)
 Halosere (saline marsh habitat)
4.0 Conclusion
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OLABISI ONABANJO UNIVERSITY
PLS317: PLANT ECOLOGY
In this lecture, you have learnt how to recognize the various ecological succession types and their
characteristics. You should now visit OOU Biome and attempt identifying various types of successions,
Clement’s mechanism phases of succession and visible seral stages
5.0 Summary
Having listening to this lecture, you should have:

a better idea of the characteristics that separate one succession type from the other

confidence to look around your environment for development process of succession

better awareness of changes in vegetation around you
6.0
References/Further readings
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OLABISI ONABANJO UNIVERSITY
PLS317: PLANT ECOLOGY
7.0 Tutorial-marked quizzes
1)
List the types of succession you know.
Ans:
1.
Primary succession
2.
Secondary succession
3.
Seasonal succession
4.
Cyclic succession
5.
Autogenic succession
6.
Allogenic succession
2)
State the mechanism phases of succession according to Clement’s theory
Ans:
Nudation
Migration
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Ecesis
Competition
Reaction
Stabilization
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