Organisms in ecological communities interact with each other in four major ways:
Predation:
One organism (by its activities) may benefit itself, while harming the others. For example organisms of one species may eat the organisms of other species.
i) Consumers that hunt other organisms are called predators.
ii) The organisms upon which predator feeds are called prey.
iii) For example frog eats an insect. Frog is predator and insect is prey. But frog itself is prey for other organisms like snakes and so on.
iv) A large prey population can support more predators. So number of prey should be greater than predators to support community.
Parasitism:
One type of organism may obtain its food from others, but may not kill it. For example host-parasite interaction.
i) In this process, organisms feed on the tissues or body fluids of another.
ii) Organism on which a parasite feed is called host.
iii) But a parasite is harmful to host and even may be fatal.
iv) Parasites depend on the body of host for many functions.
v) A large host population can support large parasites. Density of host population can affect the population of parasites. '
Competition: -
Two organisms may harm one another. This type of interaction IS common when two organisms use the _me resources and the resources are insufficient to supply their
combined needs. Such organisms are called competitors.
i) Competition occurs when two or more organism attempt to use common resources such as food, water, shelter etc.
ii) Resources are limited in environment and decrease by continuous usage.
iii) Competition between individuals of a population is called intra specific competition. While competition between different species is called inter specific competition.
Symbiosis:
Organisms of two species may develop an intimate, long term relationship or association called symbiosis. In this process both organisms may benefit each other.
Or one organism may obtain benefit from other without harming it.
i) A symbiotic relationship which benefit one but neither help other nor harm is called commensalisms. For example lichens growing on trees.
ii) A symbiotic relationship in which both species benefit is called mutualism. For example relationship between flowers and insects. Insects collect nectar and in
turn help in pollination of flowers.