• Plants and animals all have a range of limiting (ecological minimum and maximum) for certain environmental factors. The organism will survive provided the temperature, humidity, air etc are maintained within critical limits.
• V.E. Shelford (1913): The law of tolerance – The concept of limiting effect of maximum and minimum.
• Organisms with wide ranges of tolerance of all factors are widely distributed.
• Plants and animals may have a wide range of tolerance for one environmental factor but relatively narrow range of tolerance of another factor.
• Limiting factors not only include the physical factors but also biotic factors.

Physical Factors

1. Soil

• Pedology –Study of soil.
• Soil formation:
  • ​Fragmentation
  • Corrosion – chemical processes of oxidation, reduction hydration hydrolysis, carbonation, etc
  • Organic matter deposition.
• Soil components: Solid, liquid, gaseous, humus – partially decomposed organic matter added to soil.
• Types of soil: Coarser texture soil, loam soil (intermediate texture), clay (fine texture).
• Soil profile (stratification) : Horizon O , Horizon A, Horizon B, Horizon C, R Horizon (rock).
• Soil organism or biota: Burrowing rodents, reptiles, amphibians, earthworm, insects, nematodes, fungi, bacteria, etc.

2. Water

• Plants or animal body contain a large percentage of water, sometimes 90% or more. Animal inhabiting the dry land, it become essential for the organism to adopt in such a way that it can secure and retain sufficient water.
• The water factor on land seriously affects the growth and distribution of animals and plants.
• When moisture conditions of the environment become adverse, the animals either die or migrate to more favorable locations.

3. Temperature

• Temperature ranges affects may activities such as migration, hibernation, and other related activities.
• Homoiotherm (Warm blooded), Poikilotherm (cold blooded),
• Adaptation to is essential for to escape from thermal extremes.
• Hibernation: Poikilotherms (frog, lizard, fishes) sometimes mammals (bear),etc.
• Aestivation: Dormancy during the summer when the temperature is high, environment is excessively dry and food is scarce. In insect is called diapauses – morphological growth and development of animal retarded or suspended e.g. grasshoppers. Ground squirrels of South California – remain hidden in burrows during summer months and tide over the periods of water and food shortage.
• Thermal Migration: Overcoming the extremes of temperature (low or high) is to move out of that area. Larger land mammals such as bear, deer, descend from mountains in sheltered valleys, when the climate becomes too cold. In spring they return to their original homes.
• The rise of temperature of 10°C usually doubling or tripling metabolism in animals.

4. Light

• Controls the growth of and development of the organism.
• Light Composition – ultraviolet, visible and infra red light. Half – infra red produce heat. Visible and ultraviolet also produce heat after they become absorbed.
• Seasonal variation is due to the intensity of light.
• Effect of light: a) metabolism, b) Pigmentation, c) color changes, d) animal migration, etc.

5. Atmospheric Gases

• Air composition: CO₂ -0.03%, O₂ – 21%, N₂ -78 %.

Biotic Factors

• Living elements (organism) of the ecosystem.
• Inter-relationship on organism
  • Symbiosis - Both species is benefited or one is benefited (commensalism).
  • Antagonism – at one species get harm. – a) Parasitism b) Predator prey relationship.