This defines the interaction in which two or more species are mutually associated in activities centering on food and one species at least, derives benefit from the association while the other associates are neither benefited nor harmed. Eg. Barnacles attached to Whales travel thousands of miles collecting and filtering food from the moving water. The whales are not affected by the barnacles.

This is the ecological interaction in which an individual species harm another without obtaining benefit, large powerful animals harm weak animals. Eg. animals destroyed at the feet of elephants.

The maximum number of organism that a region can support without environmental degradation is called carrying capacity.

It is the maximum reproductive capacity of an organism under optimum environmental conditions.

(i) Anadromous migration - migration of fishes from sea to fresh water Eg. Salmon.
(ii) Catadromous migration - migration of fishes from fresh water to sea Eg. Eel

They function as Rheoreceptors which is helpful in echolocating objects in water.

Hibernation and aestivation

Ethology is the scientific study of animal behaviour, under natural conditions.

Migration and Courtship

In some aquatic environments, an inverse relationship between water temperature and fish meristic characters is observed - lower the temperature, more the vertebrae.

Warm blooded animals, living in colder climates, tend to have shorter limbs, ears and other appendages when compared to the members of the same species in warmer climates.

Birds and mammals attain greater body size in colder regions than warmer regions (Bergmann's rule).

Niche of an organism can be defined as the total position and function of an individual in its environment.

Species that occupy the same niche in different geographical regions, are termed 'ecological equivalents'

This is the level of exposure of plants to environmental factors that leads to neither injury nor reduction in growth and yield of crops.