(a) (i) Predation – In this kind of interaction, one organism is prey and the other is predator. It is an inter-specific interaction where organisms of higher trophic levels feed on organisms of lower trophic level. Herbivores are predators as they feed on grass.
Exotic species have no predators hence they grow very rapidly. Example- The prickly pear cactus introduced into Australia and the invasive cactus was brought under control only after a cactus-feeding moth was introduced in the country.
(ii) Interaction either among individuals of same species or between individuals of different species. It is generally believed that competition occurs when closely related species compete for same resources. For instance, in some shallow South American Lakes visiting flamingos and resident fishes compete for their common food, the zooplankton in the lake.
(b) Mutualism confers benefits on both the interacting species. For example, Mycorrhizae is an association between a fungus and roots of higher plants. The fungus helps the plant to absorb the essential nutrients from the soil whereas plant provides the fungus with energy-yielding carbohydrates.
Animal-Plant associations often involve co-evolution of mutualists. The evolutions of the flower and its pollinator species are tightly linked to each other like the fig trees and wasps (pollinator). The fig species can be pollinated only by its partner wasp species. The female wasp uses the fruit not only for laying the egg but also uses the developing seeds of the fruit as nourishment for its larvae and while doing this, it pollinates the inflorescence.
Succession is a process that starts where no living organisms are there – these could be areas where no living organisms ever existed (primary succession) or in the areas that somehow lost all the living organisms that existed there (secondary succession).
Ecological successions in a newly created pond by primary succession –
• There must be soil for the establishment of a new biotic community of diverse organisms.
• The establishment of a new biotic community is generally slow. Depending mostly on climate, it takes hundreds to thousands of years to produce soil on barren rock.
• The pioneer species invade a bare area. In primary succession in water, these are small phytoplanktons.
• These are replaced by rooted submerged plants, rooted floating angiosperms followed by free-floating plants.
• Then there occurs read-swam, marsh-meadow, scrub and trees.
• The climax is finally a forest. With time the water body is converted into land.
Such succession is called Hydrarch succession as it takes place in wetter areas and the successional series progress from hydric to the mesic conditions.
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