It is the maintenance of a functional dynamic balance or state of equilibrium amongst various components of an ecosystem. Homeostasis is maintained through a number of controls/cybernetics/ limitations like:
(i) Carrying Capacity:
It is the maximum number of individuals the environment can support. Near it, the rate of population growth begins to decline. Beyond it, the population decreases rapidly.
(ii) Recycling of Wastes:
It controls the availability of raw materials and space.
(iii) Self regulation:
Mortality decreases and natility increases in case of small population while reverse is true in case of larger population.
(iv) Feedback System:
It is of two types, positive and negative. In positive feedback the increased availability of a resource increases number of utilisers.
For example, predator population will increase with the increase in population of prey. In negative feedback, the increase in number of members of a higher trophic level will decrease the number of individuals at the lower level which in turn shall reduce their number as well.
Habitat: It is a specific place/locality delimited by a combination of factors and barriers where an individual/population/community resides, e.g. pond, desert, river, bark of tree, burrow, and intestine.
It is part of the habitat having a specific property, e.g. forest floor, tree canopy, tree trunk, edge of a pond.
It is specific/part of habitat occupied by individuals of a species which is circumscribed by its range of tolerance, range of movement, microclimate, type of food and its availability, shelter, type of predator, timing of activity. Tadpole and adult frog occupy different ecological niches as the former is herbivorous aquatic while the latter is carnivorous amphibian.
Water Bug and water Boatman live in shallow edges of ponds but occupy different niches as the former is predator while the latter scavenger. Both owl and cat feed on shrews and mice. They occupy the same niche because of being ecological equivalents though their habitats are different.
Raunkiarer (1934) has distinguished plants into five forms on the basis of size, shape, branching, crown, life span and perennation.
Annual plants which perennate in the form of seeds.
Perennial plants with underground storage parts,
Subterranean perennating structures (root, root tuber, bulb, stem tuber, rhizome, and corm).
(Marshy plants). Perennating structures are embedded in mud.
Peremating structures occur at ground level. Aerial shoots die on the onset of winter, e.g. rosette plants.
Small plants of cold areas where perennating buds or shoot apices lie at or above the ground level.
Pernnial herbs, shrubs, and trees, epiphytes, succulently lianas etc. where perennating buds occur at 10 cm or more high above ground level.