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ECOLOGY
This is the study of inter-relations (interactions) between an organ ism or a group of organisms and their
environment.
TERMS USED IN ECOLOGY.
1. Habitat: is a place where an organism lives e.g. land habitat is known as terrestrial (mainly forest,
deserts and savannahs), water habitat is aquatic (includes fresh water bodies and marine water bodies)
2. Biosphere: is the part of the earth and atmosphere where life can exist. This ranges from deep water
bodies, land and a few metres in the atmosphere.
3. Species: this is a group of organisms which can interbreed to give rise to a viable or fertile offspring.
4. Population: a group of organisms of the same species occupying the same area at a given time e.g. a
population of elephants in Queen Elizabeth national park, population of hippos in kasinga channel,
population of parrot birds in Gayaza High School etc.
5. Community. This is a collection of populations of different organisms occupying the same area or a
group of different species of organisms in the same area. E.g. a community of antelopes, elephants,
lions, in Queen Elizabeth National park
6. Ecological niche: This is a term used in relation to a particular organism. It refers to the role/
profession of an organism in a given habitat eg the niche of a spirogyra in a pond is to photosynthesis
or to produce food.
7. Biome: These are very large ecological divisions found all over the world. They have characteristic
plant and animal communities, e.g. equatorial rain forests biome, Amazon, savannah grasslands and
wood lands, temperate forests etc.
8. Environment: surrounding of an organism e.g. in Gayaza environment we have organisms like
birds, leopards, foxes, rats etc.
9. An ecosystem. This is any unit of environment consisting of both living and non living
components existing together as a harmony e.g. a pond where living components like fish, insect
larvae, amphibians, and plants like spirogyra interact with the non living components such as water,
rocks, sand etc.
An ecosystem consists of two components/environments;
a) The biotic environment. (living component)
Consist of the animal and plant communities. Therefore biotic is considered to be the
living organisms, whether micro or macro in size. These form a vital environment of an
organism and are in a constant interaction with each other. The plant community is known
as flora and the animal community is known as fauna.
b) The abiotic environment.
These are the non living components of an eco system.
They include;
i.
Climatic elements of the atmosphere such as rainfall, light, temperature, humidity,
air currents (wind), atmospheric pressure, cloud cover etc.
ii.
Water bodies of all sizes and characteristics.
Some are fresh water bodies; others are marine (high salt concentration).
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iii.
iv.
Edaphic (soil) factors; include soil structure, profile, texture, pH, temperature etc.
Lithosphere (rock types) factors or land forms e.g. metamorphic rocks,
sedimentary rocks and igneous rocks.
RELATIONSHIPS WITHIN AN ECOSYSTEM
Food relations in an ecosystem
Food is a source of energy i.e. energy in chemical form. Food in an ecosystem exists as organic
matter (biomass).
Biomass is the measure of the amount of living or organic material in an organism. It considers the
dry weight (minus water and other fluids in the body).
Food relations is a common form of interaction which consists of eating (consuming) and being eaten
(being consumed).
Within the relation there are different modes of feeding.
The modes of feeding depend on;
The nature of food and the feeding level. Green plants (Autotrophs) make their own food using sun
light energy. They incorporate water and carbon dioxide into organic material (starch). This process is
known as photosynthesis.
Some of the food energy is used by the plant for its own metabolic activities e.g. respiration. Some of
the energy is lost during respiration in form of heat. The lost heat energy becomes part of the abiotic
environment once it enters the atmosphere.
The balance of energy in the plant is therefore available to the next trophic level made up of the
herbivores (primary consumers); omnivores- lower carnivores (secondary consumers) - top carnivores
(tertiary consumers) - scavengers and decomposers.
Scavengers feed on carcasses of the animal killed by the carnivores. Primary consumers, carnivores,
scavengers and decomposers are heterotrphs because they cannot manufacture their own food.
Trophic levels refer to energy levels (usually in terms of food). Within an eco system, green plants
are therefore referred to as producers since energy enters the system through these plants from the
sun.
NB, since the consumer does not eat all parts of the plant, it means that the available energy in plants
is not all utilized.
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FOOD CHAINS.
A food chain is a linear feeding relationship between producers and consumers in an ecosystem. It
represents the transfer of food energy from green plants through repeated stages of eating and being
eaten.
There are two types of food chains
1. Grazing food chain. Starts with green plants
2. Detritus food chain. Starts with dead organic material (debris or detritus)
In construction of food chain, an arrow is used to link the different levels of organisms and the
direction in which the arrow point is from the organism that is being consumed to the next consumer.
Examples
1. Water weeds
tilapia
nile parch
crocodiles
bacteria.
2. Plant debris
bacteria
protozoa
mosquito larva
From one level to the next food energy is being transferred.
These different levels are referred to as energy levels/trophic levels. At various consumer levels,
some of the food energy is utilized for respiration, while some of the energy is lost in form of heat
through various processes such as;
1. urination
2. sweat
3. Panting.
4. Exhalation.
Therefore the amount of energy gained by the higher trophic levels keeps on decreasing such that at
the final level (decomposers) the amount of energy is negligible.
Food web.
In a natural community, several food chains are interlinked to form a food web. Several herbivores
may feed on one plant. Similarly a given herbivore may be eaten by different carnivores
Examples
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Pyramid of numbers
When the numbers of organisms at each trophic level are considered and the results represented in a
graphic form, a pyramid shape is obtained. This is because one herbivore feeds on many green plants.
One carnivore also feeds on many herbivores
Carnivores (tertiary consumers)
Carnivores (secondary consumers)
Herbivores (primary consumers)
Green plants (producers)
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©2009 GHS
lesson notes