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<p><strong>Ecology</strong> (from Greek: οίκος, <em>oikos</em>, "household"; and λόγος, <em>logos</em>, "knowledge") is the scientific study of the distribution and abundance of living organisms and how the distribution and abundance are affected by interactions between the organisms and their Ecosystem includes both physical properties, which can be described as the sum of local abiotic factors such as insolation (sunlight), climate, and geology, and biotic factors, which are other organisms that share its habitat. The term <em>oekologie</em> was coined in 1866 by the German biologist Ernst Haeckel.</p>
<p>The word "ecology" is often used in common parlance as a synonym for the natural environment or environmentalism. Likewise "ecologic" or "ecological" is often taken in the sense of environmentally friendly. </p>
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<h2><span class="mw-headline">Scope</span></h2>
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<h3><span class="mw-headline">Disciplines of ecology</span></h3>
<p>Ecology is a broad discipline comprising many sub-disciplines. A common, broad classification, moving from lowest to highest complexity, where complexity is defined as the number of entities and processes in the system under study, is:</p>
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<h2><span class="mw-headline">History of ecology</span></h2>
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<h2><span class="mw-headline">Fundamental principles of ecology</span></h2>
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<h3><span class="mw-headline">Biosphere</span></h3>
<p>For modern ecologists, ecology can be studied at several levels: population level (individuals of the same species in the same or similar environment), biocoenosis level (or community of species), ecosystem level, and biosphere level.</p>
<p>The outer layer of the planet Earth can be divided into several compartments: the hydrosphere (or sphere of water), the lithosphere (or sphere of soils and rocks), and the atmosphere (or sphere of the air). The biosphere (or sphere of life), sometimes described as "the fourth envelope", is all living matter on the planet or that portion of the planet occupied by life. It reaches well into the other three spheres, although there are no permanent inhabitants of the atmosphere. 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.</p>
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<h3><span class="mw-headline">The ecosystem concept</span></h3>
<p>The first principle of ecology is that each living organism has an ongoing and continual relationship with every other element that makes up its environment. An ecosystem can be defined as any situation where there is interaction between organisms and their environment.</p>
<p>The ecosystem is composed of two entities, the entirety of life, the biocoenosis, and the medium that life exists in, the biotope. Within the ecosystem, species are connected by food chains or food webs. Energy from the sun, captured by primary producers via photosynthesis, flows upward through the chain to primary consumers (herbivores), and then to secondary and tertiary consumers (carnivores and omnivores), before ultimately being lost to the system as waste heat. In the process, matter is incorporated into living organisms, which return their nutrients to the system via decomposition, forming biogeochemical cycles such as the carbon and nitrogen cycles.</p>
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<h3><span class="mw-headline">Dynamics and stability</span></h3>
<p><strong>Ecological factors</strong> which affect dynamic change in a population or species in a given ecology or environment are usually divided into two groups: abiotic and biotic.</p>
<p><strong>Abiotic factors</strong> are geological, geographical, hydrological and climatological parameters. A <strong>biotope</strong> is an environmentally uniform region characterized by a particular set of abiotic ecological factors. Specific abiotic factors include:</p>
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<h3><span class="mw-headline">Spatial relationships and subdivisions of land</span></h3>
<p>Ecosystems are not isolated from each other, but are interrelated. For example, water may circulate between ecosystems by the means of a river or ocean current. Water itself, as a liquid medium, even defines ecosystems. Some species, such as salmon or freshwater eels move between marine systems and fresh-water systems. These relationships between the ecosystems lead to the concept of a <em>biome</em>.</p>
<p>A biome is a homogeneous ecological formation that exists over a large region as tundra or steppes. The biosphere comprises all of the Earth's biomes -- the entirety of places where life is possible -- from the highest mountains to the depths of the oceans.</p>
