Ecology is a scientific study of relationship of organism with their natural surroundings


Is the study of relationships of living organisms to each other and their surrounding (physical surrounding)

Importance of studying Ecology

It gives us scientific foundation of understanding some fields of studies such as agriculture which concern with crop cultivation and animal husbandry, forestry, fishery and so on

The study of ecology gives us the basis for predicting and remedying environmental degradation (how to conserve environment)

Help us to understand the likely consequences of massive interventions in the environment e.g. construction of huge dams, deforestation to open space for plantation, agriculture e.t.c

Ecology is an important interdisciplinary science linking physical, biological and social science.

Ecology has given rise to a growing public awareness on environmental issues. This has given rise to development of laws on environment protection, formation of new political perspective e.g. environmentalism in Europe, emergence of environmental consultancies, development of environmental data services / base, e.t.c.

Definition of terms

Environment Refers to the surrounding of organisms. OR
Everything that surround an organism and influence it.

Population is a group of organisms of one species occupying a defined area or habitat at the same time.Community – Any group of organisms belonging to a number of different species that co-exist in the habitat or area and interact through trophic and spatial relationship.

Ecosystem – A community of organisms and their physical environment interacting as an ecological unit.

Habitat is a typical environment of a particular organism or population or community.


An area occupied by a particular organism or population or community.

Biosphere – Is the total volume of the earth in which life permanently exists.

Approaches to Ecology

A proper understanding of ecology requires simultaneously consideration of all factors interacting in a particular place.

Ecologists adopt one of the several main approaches when undertaking a new investigation.

Five approaches can be identified.

Ecosystem Approach

This approach focuses on the flow of energy and cycling of matter in the ecosystem i.e. between the living and non-living component of the ecosystem. In this approach an ecologist relationship (such as feeding) between organisms and environment rather than description of the species.

Community Approach.

This focuses in particular on the biotic component of the ecosystem. In this approach e.g. one examines the plants, animals and microbiology of recognizable biotic unit such as wood land, grass land and heat land. The functional aspects of physical environment is not studied in detail, it emphasis on identification and description of species present and factor that control their presence. Community approach is synonymous to synecological approach.

Population Approach (Ant ecological approach)

This approach focuses on identification and description of individual species in relation to its environment.

Habitat Approach

This focus on description of typical environment of a particular organism, population, community or ecosystem.

Evolutionary and historical approach
This focuses on the changes that have occurred in the organisms over time and the development of technology and culture of the human species.


The ecosystem refers to a community of organisms and their physical environment interacting as an ecological unit.
The term describe the whole complex of organisms living together as a sociological unit and its habitat.

Component of the Ecosystem

The ecosystem is made up of living and Non- living components

The living component of the ecosystem is known as biotic component, these include plants, animals, microorganisms e.t.c

The Non- living component is known as Abiotic component. The Non- living component of an ecosystem is divided into:-

  • Soil
  • Water
  • Climate

Soil and water contain a mixture of inorganic and organic nutrients.

Climate includes environmental variables such as light, air, water, temperature.


The essence of ecological studies lies in understanding how connections between the different organisms and their Abiotic environment work.

Energy flow and biochemical cycling are important functional links between the different ecosystems.

The two factors maintain the stability of the ecosystem. Stability of ecosystem means that the ecosystem can adjust to changes within itself.

The ecosystem is also sustainable i.e. it continues on its own without the necessity for human intervention.

Energy is defined as the capacity to do work.

Living organisms are likened to machines in that they require energy to keep them working i.e. to stay alive.

The Ecosystem like machines is kept working by an input of energy and nutrients. The ultimate source of energy in the ecosystem is the sun.

The sun is a star which releases vast amount of solar energy in space. The solar energy is captured by autotrophs in photosynthesis converting it into chemical energy (in form of food sources)

In the Biotic component photosynthetic organism utilize the sun’s energy directly and pass it to the other components of the ecosystem.

The energy is passed from the photosynthetic organism to the other through feeding relationship. The passage of energy through various component of the ecosystem is known as Energy flow. It is referred to as energy flow rather than energy circulation because (the energy released from the sun after passing through the component of ecosystem does not go back to the sun it is dissipated in the atmosphere as heat remain locked in some component of the ecosystem) it is changed into forms which cannot be used again by the system mainly heat energy.


The chemicals found in living organisms are derived originally from the abiotic components of the ecosystem such as soil, water, air to which eventually return by the way of decomposition dead organic matter.

Bacteria and fungi bring about decomposition obtaining the energy from the dead organism in the process.

Biochemical cycling is the constant cycling of chemical matters needed by living organisms within the ecosystem, the process is called biochemical cycle since both living and non- living part of the ecosystem is involved.

  • Light Biotic component heat energy
  • Energy
  • Nutrients
  • Abiotic component
  • Energy flow

Cycling of nutrient


The concept of food chain, tropic level and food web.

Energy containing organic molecules produced by autotrophic organisms is the source of food (materials and energy) for heterotrophic organisms.

Green plants, algae and some few bacteria (blue – green bacteria) are photosynthetic. Green plants mainly convert sunlight energy into chemical energy (food) which is used by animals some animals feed on plants in turn these animals are fed on by other animals. In this way the energy is transferred through a series of organisms.


Refers to the series of organisms each feeding on the proceeding organism and providing raw materials and energy for the next organism.

Each food chain starts with producers

Producers – are the autotrophic organisms or the organisms which in turn are eaten by other organisms.

On the basis of food relations the biotic components of the ecosystem can be put into the following categories.

Producers: These are autotrophs which synthesis the food using sunlight energy.

They include green plants, algae, protoctists and phototrophic bacteria.

Major producers of the aquatic ecosystem are algae, often minute unicellular algae that make up the phytoplankton on the surface layer of the oceans and lakes.

On land the producers are large plants, namely angiosperms and conifers which form the forest grass lands.


These are heterotrophs that obtain energy from producers directly or indirectly.

They can be put in various categories.

Primary consumers

These are consumers that feed on producers.

They are referred to as herbivores on land; typical herbivores include insects as well as reptiles, birds and mammals.

In aquatic ecosystem (fresh water and marine) the herbivores are typically small crustaceans and molluscs. Most of these organisms such as water fleas, cope pods, crab larvae, barnacles and bivalves are filters feeders.

Secondary consumers.

These are consumers that feed on herbivores

They are carnivores i.e. feed on flesh

Examples of secondary include carnivores such as wolf, snake.

Tertiary consumers

These organisms feed on secondary consumers (the carnivores)

Example are carnivores like lion, tiger, hawk e.t.c


Secondary and tertiary consumers may be

Predators which hunt capture and kill their prey

Carrion feeder which feed on corpses

Parasites – in which case they are smaller than their host.


Decomposers – Are microorganisms mainly fungi and bacteria which live as saprophytes and feed on dead organic matters. They secrete digestive enzymes on to dead materials and absorb the product of digestion.

Detrivores – These are organisms that feed on small fragments of decayed or dead materials termed detritus.

Many small animals feed on these, contributing it to the process of breakdown, because of combined activities of the true decomposers. (Fungi and bacteria) and detrivores (animals), they lead to the breakdown or decomposition of material.

Examples of detrivores are the earth worm

Decomposers and detrivores form their own food chain.


Refers to the stages of food chain

Each group of organism in a food chain form the tropic level (trophos – feeding).

The energy flows one way through various trophic levels.

There are usually four or five trophic levels and seldom more than six. Why?

Energy decreases as one move from one trophic level to another. There is less energy to support the organisms.

The first Trophic level is occupied by producers (autotrophs).

The second trophic level is occupied by the herbivores

The third trophic level is occupied by secondary consumers – the carnivores.

The fourth trophic level is occupied by the carnivores (Tertiary consumers)


Feeding relationship and energy transfer through the biotic component of ecosystem may be quantified and show diagrammatically as ecological pyramids. These shows the induced changes within a single system. Ecologists use these pyramids in gathering data for quantitative comparison of all major world ecosystem.

Pyramids of Numbers
In ecosystems the smaller organisms usually outnumber the large organisms. Pyramid of numbers shows the number of organisms in each trophic lever and how they change in successive levels of ecosystem.
.In a trophic lever based pyramid of numbers the organisms of a given area are first counted and then grouped in their trophic levers.
.There is a progressive decrease in the number of animals at each successive level
.Plants in the first trophic level often outnumber animals at the second trophic level but it will depend on the relative size of organism

Types of Pyramid of numbers.

Pyramid of Biomass

This take consideration of the total mass of the organisms (biomass) estimated at each trophic level. Ideally the dry mass is compared.

The estimation of dry mass is done by weighing representative individuals (sampling).

The rectangle is drawn in proportation of the mass at a particular trophic level. The biomass at the time of sampling is considered.

This is known as the standing mass or standing crop mass.

Drawback of Pyramid of Biomass

It is more laborious and expensive in terms of time and equipment.

It does not allow for changes in biomass at different time of the year e.g. deciduous tree have a large biomass in summer than in winter, when they have shed their leaves.

The rate at which the biomass accumulates is not taken into account. A mature tree has a large biomass which increases slowly over many years.

Inverted pyramids of biomass are obtained only for aquatic ecosystem. This frequently happens in food chains which start with phytoplankton. These organisms are very small and have a much more rapid town over than their 200 plankton predators.

The pyramid of biomass can be bulged at the middle.

They do not show the rate production (productivity that is the amounts of materials and energy passing from one trophic level to the next).

In a given period of time, period such as one year for example a fertile, intensively grazed pasture may have a small standing crop of grass but higher productivity.

Pyramid of Energy

These are type of ecological pyramid drawn based on the amount of energy at each trophic level.

This shows how much energy passes from one trophic level to the next the length of the producers bar is proportional to the amount of solar energy annually in photosynthesis.

The length of other basis shows the rate at which energy passes along the food chain.

The pyramids of energy take into account the rate of production in contrast to pyramids of numbers and biomass which depict the standing states of organisms at a particular moment in time. The energy at each trophic level is estimated by establishing of the energy value for that trophic level.

NB: The transfer of energy from producers to primary consumers is less efficient than between the other trophic level.

The average efficiency of transfer from plants to herbivores is about 10% and from animals to animals is 20%.

Like other type of ecological pyramids, the energy decreases as you move from lower to higher trophic levels.

The following are the possible causes of this:

Some energy is used for metabolic activities at each trophic level, mainly respiration.

A lot of energy is lost in form of heat hence is not available in the ecosystem energy lost in respiration cannot be transferred to other living organisms.

Some energy is locked in animal or plant parts which cannot be eaten e.g. Bones, horns, nails, and feathers of animals and cellulose materials of plants which are indigestible.

Organisms do not assimilate some of the materials taken in as food.

The consumer population is unable to harvest enough of the food population.

The diagram below represents a pyramid of energy for an aquatic ecosystem.

Carnivores to top carnivores 88

Herbivores to carnivores 1603

Producers to herbivores 14,098

pyramid of energy for silver springs, Florida (energy flow in KJ m-2 yr-1)

Each bar of a pyramid of energy represents the amount of energy per unit area or volume that flow through that trophic level in given time period.

Usefulness of Pyramid of Energy.

It takes into account the rate of production, in contrast to pyramids of numbers and biomass which depict the standing states of organisms at a particular moment in time.

It allow different ecosystem to be compared including the relative importance of population within one ecosystem.

They tell how much energy is required to support each trophic level because only a proportion of energy in a level is transferred to the next.

Energy pyramid are never invested nor do they have a central bulge

Energy pyramids are more informative than the pyramid of number and biomass.

Input of solar energy can be added as an extra rectangle at the base of pyramid of energy.

Disadvantages of Ecological Pyramid of energy.

They are the most difficult to obtain data

They are not an accurate method of representing energy content of the ecosystem.

General criticisms of Ecological pyramids

The pyramids of numbers, biomass and energy depend on assigning living organisms to trophic level. While the correct level is obvious for plants and obligate herbivores. Many carnivores and omnivores eat a varied diet and thus their trophic level varies according to the food selected.

It is hard to fit dead material (detritus) and other waste together with their consumers into conventional pyramids. These materials are important as a food source.

BIOCHEMICAL CYCLES – The cycling of Matters

The chemicals found in living organisms are derived originally from the abiotic components of the ecosystem such as soil, water and air to which they eventually return by way of the decomposition of waste products or dead bodies of organisms. Bacteria and fungi bring about decomposition; obtain energy from the waste products and dead organisms in the process.

Biochemical cycling is the constant cycling of chemical materials needed by living organisms within the ecosystem.

The process is called biochemical cycle since both living and non-living parts of the ecosystem is involved.

Distinction between chemical cycling and energy flow.

Chemicals in the ecosystem are constantly recycled and used again, on the other land; energy transferred within the ecosystem is changed into forms which cannot be used again by the system, mainly heat energy. Because some of the energy is lost we cannot talk of recycling rather than the flow of energy through the ecosystems.

To maintain the ecosystem, frequent and regular inputs of solar energy is needed.

Cycles can be recognized for all chemical elements that occur in living systems. The biogeochemical cycles for carbon (C), Nitrogen (N), Sulphur (S) and Phosphorus (P) are very important. These elements from the major macronutrients in Biochemical cycles for Nitrogen and carbon.


Nitrogen is an abundant element in the atmosphere. Nitrogen makes up about 78% of the atmosphere by volume, yet very few organisms can use this gaseous nitrogen directly instead they depend upon soil minerals, especially nitrates as their source of nitrogen plants cannot incorporate nitrogen into organic compounds and therefore depend on various types of bacteria to make nitrogen available to them.

Nitrogen deficiency commonly limits plant growth. This is the main reasons that nitrogen is commonly applied in the form of artificial fertilizers.

The nitrogen cycle can be summarized as follow.

Nitrogen Fixation

This refers to the conversion of the free nitrogen (N2) in the atmosphere into nitrates, ammonia or other ammonium compounds. This is accomplished in several way

i.Biological fixation – This occurs when nitrogen (N2) is reduced and added to organic compound by action of Nitrogen – fixing bacteria such as Azobacter and clostridium, the cyano bacteria in aquatic system and some free living bacteria in the soil are able to reduce nitrogen gas to ammonia (NH3).

Other nitrogen – Fixing bacteria e.g.: Rhizobium infects and lives in modules on the roots of leguminous plants. They make reduced nitrogen and organic compounds available to the host plants.

ii.Electrochemical and photochemical fixation

In this process nitrogen gas is converted to nitrate (NO3) in the atmosphere by lightening and other cosmic radiations on oxygen and Nitrogen lightening and other cosmic radiation provide high energy needed for nitrogen to react with oxygen.

iii.Industrial fixation – Fixed by chemical fertilizer industries to the nitrogen cycle when they convert nitrogen gas to nitrate for use as fertilizers.


Nitrification is the production of nitrates. Nitrogen is converted to Nitrate (NO3) in several ways.

By lightening and other cosmic radiation

By the action of nitrifying bacteria ammonia (NH3) in the soil is converted to Nitrates by certain soil bacteria in a two – step process flost, nitrite producing bacteria convert ammonia to nitrite (NO2) this is achieved by free living bacteria such as Nitrosomonas.

2NH3 + 3O2+ 2NO2 + 2H+ + 2H2O

Ammonia oxygen nitrite hydrogen ion water

The second step involve the oxidation of the Nitrite by other free living bacteria e.g. Nitrobacteria and nitro coccus

2NO2+ O2 2NO3

Humans make a most significant contribution to the nitrogen cycle when they convert nitrogen gas to nitrate for use in fertilizer.

Nitrogen used by plants and animals.

Plants take the nitrates from the soil and form proteins. When animals eat plants the proteins are converted into animal proteins. The breakdown of protein is excreted in the form of urea or uric acid or ammonium compounds. In the soil or water, decomposition of the waste takes place and nitrogen is converted back to free nitrogen involving number of steps.

Decomposition by Microorganisms

Like Actinomycetes and fungi and by ammonofying bacteria. These convert wastes and decayed and dead boodles to ammonia or ammonium compounds.

Denitrifying bacteria

Denitrification is the conversion of nitrate to nitrogen gas. These are denitrifying bacteria in both aquatic and terrestrial ecosystem. Examples are the Pseudomonas and Thiobacillus, Detoxification counter balance nitrogen fixation but not completely. More nitrogen fixation occurs especially due to fertilizer production.


Carbon is an element found in all organisms. It is a basic building block of all living things it is essential part of carbohydrates, fats and proteins. Carbon is present in the atmosphere as carbon dioxide the carbon enters the ecosystem through the producers.
In carbon cycle organisms in both terrestrial and aquatic ecosystem, exchange CO2 from the air and through photosynthesis they incorporate carbon into food that is used by themselves and heterotophs.

When any organism respires a portion of carbon is returned into the atmosphere as CO2.
In aquatic ecosystem, the exchange of CO2 with atmosphere is indirect. Carbon dioxide from the air combines with water to give carbonic acid, which break down to bicarbonate ions.

(HCO3). Bicarbonate ions are the source of CO2 for algae, which produce food for themselves and for heterotrophic.

Similarly when aquatic animals respire, the CO2 they give off becomes bicarbonate. The amount of bicarbonate in water equilibrates with the amount of CO2 in air.
Carbon cycle can be summarized as follows.

The producers (green plants and algae) use CO2 to make food.

Herbivores eat plants and carbon gets into the body of carnivores.

Both plants and animals respire. The process returns CO2 to the atmosphere.

When plants and animals die, the decomposers break down dead bodies and carbon is released to the soil where it is absorbed by plant roots.

Some organic matter does not decompose easily instead, it build up in the earth’s crust oil and coal were formed from the building of the plants and animal’s matters millions of years ago.

The burning of fossil fuels has added much of carbon in the atmosphere in form of CO2.

Reservoirs of Carbon

Oceans and seas are large reservoir of carbon in form of HCO3. This can be used to build up shells of marine organisms. Some reaction change bicarbonate into CO2 that return to the atmosphere.

Living and dead organisms contain organic carbon and serve as one reservoir for carbon cycle.

Living things particularly trees remains of plants and animals are estimated to hold billions of tons of organic carbon.

Some plants and animals remains before complete decomposition, were subjected to physical process that transformed these into coal, oil and natural gas. We call the material fossil fuels.

Calcium carbonate that accumulate in limestone and calcium carbonate in carbonate shells.

The influence of Human on carbon cycle

The activities of human beings have increased large amount of CO2 in the atmosphere. These activities includes:

Burning of fossil fuels e.g.; coal and oils used for running machines and automobiles. These results into release of much CO2 and other gases in the atmosphere.

Burning of fuel wood i.e. firewood and charcoal

Deforestation i.e. destruction of forests through burning on cutting trees.

Deforestation reduces the total world volume of photosynthetic materials and thus reduces consumption of atmospheric carbon dioxide in photosynthesis.

Removal of the tree canopy exposes the forest floor to sunlight and warmer temperatures. In forest or woodlands with significant filter and soil humus contents this expose will favor accelerated rates of decomposition and carbon dioxide release.


Ecological niche is the ecological team which is used to refer to the physical space as well as its functional role of a particular group of organisms.

Ecological niche have been defined in different ways.

The niche of organism is defined as its profession or total role in a community, e.g. an organism can be producer, consumer, predator, scavenger or a decomposer.

Defined as a place occupied by a species in an ecosystem and the way it use the resources of the ecosystem.

The niche of an organism means its place in a biotic environment and its relation to food, enemies, habits and biological factors.

A Population of each species within a community has a separate need. No two species within a community can have the exact same need. If two species do occupy the same need, it leads to competition until one is displaced.

Similar habitat in the world have similar ecological niches but may have different animals e.g. Open grasslands all over the world produce a need for fast running herbivores like horses, kangaroo, and antelopes.


Formation of a community

A group of organisms of different populations co. existing in the same habitat

Community ecology focuses on the development and stability of the communities.

A community is built up over a period of time

Does the community remain the same indefinitely?

A community is a dynamic unit

A stable community is established through number of stages which are orderly.

During the time of development there will be an orderly and progressive replacement of one community by another till a relatively stable community is established. This is called ecological succession.

Ecological succession is the process in which a community is evolved from simple beginning to more complex which is more or less stable. A complete succession is called a sere.

A sere is made up of a number of several stages.

A complete stable community is called a climax community.

Types of Ecological succession

Primary succession

Secondary succession

Primary succession – Is a type of succession when the community is established where no community has previously existed.

E.g. On sandunes, volcanic island larva flows (bare rocks). The area is devoid of any organisms.

2.Secondary succession – Occurs where a community has been disrupted and the surface is completed or largely devoid of vegetation. It may be due to earth quake, fire or even clearing of forest by man.


Sampling Technique

Sampling technique is a method of establishing a sample.

Sample – is a number of items all things taken from large group and used to provide information about the whole group.

Types of sampling

(i) Random sampling

Is a type of sampling in which every item of the universe has an equal chance of inclusion in the sample

(ii) Systematic sampling

It involves selection of every in the item in a list (an element of randomness is introduced into this kind of sampling by using random numbers to pick up the unit to which to start.

(iii) Stratified sampling

Is a type of sampling in which the population is divided into several sub population on that are individuals more homogenous group than the total population.

The size of a sample (sample size)

This refers to the number of item to be selected from the set of objects (population or universe) to constitute a sample excessively.


It makes the study easier since few organisms are involved.

Since only few organisms are under study this save time and reduce the financial cost if large group of organisms were to be studied.

Sampling methods

  • By transects
  • By quadrants
  • Point frame
  • Pit fall
  • Box trapping.
  • Ways of establishing a sample
  • Transects – line transect
  • Belt transect.
  • Quadrants – quadrat
  • Pin frame (point quadrant)
  • permanent quadrat.

Line transect

Is a method where a tape or string is run along a ground in a straight line between two points or poles .

Belt transect

A belt transect is simply a strip of chosen width through the habitat made by setting up two line transects say 0.5m to 1m a part.

What is a Quadrant?

A quadrant frame is a metal of wooden frame preferably collapsible to facilitate carrying, which forms a square of known area such as 0.25m2 or 1m2

The way a quadrant is used

i) Random throw

ii) Used with line transects

The use of these methods depends on (number of factors) nature of investigation.

Other types of quadrants

Pin frame (point quadrant).

This is a frame bearing a number of holes through which a pin “such as knitting needle can be passed”

Permanent quadrant

This is used in long term ecological investigation involving the study of community change (succession or seasonal changes).

  • Other methods
  • Computer program
  • Direct observation
  • Photographs
  • Pit fall trap
  • Box trapping

Capture – recaptured methods

This methods involves capturing the organisms, marking it in some way without causing it any damage and replacing it so that it can resume a normal role in a population e.g. Fish are netted.

The capture – recapture method of sampling is used to try to estimate the entire population, a sample of animals is caught and tagged their number noted and then released into their habitat. Later another sample is captured and the proportion of tagged animal in this sample should be representative of the proportion of tagged animal in the whole population and then the total population size can be estimated using this formula.

Total = original no tagged x total recaptured

No. of tagged on recapture

Some examples of how to use this formula

Example 1

50 animals are caught and tagged and released. Later 220 animals are caught and it is noted that 35 of their animals are tagged. What will be the total population estimate?

= 50 × 220 ÷ 35

= 314.28

Example 2.

A biologist caught 100 deers in a forest, tags them and releases them back in the forest. A year later he caught 90 of which 12 had tags, estimate the total population of the dear.

The use of quadrats direct observation and photography are known as direct counting methods, where as capture recapture technique is indirect counting method.

Different methods that are used to establish the samples provide the means of calculating three aspects of species distribution.

Species density

This is the number of individual of a given species in a given area such as 10 per meter2 (10m-2)

Species Frequency

This is measure of the probability (chance) of finding a given species with any one throw of a quadrat in a given area.


If the species occur once in any 10 quadrats it has a frequency of 10%.

Species cover

This is a measure of the proportion of ground occupied by the species and gives an estimate of the area covered by the species as a percentage of the total area.

Capture method by removal

In this method the number of animals captured is recorded and the animal kept. This procedure is repeated a further three times and the gradually reducing number recorded. A graph is plotted of number of animals captured per sample against the previous cumulative number of animal captured. By extrapolating the line of the graph to the point at which no further animal would be captured (i.e. number in sample = 0)


No. in sample
Cumulative sample size

Population dynamics

A group of organism of the same species occupying a particular species and usually isolated to some extent from other similar groups by geographical factor / topography.

Population studies are not just about the number of a given species living in a given area at given moment in time but it includes also how population grow, how population is maintained and how and why population decline.

Define population dynamics

Population dynamics is the study of how and why population size changes over time. It examines the characteristics of a group of organisms such as density, natality (birth rate), survival ship, age structure, migration and from of growth of the population.

The population size – refers to the number of individuals / species in a population.

Factors that affect the size of population

1. Birth rate (Natality rate)

2. Mortality rate

3. Migration

Population size increase or decrease depending on the number of factors

What causes population increase?

Population size increases as a result of immigration from neighboring populations or by reproduction of individuals within a population. Reproduction is expressed as birth rate or natality.

Birth rate – refers to the number of Youngs produced per female per unit time (usually per year)

Population size may decrease as result of emigration or death (mortality). In population biological mortality strictly means rate of death it can be expressed in terms of percent or numbers per thousand dying per year.

Population growth – Refers to the increase in population.

Population growth can decline in characteristics ways

The factors that affect population growth

Reproductive potential of the organism

The rate of reproduction given unlimited environmental resource.

Environmental resistance

This is the sum of total limiting factor both biotic and abiotic which act together to prevent the maximum reproductive potential from being realized. It includes external factor such as predation, food supply, heat, light and space, and internal regulatory mechanisms such as intra specific competition and behavioral adaptation.

Factors within the species which affects population growth

Population growth may change as a result of changes in birth or death rate. Food shortage and increase in predation are two factors which have direct effect on mortality.

Birth rate is affected by two regulatory mechanisms;

The territorial behavior

Physical effects of over crowding

Many animals exhibit territorial behavior

A territory – is an area usually fixed in location that individuals defend and from which other members of the same species are usually excluded.

Territories are typically used for feeding, mating, rearing of young or combination of these activities.

Territorial animals benefit in several ways they have exclusive access to food supplies and breeding areas within their territories.

Also familiarity with their areas help them to obtain food there and avoid predators

Moreover they can care for their young without interference from other individuals of the same species.

Over crowding

In a number of mammals high population density reduces greatly the birth rate even if there is good shortage.

Various hormonal changes occur which affect the reproductive behaviors in a number of ways e.g. Failure to copulate infertility, number of abortion and eating of the young by the parents all increase and parental care disease.

Factors between species which affect population growth

A number of well recognized types of interactions may occur between populations of different species. These are termed as interspecific interaction, population from different trophic levels may also interact as for e.g. in case of predator- prey relationship and host parasite relationship.

Population growth curves

Two basic forms of growth curves can be identified.

The j-shaped growth curves

The S-shaped growth curves or sigmoid growth curve.

The S- Shaped or sigmoid growth curve

This describes a situation in which in new environment, the population density of an organism increases slowly initially, as it adapt to new conditions and establish itself, then increases rapidly approaching an exponential growth rate. It then shows a declining rate of increase until zero population growth rate is achieved where rate of reproduction (Natality) equals rate of death (mortality).

The slowing rate of population growth result from increasing competition for a essential resources such as food or nesting material.

The decline in growth rate continues until eventually feedback in terms of increased mortality and reproduction fails (fewer mating, stress induced abortion) reduces population growth rate to zero.

This type of population growth is said to be density dependant since for a given set of resources, growth rate depends on the numbers present in the population.

J-Shaped growth curve

This type of growth curves describes a situation in which after initial establishment phase (lag phase) population growth continues in an exponential form until stopped abruptly as the environmental resistance becomes suddenly effective.

Growth is said to be density independent since regulation of growth rate is not tied to the population density until the final cash.

The crash may be triggered by factor such as seasonality or the end of a breeding phase, either of the organism itself or of an important prey species. It may also be associated with a particular stage in a life cycle such as seed production or it may be included by human intervention.


A biome is a large region in the biosphere that possesses characteristic physical condition on that support organisms which show adaptations to those condition found there.


Is a collection of similar ecosystem in a particular region of the earth, it could be a habitat or zone such as desert forest, grassland or water bodies such as ocean, lakes etc.


Is a largest terrestrial communication or a largest ecological unit.

A biome has a specific kind of plants and animal species within a geographical area that has distinct climatic conditions. A biome is a product of physical factors that influence the rainfall, temperature and light.

Example of terrestrial biomes.

A major biomes includes


Northern coniferous forest or Taiga

Deciduous forest

The Mediterranean shrub

Tropical savannah



Biomes that involve aquatic ecosystems

Marine environment

Fresh water environment

Human population is the most abundant (about 7 billion) which is next to certain species of fishes and insects.

Human population is widely distributed on earth in almost all climatic conditions from arctic to Antarctica.

The population differ economically, socially, culturally and color and height in different part of the world.

The study of trends in human population growth and the prediction of future development is known as demography.

Demography involves the study of various parameters along with number and proportion of different age group, educational requirements training and employment.

Factors affecting patterns of human population.

The human population growth patterns differ in different region of the world due to various factors some of these are discussed below;

Climatic and Edhapic factor

The region of extreme heat like deserts or extreme cold like Arctic and Antarctica are less populated.

Location of natural resources

Transport facilities.

Industrial development and education

Demography factor

The birth rate and death rate of a population determine an overall population growth. It varies in different countries.

Human population growth patterns

Rate of growth of human population is not uniform in all the countries, the developed countries have stable or negative growth rate (both the birth and death rate are low).

The developing countries have high birth rate and the population is increasing at an enormous rate.

Rate of growth differ among different group of people within a country.

The population of the urban areas is leading to overcrowding and is causing adverse environmental implications.


The human population as a whole is growing exponentials having doubled three times in the last three centuries, it now stand at 6 billion and may reach 8 billion by the year 2020.

Most of the increase is due to improved health and technology which have decreased the death rate. The human population faces uncertain feature, although some are optimistic about our ability to expand, earth’s carrying capacity, others are concerned that our increase in numbers may damage the biosphere beyond repair.

Human impact on the ecosystem

Since the development of agriculture and technology on increasing human impact on the environment has occurred. In last two centuries especially wide spread industrialization has lead to potentially damaging environmental pollution.


Is the release into the environment of substances or energy in such quantities and for such duration that they cause harm to the people or other organisms or their environment.

The harmful substances are collectively known as pollutants

Pollutants destroy the natural quality of the environment.

Example of pollutants

Agricultural chemicals such as fertilizers, pesticides and herbicides

Industrial by products or emissions such as sulphur dioxide, mercury, carbon monoxide, CFC’S lead, cadminium




Radiations such as gamma rays, x-ray



Natural resources:-

Materials form the natural environment / ecosystem that man can use.


Renewable resources: – Are those which can be replaced within a short period of time after being used e.g. water, wildlife forest e.t.c.

Non- renewable resources: – Cannot be easily replaced within a short – time e.g. tonsil foils, minerals.

Conservation – retaining the status quo through careful management i.e. preservation of species, habitats and living system from harmful influence of man this avoiding decline and extinction of species and permanent detrimental / degradation to the environment. 

Reasons for conservation

We conserve to maintain world ecosystems by conserving the terrestrial, aquatic & aerial habitats,

Ethical reasons – cultural, tradition, religious beliefs, political persuasion, shape our attitude toward nature.

Nature does not exist simply for humans to transform & modify because all living species have a right to coexist with us on earth. Man has no right to cause the extinction or to diminish the quality of life of any organism.

Custodianship – Man has to pass on to the future generations to all the diversity of life & quality of environment that we inherited.

Athletic reasons – Humans derive pleasure from pleasant environment & the presence of other living organisms.

Local national & international organization exist worldwide to promote wildlife contribute to our immediate needs e.g. in forestry many plant species have important medical uses.

Fisheries from water bodies as direct source of food

Agriculture – We have to conserve food stocks and soil quality for crops.

Usage of pollinating insects & beneficial predators in pest control.


Maintenance of balanced biochemical cycles to avoid pollution & regulation of the earth’s climatic conditions.

To avoid deforestation & desertification.

To avoid loss of vegetation cover this may affect soil erosion leading to accumulation of mud on river beds & costs.

Reduce extinction of species to retain diversity gene pool (retaining biodiversity)

To preserve care species that may have generation potential.

To minimize effects of mining / drilling/ urbanization.

Measures Taken to conserve the environment / Need for sustainable use of environment resources.

People should be educated on the importance of our environment by:-

Encouraging them to plant trees

Encouraging the use of organic manure & good agricultural practices in agriculture such as terrace farming on hill sides, crop rotation.

Discouraging harmful traditions such as burning / slash method of farming to clear the land.


Laws that govern the protection of national parks/ grass kinds & punishments for those who start bush fires

Laws that protect the endangered species as a means of preventing extinction e.g. rhino

Some animal species must be regulated to avoid over – population e.g. wild beasts.

Reduction of pollution e.g. by using lead free petrol, alternate energy source (solar power, ethanol cars) use of bio degradable products, recycle waste such as paper to avoid deforestation, glass & cans water as resource & its sources must be preserved. Government should increase biodiversity by increasing botanical gardens, seed banks & field gene banks.

Sustainability – exploitation of natural resources & conserving then for future generations.


Avoid excessive use of chemicals such as pesticides and herbicides.

Encouraging biological control.


Is the artificial control of pests & parasites those which compete with human for food or damage the health of humans or livestock by the use of organisms or their products & therefore it is based on predator – prey relationship. The control agent either control the pest by feeding on it (lady bird or aphids, caterpillars larvae of butterflies & moths) are parasitized by bacillus species or by causing disease to the pests e.g. Virus sprays on army worm caterpillar.

Aim of biological control

Is to bring the population of the pest down to a tolerable level and not to eradicated by its natural enemy.


It doesn’t pollute the environment

It’s easy to apply as it doesn’t involve the use of sophisticated machine

Its effective through generations as the pest will not develop resistance to the predator as it is with the pesticides & herbicides. Thus time to time application is not important.

The predator eliminates or feeds / affects the intended organisms or i.e. it is selective.

It is cheap.


The beneficial organisms may also be eliminated due to lack of food if it dominates the harmful organisms or pest which may cause / lead to disruption of food chain.

The predator (agent) may turn into a pest by feeding on other useful organisms instead of feeding on the intended organisms’ e.g. after controlling the pest population it may become a pest itself.

It’s expensive i.e. involves studying the biology of the pest & the predator & this may take a long time.

If important agents / predators may fail to survive when the environment of the new country changes.

Biological control may not be effective if the pest outbreak is high because the agent/ predators are fairly slow to react / to eat to large numbers of pests. The population of pest species left may still be great enough to continue causing damage.










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