Earth consists of three components: Lithosphere (or sphere of Land), Hydrosphere (or sphere of water) and Atmosphere (or sphere of Air).
The life supporting zone of the earth where atmosphere, hydrosphere and lithosphere meet, interact and make life possible, is known as Biosphere (or sphere of life).
The Biosphere consists of smaller functional units known as Ecosystems or Ecological systems.
Relative to the volume of the Earth, the biosphere is only the very thin surface layer which extends from 11,000 meters below sea level to 15,000 meters above.
It is thought that life first developed in the hydrosphere, in the photic zone. Multicellular organisms then appeared and colonized benthic zones.
Terrestrial life developed later, after the ozone layer protecting living beings from UV rays formed.
The Concept of an Ecosystem
An ecosystem can be defined as 'a structural and functional unit of biosphere or segment of nature consisting of community of living beings and the physical environment, both interacting and exchanging materials between them'.
E. P. Odum, a founder of ecology, stated: ‘Any unit that includes all of the organisms (i.e. the "community") in a given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity, and material cycles (i.e. exchange of materials between living and nonliving parts) within the system is an ecosystem.’
Within the ecosystem, species are connected and dependent upon one another in the food chain, and exchangeenergy and matter between themselves and with their environment.
AnEcosystem is a self sustaining structural and functional unit of the biosphere.
The study of ecosystems mainly consists of the study of certain processes that link the living, or biotic, components to the non-living, or abiotic, components.
The ecosystem is composed of two entities, the entirety of life (called the biocenosis) and the medium that life exists in (the biotope).
Ecosystems are interrelated. For example, water may circulate between ecosystems by the means of a river or ocean current. Some species, for example, fish move between fresh-water and marine systems.
These relationships between the ecosystems lead to the concept of a biome. The biosphere comprises all of the Earth's biomes - the entirety of places where life is possible.
A biome is a homogeneous ecological formation that exists over a vast region.Biomes are defined as "the world's major communities, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment" (Campbell). Biomes are classified in various ways. This page will group biomes into five major types: Aquatic, Deserts, Forests, Grasslands and Tundra.
The ecosystem can be units of variable size, such as a pond, a field, etc. A unit of smaller size is called a microecosystem.
A mesoecosystem could be a forest, and a macroecosystem,a whole ecoregion, with its watershed.
Ecosystems can be natural or artificial. Natural ecosystems may be terrestrial (forests, grasslands, deserts and hillsides) as well as aquatic (ponds, rivers, lakes, seacoasts and oceans).
Artificial ecosystems that are man-made are croplands, gardens, parks, aquariums, etc.