Ecology Of Populations

Ecological succession is a chain of events in which one community is gradually replaced by

another in an orderly series, until a suitable community climax which is best adapted to the

environment is established. The terminal climax community is a state of stability with the

ecological conditions existing within the locality.

General characteristics and outcome of succession.

  1. Succession brings about greater species diversity, greater species population

density and large life form.

  1. Succession is predictable and occurs along one direction in the ecosystem

iii. As communities are constantly undergoing changes. It shows that the biosphere

and ecosystem are dynamic

  1. Succession is caused by the modification of physical environment by the

community itself.

  1. Ecological successions show that some organisms are more easily dispersed and

are more vigorous and grow more rapidly than others.

  1. Succession occurring in different places and at different times involved are often


vii. Climax communities are formed after a long period of time and once formed

they maintain their structures.

viii. Succession makes the food web become more complex and the relations

between the species become better defined or more specialized.

  1. The amount of inorganic nutrients held by the organisms and soil of the

ecosystem increases

Types of Succession

  1. Primary Succession is a type of succession that occurs on a bare surface where no

Community of plant existed before it involves the formation of new soil. It begins from

(a) Dry rock slope which eventually changes to a forest

(b) Shallow lake gradually filled up with vegetation to become a marsh and eventually a


(c) Mouth of a river where silt or mud is deposited thereby forming a bank on which a

mangrove swamp develop and eventually a tropical forest.

  1. Secondary Succession is a succession or changes on a surface that already or previously

has a community of plant to be replaced by another. For instance changes occurring on (i)

overgrazed grassland (ii) abandoned farm land.


A climax community is the end product of the succession of several seral communities over

a long period at one place. Once climax community is established it may remain indefinitely.

The climax community is regarded as steady state which has restored the community

structure towards steady state.

Characteristics of a stable ecosystem or climax communist

  1. It is generally believed that once the climax is attained, the community does not

change at all. Climax community changes due to aging and it is heterogeneous

  1. The climax community depends on the broad climax of the region

iii. Climax ecosystem has numerous micro-habitat which are inhabited by different

types of organisms.

  1. Climax community does contain many sub-communities.


Over-grounding is defined as a situation which occurs when a population in a given habitat

Increases beyond a point where the resources in the habitat such as space and food are not

Enough to support the individual in population.

Factors responsible for over-grounding

  1. Limited space
  2. Increase in birth rate

iii. Limited food supply

  1. Flux of immigrants
  2. Less emigration
  3. Decrease in mortality rate

vii. Increase in survival rate

viii. Barriers

Effect of over-grounding

  1. Shortage of space
  2. Shortage of food

iii. Competition

  1. Anti – social behaviour
  2. Spread of diseases
  3. Preying on each other

vii. Death of the organism

Adaptation to avoid over-grounding

  1. Territorial Behaviour – is an act in which an organism defend an area or a territory against

an intruders especially in animals lizards, birds.

  1. Dispersal of seeds and fruit – the disposal of seeds and fruit either by water, winds,

Animals, insect and explosive mechanism reduces the chance of over-grounding.

  1. Emigration is the movement of organisms away from habitat or a particular locality.
  2. Swarming – it contain insects such as termite and bees to form new colony is a way of

decongesting the population.

  1. Production of chemicals by plant as this prevent the growth of plants sometimes prevent

the growth of other plants.

  1. Production of canopies by tall trees which prevent the trees underneath from growing.


1a.What is climax community

  1. Discuss briefly the various stages starting with a bare rock to a climax community

2a.Define succession

  1. Describe a succession in a pond or abandoned farmland

c.State some effect of over-crowding.

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