Organism and Population

Download PDF


The term ecology was coined and described by Ernst Haeckel. The term ecology was first authentically used by Reiter. The very first term of ecology was employed for the study of plants by Warming. Further ecological hierarchy is given by: Organism-----Population------ecosystem-------Landscape--------biome--------Biosphere. Their size and complexity increase towards the higher level i.e biosphere. 

Branches of Ecology

Based on organism level, branches of ecology are of two types:

  • Autecology: Study of the interaction of a population with its environment is known as autecology.

  • Synecology: Study of the interaction of a population of a community with its environment is known as synecology. 

Types of Biome

There are different types of biome based on their living habitat and nature of adapting capacity, some of the important biome are discussed below:

  • Terrestrial Biome: A large area of land is delimited by a specific climatic zone, having a particular major vegetation zone and its associated fauna, e.g., tundra desert, temperate deciduous forest, tropical rainforest, ocean, etc. They exist above the sea surface of any place. Temperature and light intensity is maximum at the equator, decreasing gradually towards the pole. 

  • Tundra Biome: This region lies above 60 degrees north latitude is known as tundra. In this region, the soil is covered by snow and ice for almost the whole of the year. At 3600 meter height, Himalaya is called Alpine tundra. The annual rainfall is low and generally below 25cm/year. This biome is without a tree so it is called a treeless biome. The trees and shrubs are absent in the biome so it is also known as Arctic desert. It is the most delicate and fragile biome. In this biome vegetation are lichens, mosses, grasses, etc and the animals which can survive in this area are Fox, reindeer, migratory birds, polar bear, etc. 

  • The Northern Coniferous or Needle-Leaf Forests: The northern and temperate coniferous forests are also known as Taiga or North wood forest. These are situated immediately south of the tundra. They are distributed over 1700 to 3000 meter altitude in Himalaya. 

  • Annual rainfall is 50-170 cm/year and the average winter temperature is 6 degrees and 20 degrees in summer.

  • Temperate deciduous forests: The deciduous forest lies in a temperate zone about 40 degrees to 60 degrees north latitude and 1500-2400 meter altitude central location. Annual rainfall is about 100-250 cm. Here most common vegetation is Oak, Maple, Hickory beech, etc and their trees shed leaves in autumn and bear again in spring. The most common animals in this area are turtles, lizards, rabbits, deer, etc.  

  • Tropical Rainforest: the tropical rainforest biome lies in the equatorial region around the earth. In tropical rain forests are found in Eastern Himalayas and western ghats. Tropical rain forests are present in Assam, West Bengal, Kerala and Andaman in India. The main feature of this biome is the large amount of annual rainfall which is more than at least 200-300 cm per year. The tropical rain forests are rich in flora and fauna. The temperature is high and uniform throughout the year and the climate is warm and humid. 

  • Tropical deciduous forest Occurs widely in the northern and southern parts of our country in plain and low hilly areas. Annual rainfall is about 90-160cm/year. Leaves of most of the trees fall before the summer. The most common vegetation of this forest is sal, teak, tendu, khair, etc.

  • The Grassland Biome: Annual rainfall ranges from 25-75 cm. Winter and summer have a longer duration and maximum rainfall occurs in summer. Examples of some grassland biomes are Pampas, Tussocks, Veldts, Prairies, etc. 

Abiotic Environmental Factors 

Key elements that lead to so much variation in the physical and chemical conditions of different habitats are temperature, water, light, soil, and topography:

  • Temperature: Temperature is measured by the thermometer and underwater by the thermistor. Temperature is the most ecologically relevant environmental factor. The temperature on land depends on various factors like season, decreasing progressively from the equator towards the poles and from plains to the mountain tops. 

It ranges from the subzero level in polar areas and high altitudes to > 500C in from plains to mountain tops. There are so many unique habitats in terms of temperature such as thermal springs and deep-sea hydrothermal vents where average temperatures exceed 1000C. It is known that mango trees do not grow in temperate countries like Canada and Germany, Snow leopards are not found in Kerala forest and tuna. 

The extent to which organisms can tolerate temperature defines the geographical distribution of organisms. Thermal stratification in lakes: Thermal stratification occurs in deep water bodies because of the difference in temperature of water at different depths.

  • Water: Next to temperature, water is the most important factor influencing the life of organisms. Organisms living in oceans, lakes, and rivers face many water-related problems. Some organisms can tolerate a wide range of salinities but others are restricted to a narrow range(stenohaline). There are so many freshwater animals that cannot live for a long time in seawater and vice versa because of the osmotic problems they would face. 

  • Light: It is a complex physical environment factor. It is an electromagnetic spectrum. Light is measured by a lux meter or photometer. 

  • Solar constant: Solar radiation before entering the atmosphere carries energy at a constant rate i.e 2 cal/cm square/ min known as the solar constant. 

  • Soil: Soil is the uppermost layer of the earth crust formed by weathering of rocks. It is a mixture of living or non-living materials. A typical soil consists of minerals 45% + water 25% + Air 25% + organic matter (living non living) 5%. Soil formation is a slow process ( 1 inch of soil is formed in 500-1000 years ). 


It includes the physical features of the earth like altitude, slope, exposure, mountain chains, valleys, etc. It affects the distribution of organisms by influencing climatic factors like light, wind, rainfall, etc. 

Response of Abiotic Factors

During evolution, many species would have evolved a relatively constant internal environment that permits all biochemical reactions and physiological functions to proceed that maximal efficiency and this will increase the overall fitness of the species. This constancy, for example, could be in terms of optimal temperature and osmotic concentration of body fluids. On the basis of response to environmental factors organisms are of two types-regulators and conformers. 

A. Regulators: Some organisms are able to maintain homeostasis by physiological means which ensure constant body temperature, constant osmotic concentration, etc. All birds and mammals and a very few lower vertebrates and invertebrates species are also capable of thermoregulation and osmoregulation. 


Organisms that cannot maintain a constant internal environment with the changing external environment are called conformers. An overwhelming majority of animals and nearly all plants cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. 

Adaptations: An ability of an organism that enables an organism to survive and reproduce in its habitat.   

Adaptation for Temperature: Temperature affects the absolute size of an animal and its body parts. 

Share this with your friends