1. Eurythermal: Organisms which can tolerate a wide range of temperature fluctuations.
2. Stenohaline: Organisms which can withstand only small range of salinity.
3. These variations the organisms also grow in different environment.

The interaction of organisms with their environment results in the establishment of grouping of organisms
Levels of ecological hierarchy

The differences between habitat and niche are as follows.

S. No	Habitat	Niche
1	A specific physical space occupied by an organism (species).	A functional space occupied by an organism in the same eco-system
2	Same habitat may be shared by many organisms (species).	A single niche is occupied by a single species.
3	Habitat specificity is exhibited by organism.	Organisms may change their niche with time and season

Soil is commonly stratified into horizons at different depth. These layers differ in their physical, chemical and biological properties. This succession of super-imposed horizons is called soil profile.
Horizon Description O-Horizon (Organic horizon) Humus It consists of fresh or partially decomposed organic matter.
01 - Freshly fallen leaves, twigs, flowers and fruits.
02 - Dead plants, animals and their excreta decomposed by micro-organisms.
Usually absent in agricultural and deserts. A-Horizon
(Leached horizon)
Topsoil - Often rich in humus and minerals. It consists of top soil with humus, living creatures and in-organic minerals.
A1 - Dark and rich in organic matter because of mixture of organic and mineral matters.
A2 - Light coloured layer with large sized mineral particles. B-Horizon (Accumulation horizon) (Subsoil - Poor in humus, rich in minerals) It consists of iron, aluminium and silica rich clay organic compounds. C - Horizon (partially weathered horizon) Weathered rock Fragments - Little or no plant or animal life. It consists of parent materials of soil, composed of little amount of organic matters without life forms. R-Horizon (Parent material) Bedrock It is a parent bed rock upon which underground water is found.