In this article we will discuss about the interaction between different species.
In the great web of life, which exists in nature, living organisms not only live in an environment, but are also themselves a part of the dynamic environment for other organisms.
The relationship between one species and another within a community has evolved through their interactions, based on the requirement and the mode of nutrition and shelter and also on the habits of species. The relationships between members of different populations are termed interspecific relations.
The interactions between populations of species in a community are broadly divided into two categories:
(i) Positive (beneficial) and
(ii) Negative (inhibition) interactions.
This depends upon the nature of effect on the interacting organisms of different species.
Positive Interactions:
Symbiosis or Mutualism:
When two species live together in a close association that is helpful to both species, the relationship is known as symbiosis. The oxpecker bird and the rhinoceros exhibit this relationship. The oxpecker receives protection and obtains food from the ticks and other pests infesting the rhino’s skin.
The rhino receives cleaning and warning of approaching dangers. Algae and fungi live together in symbiotic relationship in lichens, whereas the fungi live on the roots of higher plants, and the association is known as mycorrhiza. In lichens, the algae are able to produce food by photosynthesis, and the fungi obtain water and minerals and provide attachment for the lichen.
The bacterium Rhizobium leguminosarum found in the root nodules of leguminous plants fixes atmospheric nitrogen in the soil in the form of nitrates which is used by the plant, and in return plant supplies water, minerals and organic food to the bacterium. The cyanobaterium Anabaena also lives in symbiotic association with water fern Azolla. Bacteria in the gut of some domestic animals help in cellulose digestion.
Sea anemone is a typical example of facultative mutualism, wherein animal gets attached to the shell of hermit crab. The sea anemone growing on the back of the crab provides camouflage and protection, and in turn, the sea anemone is transported to reach new sources of food. This type of mutualism in called protoco-operation.
Green Hydra presents another example of mutualism, this animal has green photosynthetic alga in the protective ectoderm. The alga gives off oxygen benefitting the animals which, in turn supplies CO2 and nitrogen to the plant.
Commensalism:
Some organisms live together so that one organism benefits by the relationship while the other organism is neither helped nor harmed. This type of relationship is known as commensalism. An example of this association is the relationship between the shark and the small remora fish.
The remoras may attach themselves to the shark as it swims through the water. When the shark finds food, the remoras eat some of the food not consumed by the shark. The shark is not harmed by the remora, while the remora is helped. The attachment of the sedentary sea anemone to the body of a hermit crab and barnacles to a whale are other examples of commensalism.
Some epiphytes, such as orchids, mosses, ferns, etc., are the best examples. Epiphytes depend upon the other trees for support and nutrients. They manufacture their own food but do not help the supporting plant any way.
Several woody climbers (lianas) take the support of the trees for exposing their canopy above ground without doing any harm to the supporting trees.
Negative Interactions:
Certain interactions between different species give rise to negative effect on either or both species. Parasitism and predation are interaction where one species gains and the other suffers. While in the interaction called competition both species are harmed.
Parasitism:
This is a relationship in which one organism, the parasite spends much or all of its life living in or another organism, the host. The parasite is dependent upon the host for food.
The parasite benefits from the relationship and the host is always harmed. Parasites may bring about the death of their host, but most often only weaken their host. Human parasites may be external (ectoparasites) such as body lice, ticks, mites and leeches, or internal (endoparasites) such as tapeworms, some types of roundworms, malarial parasite, microfilaria and guineaworm.
The dodder (Cuscuta), broomrape (Orobanche), mistletoe (Viscum), Dendrophthoe, Striga and Rafflesia are parasitic plants. Certain bacteria are parasitic on human beings and animals and cause fatal diseases such as Vibrio coma (cholera), Mycobacterium tuberculosis (tuberculosis).
Salmonella typhosa (typhoid fever), Mycobacterium leprae (leprosy), etc. A large number of fungi are parasitic on several crop plants causing diseases like rusts, smuts, blights, mildews and wilts.
A parasite usually parasitizes a host which is larger in body size than it, and ordinarily it does not kill the host, at least not until it has completed its reproductive cycle.
Predation:
This is commonly associated with the idea of strong attacking the weak such as the tiger pouncing upon the deer, the hawk upon the sparrow, and the frog upon the insects and so on. A species such as the frog may be both a prey and a predator. The relationship between a snake and a rat is more than that between a prey and a predator as the snake also seeks shelter in the rat holes.
Thus “predation represents a direct and often complex interaction of two or more species, of the eaters and being eaten.” This is a negative interaction which results in negative effects on the growth and survival of one of the two populations.
In this type of association and interaction one species (predator) kills and feeds on second species (prey). Predation is important process in the community dynamism. Predator is always stronger than pery. From population ecology point of view predation is the action and reaction in the transfer of energy from one trophic level to the other.
It represents a direct and complex interaction between two or more species of eaters and eaten.
Parasites and predators have some points of difference, they are as follows:
Parasites, like the predators, limit the population of the host species, but they are generally host-specific, and do not have choice or alternatives like predators.
Parasites are smaller in size and have higher biotic or reproductive potential composed to the predators.
Parasites have poor means of dispersal and require specialised structures to reach or invade the host. While the predators are quite mobile and swift, and capable of capturing the prey.
However, newly acquired predators and parasites are more damaging than the older ones, as the latter are familiar and the species getting affected have adjusted by then.
Competition:
The amount of food, light, space, minerals and water that are available in a particular habitat is limited. As a result, organisms are in competition with one another for one or more of these factors. Competition occurs not only among individuals of a given species but also between members of two or more species.
For instance, carnivorous animals such as tigers and leopards, compete for the prey. The members of kingdom Plantae, such as trees, shrubs and herbs in a forest are to compete for sunlight, nutrients and water and biological agents for pollination and dispersal.
Populations may compete directly, leading to the extinction or adaptation of one of them. Many animals establish territories within which they live and which they will defend against other of their species who try to intrude. By staying in their own territories, competition and combat are lessened.
This is of two types:
(i) Interspecific competition occurs between the individuals of the same species and their requirements are common and,
(ii) Interspecific competition occurs between individuals of two different species occurring in a habitat.
Generally the intraspecific competition is more intense than interspecific competition. Requirements of individuals of same species are similar, and therefore, competition is more intense.
Scavanging:
This is a type of direct food relationship where animals such as a vulture or hyena, or a jackal feed on other animals which have died naturally or have been killed by another animal. For instance, the omnivorous animals such as the common crow consume many types of foods including dead animals.
Other Relationships:
Many insects, reptiles, birds and mammals get shelter and protection on trees and shrubs. Many animals protect them by a highly interesting device, called mimicry. This phenomenon is seen in many insects where they develop a superficial resemblance in shape and colour to specific plant parts on which they live.
The examples are—the stick insect (Carausius morosus) mimics thin dry branches; the dead leaf butterfly (Kalima parolecta) resembles a dry leaf, whereas the praying mantis (Mantis religiosa) and Rhyllium frondosum resemble with the green leaves. By their mimicry, they conceal themselves from predators and other foes.
For the survival of a community, the availability of the other nonliving components is also important, and sometimes one of the components plays a dominant role in determining the character of the community. For example, a community having fruit bearing trees may consist mainly of fruit eating animals, such as bats and insects.
On the other hand, in a grassland there will be only seed eating birds, mice, voles and predatory birds living on others lower down the food chain. In a marshy land, frogs, toads, fish, aquatic insects and water birds which feed on aquatic insects are maximum.
Aquatic plants adapted to different intensities of light may be found either at the surface or at different depths in water. Thus the environmental factors act as the determinants of the types of individuals in a community.