Definition of Concepts



Ecology: The study of the interrelationships between living organisms and the living and non-living components and processes in an environment


Biome: A major ecological region within which plant and animal communities are similar in general characteristics and in their relationships to the physical environment. Eg. vegetation zones such as the Tundra, Desert & Rainforests.


Ecosystem: The collection of all living organisms in a geographic area, together with all the living and non-living things with which they interact.

·    Acquatic Ecosystems (water-based) ecosystems

·    Terrestral Ecosystems (land-based) ecosystems.


Population: A group of organisms of the same kind living in a given area



Natural Community: Populations of different plant and animal species interacting among themselves in an area.


Habitat: The specific physical location where a particular organism lives or is adapted to live in a community.


Ecological Niche: An organism’s role or occupation within a community.



Bio-geography: A study of the distribution of plants and animals, the diverse spatial patterns they create, and the physical and biological processes (past & present) that produce this distribution.




1. Boitic and Abiotic


Every ecosystem is composed of two basic units:

a)         Biota: the living organisms - all plant & animal species

b)        Abiotic: the non-living physical and chemical component consisting of wind, temperature, water, soil, precipitation etc.


The single abiotic factor most lacking in a particular environment is termed a Limiting Factor. e.g. water – in a desert and temperature - Tundra.


The variation in physical factors that a population can withstand and continue to thrive in an environment is termed Range of Tolerance.





Green plants that carry on photosynthesis. Producers are termed auto-trophs because they are self-nourished they do not depend on other species to feed.



During photosynthesis, plants capture light energy with their chlorophyll and use it to convert carbon dioxide and moisture (absorbed from air) into sugar (chemical energy). Oxygen is released as a by-product



Every major ecosystem has its particular green plants that carry on photosynthesis and release chemical energy (carbohydrates, protein etc.) on which non-producers feed. (algae & plankton in aquatic systems, plants in terrestrial systems)





a) Consumers are heterotrophs (other-nourished) for they rely on chlorophyll-containing plants or the products of such plants for nourishment.

b) Consumers are subdivided into groups according to their food source.



Primary consumers: Species that feed directly on producers (plant-eating species). They are also called Herbivores. E.g. elephants, goats, cattle



Secondary Consumers: Species that feed on primary consumers. Secondary and higher order consumers are called Carnivores. E.g. fox, cat.



Tertiary and higher level Consumers: Species that obtain their nourishment by eating other meat-eating species. E.g. tiger


Multiple level Consumers: Species that obtain their nourishment from eating both plants and animal species. Also called Omnivores




They are the final link in the food chain. Comprise of organisms that feed on dead matter and break it down to release chemical energy back into the soil for plants to re-use them. E.g. fungi, bacteria, insects, worms and others.



Detritivores: feed on detritus matter (dead plants and animals) e.g. crab, vulture, termites, wood beetle and crayfish. Also called scavengers.





The Food Chain.


A food chain or food web comprises a sequence of organisms through which energy and nutrients are taken in and used up. A food chain in a wet meadow could be: Grass--> Grasshopper--> Snake--> Hyena.



Food chains begin from producers to consumers and the major feeding levels are called Trophic Levels.



Producers belong to the First Trophic Level. Primary consumers, whether feeding on living or dead producers feed from the Second Trophic Level. Organisms that feed on other consumers belong to the Third Tropic Level. Only about 10% of the calories in plant matter survive from First to the Second trophic level.





1. Mutual relationships:

Relations between organisms can be

(a)     mutually beneficial to both species, For example, relationship between flowers and insects is a mutually supportive relationship, or …

(b)    Parasitic, in that such a relationship benefits only one party. Examples include ticks, fleas, mosquitoes, mistletoe plants and fungi.


Mutually beneficial relationships are also termed Symbiotic (sym = together, bio = living) and can be described as

a)        Commensalism is a mutual interaction between two different species in which one organism benefits but the other is neither harmed nor helped in any way, or…

b)        Mutualism is a type of species interaction in which both participating species benefit.


2. Competitive Relationships:

Plant and animal species compete over food, water, territorial space and mating with the opposite sex.


The Principle of Competitive Exclusion: explains that no two species can occupy the same niche (food or space) successfully in a stable community.

Closely related species therefore live far from one another. This is because plants and animals must compete for water, nutrients, light and space. The outcome of this competition determines the character of an ecosystem.





Processes through which elements that sustain life (water, carbon, phosphorus and nitrogen) are continuously made available to living organisms.



Well known chemical cycles include:

a)         Nitrogen Cycle,

b)        Hydrological cycle,

c)         Carbon cycle, and …

d)        Phosphorus cycle




1.         Equatorial and Tropical Rain Forest

a) evergreen broadleaf forest

2.         Tropical Seasonal Forest and Scrub

a) Tropical monsoon forest

b) Tropical deciduous forest

3.         Tropical Savanna

a) Tropical grassland b) Savanna woodland

4.         Mid-latitude Broadleaf and Mixed Forest

a) Temperate broadleaf

b) Midlatitude deciduous forest

5.         Needleleaf Forest & Montane Forest

a) Taiga, b) Boreal forest, Montane forest

6.         Temperate Rain Forest

a) West coast Forest, b) Coast redwoods

7.         Meditarranean Shrubland

a) Sclerophyllous shrubs

b) Australian eucalyptus forest

8.         Warm Desert and Semi-Desert

a) Subtropical desert and scrubland

9.         Cold Desert and Semi-Desert

a) Midlatitude desert, scrubland and steppe

10.  Arctic and Alpine a) Tundra