This blog post provides readers with the following objectives. The reader will be able to:

o     Discuss basic concepts in ecology.
o     Outline the general characteristics of aquatic and terrestrial habitats
o     Explain the effects of abiotic and biotic factors on life in aquatic and terrestrial habitats
o     Explain how organisms in aquatic and terrestrial habitats are adapted to their habitats
o     Identify the components of a food chain, food web and ecological pyramids.
o     Explain how food chains and food webs can be determined.
o     Identify the different symbiotic relationships

Feeding relation among organisms


Ecology is the scientific study of the interaction or inter-relationship of living organisms with each other and with their environment.

Ecological Terms 

1.     Environment: The environment is the total surroundings of an organism including all the biotic and abiotic factors that affect the organism in one way or the other. 

    i.    Biotic factors (living components) include genes, cells, organisms, members of the same species and other species that share a habitat. 

      ii.    Abiotic or non-living factors includes water, light, temperature, humidity and rainfall.

2.  Habitat: Habitat is a particular locality within an environment, where organism can live successfully. E.g., pond or forest.

3.     Species: is a group of organisms which can interbreed and produce fertile offspring.

4.     Population: is a group of organisms of the same species living together in the same environment or habitat e.g., population of monkeys in a forest.

5.     Community: is the interactions among different species that inhabit the same geographic area. Most often communities are named after the dominant species. 

6.     Ecosystem: is a group of living organisms and nonliving components of the environment, which function together as unit.  OR Ecosystem is a natural unit made up of living and non-living things interacting together to produce a stable system.
7.     Ecological niche: is the description of the function or role each organism plays within ecosystem.  
8.   Biosphere: This refers to part of the earth surface and the atmosphere where life exists. The biosphere is the total sum of ecosystems on the planet. It consists of land, sea, freshwater and air. The biosphere is made up different ecosystem. 
9.    Biome: A biome is a large natural area with a particular climate. Biomes include tropical rainforest, temperate deciduous forest, savanna, tundra, and desert.
10.    Biomass: is the amount of organic matter present in an organism at a given time. Biomass can refer to either species biomass; which is the mass of one or more species or community biomass; which is the mass of all species in the community. The mass can be expressed as the average mass per unit area, or as the total mass in the community.

Trophic Levels

Species are categorized as autotrophs (or primary producers), heterotrophs (or consumers), and Detritivores (or decomposers). Each of these constitutes a trophic level. 

Primary Producers (Autotrophs): are organisms that produce their own food by photosynthesis. Plants capture energy from sunlight and use it to combine carbon dioxide and water to produce carbohydrates. The rate at which energy is bound in organic material by photosynthesis per unit area of vegetation is called primary production.

The photosynthesis carried out by all the plants in an ecosystem is called the gross primary production (GPP). About 48–60% of the GPP is consumed in plant respiration. The remainder, that portion of GPP that is not used up by respiration, is known as the net primary production (NPP). NPP = GPP - respiration (by plants). 

The energy incorporated into plant tissues (net primary production) is either consumed by animals or it remains uneaten when the plant dies and becomes detritus.

Consumers (Heterotrophs): are organisms that feed on others for nourishment and energy. 

1.  Primary consumers: these are organisms (herbivores) that consume plant tissues. E.g. grasshopper, goat, sheep, fish, parrots etc. 

2  Secondary consumers: animals that feed on primary consumers (i.e., carnivores that feed exclusively on herbivores). E.g., toad, lizard, dogs, cats, snakes

3.  Tertiary consumers: these are animals that feed on secondary consumers. E.g., hawk, lion. Omnivores such as human or bush pig may feed on both plants and animals. An omnivore can be a primary consumer or secondary consumer. 

Decomposers: these are organisms that breakdown dead organic materials and absorb simple food material to obtain energy. They include bacteria and fungi. Decomposers play a pivotal role in the nitrogen and carbon cycles. The carbon and nutrients in dead organic matter are broken down by processes known as decomposition. This releases nutrients back into the soil and returns carbon dioxide to the atmosphere (or water) where it can be used by plants. 

Food Chain

Food chain is feeding relationship involving transfer of energy from one trophic level to another.  Food chain is also defined as the feeding relationship in which energy is transfer from plants through series of organisms, with each stage feeding on the preceding stage and providing food for the succeeding one. Food chains trace the transfer of energy from one organism to another. 

o Producers incorporate energy from the sunlight into organic compounds. They form the bases of all food chains (i.e. they occupy the first trophic level).
o Primary consumers occupy the second trophic level.  
o Secondary consumers occupy third trophic level 
o Tertiary consumers (feed on secondary consumers) occupy fourth trophic level. 
o The last trophic level is occupied by decomposers e.g. bacteria and fungi.    
A food chain can be short consisting of only two links or three or more links.

Importance of studying food chains

Help in developing biological control for pest.
Prevent extinction of species.
Following the accumulation of poisonous materials to prevent biological magnification.


food chain

Food Web

Food web is feeding relationship made up of several food chain interconnected together. Food web shows a clear picture of the feeding relationship in any community. Interaction and associations within a community are such that simple food chains are seldom found. Instead, a number of food chains are linked to form a core complex food web.

Example of food web

Methods of Determining Food Chains and Food webs

Direct observation 

This is where the feeding habits of the same species are observed in the community e.g. butterfly sucking fruit juices. From such observation food chains and food webs may be constructed.

Gut examination 

This involves capturing, killing and dissecting animals to obtain samples of their gut contents. This provides direct information about the organisms on which each consumer feeds.  

Radioactive or tracer methods 

It involves the use of labeled radioactive food substances in the field. The labeled food may be in the form of radioactive isotopes of phosphorus (P32) or Sulphur (S32) which are readily incorporated into inorganic fertilizers.  The labeled fertilizer is absorbed from the soil by the roots of the plants and incorporated into plant materials. By using sensitive counters, the path of P32 can be traced. Animals that are found to be radioactive may have consumed material from the plant or eaten one or more animals that already fed on the plant. Herbivores e.g. grasshopper, become radioactive first followed later by the predators.

Energy Flow

It refers to the flow of energy through a food chain. The transfer of energy from producer to primary consumer is only 10% efficient. The reason is that 

not all the plant is eaten by herbivores  
some of the food eaten will not be digested, as it will be egested as feces 
some are used for the metabolic activities like respiration and excretion 

Therefore, primary consumers get about 10% of the energy produced by plants, while secondary consumers get 1% and tertiary consumers get 0.1%. This means the top consumer of a food chain receives the least energy, as a lot of the food chain's energy has been lost between trophic levels. This loss of energy at each level limits typical food chains to only four to six links.

Ecological Pyramids

Ecological pyramid is a graphical representation which shows the relationship between biomass or biological productivity and trophic levels in a given ecosystem. Ecological pyramids begin with producers on the bottom and proceed through the various trophic levels. 

Pyramid of Numbers 

It shows graphically the population of each trophic level in a food chain. The length of each bar is proportional to the number organisms. The number of organisms reduces progressively from the base to the top. The pyramid decreases markedly at each higher level. It must be noted that, although the number of individuals decreases, the size of the individuals generally increases.

o One instance where this is not the case is where the producer is large and supports a community of consumers. This results in an inverted pyramid. 

Ecological pyramid

Disadvantages of Pyramid of Number

i. Each individual is regarded as one regardless of size. Therefore, one grass plant is equal one elephant in a pyramid of number.

ii. Single individual is often difficult to distinguish where several are massed together e.g. moss plants.

Pyramid of Biomass 

It is a graphical representation of the total amount of organic matter in organisms at each tropic level per unit area. Organisms at each trophic level of a particular food chain are collected, dried and weighed. It is measured in grams per meter2, or calories per meter2.

Ecological Pyramid of biomas

Pyramid of Productivity or Energy

It shows the flow of energy from one level to another in food chain. It’s measured in kilojoule per meter2 per year.

Healthy ecosystem produces a standard ecological pyramid, because for ecosystem to be stable, there must be more energy at lower trophic levels than there is at higher trophic levels. When energy is transferred to the next trophic level, only 10% of it is used to build new level. The remaining ninety percent goes to metabolic processes or is dissipated as heat. This energy loss means that productivity pyramids are never inverted. Each step will be 10% the size of the previous step (100, 10, 1, 0.1, 0.01).

Ecological Factors and Ecological Instruments

The environment of an organism includes all the living and non-living things that surround it. They all affect the organism in some way and are referred to as ecological factors. 

These factors can be grouped into abiotic (physical) factors and biotic (biological) factors.

Abiotic Factors 

These form the non-living part of the habitat or ecosystem, which include rainfall, temperature, wind, pressure, light intensity, pH, humidity, oxygen and carbon dioxide concentration, altitude and slope of land. 


Temperature has a lot of influence on living and non-living thing in the habitat. 
Temperature affects organisms on land more than those in water habitat. 
It affects metabolic activity, growth rates and primary production. 
It results in excessive water loss (transpiration) in plant which causes wilting. 
It results in evaporation of soil water which causes dry out, making it difficult to till.
Increased in evaporation of soil water adversely affect soil organisms such earthworm.
Increase in temperature, increase the rate of decay (decomposition) of organic matter.
Temperature affects humidity, and also affects solubility of gasses (oxygen) in water.
Temperature is measured with thermometer.  

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o Green plants use the energy of sunlight to manufacture food in photosynthesis.  
o Animals depends on photosynthetic plants for food.
o Many plants produce flower when the amount of light is suitable.
o Some animals are active and feed in day light 
o Most termites swarm at night to avoid day-flying birds which feed on them. 
o Humans are capable of producing vitamin D by the action of ultra-violet on the skin cells. 
o Light intensity decreases with increasing depth of water bodies which affects the distribution of organisms. 
o Light intensity is measured with photometer.   

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Onset of rainfall induces winged termites to go on nuptial flight.
Rainfall determines salinity of aquatic habitats which determines distributions and abundances of organisms.
Affects environmental temperature which affects distribution and activity of organisms.
It makes water available to organisms
Rainfall variations can result in drought or floods which destroy vegetation animals.
It determines water level in streams, springs, rivers etc. which affects life of organisms
It determines degree of turbidity (transparency) of water bodies which affects abundance and distribution of organisms.  
It determines level of soil erosion which affects growth and distribution of plants
It affects humidity which affects transpiration. Rainfall is measured with a rain gauge.  

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Humidity is the measure of the moisture content of the atmosphere. 
Low humidity leads to increase evaporation and transpiration.  
Organisms regulate water loss by having a waterproof covering or live in damp place. In plants the waterproof covering on leaves is the cuticle and corky bark covers the stem. 
Earthworms, termites and mosses are restricted to humid area to avoid dehydration.  
Birds have feathers and reptiles have scales, both of which help to reduce water loss. 
Humidity varies with temperature, the lower the temperature, the higher the humidity.
Humidity of the atmosphere is determined with a wet and dry bulb hygrometer.    


Many habitats are affected by the direction and strength of the wind. 
Winds control movements of clouds and influence rainfall patterns in an area.  
Wind increases the rate of evaporation of water from surface of ponds, lakes, and seas. 
It also increases the rate of transpiration in leaves. 
Wind helps the dispersal of fruits and seeds. 
Flying animals such as insects and bats are influenced by the direction and speed of wind.
Strong winds cause soil erosion, damages trees and uproot smaller plants. 
Wind speed is measured with an anemometer. 
A wind vane is used in measuring the direction of wind.   

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Hydrogen ion Concentration (pH)

pH is the measure of the acidity or alkalinity of water or soil solution. 
pH expressed in terms of pH scale which ranges from 1-14. pH 7 indicates neutral, 7-1 indicates increasing acidity and 7-14 indicates increasing alkalinity.
pH affects the distribution of plants and animals in an environment. 
Decaying bacteria and earthworms are reduced in greatly acidic soils. 
Some plants do not grow well in strongly acidic soils. 
Fresh water mollusks tend to be absent in water with pH less than 6. 
pH is measured using the universal indicator or pH meter.   

Carbon Dioxide & Oxygen Concentration

o Organisms use up oxygen and release carbon dioxide through the process of respiration. 
o During photosynthesis green plants use carbon dioxide and release oxygen. 
o Respiration and photosynthesis are balanced so that the amount of carbon dioxide and oxygen in the air remains constant. 
o Burning (combustion) may temporally upset this balance by absorbing oxygen and releasing carbon dioxide.  
o If the amount of carbon dioxide is too great, plants cannot use all and this leads to global warming.  


Salinity is the saltiness or dissolved salt content of water body. 
It affects distribution of living organisms e.g., marine, lagoon, estuarine and freshwater bodies have a variety of living organisms.  


Altitude refers to vertical height above sea level. 
Air pressure and oxygen level decrease as altitude increases. 
Organisms living at high altitude have adapted to cope with these conditions. 
Abetifi-kwahu in Eastern region of Ghana, experience lower temperatures and stronger wind. Altitude is measured with the altimeter.   

Biotic Factors 

These factors are concerned with the way in which living organisms interact with one another in the habitat. These interactions may have both useful and harmful results. Some examples of useful biotic factors are:

insects and birds acting as agents of pollination
animals enrich soil through death and decay
animals acting as agents of fruit and seed dispersal
trees providing shade and shelter to animals and other plants
plants having weak stems use other plants for support in order to reach light
bacteria and fungi helping to decompose dead organic matter
symbiosis relationships between organisms where one or both partners benefit, e.g., lichens (association between fungi and an algae)
termites and earthworms aerate the soil through their burrowing activities.    

Harmful biotic factors include:

plant-eating animals (herbivores) e.g., herds of goat which feed on and may destroy plants
flesh-eating animals (carnivores) which feed on other animals
transmission of pathogens e.g., white fly is a vector of the virus that causes cassava mosaic
parasites live on or inside a living host: the host may tolerate it or eventually die

Human have a great influence on their surroundings, much of it harmful. Examples include felling of trees for timber, clearing of land for agriculture and building purposes, damping of waste materials and other pollutants.  Misuse of agrochemicals, such as fertilizers, pesticides, and herbicides, damage the environment. These result in destruction of many natural habitats, rendering animals and plants homeless.

List of Ecological Factors and Ecological Instruments







Light intensity



Rain gauge




pH meter

Wind speed


Wind direction

Wind vane or wind gauge


Secchi disc

Density of water



Tide gauge         



Biological Association 

Some organisms form close relationships with other organism. The relationships may be intra-specific (between organisms of the same species) or interspecific (between organisms of different species).

Symbiosis: is an interspecific relationship where the body of one organism provides a habitat for another. Symbiosis may be commensalism, mutualism or parasitism.


Commensalism is a close relationship between two organisms of different species, which is beneficial to one (commensal) but does not affect the other, the host. The gain may be in terms of food or free transport. Example:

o   A small fish, the remora lives as a commensal on the shark, attached by its sucker. When the shark feeds, remora detaches itself and feed on scraps of food discarded by the shark. The shark neither benefits nor harmed by the relationship. 


Mutualism is a close relationship between organisms of different species in which both partners benefit. It may be a relationship between two plants, two animals or between a plant and an animal. Example;

o   Lichen (association between an alga and a fungus). The alga obtains support and shelter from the fungus whiles the fungus obtains food manufacture by the algae. 

o  Bacteria living the intestine of ruminants. The ruminants provide protection and nutrients for the bacteria, whiles the bacteria digest cellulose for the ruminants. 

o  The association between hermit crab and sea anemone. The tentacles of the sea anemone protect the crab from predators. Anemone derives food by picking up pieces of food that float away from the crab.  

o  The nitrogen fixing bacterium (rhizobium), which lives in the root nodules of leguminous plants obtain food and protection. The bacterium converts atmospheric nitrogen into nitrates which are readily absorbed by plants for the synthesis of proteins.


Parasitism is close relationship between organisms, in which one, the parasite lives in or on the body of the other, the host, deriving benefit from it and causing harm to it. The parasites may or may not kill the host. The association may be ectoparasite or endoparasites.

o     Ectoparasites: live on the surface of the host e.g. lice living on human head, ticks living on a cow.

o    Endoparasites: live in the body of their host e.g. tapeworms, Ascaris living in the small intestine of man.

Parasites have special adaptations that enable them to survive. They may have high reproductive rate, organs of attachment (e.g. haustoria of dodder). They may also have boring devices used to enter the host (nematode worms). Parasites which obtain their nutrient parasitically until the host dies and adopt a saprophytic mode of feeding are called facultative parasites.


Saprophytism is a type of nutrition, where organism obtains nutrients from dead organic matters. Organisms that practice saprophytism are referred to as Saprophytes e.g. fungi and bacteria. They play pivotal role in the ecosystem by acting as decomposers. They cannot manufacture their own food because they lack chlorophyll. Saprophytes (such as Rhizopus), secrete digestive enzymes unto dead organic material. The enzymes break down the food into soluble components. The products are absorbed through the body surface of the saprophytes. The digestion occurs outside the body of the organism and so it is called extracellular digestion


This is a type of association which occurs between plants, usually between a tree and a much smaller green plant called the epiphytes. Epiphytism occurs in the forest where the leaves of the big trees form a canopy or shade over smaller trees. Epiphytes depend on the host for only support. Epiphytes are capable of photosynthesis and live high on the tree branches. The epiphytes root systems absorb nutrients from the water that drips down host stems.


This is a kind of relationship where two or more organisms demand the same environmental resources that are in short supply. Competition between organisms of the same species is referred to as intraspecific competition while competition between different species is called interspecific competition. E.g. Plants competing for light in the forest


Predation is a relationship between two animals in which one, the predator, hunts and kills the other for food, the prey. Predator-prey relationships are important in that they affect the population sizes of predators and prey. Predators have adaptations to enable them capture prey whiles the prey is also adapted to protect itself from predators.

Mechanism Preys Use to Escape from Predators 

o         Emission of offensive smells e.g. some insects
o        Possession of spines e.g. hedgehog, grasshopper
o        Camouflage or cryptic coloration adapt to the environment e.g. chameleon, grasshopper
o         Presences of poisonous gland or foul tasting e.g. frog or toad
o         By playing dead or temporary swelling up e.g. millipede, anteater, or some snakes     

Importance of predation

1.     Biological control
2.     Checking the population
3.     Maintaining ecological balance

 Click Here for WAEC/ SSCE/ WASSCE Past Questions and Answers  on Ecology

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