Community Dynamism: Disoperation and Co-Operation | Ecosystem

In this article we will discuss about the disoperation and co-peration of community dynamism.

Disoperations of Community Dynamism:

The major disoperations present in a community are parasitism, predalion and competition.

Parasitism:

Parasitism is a relation between two individuals whereby the para­site receives benefit at the cost of the host. Parasitism is a form of disoperation which is mainly food oriented but the parasites sometimes derive shelter and protection from the host as well. For its own survival the parasite does not kill its host at least not until the parasite has completed its reproductive cycle.

Classification of parasites:

Parasites are commonly classified as Ectoparasites, Endo-parasites and social parasites.

Ectoparasites live outside the body of the host. Ectoparasites at the adult stage only are mosquito, flea and bed-bug. But the blood-sucking lice and flies, biting lice, mites and ticks are ectoparasitic both at larval and adult stages. Endoparasites are those which live in the alimentary tract, body cavities, blood or other tissues of the host.

Endoparasites, in general, are parasitic in all stages of their life though there may occur a change of host for the completion of the life cycle. Entamoeba, malarial parasites, trichomonad flagellates, nematodes, cestodes are some of the exam­ples of endoparasites.

Social parasitism describes the exploi­tation of one species by another for the sake of some advantages. Cuckoos do not build nests of their own. They lay their eggs in the nest of other birds abandoning eggs and the young’s to the care of the foster parents.

Parasitic relations develop not neces­sarily between animals. Animals may also be parasitic on plants. Nematodes infest the roots of plants. Wasps and gnats produce galls on oak trees. Varieties of insect larvae are leaf miners, wood borer, cam­bium feeder and fruit eaters.

Host specificity:

Parasites maintain in general a host specificity. Most parasitic genera are adapted to hosts of one phylum only. The acanthocephalans Gracilisentis and Tanarhamphus are found only in the gizzards of shad fish. Each order of birds possesses its own particular species of tape­worm. This remains true even if several orders of birds live close together.

Copepods of all parasites exhibit a loose host specificity. They have been re­ported from various invertebrates and fish. Assignment of host specificity in case of protozoan parasites is a difficult one. Many species of parasitic protozoa have invaded more than one taxonomic host group and often several species of a single genus of parasitic protozoa invade the same host species.

Effect on parasite:

Because of parasitic adaptation the parasites become restricted to special niche. Many parasites undergo degenerative changes in their organs of locomotion, sense organs and even in their alimentary canal. The reproductive struc­tures however become well developed and some organs for attachment become new addition.

Effect on host:

The parasites cause di­seases of the host. By the term disease is meant a condition which affects the body or part of the body that the normal phy­siological functions of the body is impaired. In general, the animal parasites do not cause immediate mortality but they do cause damage to body structures and the damage when becomes too much cause death.

External parasites like mosquito, flies, ticks, fleas and lice commonly do not produce mortality of the host by them­selves but they often act as vectors and transmit protozoan, virus and bacterial diseases.

Protozoan parasites cause damage of alimentary canal and blood.

Worm parasites like nematodes, tape­worm, etc., may wander through host’s body. They cause mechanical injury and as well as destroy and consume tissues.

The host may undergo nutritional defi­ciencies and physiological stress because of infection by the parasites.

Evolution of parasitism:

The Story of the evolution of parasitism is a matter of speculation. The ancestors of parasites were all free living in water or vegetation. But how these free-living creatures became adapted to parasitic mode of life? The answer to the question is a difficult one.

It may be imagined that a free-living indi­vidual living in water or vegetation got settled on the outer body surface of a larger individual accidentally. The free- living organism (the organism destined to become future parasite) in this new site found condition favourable for survival. The organism found a rich source of food in the niche and adjusted itself to become ectoparasite.

It is believed that the biting lice have evolved from psocid insects that live beneath the bark of trees. They may have migrated from this niche to the nests of birds and then to the birds themselves. Most ectoparasitic insects are probably derivatives of carnivorous, saprovorous or suckers of plant juice.

Endoparasites may in some cases have evolved from ectoparasites but more likely they come from free-living ancestors or commensals. Protozoan or flat worms might have had their first entrance into their hosts through drinking water and later invaded other organs of the body.

These organisms however needed some pre­adaptation to live at low oxygen concen­tration, to avoid being digested or being carried away with the faeces. In successive generation the parasites became more suit­ably adapted.

Predation:

Predation is a disoperation wherein one species kills and feeds on a second species. The killer individual is call­ed predator while the individual that is killed is called prey. According to one ecologist “the difference between parasites and predators is that the predators live on the capital while the parasites live on the in­come.”

Competition:

Competition is insepar­able in life. Clements has defined competi­tion in the following way. Competition is the more or less active demand in excess of the immediate supply of material or condition exerted by two or more organisms.

The materials and conditions sought by ani­mals are food, shelter and mates. Compe­tition may be direct or indirect. Direct com­petition results in active antagonism or combat between individuals. Fighting amongst Bull seals for larger harem is an instance of direct competition.

In indirect competition one individual or species tries to monopolize a resource or renders a habitat unsuitable for the establishment of other organisms having identical requirements.

Indirect competition is very common among plants when certain plants mono­polize the water and nutrient of the soil and available light in such a way that others cannot maintain themselves. Ani­mals often render a habitat unsuitable by their excreta for a species which otherwise would occur.

Amensalism:

‘Amensalism is a condition in which the mere presence of a species causes hardship or difficulties of another species though the former species is neither harmed or helped. The classical example of amensalism is the Penicillium.

Penicillium in cultured condition produces cer­tain toxic substances which inhibit the- growth of many kinds of bacteria. The mold of Penicillium, however, is not affec­ted by the presence of the bacteria neither it gains by the death of the bacteria.

Co-Operation of Community Dynamism:

The co-operation amongst living organ­isms involves commensalism, proto- co-operation and mutualism.

Commensalism:

Commensalism exists between two members of different species which live together and any one out of the two becomes benefited and the other is not helped or harmed. The one which de­rives benefit in such associations is called commensal.

A large number of insects live as commensals in the nests of birds. Commensalism is very common in the marine habitat. The oysters keep small crabs as commensals in their- mantle cavi­ties. Some small fishes live as commensals in the cloacal respiratory trees of sea- cucumbers. Shelter and waste scraps of food are gained by the commensals.

Proto-co-operation:

Proto-co-operation re­sults when two members of different species form an association in which both gain benefit out of it. The association is not very rigid and each is capable to survive without the association. As for example the association between marine crab and hydroid co-elenterates may be cited. Hydras live on the carapace of the marine crab.

In such an association the hydras gain by being moved about in the habitat and by occasionally securing food bits from the crab’s diet. The crab gains by being camouflaged from the presence of hydras.

Mutualism:

Mutualism occurs when two members of different species become so intimately associated that neither can sur­vive without the other. The protozoa Trichonympha lives in the digestive tract of termites. Trichonympha secretes the enzymes which hydrolyse the cellulose in the termite’s diet of wood.

It has been seen from experiments that if the termite is freed from the presence of the protozoa, it dies of starvation. Trichonympha inside the digestive tract of termites is so adjusted that it cannot survive outside the tract excepting in cystic condition.

Intraspecific interrelationships:

Only under rare and exceptional circum­stances, an individual of a species becomes the sole representative of that species in a given area. The different members of a species living in a habitat form different types of association amongst themselves. These associations result in social organisa­tions, territorial segregations and communica­tions between themselves.

Needs for association:

It is a common observation that animals vary in their ability of moving from place to place. Many animals are free-living. Free-living animals can crawl, swim, walk or fly. Some animals are sessile.

Sessile animals remain permanently attached to rock or any other object available in their habitat. Many marine animals remain in one place for most of their lives. They are called seden­tary. Many animals are planktonic. They float in water and are carried about by the action of currents and winds.

The type of locomotory ability exerts influences on the type of association that is going to be formed. Some animals are solitary. Solitary individuals live alone except during reproductive season. Many animals are gregarious. Gregarious animals form groups, flocks, herds, colonies, etc.