Topic: Inter-Relationship Among Living Things
At the end of this article, readers should be able to:
Explain inter-relationships among living things.
There are inter-relationship among living things in a particular environment. These inter-relationship include the following:
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 enable it to grow and survive while the other neither grow nor survive leading to its elimination.
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
a. 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.
b. 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.
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 benefit from and causing harm to it while the host loses in the process. The parasite benefits from the association while the host usually suffers harm or may die.
Examples of Parasitism
a. 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.
b. Mistletoe and flowering plant: The mistletoe is a plant parasite that lives on the 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 suffer harm by loosing to the parasite part of the water and mineral salts that it has absorbed.
Fungal parasites of host plants include:
a. Ustilago on maize.
b. Puccinia on maize wheat or barley.
c. Phytophthora palmivora on cocoa.
d. Phytophthora infestans on tomato/potato.
e. Alternario on tomato.
Definition: Symbiosis is a close association between two organisms which both of them benefit from each other. Symbiosis is a beneficial association and each member is called a symbiont.
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 uses some of the water absorbed by the fungus while the fungus benefits by using part of the food manufactured by 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 leguminous 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 bacteria.
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 two organisms living together in which only one (commensal) benefits from the association while the other is neither benefited nor harmed.
Examples of Commensalism
a. 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 remora fish.
b. Oyster and crab: 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.
c. Man and intestinal bacteria: Some bacteria in the large intestine 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.
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 chicks) 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 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.