SUBJECT: BASIC ECOLOGICAL CONCEPTS

CONCEPT: 1. Ecological concepts

2. Components of an ecosystem
3. Local biotic communities or biomes
4. Major biomes of the world

Sub – Topic 1: ECOLOGICAL CONCEPTS

Ecology is the study of living organisms in relation to their
environment.
The study deals with the relationship of living organisms with
one another and with the environment in which they live.
Ecology measures factors affecting the environment; it studies
the distribution of living organisms and how they depend on
one another and their non-living environment for their survival.
Ecology is divided into two
(i) Autecology which is the study of a single individual
organism or a single species of organism and their
environment. E.g. the study of Tilapia fish in a particular
stream.
(ii) Synecology which is the study of inter–relationships
between groups of organisms or species of organisms living
together in an area. E.g. the study of all organisms in a
particular stream in relation to their environment.

Ecology Concepts
1. Environment: This refers to all the factors in an
organism’s surroundings, living or non-living. The
factors include the place where the organism lives and
the physical conditions in the place, the food, water and
air it takes in, the animals that prey on it and the
disease that affect it.
2. Habitat: This is the place where an organism lives. It is
the place that is suitable to the organism’s way of life
e.g. the habitat of fish is water.

Examples of habitats include:

I. Aquatic habitats e.g. puddle streams, ponds, seas,

oceans.
II. Terrestrial habitats e.g. Savanna, rain, Forest, désert,
etc.
III. Arboreal habitat i.e. tree tops and tree trunks.

3. Ecological Niche: This is the functional role and the

space / specific portion of habitat occupied by a
particular organism or species. E.g. a caterpillar and an
aphid may live on the same plant but occupy different
positions. The caterpillar lives on the leaves and feeds on
them while the aphid lives on the young shoot / stem and
sucks sap from it. The functional role includes the
organism’s behaviour, its feeding habits and breeding
habits i.e. the activities carried out while occupying the
spaces in the habitat.
4. Population: This is the total number of all organisms
of the same species or kinds, living together in a given
area / habitat. E.g. the total number of Tilapia fish in a
pond constitutes the population of Tilapia fish in that
habitat.
5. Community: This is made up of all the populations of
living organisms that exist together in a habitat. It is
any natural occurring group of different organisms living
together and interacting in the same habitat. E.g. the
community on a rotting log will include insects like
termites, ants, lizards, small birds and decomposers such
as bacteria and fungi.
6. Biosphere: This refers to all parts of the atmosphere,
hydrosphere and lithosphere where life can be found.
It is the largest and highest level of biological organization
and is made up of various ecosystems.
7. Ecosystem: This is self – supporting unit that is made up
of a living part and a non-living part. It is a community of
plants and animals interacting with themselves and
with the non-living factors in their environment.

EVALUATION
1. Define ecology
2. Mention four ecological concepts and explain them

Sub- Topic 2: COMPONENTS OF AN ECOSYSTEM

The living part of the ecosystem is called its biotic component
while the non-living parts are called the biotic component.
(a) Biotic component: This includes all living
things/organisms in an environment. It is also called the biotic
community. It is made up of;
I. Food producer’s e.g. autotrophs (green plants),
chemosynthetic bacteria and protophyta.
Ii. Food consumer’s i.e. heterotrophs such as animals,
protozoa and some bacteria.
Iii. Decomposer’s i.e. saprophytes like fungi and some
bacteria.

(b) Abiotic component: This consists of abiotic resources and

abiotic conditions
Abiotic resources: These are what organisms need so as to
stay alive. E.g. sunlight (a source of energy) and inorganic
nutrients like water, nitrogen, carbon dioxide, phosphorus etc.

Abiotic conditions: These are those factors that determine

the kind of organisms that are found in a particular ecosystem.
These factors affect the behaviour, growth and breeding
patterns of organisms, they include;
(a) Climatic factors such as temperature, wind, light intensity,
humidity, water currents, turbidity, rainfall, e.t.c.
(b) Edaphic factors such as soils, rocks, topography, etc.
other factors include air, water, storms, etc.

Characteristics of an Ecosystem
(i) there is a flow of energy
(ii) there is recycling of inorganic nutrients.

The major interaction between the biotic and abiotic

components involves feeding. Food producers like plants, trap
sun-light energy and nutrients (e.g. carbon dioxide, nitrogen)
etc. from the abiotic environment to make food. The energy
and nutrients in the food is passed on to heterotrophs
(consumers) such as animals which feed on plants or on one
another. The animals and plants eventually die and
decomposers feed on them thereby obtaining their own
energy. However in the process, the decomposers release the
nutrients in the animals and plants back into the abiotic
environment (i.e. the soil). These nutrients can be re-used
again by the food producer’s. Plants also give out oxygen
during photosynthesis and this is used by animals for
respiration. Animals give off carbon dioxide during respiration
which plants take up.

NB: As the energy in food is passed from one organism to

another it eventually escapes into the environment and cannot
be re-used.

EVALUATION
1. Define (a) biotic factor (b) abiotic factor
2. Give two examples each of the concepts defined above
3. What characteristics make an ecosystem a self- supporting
unit.

Sub – Topic 3: BIOMES

Biomes are large natural terrestrial (land) ecosystems. It is the
largest community of organisms interacting with the non-living
environment. Biomes are identified by their vegetation.
Examples include forest, desert, savannas, etc. The type of
vegetation is largely determined by climatic factors especially
rainfall and temperature, as such, regions in the world which
have similar climates also have similar biomes.

Local Biomes In Nigeria

This can be grouped into two major zones
(1) The forest zone (2) Savanna zone

(1) The forest zone: This is made up of vegetations having

mainly trees, they
include:

Mangrove swamp:
A forest of tall woody trees with aerial roots. The rainfall is high
and the soil is water logged throughout the year.
Plants here include the white and red mangroves, raffia palms
and coconut.
Found in states like the Delta, Cross River, Bayelsa etc. The
climate is hot and wet throughout the year. Rainfall is heavy
usually above 2500mm and the average monthly temperature
is around 26ºc for most months of the year.

Tropical Rainforest:
Consists of tall trees with buttress roots, with evergreen and
broad leaves. The trees exist in canopies i.e. different layers,
and prevent sunlight from reaching the forest floor, thus the
vegetation on the forest floor is sparse. Epiphytes and climbers
are common features in the trees.

The climate is hot and wet throughout the year. The mean
annual temperature is 27ºc while the mean total annual rainfall
is 2000mm. These forests are found in states like Oyo, Edo,
Cross River, Ogun, Ondo, Imo and Rivers State.

Savanna zone: This is made up mainly of grasses and

includes;

Southern Guinea Savanna:

Consists mainly of tall grasses, with a few tall trees with

broad leaves. The trees are scattered and deciduous. Examples
include the locust beans trees, shear-butter and isobelina.

It has a moderate rainfall of between 100-150cm per annum.

They are located in Enugu, Kogi, Benue, Kwara, Osun, Oyo,
Ebonyi, and Ekiti States.

Northern Guinea Savanna (Sudan Savanna);

This has short but numerous grasses. The trees are scattered,
short and deciduous. The trees have thorns while others have
thick barks. The trees include acacia, date palm, baobab and
silk cotton plants.
The rainfall is low, about 50-100cm per annum. They may be
found in states like plateau, Kaduna, Bauchi, Niger, Taraba,
Adamawa and Kano.

Sahel Savanna:

It has very short and scanty grasses. There are short and tough
shrubs or trees. The plants are mainly drought resistant and
scattered examples include acacia, gum arabic and date palm.
The temperature is very high and rainfall is very low, below
50cm per annum. It may be found in States like Bornu, Katsina,
Sokoto, Yobe, Kebbi, Zamfara, Kano and Jigawa.

EVALUATION
1. What is a biome and how can it be identified?
2. Mention the two major biomes in Nigeria and the types

OBJECTIVE TEST
1. Epiphytes are usually found in (a) grassland (b) desert (c)
forest (d) marsh land
2. The highest amount of rainfall is recorded in (a) Rainforest
(b) Mangrove swamp
(c) savanna (d) desert
3. The Sahel savanna is found in …….. state of Nigeria (a)
Akwa Ibom (b) Kogi
(c) plateau (d) Zamfara
4. Most trees in the savanna region (a) have buttress roots (b)
have pneumatophores
(c) are deciduous (d) are ever green
5. Which of the following is not an abiotic factor? (a) air (b)
food (c) light (d) water

Sub – Topic 4: MAJOR BIOMES OF THE WORLD

Zones of different biomes occur from the equator to the arctic
and to the antarctic due to differences in climate. In the
equatorial and tropical areas where temperature and rainfall
are high all year round, tropical forests occur while in the cold
arctic regions, treeless plains called tundra are found.
Climates change with distance from the equator and also with
height above sea level, as such
zones of different biomes occur from the equator to the poles
and on a mountain side.

Examples of major biomes of the world

(1) Tropical rain forests: These consist of dense forests with
many types of trees, epiphytes and climbers. Rainfall is
abundant throughout the year and an average temperature of
27ºc is recorded throughout the year. Located around the
equator e.g. around coasts of West Africa, Amazon basin of
South Africa, etc.
(2) Temperate forests: These consist of broad-leaved
deciduous trees which shed their leaves during winter. A lot of
different plants grow at many levels from the ground as the
trees are not densely packed as in the tropical forest. It has a
moderately wet climate and a dry or cold season. Examples are
found in North America, lowlands of North – West Europe (e.g.
France), and Britain.

(3) Coniferous forest: These consist of needle leaved,

evergreen conifers e.g. pines, fires and spruces. Only a few
types of tree are found in these forests. Other plants such as
shrubs, ferns and mosses are also present. The temperature is
cool and rainfall is light. There is also light snow. Examples are
found in Eurasia and North America.

(4) Temperate shrubland: Consist of drought-resistant

shrubs, aromatic plants and dwarf trees. The temperature is
very high (over 30ºc), rainfall is low, the summers are hot and
dry and the winters are mild and rainy. Examples are found in
North-Eastern Brazil, Australia, and close to the Sahara in West
Africa.

(5) Savanna: These are tropical grasslands with few scattered

trees. It has a moderately dry climate, a warm dry season and a
hot rainy season. Examples are found in Central America,
Interior of Brazil, West Africa, East Africa, and South-East Asia.

(6) Temperate grassland: Consist of large stretches of

perennial grasses growing on very fertile soil. Examples are the
steppes, prairies, plains, pampas and veld. The climate is
moderately dry with a cold winter and hot summer. Examples
are Found in the interior continents in Asia, North America,
South America, (Argentina), South Africa and Australia.

(7) Desert: Consist of very sparse vegetation which are mainly

succulent perennials with deep root systems and annuals which
exist mainly as seeds, germinate and grow rapidly, flower and
produce seeds during brief periods of rain. Rainfall is very low
and temperature is very high. E.g. Sahara desert (North Africa),
Arabian Desert (Arabia), e.t.c.
(8) Tundra: Consists of treeless marshy vegetation composed
mainly of dwarf shrubs, grasses, sedges, lichen and moss. The
climate is clod with long icy winters and very short summers.
The average temperature is 10ºc. Examples are the coastal
strip of Greenland, Northern Canada and Alaska, Arctic
seaboard of Eurasia.

(9) Mountain vegetation: Consist of evergreen rain forest

occurring on the slopes of mountains. The forests are less
luxuriant than the tropical rain forest. The Afro-alpine
vegetation occurs at height above 3000m on mountains. The
vegetation consist mainly of heaths, grasses and sedges. In
Africa it is found in Cameroon mountain, Kenya highland and
Kilimanjaro mountain. Temperature decrease with altitude.
Rainfall is heavy on the windward side and less on the leeward
side of the mountains.

EVALUATION
1. List six biomes of the world
2. Briefly discuss two biomes of the world.

WEEKEND ASSIGNMENT
Make a drawing of the map of Nigeria and outline the local
biomes

SUGGESTED PRACTICAL
Make a local visit to any nearby vegetation and make a report
of your observations.

WEEK 9
TOPIC: BASIC ECOLOGICAL CONCEPTS
CONTENT:
1. Population studies by sampling
method
2. Ecological factors

Sub – Topic 1: POPULATION STUDIES

A population is defined as the total number of organisms of the
same species living together in a given area at a particular
time. In any ecosystem, the community is made up of many
populations of different species.
To study a habitat’s populations, the following are usually
investigated.
1. The type of organisms in the habitat: This involves
listing all the different types of populations found in that
particular habitat. This helps to determine the relationships that
exist between the different organisms in the habitat.

2. The dominant species: This refers to the species of

organisms in a community which exert a great influence on the
habitat and on the other populations. Dominance may be
expressed in terms of their number, size, the portion of space
occupied and contribution to the energy flow of the habitat.

3. The characteristics of the population: This refers to;

(a) Population size: The total number of individuals of the
same species in the habitat (the total numbers of individuals in
a population). A large population stands a better chance of
surviving unfavourable conditions such as fires, diseases, harsh
climate changes, while a small population can be easily wiped
out. A large population also has the advantage of increasing its
vigour through breeding which invariably increases its ability to
withstand adverse conditions.
(b) Population density: This is defined as the number of
individual organisms per unit area or volume of the habitat.
Mathematically represented as;
Population density = Total population or Population size
Area of habitat.

Example: If an area of land of 100m² has an elephant grass

population of 1000 plants, the density of elephant grasses will
be;
Total number of individuals
Total area

= 1000 elephant grasses

100m²

= 1OØØ elephant grasses

 1ØØm²

= 10 elephant grasses / m²

Population density can be used to estimate the total number of

individuals of a population i.e. population size.
(c) Population frequency: This refers to how often the
species occurs at different sites in its habitat. It is recorded as
the number of times the organism is sited (seen).
(d) Population growth rate: This refers to the total and final
effect of birthrate and death rate of organisms in the habitat.
(e) Percentage cover: This is the area of ground or space
covered (or occupied) by a given species its habitat. It is
expressed in percentage.

Methods of studying populations

To conduct population studies the following procedure is used;

i. Choose the habitat to be studied

ii. Choose a sampling method

iv. Identify the species in the habitat

vi. Collect, count and record the different types of

organisms present.

viii. Repeat the population studies at different periods.

The following methods can be used to study specific

populations;
1. Collection of plants: In a small area plants are easy to
count and their distribution can be recorded on a map or scale
diagram of the area, however for larger areas quadrats or
transects are used.
(a) Quadrat Sampling: A quadrat is made of a square or
rectangular piece of wire, plastic, wood or metal frame with
predetermined area. E.g. the area of a quadrat may be 25cm².
A quadrat is used to sample the number of plant species in a
habitat. It is not suitable for sampling animals because they
move around so much. A quadrat is used by throwing it over
the shoulder at random several times and on each landing, the
area covered/enclosed by it is observed. The type of plant
species and their number within the quadrat are recorded.
From the results, the average number of plant per m² is
calculated. If the area of the habitat is known, the total number
of plants it contains can be estimated.
Permanent quadrats, with mapping grids attached can be made
to study seasonal variations of plants. These quadrats are
sturdier, larger and remain permanently fixed on a marked
area.
(b) Transect method: A marked tape is used in this method.
The tape is marked at convenient intervals and then stretched
across the area to be studied. The plants encountered at the
interval marks are counted and recorded. This procedure is
repeated a few times. In this way, a fairly accurate estimate of
the number and types of plants in the habitat are obtained.
Plants are usually collected in plastic bags and then pressed
and dried in a plant press. The dried plants are mounted on stiff
paper, fixed in position with masking tape/cellotape and labeled
with both the scientific and common names.

(2) Collection of Animals: Animals are more difficult to

collect than plants; however their presence can be inferred by
looking for signs of their presence such as nests, eggs, feaces,
tracks, feathers, etc and by studying the vegetation with which
they are associated. To study animals different types of nets
and traps are used in capturing them. The following methods
can be used.
(a) Capture - Recapture method: In this method animals of
one type in a particular area are caught, counted and marked
with ink and released. Their number is recorded as A1. The
following day another set is captured and the number recorded
as A2.This second batch may include animals which had been
caught and marked the previous day, their number is recorded
as A3. The population of animals present in the area is found
using the formula;
Population in area = A1 x A2
A3
This method is based on the assumptions that;

i.Individuals do not move out of or into the ecosystem

 ii. The marked individuals are randomly distributed in
the population.

iv. The marked individuals are a random sample.

vi. The initial capture and markings do not influence

recapture.

viii. That none of the marks have worn off during the
interval between the two catches.

NB : The results obtained by this method are approximations.

(b) Collection of soil animals with quadrats: The soil

animals in an area can be studied by collecting samples of soil
from several sites chosen by tossing a quadrat randomly. A
25% sodium chloride solution is added to each soil sample and
the animals are collected as they float in the solution.
For earthworms, the sites chosen with the quadrat are irrigated
with 25% formalin solution and the earthworms are collected as
they move to the surface of the soil.

EVALUATION
1. What are the major investigations carried out when studying
a habitat?
2. A pond with an area of 200m² has a duckweed population of
1,500 plants. Find
(a) The population density
(b) If the western half of the habitat contained ¾ of the
duckweed. What is the density of the eastern half?
3. Explain what a Tullgren’s funnel is and what it is used for.
4. Make a list of traps used for capturing animals for study and
describe how captured animals are kept or preserved.

Factors That Affect Populations

Populations in a habitat may show changes in size or
distribution. These
changes may be due to;
1. Natality (birth rate): Increase in birth rates especially
during breeding periods, lead to increase in population size
while a decrease in birth rate results in a decrease in the
population.
2. Mortality (death rate): This refers to the rate at which
organisms die. An increase in death rate leads to a decrease in
the population and vice versa.
3. Immigration: This is the movement of organisms from
different habitats into a particular habitat. This increases the
population size of the habitat being moved into.
4. Emigration: It is the movement of organisms out of a
habitat ant it leads to a decrease in the population. Emigration
may be caused by scarcity of food, unfavourable conditions,
seasonal climate changes or breeding purposes.
5.Availability of food: An abundance of food in a habitat
tends to lead to an increase in the population of organisms due
to increase in birth rate (reproduction) and influx of organism
from other areas and vice versa.
6. Seasonal climate changes: Adverse climate changes may
lead to a decrease in number of organisms due to death or
emigration. Favourable conditions leads to an increase in
population.
7. Natural disasters e.g. fire; flood, drought etc. may lead to
a decrease in population due to death and emigration.
(others include availability of water, availability of space,
war)

Sub –Topic 3: Ecological Factors

These are factors in the environment that influence life in the
ecosystem. These factors affect the living organisms or cause
changes in the habitat (aquatic or terrestrial).

These factors are grouped into two

(i) Biotic factors
(ii) Abiotic factors.

(i) Biotic factors

The biotic factors are those concerned with the effects of plants
and animals on one another in a given habitat e.g. competition,
predation parasitism, etc.

(ii) Abiotic factors.

Abiotic factors include climate topographic (or physiographic)
and edaptic (soil factors). Variations in the ecological factors
bring about changes in the habitat. Abiotic factors also
determine the type of biotic community found in a habitat.
Ecological Factors Affecting Terrestrial Habitats
(1) Topographic Factors: These factors are associated with
the structure of the habitats e.g. effects of hilts, valleys, plains
mountains and rivers. These factors bring about variation in the
vegetation and types of animals in an area.
Topographic factors include:
(a) Altitude (elevation): This refers to height of the land
above sea level. This affects the growth of plants and the level
of erosion in an area. As altitude increases, temperature falls
by approximately 1ºc per 150metres, as a result of this,
mountain tops are generally cold places cold air causes clouds
to condense and fall as rain, thus the annual rainfall on
mountains is high especially on the windward side. As one
ascends a mountain, the air become less dense, there is less of
it to filter the sun’s rays, so organisms at the top of mountains
are exposed to intense solar radiation.
(b) Slope: Water flows faster on a steep slope than on a gentle
slope as such, run-off is greater and less water sinks into the
soil on steep slopes. Also, erosion tends to be more. Gentle
slopes are more favourable to plant growth.
(c) Exposure: This refers to the extent to which living things
are not protected from climatic factors such as rainfall,
sunshine and wind. Exposure is usually high on mountains and
low within a forest. Winds tend to be stronger in exposed
habitats and relative humidity is lower than in sheltered
habitats. Low degree of exposure ensures the availability of
nutrients to plants.

(2) Edaphic Factors: These are factors related to the nature

of soil particles. The word edaptic refers to the influence of soils
on plants and animals. Differences in the soil of a locality
usually produce difference in vegetation since plants are
dependent on the soil and the type of plants determine the
type of animals that will be found in the habitat. Edaphic
factors include:
(a) Soil Types: this could be sand, loam or clay. The type of
soil determines the fertility of the soil, its porosity and water
retaining capacity.
(b) Soil Texture: The amount of sand, silt and clay in a soil
affects its water retaining capacity. Soil texture refers to the
degree of fineness or coarseness of soil particles. It also affects
leaching and erosion.
(c) Soil structure: This refers to the arrangement of the
various soil particles in soil. This affects the level of soil
aeration and percolation and the type and level of soil
organisms in the soil.
(d) Soil pH: The pH of soil also affects the type of plants in the
habitat e.g. some plants grow best in acid soils while others
prefer alkaline conditions.

(3) Atmospheric factors (Relative Humility) : This is a

measure of the amount of moisture in the air. It affects the rate
of transpiration from plants and evaporation from animals. As
relative humidity falls, evaporation and transpiration rise as
such organisms that live in areas where humidity is low must
prevent water loss from their body surfaces. E.g. in deserts, the
leaves of plants like the cactus are reduced to spines to
prevent loss of water.

Ecological Factors That Affect Aquatic Habitats

(1) Salinity: This refers to the concentration of salts in the
water. Salinity affects the movement of water and salts across
the body tissues of aquatic organisms. Salinity is low in fresh
water, high in sea water and moderate in brackish water.
Aquatic organisms have to maintain the osmotic balance
between their body fluids and their aquatic surroundings in
order to survive. Those living in fresh water have adaptive
features which enable them get rid of excess water that enters
their bodies; those living in sea water have body fluids with
almost the same salt concentration as the sea water while
those living in brackish water have body tissues that can
tolerate wide and sudden fluctuations in salt concentration of
their body fluids.

(2) Depth Of Water: As a body of water becomes deeper, the

amount of light and dissolved oxygen become less, so at the
bottom of deep lakes and oceans, there may be too little light
for photosynthesis as such no green plants can grow there.
Shallow bodies of water such as ponds are usually well supplied
with oxygen and light and support a lot of plants and animals.
However, these habitats are subject to evaporation and drying
up in the dry seasons, the plants and animals therefore have to
develop adaptation to survive such conditions. E.g. formation of
cysts by some protozoans.

(3) Turbidity: This refers to cloudiness of water. It is caused as

a result of suspended materials in water. Light penetration is
low in cloudy or muddy water and this hinders green plants
from growing at some depths.

(4) Dissolved Gases: This refers to dissolved oxygen. Oxygen

concentration of water decreases with depth. Oxygen is
required by most aquatic organisms for respiration as such
organisms which live in stagnant or very deep water have to be
able to tolerate low levels of oxygen concentration. Organisms
that require high oxygen concentration, usually live near the
surface of deep water or in fast-flowing rivers and streams e.g.
the simulium larva lives in fast flowing streams.

(5) Tides and Wave Action: Tidal movement refers to the

regular rise and fall in the level of the sea. Organisms which
live in the intertidal zone of a seashore have to be able to
tolerate being alternately covered by sea-water and then
exposed to air twice daily.
Wave action is also important both in the intertidal and splash
zones of the seashore. Most organisms in these areas are
attached to the substratum or live in burrows. Some attach
themselves firmly to rocks and other immovable objects, while
some others have hard body covering to prevent evaporation of
water from their bodies. Waves cause the aeration of the
surface waters of the open sea, thus enabling aquatic
organisms to have sufficient supply of dissolved gases for their
needs.

(6) Speed of Flow (currents): Plants and animals are

affected by the rate at which the water flow. Some organism’s
e.g. spirogyra prefer to live in slow moving stagnant water
while others e.g. Tilapia, prefer fast-flowing water. Many
organisms which live in fast-flowing rivers and streams have
adaptations which serve to prevent them from being swept
away from their support by currents in water. Water currents
increase aeration and the turbidity of the water. Currents also
carry warm water to colder regions and this affects the
distribution of organisms.
(7) Density: Density of water varies with the type of habitat.
The density of fresh water is about 1.00 while that of sea water
is 1.028 at atmospheric pressure and 0ºc. It is easier to move
through air than water because water is more dense, as such
aquatic organisms have a streamlined shape to help them
move easily through water. Some organisms that float on the
surface are sensitive to changes in density e.g. eggs of aquatic
organisms sink to different depths depending on the density of
the water.

Ecological Factors Common To All Habitats

The ecological factors that affect both the terrestrial and
aquatic habitats are mainly climatic e.g. temperature, rainfall,
relative humidity, wind, high intensity hydrogen ion
concentration (pH) and pressure. Of these factors temperature
and rainfall determine the type of vegetation in a region.

(1) Temperature: This refers to degree of hotness or

coldness. Variation in temperature results in hot or cold
climate. It affects the terrestrial habitat more than the aquatic
habitat. In the terrestrial habitat temperature varies with
season, while in the aquatic habitat it decreases with depth.
A rise in temperature usually results in a higher rate of
transpiration in plants and higher rate of metabolism in most
animals (except homoiotherms). Most living organisms are
killed by high temperatures and it reduces the performance of
some. Low temperatures lead to inactivity or dormancy. In
some organisms (e.g. tadpoles, insect larvae and bacteria) a
rise in temperature results in faster rate of growth and shorter
length of life-cycle. A higher rate of evaporation of water from
the soil, ponds and lakes and a lower relative humidity are also
observed.
Too high or too low temperature inhibits the growth and life
activities of living things. However most organisms have
various adaptive features that allow them to live at low or high
temperatures e.g. Bears living in the arctic regions have very
thick furs.
(2) Rainfall: Rain is the main source of water to most
organisms. It also supplies water to soil on which land plants
depends. It is also the major source of water in rivers, ponds,
lakes, oceans etc. The amount of rainfall in an area has a major
effect on the type of vegetation found there. Low amount of
rainfall usually causes drought on land and drying up of
freshwater habitats (which leads to death of animals). Too
much rain causes floods and destruction of vegetation through
erosion.
Rainfall increases relative humidity and also increases turbidity
of streams, rivers and lakes. Rainfall is necessary for seed
germination. It helps to dissolve nutrients in the soil thus
making them available to plants. It is also necessary for the
vegetative growth of most crops e.g. flowering and proper
development of groundnut pods.
Rain water may form puddles and small pools which provide
temporary habitats for mosquito larvae, algae and tadpoles. It
is also necessary for the start of new termite colonies.

(3) Light: Light is necessary for photosynthesis in green

plants. It affects the productivity of crops and facilitates
flowering and fruiting in some plants. Light is the ultimate
source of energy for all organisms. Light affects the activities of
animals e.g. some animals are active during the day (butterfly)
while others are active at night (cockroaches). The ultra-violet
rays of the sun enable animals to manufacture vitamin D.

(4) Wind: Winds are important because they cause water

currents and waves thus mixing water and making food
available in aquatic habitat, Winds carry rain bearing clouds.
They also determine a season e.g. In Nigeria, the S/W wind is
responsible for the rainy season while the N/E wind brings the
harmattan. Wind has drying effects (on land) and so it
increases the rate of transpiration in plants. In an area exposed
to strong winds only xerophytes can grow there. Winds also aid
pollination of flowers and dispersal of seeds and fruits. Winds
increase the rate of evaporation from the soil and in savanna
and desert areas it is a major cause of soil erosion. Winds also
play an important role in the establishment of insects in a given
area.
(5) Pressure: Atmospheric pressure decreases from the
depths of the ocean upwards to the higher attitude of the
atmosphere. Plants and animals have special adaptations to a
particular level of pressure to enable them survive. For instance
in the oceans, the pressure increases by 1.03kg/m² every 10m,
so organisms found at depths of about 400m live in conditions
of enormous pressure but are well adapted to such conditions
and will not survive at levels with lower pressure.

(6) Hydrogen ion Concentration (pH): This refers to the

acidity or alkalinity of the soil or water in a habitat. pH affects
the types of plants and animals in a habitat. E.g. some plants
grow best in acidic conditions while others can only grow in
alkaline conditions. In aquatic habitats pH varies with the
salinity of the water. Freshwater is neutral while sea water is
fairly alkaline (pH 8.5). Organisms like the freshwater mollusks
(Mytilus) are usually absent in water with a pH less than 6 (i.e.
acidic water).

Biotic Factors Affecting the Ecosystem

Biotic factors refer to the effects of plants and animals on
themselves or one another. The biotic factors include:
(1) Parasitism: One organism called the parasite lives in or on
another organism called the host. The parasite benefits while
the host suffers harm or may die.

(2) Competition: This may occur between organisms of the

same species or different species. Competition may be for food,
space, mates, etc. One of the organisms will eventually over
come the other.

(3) Commensalism: This involves two organisms living

together. One of the organisms (the commensal) benefits from
the association while the other organism neither benefits nor is
harmed.

(4) Predation: This involves an organism (called the predator),

killing / feeding on another organism (the prey).

(5) Trampling: Grazing animals trample on plants and

invertebrates.
(6) Pollination of flowers by insects (this aids continuity and
increase).

(7) Aeration of the soil by some animals e.g. earthworms,

termites, etc.

(8) Support provided to climbing plants by trees or bigger

plants.

(9) Shade provided by trees, etc.

Evaluation
1. State five ecological factors that (a) affect terrestrial
habitats (b) affect aquatic habitats (c) are common to both
habitats
2. Discuss two of each set of factors mentioned above.

WEEK 10

CONTENT:
o Simple measurement of Ecological Factors
o Relationship between soil types and water
holding effects of soil on vegetation

Sub – Topic: SIMPLE MEASUREMENT OF ECOLOGICAL

FACTORS
(1) Temperature: This is measured using a mercury
thermometer read in degree celcius (ºc). At least two readings
are taken in a particular area of the habitat being studied to
ensure accuracy. A soil thermometer is used for soil
temperature, a maximum-minimum thermometer for recording
the highest and lowest temperature of the day, and a waxed
bulb thermometer for temperature of water at different depths
in a pond, stream, etc. The waxed bulb thermometer is usually
tied to a string knotted at regular intervals to indicate depth.
Outdoor thermometer Thermometers

(2) Rainfall: This is measured with a rain gauge. This can be

made from a tin can,a plastic funnel and a 50ml measuring
cylinder. The amount of rainfall is calculated in millimeters, with
the formula

d
D²x h = rainfall for a period where;

d = diameter of mouth of funnel

h = height of rainwater in the cylinder
D = diameter of collecting cylinder
Usually, the height of the water in the cylinder indicates the
amount of rainfall after every storm.

(3) Relative Humidity: Is measured using a wet and dry bulb

hygrometer, or a pocket hygrometer. The pocket hygrometer is
exposed to air and the reading taken after the lever arm has
stabilized. The wet and dry bulb hygrometer is swung in air for
30seconds and the reading on the thermometers taken and
converted to relative humidity units using a table of conversion.
The hygrometer may also be kept in a Stevenson’s screen.

(4) Wind: Wind has both speed and direction. Wind direction is
measured / indicated by a wind vane while wind speed is
measured with an anemometer (recorded in ms¹‫)־‬.

(5) Light Intensity: Is measured by a light meter or

photometer. The readings on the meter are expressed in lux
units. The greater the intensity of light, the higher the readings
on the meter and vice-versa.

(6) Pressure: Atmospheric pressure is measured with a

barometer. It is measured in millibars (or millimeters of
mercury, mmHg). The readings are taken directly from a scale.
(7) Water Depth: Is measured with a meter rule or a marked
and weighted line knotted at one meter intervals. The meter
rule is attached to a GYYYGG
weighted line to ensure that it is vertical in water.

(8) Water Flow: To measure the speed of flow of a water

body, the distance (m) covered per unit times by a float is
taken. The float may be a weight tube and the distance covered
has to be pre-determined. Speed of the current is calculated in
meters per second. A simple water-speed meter can be used to
compare the speed of water flow at different positions in a
stream

(9) Turbidity: Is measured by slowly sinking a weighted white

disc called a secchi disc into the water, noting the depth at
which it just cannot be seen anymore. This is not a real
measurement of turbidity but a useful method of comparing the
turbidity of different aquatic habitats, different sites of the
same habitats, or at different times.

(10) Slope: Is measured with a simple slope gauge

constructed with a meter rule to which a protractor is attached.
The angle readings on the protractor are read and recorded.
Small angles indicate a steep slope.

(11) Height: The height of objects like tall trees is measured

using the principle of similar triangles.