Ecology Lecture notes 2023

METROPOLITAN INTERNATIONAL UNIVERSITY

PLANT IDENTIFICATION ECOLOGY
BTM 1102

Ecology is the study of organisms in relation to their environment.

Definitions of terms used in ecology.

1. Environment:
This refers to everything in the surrounding of an organism that influences its life. The
environment of a tadpole for example is everything in the water where it lives.

2. Biosphere
This is the part of the earth and its atmosphere that is occupied by living things or where life
exists. It’s the largest habitat.

3. Habitat
This is a place where an organism lives. In the habitat, the organism obtains water, shelter and it
is able to reproduce there. The habitat of a tapeworm is the mammalian intestines.

4. Population
This is the total group of organisms of the same species living in a particular place at a given time.

5. Ecological niche
This refers to a particular place an organism occupies within a habitat and the role it plays there.

6. Community
This is a collection of populations living and interacting with non-living components. It is
therefore the total of all organisms in an area.

7. Autecology
This is the study of only one species of organism in relation to its environment, e.g. the study of
a frog in relation to its habitat.

8. Synecology
This is the ecological study of a community of plants and animals in a particular area.
9. Ecosystem
This is a unit of the environment consisting of both living (biotic) and nonliving (abiotic)
components interacting to form a self-sustaining unit. E.g. living things may include fish,
cockroaches, and nonliving things may include lake, pond, forest, etc.

The two major factors within an ecosystem include:

 The flow of energy through an ecosystem.
 Cycling of matter within an ecosystem.

COMPONENTS OF AN ECOSYSTEM
The ecosystem is made up of two components;
1. The abiotic component (non living component)
2. The biotic component (living component)

THE ABIOTIC COMPONENT OF THE ECOSYSTEM.

This is the non-living component of the ecosystem. Living organisms interact with the nonliving
components in their community to form a self-sustaining unit called an ecosystem. The abiotic
components in the ecosystem include the soil factors (edaphic factors).

Edaphic factors:
These are physical and chemical factors in soil and atmosphere that influence the life and activities
of living organisms. These factors affect different organisms differently. Such factors include.
1) Light intensity. Light intensity affects the process of photosynthesis in plants, visibility in
some animals and causes responses such as phototropism.
2) Temperature. This affects the activity of enzymes in the body of organisms and therefore
determines the overall activity of an organism. Temperature also affects germination of seeds.
3) Water. This is a very important edaphic factor. Water is a component of the bodies of living
organisms. It is a raw material for photosynthesis, it aids dispersal of seeds, it is an agent of
pollination, it is a habitat for some organisms, it is a condition for germination, etc.
4) Humidity. This is the amount of water vapour in the atmosphere. Humidity affects the rate of
transpiration in plants; it also affects the rate at which water is lost from the bodies of animals
through evaporation.
5) PH. This is the alkalinity or acidity of soil. PH affects the dissolution of mineral elements in
water; it affects growth of plants and microbes in an area, etc.
6) Nutrients. Presence or absence of a particular nutrient in soil determines the organisms,
which can grow in that soil. Nutrients are required for proper growth of all organisms in the
ecosystem.
7) Oxygen concentration. Most of the organisms are aerobic, i.e. they require oxygen for their
respiration. Oxygen is abundant in air (21% by volume) however in water the concentration
of oxygen varies due to factors that affect its dissolution in water and over exploitation by
 Ecology Lecture notes 2023

organisms. This affects the growth of organisms in water. In such a case anaerobic organisms
can thrive and aerobic ones die.

BIOTIC COMPONENTS
This is made up of living organisms in the ecosystem. They are categorized into the following.

i) Producers
These are green plants and some bacteria that are able to manufacture their own food by use of
light, chlorophyll, Carbondioxide and water in the process called photosynthesis and
chemosynthesis. They are nutritionally referred to as autotrophs.

ii) Consumers
These are organisms, which are not capable of manufacturing their own food. The consumers get
their food by feeding on other organisms.

LEVELS OF CONSUMERS
Consumers are classified into feeding levels called trophic levels. The classification is based on
the type of food they feed on.
The feeding levels/trophic levels of consumers include:
 Primary consumer
 Secondary consumer
 Tertiary consumer

The primary consumers (1st order consumers):

These are organisms that feed directly on plants (producers). They are called herbivores.
Examples are cattle, grasshoppers, goats, sheep, etc.

The secondary consumers (2nd order consumers):

These are organisms that obtain their food by feeding on primary consumers. They are also
referred to as carnivorous organisms since they feed on flesh. Examples include cats and reptiles.

The tertiary consumers (3rd order consumers):

These are organisms that obtain their food by feeding on the flesh of secondary consumers. These
are usually big carnivorous animals like lions, crocodiles, vultures and tigers

iii) The decomposers

These are organisms that feed on dead decaying organic matter. They are commonly called
saprophytes. The major examples are bacteria and fungi.
Decomposers are important because they bring about decay of plant and animal tissues. This helps
in the recycling of materials in the soil.
They also reduce the amount if wastes and litter in the environment
 BIOTIC INTERACTIONS
Each category of feeding is known as a trophic level. Feeding methods are useful in showing the
relationship that exists in a community by means of food chains and food webs.

TYPES OF FOOD RELATIONSHIPS

FOOD CHAIN
This is a feeding relationship between organisms showing which organism feeds on what. It is
always expressed in a linear fashion beginning with primary producers and ending with tertiary
consumers.
Organisms at the beginning of a food chain are usually numerous while organisms at the end of
the food chain are often large and few in number.
The food chain shows the passage of energy from producers to consumers. Energy from the sun
is fixed by producers (plants). The herbivores eat the plants and obtain this energy. The carnivores
feed on herbivores and obtain this energy. At successive levels some energy is lost. At the end of
the food chain energy reduces.

Example 1:

Grass grasshopper dove cat

In the food chain above, the grass is the primary producer, the grasshopper is the primary
consumer, the dove is a secondary consumer and the cat is a tartially consumer.
Arrows are used to show the movement of energy from one organism to another. Energy moves
from the producers to tertially consumers through the food chain.
There are usually few links in the chain because as the links increase energy reduces and
organisms feeding at the terminal end of the chain gain little energy.
Chemicals on the other hand accumulate in tissues and increase in succeeding levels in the food
chain.
Elimination of one level from the food chain disrupts the food chain. For example in the above
food chain, when the grasshoppers are eliminated from the ecosystem, the following occur.
1) The grass grows and increases in number because the grasshopper that used to feed on it has
been removed.
2) The doves lack food because they feed on grasshoppers, which have been removed. This
causes their numbers to drop.
3) The cats also reduce in number because as the doves die due to lack of food, the cats lack food
and start to reduce because they feed on doves.
 Ecology Lecture notes 2023

Example 2
Draw a food chain for the following organisms; a)
Vegetation, beetle, owl, fox
Vegetation beetle owl fox

b) cow, man, lion and grass.

Grass Cow Man Lion

c) Nile perch, algae, water flea and tilapia

Algae Water flea Tilapia Nile perch

FOOD WEB
A food web is a number of interlinked food chains. From the above food chains in example 1
and example 2a, the food web below can be obtained.

From the food chain b and c in example 2 above, the food web below can be drawn.

Note.
When drawing the food web, the organisms should be arranged in trophic levels. The produces
should be at the bottom followed by primary consumers and tertiary consumers at the top of the
food web.

ECOLOGICAL PYRAMIDS
These are used to show either the number of organisms or energy present at each level in the food
chain and food web. There are three types of pyramids namely;
 1. Pyramid of numbers
2. Pyramid of biomass
3. Pyramid of energy

1. Pyramid of numbers:
This is used to show the number of individuals at each trophic level.
The number of organisms at each trophic level is counted and a pyramid is drawn with the primary
producers at the base. The width of each rectangle represents the number of organisms
at each trophic level.
Illustration
Tertiary consumers
Secondary consumers
Primary consumers
Producers

Example 1
Draw a pyramid of numbers for 20 Nile perch, 40 planktons, 34 tilapia, 4 men

4 Men

20 Nile perch
34 Tilapia
40 Planktons

Example 2.
Draw a pyramid of numbers for the food chain below.
1 Guava plant 100 caterpillars 20 birds
Birds
Caterpillars
Guava

A big fruit tree may have several birds feeding on a fruit, man may be an alternate consumer of
the birds while at the same time, several lice may be parasites to man. The pyramid of numbers
of such a chain may have the following form.
 Ecology Lecture notes 2023

Lice
Man
Birds
Tree
The problem with the pyramid of numbers is that it does not account for size of the organism at
each trophic level. For this reason the pyramid of biomass is used.

Question:
Husnah carried out an ecological study in Kabowa. In one of the sections, she found 15 toads, 180
plants, 4 snakes and 120 grass hoppers. Use the information to answer the questions.
a) Construct a possible food chain for the above information.
b) State the trophic levels occupied by each of the organisms in the community.
c) Draw the pyramid of number for the community.
d) Explain what would happen to the rest of the organisms if all toads were destroyed.

Solution:
a) Plants grass hopper toad snakes
b) Plants – producers
Grass hopper – primary consumer
Toad – secondary consumer Snake
– tertiary consumer
c) Pyramid of numbers
Snake Tertiary consumers

Toad Secondary consumers

Grass hopper Primary consumers

Plants Producers

d) The number of grass hopper increases and that of plants decreases due to the increase in
the number of grass hopper.

2. Pyramid of biomass:
This gives the mass of the organism at each trophic level. Biomass refers to the mass of a living
organism. Biomass decreases from producers to tertiary consumers. Producers have a higher
biomass than all other trophic levels.
Considering the food chain in the example 2, above, the pyramid of biomass would be.
Birds
Caterpillar
Guava tree
Even if the guava is one, it has a bigger biomass than caterpillars and caterpillars have a larger
biomass than birds.
In most cases the pyramid of bio mass is constructed using dry weight of organisms. This is The
problem with biomass is that it varies greatly as the organism grows. Using a pyramid of energy
can solve this problem.

3. Pyramid of energy:
This shows the amount of energy at each trophic level. Energy decreases with succeeding trophic
levels. Producers contain more energy than tertiary consumers. The pyramid of energy
gives the most accurate representation.
Pyramid of energy. Tertiary consumer

Secondary consumer
Primary consumer
Producer

Energy flow in an ecosystem

Energy flows through food chains and food webs. Energy is obtained from the sun by green plants.
The plants trap light energy and use it to carry out photosynthesis. During photosynthesis, light
energy is converted into chemical energy. When primary consumers eat the plants, they obtain
this energy. The energy is then passed on to other organisms through their feeding relationships.
At each trophic (feeding) level there is loss of energy because;
i) Some energy is used up during respiration.
ii) Some energy is lost from herbivores in form of indigestible plant material.
iii) Some organisms die before they are eaten.
iv) Some of the chemical energy is converted into other forms such as sound, light energy,
heat energy, which easily escapes from the organisms.
At each trophic level, decomposers (saprophytes) such as bacteria and fungi break down dead
organic matter to release some of the energy locked in it.

POPULATIONS
Population is the total number of organisms of same species living in a particular area at a given
time.
Organisms live in a population in order to:
 Gain more protection as the population
 Have increased chances of gathering mates and breeding.
 Ability to get shelter
because the fresh mass of an organism varies so much with water content.
Dry weight is the mass of an organism without water.
Tertiary consumers
Secondary consumers
Primary consumers
Producers
 Ecology Lecture notes 2023

However organisms in a population face:

 High chances of overcrowding
 High competition among themselves for food, shelter, etc.
 Increased chances of predation.

PATTERNS OF POPULATION DISPERSION

The distribution of individuals in an area is known as population dispersion. It refers to the way
individuals in a population are distributed in a particular area in which they are living.

Types of population dispersion

1. Random dispersion.
This happens when the environment is uniform throughout the area and therefore there is no tendency to
aggregate. There is no particular order of distribution

2. Uniform dispersion.
This occurs when competition is very high due to scarcity of resources and the organisms are evenly
distributed in all parts of the environment.

3. Clumped dispersion
Here organisms are found in high numbers in particular areas and low numbers in other areas.
This results from:
1. Self-dispersal
2. Resources being clumped
3. Tendency of individuals in an area to live together.
4. Territorial behaviour
5. Aggregate behaviour where organisms feed together in a group.

There are two types of clumped dispersal.

Regular illustration
Irregular illustration

Importance of distribution
 Individuals acquire themselves enough space within which they can live and breed i.e. a home
with enough resources and suitable breeding resources.
 It improves on the chances of obtaining a mate.

POPULATION GROWTH
This refers to the increase in number of organisms of the same species. Growth takes place when
the birth rate is higher than the death rate. The increase in number over a period of time when
plotted on a graph makes what is known as a growth curve.

Carrying capacity
This is the total population the environment can support at a particular time without exhausting
the resources.

The population growth curve

The growth curve is S-shaped and it is referred to as a sigmoid curve. It is divided into five
phases.
 Ecology Lecture notes 2023

Phase A
In this phase the rate of growth is low because the numbers of organisms multiplying are few and
the organisms are still adapting to the conditions.
Phase B
The rate of growth increases because the number of reproducing organisms has increased and the
organisms have adapted to the conditions.
Phase C
The rate of growth starts to slow down as the organisms start to die. This is due to the fact that
their number has become big and they have started competing for food, shelter, mates and space.
The available resources cannot support a big number of organisms.
Phase D
In this phase, the rate of birth is equal to the rate of death hence the population remains constant.
Phase E
The population is declining because the rate of birth is lower than the death rate. The organisms
die at a higher rate due to competition between them and the exhaustion of resources.

Growth of the human population

The population is presently growing exponentially. This is shown in the human population growth
curve below:

The exponential human growth is usually due to:

 Advancement in science and technology leading to prevention of infectious diseases.
 Early warning on natural catastrophes.
 Proper nutrition.
 Decrease in infant mortality.
 Increase in life expectancy in developing countries.
 Increasing agriculture hence leading into more food.

Factors affecting population growth These

factors are grouped into two categories.
1. Density dependent factors; these are factors whose effect depend on the size of the
population, e.g. food, diseases, space, pollution, predation, competition, light, etc.

2. Density independent factors; these are factors which affect the population regardless of the
population size e.g. earth quakes, floods, droughts, thunderstorm, lightening, fire strong
winds, etc.

POPULATION SIZE
This refers to the number of organisms of the same species in a particular area at a particular time.

Determinants of population size Population

size depends on the following factors.

1. Natality (birth rate). This is the frequency of birth. Increase in natality results into increase in
population size.

2. Mortality (death rate). This is the frequency of deaths. When the death rate increases, the
population size decreases.

3. Emigration. This is the movement of individuals out of the population. It results into a
decrease in population size.

4. Immigration. This is the movement of individuals into the population. It causes the
population to increase.

METHODS OF ESTIMATING POPULATION SIZE

1. Direct count
This is suitable for large organisms living in an open habitat, e.g. elephants, lions and buffaloes.
In this method, one moves through the area along predetermined paths and counts the organisms
in question. When counting aggressive animals, a low flying aircraft is used. Several counts are
made and an average is taken to get an estimate of a particular area.

2. Aerial photography
This is suitable for large organisms living in an open area. Photographs are taken from a low
flying aircraft over the study area. When the photographs are developed the number of organisms
in the photographs is determined. The photographs are taken several times and the average
number is taken for the population of that particular organism in the area.

3. The quadrat
This is a method used for small static organisms like plants or slow moving animals. A quadrat is
a square metal or wooden flame of 1-meter long sides. It therefore encloses an area of 1m2.
 Ecology Lecture notes 2023

The quadrat is thrown at random in the study area and the individuals covered counted. Several
quadrats are thrown at random and the average number of organisms is taken.
The average number is then multiplied by the total area of the study to get the estimated
population.

4. Line transect method:

This method involves lying along measuring tapes along a selected strip within the habitat. A
record is made of the organisms touching or covered by a line at all points at regular intervals.

5. Belt transect method:

This is a strip usually a meter wide marked by putting a second line transect parallel to the other.
The species between the line are carefully recorded.

6. Capture mark recapture method:

This is suitable for animals, which are fast moving. E.g. rats and grasshoppers.
In this method animals in an environment are captured and counted (n1). They are then marked
and released back into the environment.
The traps are then laid after a given period of time.
The organisms captured are counted (n2).
The organisms that were marked and recaptured are also counted (n3). The population is then
calculated from:

Total population = number of individuals in 1st capture X number of individuals in 2nd capture
Number of individual in 2nd capture with a mark
P = n1 x n2
n3
Where;
P = population
n1 = number in the first capture n2 = number in
the second capture n3 = number in the second capture
which are marked.

Examples
1. 30 rats were caught in the bush around the school. They were all marked with ink on the tails
and released. After 3 days 20 rats were caught from the same area. 6 out of the 20 rats had a mark.
Estimate the population of rats in this bush. Solution.

Using. P = n1 x n2
n3

P = population.
n1 = 30 n2
= 20 n3 =
6
P = 30 x 20
6
= 100 rats.
Assignment:
Arthur captured and marked and replaced 45 cockroaches on the first day. She captured 26
cockroaches from the same area 17 of which were not marked. Estimate the population in the
area.

INTERACTIONS BETWEEN POPULATION

Individual organisms in the population do not live in isolation in a community. They are
continuously interacting with each other in the following ways:
 Competition
 Predation
 Mutualism
 Parasitism

COMPETITION
As the population of the individuals increase, the resources become limited and the organisms
compete for them. Examples of resources competed for include, food, space, mates, etc.
Competition is of two types;

1. Interspecific competition; this is the competition between organisms of different species,

e.g. the competition between goats and cattle for pastures.

2. Intraspecific competition; this is the competition between organisms of the same species,
e.g. the competition between goats for grass.

PREDATION
This is the relationship between a predator and the prey.
A predator is an organism that hunts and kills another organism (prey) for food.
A prey is an organism that is hunted and killed for food.

The graph showing the predator-prey relationship

 Ecology Lecture notes 2023

Description and explanation of the graph:

The population of the prey is higher than that of the predator at the start. This leads to an increase
in the number of predators.
The prey reaches a peak earlier than the predators. Further increase in the predator population
leads to a decrease in the prey population due to the fact that they are being fed on by the predators.
When the number of prey goes down, the predators starve and this makes their population to go
down. When the predator number decreases below that of the prey, the population of the prey
increases again due to the fact that the predators are few which would feed on them.
Note. Both the predator and prey control the population of each other.

Adaptations of predators that enable them to feed on prey

1. They have keen eyesight to see their prey.
2. They have strong jaw muscles to tear flesh of the prey.
3. They have sharp claws to hold and kill their prey.
4. They move very fast to enable them chase the prey.
5. They have streamlined bodies to cut through air during movement.
6. Some have very sharp canines to tear flesh of their prey.
7. They have colours, which help them to camouflage.

Adaptations of the prey to avoid being eaten by predators

1. They perceive sound with high accuracy and are able to sense their predators at a distance.
2. They are very fast in movement to escape from their predators.
3. They have developed structures for defense such as horns.
4. They normally move in groups to scare their predators.
5. They prefer to stay in areas, which give them good visibility such as grasslands.
6. They have colours, which help them to camouflage.
7. Mimicry; this is where a palatable harmless organism attains colours of an unpalatable
harmful organism and it is confused for a harmful organism.
FEEDING RELATIONSHIPS BETWEEN ORGANISMS

SYMBIOSIS
This is the relationship between two organisms of different species in which both organisms
derive benefits from the association.
Examples
1. In the stomach of cattle and sheep there are bacteria. These bacteria help to digest cellulose,
which is used by the cow. The bacteria benefits by getting food and shelter from the cow.
2. The nitrogen-fixing bacteria in root nodules of leguminous plants. The bacteria provide
nitrates to the plant by converting nitrogen to nitrates and the bacteria are protected in the root
nodules. The bacteria may also use sugars produced by the plant during photosynthesis
3. The lichen is composed of a fungus and filament of algae. The fungus provides water and
mineral salts to the algae and the fungus benefits by using the sugars produced by the algae

COMMENSALISM
This is the relationship between the organisms of different species in which only one organism
(commensal) benefits but the other organism neither benefits nor loses.
Examples.
1. The shark and the ramora. The ramora is a small fish that lives as a commensal attached to
the shark by its sucker. When the shark feeds, the ramora feeds on left overs of the shark. The
shark neither benefits nor loses.
2. The cattle/buffalos and the egret. The egret gets food in form of insects forced to fly by grazing
animals. The cattle do not gain and do not lose.

FIRE AS AN ECOLOGICAL FACTOR

Effects of fire to the ecosystem

This is measured in the destruction made and it depends on the following factors.
1. Kind and amount of burning fuel e.g. grass generates less heat compared to wooden materials
hence is less destructive.
2. Weather conditions. Fire is spread very fast in dry conditions and thus destroying a wide area
of the eco system than in cold conditions. In cold conditions, fire spreads very slowly due to
the high humidity hence causing less destruction.
3. Direction of wind. The effect of fire is great to the ecosystem if its burning against the
direction of wind (back fire) because it burns in a particular area for a long period of time
compared to forward fire.

Merits of fire
 It breaks seed dormancy due to hard seed coat leading to fast germination.
 It increases recycling of nutrients in an ecosystem.
 It is used in selective weeding.
 It controls pests and diseases.
 It improves on herbage in an area.
 It improves on light penetration leading to rapid under growth in the forest.
 It improves on the visibility of the prey to predators by burning the vegetation cover down.
 Ecology Lecture notes 2023

Demerits of fire
 It destroys the habitat of animals which may cause extinction of some animals.
 It causes air pollution
 It destroys green plants which are producers of the community.
 It destroys animals in the ecosystem.
 It increases predation due to improved visibility.
 It leads to loss of some nutrients from the soil by decomposition e.g. humus and nitrates.

Forests as a renewable resource Forests

are renewed by afforestation and avoiding deforestation.

Ecological importance of forests 

They act as habitats of organisms.
 Source of food to organisms.
 Used in rain fall formation, this improves on the climate of an ecosystem.
 It forms soil by dropping litter which helps in decomposition into humus.
 Maintains plants and animal diversity.

Ecological effects of deforestation

 Destruction of habitats of animals.  It leads to soil erosion
 It leads to desertification.
 It increases CO2 content in the atmosphere.
 Increases predation due to removal of vegetation cover.

Importance of forests to wild life conservation

 They are sources of food to animals  They are habitats to animals.
 Formation of rain falls to prevent drought.
 Reduces soil erosion thereby conserving soil fertility.
 Maintains the bio diversity for a variety of plant and animal species.
 Purifies the environment by removing CO2 and adding oxygen.
 Provides a variety of litter that decomposes to form humus.
 Reduces predation of some wild animals.
POLLUTION
This is the addition of substances to the environment to levels that harm or destroy living
components of the environment (ecosystem). Substances that can cause pollution to the
environment are called pollutants. E.g. sewerage, fertilizers, oil links, etc.

Types of pollution
1. Water pollution
2. Air pollution
 3. Noise pollution
4. Radioactive pollution
5. Sound pollution

Air pollution
The main pollutants of air or atmosphere are poisonous gases e.g. SO2, CO2, NO2, and CO.
Some of these gases e.g. SO2, CO2, and CO form acidic components that destroy vegetation.
Another air pollutant is smoke that causes poor vision, reduced light penetration, and reduction
of photosynthesis by coating on plant leaves.
Excess gases in the atmosphere e.g. CO2 and CFCs ( Chloro Floro Carbon) used in fridges cause
global warming.

Water pollution
This is as a result of addition of excess nutrients e.g. nitrates, phosphates, potassium to water
bodies making them too nutritive leading to increased productivity of water. The highly
productive lake is called eutrophic lake and the process of polluting water bodies by adding excess
nutrients is called eutrophication. The main pollutants that cause eutrophication are fertilizers.
Domestic wastes drained in water bodies, industrial wastes e.g. detergents which contain a lot of
phosphates and nitrates also cause eutrophication in the lake.

Eutrophication:
This is the accumulation of nutrients (nitrates and phosphates) leading to increased growth of
aquatic plants e.g. algae which decompose after death leading to a decrease of oxygen contents
as a result of being utilized by decomposers of dead plants. Due to the decrease of oxygen content,
in water, aquatic animals that need oxygen for respiration e.g. fish suffocate and die.

Soil pollution
Use of excess fertilizers, herbicides, insecticides pollutes the soil. Excess herbicides and
insecticides lead to death of living organisms in the soil there by reducing the rate of
decomposition of dead matter.
Non degradable insecticides do not break down but accumulate in animals along the food chain
to poisonous levels that can kill.

Activities of man that have led to the degradation of soil

Environmental degradation is the process of destroying the quality of the environment. Human
activities that have led to degradation of soil are:
1. Over stocking leading to over grazing that reduces the amount of vegetation cover to expose
the soil there by encouraging soil erosion.
2. Deforestation exposing soil to agents of soil erosion.
3. Use of insecticides, pesticides and herbicides which cause the death of soil organisms hence
affecting the rate of decomposition.
 Ecology Lecture notes 2023

4. Burning of vegetation that removes the vegetation cover which encourages surface run off
hence leading to soil erosion.
5. Mining, construction, quarrying leads to the destruction of soil structure which encourages
soil erosion.
6. Digging or cultivating down slope also encourages soil erosion.

Radioactive pollution
This is the release of radioactive chemicals into the environment in large amounts e.g atomic
substances are from atomic bombs.

Human activities that lead to environmental pollution

1. Drainage of excess un treated sewage into the water bodies causing eutrophication.
2. Application of excess fertilizers that are later eroded in water bodies.
3. Burning of vegetation that exposes the soil to erosion agent and it also leads to the emission
of smoke which causes air pollution.
4. Emission of excess poisonous gases in the atmosphere e.g. SO2, CO2 and CO form industries
and automobiles which cause acidic rains.
5. Use of excess herbicides and insecticides which kill the soil organisms leading to decreased
rate of decomposition.
6. Spilling of oil onto water bodies which leads to suffocation of aquatic animals.
7. Construction of noisy industries in town which cause sound pollution that can damage the
hearing process of man.
8. Decomposition of non-biodegradable materials into the soil e.g. plastics, glass, etc. which
destroy the soil structure.
9. Deforestation
10. Monoculture
11. Over stocking

UGANDA’S WATER BODIES

The major water bodies in Uganda are lakes and rivers. They are pollution by sewage from
industries; fertilizers used by man, oil from machines e.g. boat engines.
Water bodies are also invaded by water weeds especially water hyacinth which is a flowering
plant which can also reproduce asexually and with a high rate of reproduction.

Effects of water hyacinth on water bodies

 They hinder navigation
 They habour dangerous animals e.g. snakes
 Reduction in the amount of fish in water bodies as some dies due to starvation.
 They reduce on the amount of light penetration in water column.
 Siltation of water bodies i.e. they become shallow as a result of death and decomposition of
water hyacinth.
 Reduction in the amount of water in lakes as a result of increased rate of transpiration.
 They hinder smooth flow of water in lakes since they block the drainage channels.
 It has caused economic injuries to the country especially when trying to eradicate it.

Uses of water hyacinths 

Production of biogas
 Feeds for cattle and pigs.
 A good fertilizer when used as mulches.
 A good raw material for art and craft.
 Raw material for making manure.

Methods of controlling the water hyacinth

1. Physically or removing it manually by hand picking however it is not effective.
2. By use of machines (mechanical control) however the method is effective but expensive.
3. By using biological control methods e.g. use of bottles.
4. Use of herbicides (chemical control) and it involves the spraying of herbicides directly onto
the weed. The method is quick but has the following demerits:
 It contaminates water
 Destruction of aquatic life especially fish
 Pollution of water since the weed is not completely removed but decomposes in
water.
 It is expensive since it involves the use of space air crafts to apply it.