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The term ecology is derived from the Greek words Oikos, meaning home or place to live in, and logos, meaning study. Literally, it translates to the study of the home of nature. Ecology is formally defined as the scientific study of the relationship of living organisms with each other and with their environment. It deals with the ways in which organisms are moulded by their environment, how they make use of environmental resources, and how processes such as energy flow and mineral cycling occur in nature.

History of Ecology

The roots of ecology lie in Natural History, which is as old as human civilization itself. Since early history, humanity has engaged in ecology in a practical manner, both knowingly and unknowingly. In primitive societies, every individual was required to possess an intimate knowledge of their environment for survival, which included understanding the forces of nature as well as the plants and animals surrounding them.

Ancient Indian texts contain numerous references to ecological principles. The classical texts of the Vedic period, such as the Vedas, the Samhitas, the Brahmanas, and the Aranyakas-Upanishads, feature many references to ecological concepts. The prominent Indian treatise on medicine, the Charaka-Samhita, and the surgical text, the Sushruta-Samhita, demonstrate that people during this period had a sophisticated understanding of plant and animal ecology. These texts classify animals based on their habit and habitat, and categorize land in terms of the nature of soil, climate, and vegetation. They also provide descriptions of plants typical to various localities. The Charaka-Samhita notably contains information indicating that air, land, water, and seasons were indispensable for life, and recognized early on that polluted air and water were injurious to health.

Environment and its Components

Everything that surrounds or affects an organism during its lifetime is collectively known as its environment. The environment is defined as the sum total of living and non-living components, influences, and events surrounding an organism. All organisms, ranging from viruses to humans, are obligatorily dependent on other organisms and their environment for essential needs such as food, energy, water, oxygen, and shelter.

The relationship and interaction between an organism and its environment are highly complex. The environment comprises both living (biotic) and non-living (abiotic) components. Furthermore, the environment is never static; both biotic and abiotic factors exist in a state of flux and keep changing continuously.

Abiotic ComponentsBiotic ComponentsEnergyGreen plantsRadiationNon-green plantsTemperature & heat flowDecomposersWaterParasitesAtmospheric gases and windSymbiontsFireAnimalsGravity, Topography, Soil, Geologic substratumMan

To understand this practically, one can analyze the environment of a fish in a pond. The external environment of the fish consists of abiotic components such as light, temperature, and the water in which nutrients, oxygen, other gases, and organic matter are dissolved. The biotic external environment consists of microscopic organisms called plankton, alongside aquatic plants, other animals, and decomposers. Conversely, the internal environment of the fish is enclosed by its outer body surface. This internal environment is relatively stable compared to the external environment, though it is not absolutely constant. Factors such as injury, illness, or excessive stress can upset this internal balance. As a critical limitation, if a marine fish is transferred to a freshwater environment, it will be unable to survive due to the drastic change in external conditions clashing with its internal requirements.

Levels of Organisations in Ecology

The study of ecology is generally organized into several m