Population Interactions

Population Interaction

I. Predation

1. It is an interspecific interaction, where an animal, called predator, kills and consumes the other weaker animal called prey.

2. Predation is nature's way of transferring energy to higher trophic levels, e.g., a tiger (predator) eating a deer (prey), a sparrow (predator) eating fruit or seed (prey), etc.

II. Competition

1. Competition is a type of interaction where both the species suffer. It may exist between some species (interspecific competition) or between individuals of same species (intraspecific competition).

2. The competition occurs due to limited resources between closely related species.

3. Some totally unrelated species could also compete for the same resource, e.g., in some shallow south American lakes, visiting flamingoes and resident fishes compete for their common food, zooplanktons.

4. In interspecific competition, the feeding efficiency of one species might be reduced due to the interfering and inhibitory presence of the other species, although the resources are abundant.

5. For example, after the introduction of goats in Galapagos Islands, the Abingdon tortoise became extinct within a decade due to greater browsing efficiency of the goats.

6. Competitive release refers to the phenomenon of a species whose distribution is restricted to a small geographical area because of the presence of a competitively superior species, is found to expand its distributional range dramatically when the competing species is experimentally removed.

III. Parasitism

It is the mode of interaction between two species in which one species (parasite) depends on the other species (host) for food and shelter, and in this process damages the host. In this process one organism is benefited (parasite) while the other is being harmed (host).

Adaptation of parasite:

1. The parasite has evolved to be host-specific in such a manner that both host and parasite tend to co-evolve.

2. Loss of unnecessary sense organs.

3. Presence of adhesive organs or suckers.

4. Loss of digestive system.

5. High reproductive capacity.

IV. Commensalism

Commensalism is referred to as the interaction between two species where one species is benefited and the other is neither harmed nor benefited.

Few examples of commensalism:

1. An orchid growing as an epiphyte on a mango tree. The orchid gets shelter and nutrition from mango tree while the mango tree is neither benefited nor harmed.

2. Barnacles growing on the back of whale. Barnacles are benefited to move to location for food as well as shelter while the whales are neither benefited nor harmed.

3. The egrets are in close association of grazing cattle. The cattle egrets are benefited by the cattle to detect insects because cattle stir up the bushes and insects are flushed out from the vegetation, to be detected by cattle egrets.

4. The commensalism is also found between sea anemones and the clown fish. The fish is protected from predators and sea anemones are neither benefited nor harmed.

V. Amensalism

1. Amensalism is referred to as the interaction between two different species, in which one species is harmed and the other is neither benefited nor harmed.

2. For example, the mould Penicillium secretes penicillin which kills bacteria but the mould is unaffected.

VI. Mutualism

Mutualism is referred to as the interspecific interaction in which both the interacting species are benefited.

Some examples of mutualism

1. Lichens represent close association between fungus and photosynthetic algae or cyanobacteria, where the fungus helps in the absorption of nutrients and provides protection while algae or cyanobacterium prepares the food.

2. Mycorrhizae are close mutual association between fungi and the roots of higher plants, where fungi help the plant for absorption of nutrients while the plant provides food for the fungus.

3. Mutualism are found in plant-animal relationships. Plants take the help of animals for pollination and dispersal of their seeds and animals are rewarded in the form of nectar or edible pollen or oviposition (site for laying egg).

4. The male bee pseudocopulates with it and during this process of pseudocopulation, the pollen grains are dusted on the body of male bees.

5. With such pollen dusts, male bee pseudocopulates to another flower of the same species and pollination takes place.

6. Sexual deceit is the process in which petal of orchid flower bears an uncanny resemblance to the female of the bee in size, colour and markings to attract the male bee for pollination