- Define an association;
- Recognise some of the different types of association existing between different species;
- Identify beneficial harmful and neutral forms of association among organisms;
- Deduce the mode of life of a given
- organism from observed characteristics.
Lesson Summary / Discussions
Association is a biological relationship that exist between organisms of same or different species. Some of these associations are beneficial, some are neutral while others are harmful.
Types of Associations
Definition: Symbiosis is a close association between two organisms in which both of them benefit from each other. Symbiosis is a beneficial association and each member is called
Examples of Symbiotic Association
(a) Alga and fungus in lichen: A lichen
is made up of two organisms, namely a fungus and a green alga which live in a close association.
In this association, the alga benefits
because the fungus encloses and protects it from physical damage and from drying up. The alga also uses some of the water absorbed by the
fungus while the fungus benefits by using part of the food manufactured by the green alga.
b). Protozoa in the intestine of termites: The protozoa help the termite to digest the cellulose in the food while the protozoa are protected by the termites.
(c) Nitrogen fixing bacteria in the root
nodules of leguminouss plants: A
bacterium called Rhizobium leguminosarium living in the root nodules of leguminous plants obtain nutrients from the cells of the host plant, grow and multiply or reproduce there. In return, the rhizobium
(bacterium) fixes nitrogen directly into the plant from the atmosphere, thereby increasing the nitrogen requirement of leguminous plants.
d) Bacteria in the rumen of ruminants:
Bacteria and other protozoa in the rumen of ruminant animals like cattle, sheep and goat help the ruminant to digest cellulose to sugars, synthesize amino acids and vitamins from other substances while the ruminant in
turn provides food and shelter for the
(e) Flowers and insects: Insects obtain food from flowers in the form of pollen and nectars while in return, the insects bring about cross-pollination in the plant they visit, thus enabling plants to reproduce sexually.
Definition: Commensalism is a relationship or an association between two organisms of different species, in which one, the commensal, benefits or gains while the other, the host, is not adversely or significantly affected in any way, i.e. it is not harmed, it neither loses nor gains.
In other words, Commensalism is
an association between two organisms living together in which only one (commensal) benefits from the association while the other is neither benefited nor harmed.
Examples of Commensalism
Remora fish and shark: The remora fish attaches itself to the body of a shark which carries it about. The remora fish feeds on the food particles left over by the shark. By so doing the remora obtains food, protection and shelter from the shark, whereas the shark is neither harmed nor benefited as a result of the presence of the
Oyster and erab: The habitation of a crab is in the oyster shell in which case the crab is protected, yet no harm is done to the oyster.
Man and intestinal bacteria: Some
bacteria in the large intenstine of man feed on digested food there.The bacteria receive food and protection from the man whereas the man neither gains nor suffers any disadvantage from the presence of the bacteria.
Epiphytes and Flowering Plant
Epiphyte: It is a plant which grows on or supported by another plant or lives on a tree where it competes with other producers for sunlight. It does not take manufacture food from
the support plant. It is capable of carrying out its own photosynthesis. It does not harm the flowering plant that gave support to it.
Definition: Parasitism is a feeding relationship or association between two organisms, in which the parasite lives in or on the body of the host,
deriving benefits from and causing harm to it while the host loses in the process. In other words, Parasitism is a close association between two organisms in which one, known as the parasite, lives in or on and feeds at the expense of the other organism which is known as the host. The parasite benefits from the association
while the host usually suffers harm or may die.
Examples of Parasitism
Man and the tapeworm: The tapeworm is a parasite that lives in the small intestine of man where it derives the benefits of a habitat, protection and food. The man who is the host suffers because he loses to the tapeworm part of the food he has eaten and digested.
Mistletoe and flowering plant: The
mistletoe is a plant parasite that lives on other larger flowering plants. The
mistletoe benefits because the host gives it support and raises it up to a position from which it can receive sunlight. The parasite also absorbs water and mineral salts from the host while the host suffers harm by losing
to the parasite part of the water and mineral salts that it has absorbed.
Other examples of plant parasites are striga, dodder, cassytha etc.
Fungal parasites of host plants include:
- Ustilago on maize.
- Puccinia on maize wheat or barley.
- Phytophthora palmivora on cocoa.
- Phytophthora infestans on tomato/potato.
- Alternario on tomato.
Definition: Predation is a type of association between two organisms in which the predator kills the other, called the prey and directly feeds on it. The predator which is usually larger in size and always stronger than the prey benefits by deriving its food while the prey is completely eliminated.
Examples of Predation
a. The hawk and chicks of domestic
fowls: The hawk is the predator that
catches, kills and eats the prey (young ones) of domestic fowls. The hawk is stronger and bigger than the chicks. The hawk benefits while the chicks are completely eliminated.
b. The lion and goat: The lion is the
flo predator that catches, kills and eats the prey (goat). The lion is stronger and bigger than the goat. The lion benefits while the goat is completely eliminated.
Definition: Competition involves the
interactions among two organisms of the same or different species in which one outgrows the
other and survives while the other can neither grow nor survive.
Competition is often based on limited
environmental resources which can be in short supply such as food, water, nutrients, gases, light and space. During competition, one organism
controls one or more of these resources which enables it to grow and survive while the other neither grows nor survives, leading to its
When the competition is between members of the same species, it is called intra-specific competition while it is called inter-specific
competition if it is between members of different species.
Examples of Competitive Associations
Flowering plants and grasses: The
flowering plants due to its size and numerous branches and leaves are capable of eliminating the grasses by depriving the grasses of nutrients, space and sunlight. The grasses may eventually be eliminated because they have no access to these resources.
Domestic fowls and the young chicks: The adult domestic fowls are capable of eliminating the young chicks by depriving the chicks of food in the pen. The young chicks may eventually die because they may not have access to the limited food available in the feeders. The stronger and bigger fowls eat the food first and it is only when the adult fowls are satisfied that the young chicks can eat.
- Define an Association.
- Mention the forms of association with examples.