Interdependence of Organism

Interdependence of Organism
(Interactions in an ecosystem)
The organisms in an ecosystem not only interact with their physical environment but also with each other. These interactions may be beneficial or harmful.
Positive Interactions
In this type of interaction organisms form associations for mutual benefit or for benefit of one species without harming the other. Mutualism and commensalisms belong to this type.
Negative Interactions
In this type of interaction one organism gets the benefit and the other is harmed. Parasitism, predation and grazing are considered to be harmful interactions.
The interactions between the organisms lead to close associations between them. There are two basic types of associations:
Intraspecific Association
Associations between members of the same species. These associations are found in social animals for social organizations or for formation of social groups.
Interspecific Associations
Associations between different species. In these associations, members of one species feed on members of another species and may also use them as habitat. Following are the types of interspecific associations
1. Parasitism
Parasitism is an association between two living organisms in which one lives in or on the body of the other and derives nourishment from it. In other words, one gets the benefit and the other is harmed. The organism getting the benefit is called the parasite and the one which is harmed is called the host. There are following types of parasites
Ectoparasites
They live on the surface of the body of the host. Examples, leech, lice, etc.
Endoparasites
They live in the tissues or cavities of the host. Examples Plasmodium, Tnenia, Entamoeba.
2. Symbiosis
Generally the symbiosis is defined as an association between two living organisms of different species for mutual benefit or in which one partner gets the benefit and the other is neither benefited nor harmed. In other words none of the two partners is harmed. There are two varieties of symbiosis
a. Commensalism
b. Mutualism
a. Commensalism
It is an association between two living organism of different species in which one is benefited and the other is not affected, that is it is neither benefited nor harmed. Following are some examples
Epiphytes are plants that grow on trunks and branches of trees for support only but can synthesis their own food. In htis way the epiphyte is benefited without harming the tree. Epiphytes are common in tropical rain forests. Orchids and mosses are common exampels.
Small Fishes live in the cloaca of sea cucumber for protection only. No harm is done to sea cucumber.
b. Mutualism
It is an association between two species of living organisms for mutual benefit. The two partners are dependent on each other for their survival and growth. The organisms in this association may be two animals, two plants or a plant and an animal. Example of mutualism are
Nitrogen Fixing Bacteria
They live in the nodules of leguminous plants. The bacteria fix atmospheric nitrogen for the plant and in return the plant provides shelter for the bacteria.
Lichens
It is an association between green algae and fungus. The algae cells are protected by the fungus and derive moisture from it, while the fungus obtains oxygen and carbohydrates from the algae.
Sea Anemone and Hermit Crab
The sea anemone attaches itself to shell of hermit crab. The anemone gets free transport while the crab is camouflaged by the anemone and is protected from its predators.
3. Predation
In this relationship one population called predators feeds on the members of another population known as prey. Normally predators are larger than the prey and quickly capture and kill the prey. Predators are usually animals bet a few like pitcher plant and other carnivorous plants are plant predators. Mostly the predators are secondary or tertiary consumers of an ecosystem.
The prey-predators interaction keeps the population of both the prey and the predator in equilibrium. Any species of a prey without its natural predator, disturbs the balance of the ecosystem due to explosive increase of their population. The degree of harm caused by this interaction, depends upon the relative population of the prey and predators. For example Ospreys (a kind of hawk) fed on fishes of the ocean. The supply of fishes is so large that this interaction does not cause much harm. However any disturbance in the relative number of prey and predator may result in extinction of any one or both.
4. Grazing
Grazing is a feeding association between herbivores and plants. Natural herbivores include rabbits, deer, zebras, wild horses, elephants etc. Man has also introduced cattle and sheep in the grass land both direct and indirect effects on the ecosystem. Moderate grazing is not harmful, but the over grazing greatly surfaces the growth capacity of grasses and other plants. Consequently all the producers are eliminated and green pastures are turned into barren lands. The indirect effect of overgrazing is hardening of the soil and soil erosion. The plant roots and under ground stem of grasses bind the soil together. Their destruction by grazing makes the soil loose which erodes easily. Too many animals trampling the soil makes it hard and poorly aerated. This may lead to conversion grass lands into deserts. Grasses have many adaptation to save them from effects of grazing.