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Ecology

2007 Schools Wikipedia Selection. Related subjects: General Biology

   Ernst Haeckel coined the term oekologie in 1866.
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   Ernst Haeckel coined the term oekologie in 1866.

   Ecology, or ecological science, 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 environment. The environment of an organism includes both
   physical properties, which can be described as the sum of local abiotic
   factors such as insolation (sunlight), climate, and geology, as well as
   the other organisms that share its habitat. The term oekologie was
   coined in 1866 by the German biologist Ernst Haeckel, although it seems
   that Henry David Thoreau had already invented it in 1852 ; the word is
   derived from the Greek οικος (oikos, "household") and λόγος (logos,
   "study"); therefore "ecology" means the "study of the household [of
   nature]".

   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.

Scope

   Ecology is usually considered a branch of biology, the general science
   that studies living organisms. Organisms can be studied at many
   different levels, from proteins and nucleic acids (in biochemistry and
   molecular biology), to cells (in cellular biology), to individuals (in
   botany, zoology, and other similar disciplines), and finally at the
   level of populations, communities, and ecosystems, to the biosphere as
   a whole; these latter strata are the primary subjects of ecological
   inquiries. Ecology is a multi-disciplinary science. Because of its
   focus on the higher levels of the organization of life on earth and on
   the interrelations between organisms and their environment, ecology
   draws heavily on many other branches of science, especially geology and
   geography, meteorology, pedology, chemistry, and physics. Thus, ecology
   is considered by some to be a holistic science, one that over-arches
   older disciplines such as biology which in this view become
   sub-disciplines contributing to ecological knowledge.

   Agriculture, fisheries, forestry, medicine and urban development are
   among human activities that would fall within Krebs' (1972: 4)
   explanation of his definition of ecology: "where organisms are found,
   how many occur there, and why".

   As a scientific discipline, ecology does not dictate what is "right" or
   "wrong". However, ecological knowledge such as the quantification of
   biodiversity and population dynamics have provided a scientific basis
   for expressing the aims of environmentalism and evaluating its goals
   and policies. Additionally, a holistic view of nature is stressed in
   both ecology and environmentalism.

   Consider the ways an ecologist might approach studying the life of
   honeybees:
     * The behavioural relationship between individuals of a species is
       behavorial ecology — for example, the study of the queen bee, and
       how she relates to the worker bees and the drones.

     * The organized activity of a species is community ecology; for
       example, the activity of bees assures the pollination of flowering
       plants. Bee hives additionally produce honey which is consumed by
       still other species, such as bears.
     * The relationship between the environment and a species is
       environmental ecology — for example, the consequences of
       environmental change on bee activity. Bees may die out due to
       environmental changes (see pollinator decline). The environment
       simultaneously affects and is a consequence of this activity and is
       thus intertwined with the survival of the species.

Disciplines of ecology

   Ecology is a broad discipline comprised of 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:
     * Ecophysiology and Behavioural ecology examine adaptations of the
       individual to its environment.
     * Autecology studies the dynamics of populations of a single species.
     * Community ecology (or synecology) focuses on the interactions
       between species within an ecological community.
     * Ecosystem ecology studies the flows of energy and matter through
       the biotic and abiotic components of ecosystems.
     * Landscape ecology examines processes and relationship across
       multiple ecosystems or very large geographic areas.

   Ecology can also be sub-divided according to the species of interest
   into fields such as animal ecology, plant ecology, insect ecology, and
   so on. Another frequent method of subdivision is by biome studied,
   e.g., Arctic ecology (or polar ecology), tropical ecology, desert
   ecology, etc. The primary technique used for investigation is often
   used to subdivide the discipline into groups such as chemical ecology,
   genetic ecology, field ecology, statistical ecology, theoretical
   ecology, and so forth. Note that these different systems are unrelated
   and often applied at the same time; one could be a theoretical plant
   community ecologist, or a polar ecologist interested in animal
   genetics.

History of ecology

Fundamental principles of ecology

Biosphere

   For modern ecologists, ecology can be studied at several levels:
   population level (individuals of the same species), biocoenosis level
   (or community of species), ecosystem level, and biosphere level.

   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.

   It is thought that life first developed in the hydrosphere, at shallow
   depths, in the photic zone. (Although recently a competing theory has
   emerged, that life originated around hydrothermal vents in the deeper
   ocean. See Origin of life.) Multicellular organisms then appeared and
   colonized benthic zones. Photosynthetic organisms gradually produced
   the chemically unstable oxygen-rich atmosphere that characterizes our
   planet. Terrestrial life developed later, after the ozone layer
   protecting living beings from UV rays formed. Diversification of
   terrestrial species is thought to be increased by the continents
   drifting apart, or alternately, colliding. Biodiversity is expressed at
   the ecological level (ecosystem), population level (intraspecific
   diversity), species level (specific diversity), and genetic level.
   Recently technology has allowed the discovery of the deep ocean vent
   communities. This remarkable ecological system is not dependent on
   sunlight but bacteria, utilising the chemistry of the hot volcanic
   vents, are at the base of its food chain.

   The biosphere contains great quantities of elements such as carbon,
   nitrogen and oxygen. Other elements, such as phosphorus, calcium, and
   potassium, are also essential to life, yet are present in smaller
   amounts. At the ecosystem and biosphere levels, there is a continual
   recycling of all these elements, which alternate between the mineral
   and organic states.

   While there is a slight input of geothermal energy, the bulk of the
   functioning of the ecosystem is based on the input of solar energy.
   Plants and photosynthetic microorganisms convert light into chemical
   energy by the process of photosynthesis, which creates glucose (a
   simple sugar) and releases free oxygen. Glucose thus becomes the
   secondary energy source which drives the ecosystem. Some of this
   glucose is used directly by other organisms for energy. Other sugar
   molecules can be converted to other molecules such as amino acids.
   Plants use some of this sugar, concentrated in nectar to entice
   pollinators to aid them in reproduction.

   Cellular respiration is the process by which organisms (like mammals)
   break the glucose back down into its constituents, water and carbon
   dioxide, thus regaining the stored energy the sun originally gave to
   the plants. The proportion of photosynthetic activity of plants and
   other photosynthesizers to the respiration of other organisms
   determines the specific composition of the Earth's atmosphere,
   particularly its oxygen level. Global air currents mix the atmosphere
   and maintain nearly the same balance of elements in areas of intense
   biological activity and areas of slight biological activity.

   Water is also exchanged between the hydrosphere, lithosphere,
   atmosphere and biosphere in regular cycles. The oceans are large tanks,
   which store water, ensure thermal and climatic stability, as well as
   the transport of chemical elements thanks to large oceanic currents.

   For a better understanding of how the biosphere works, and various
   dysfunctions related to human activity, American scientists simulated
   the biosphere in a small-scale model, called Biosphere II.

The ecosystem concept

   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.

   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), 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.

   The concept of an ecosystem can apply to units of variable size, such
   as a pond, a field, or a piece of deadwood. A unit of smaller size is
   called a microecosystem. For example, an ecosystem can be a stone and
   all the life under it. A mesoecosystem could be a forest, and a
   macroecosystem a whole ecoregion, with its drainage basin.

   The main questions when studying an ecosystem are:
     * Whether the colonization of a barren area could be carried out
     * Investigation the ecosystem's dynamics and changes
     * The methods of which an ecosystem interacts at local, regional and
       global scale
     * Whether the current state is stable
     * Investigating the value of an ecosystem and the ways and means that
       interaction of ecological systems provide benefit to humans,
       especially in the provision of healthy water.

   Ecosystems are often classified by reference to the biotopes concerned.
   The following ecosystems may be defined:
     * As continental ecosystems, such as forest ecosystems, meadow
       ecosystems such as steppes or savannas), or agro-ecosystems
     * As ecosystems of inland waters, such as lentic ecosystems such as
       lakes or ponds; or lotic ecosystems such as rivers
     * As oceanic ecosystems.

   Another classification can be done by reference to its communities,
   such as in the case of an human ecosystem.

Dynamics and stability

   Ecological factors which can affect dynamic change in a population or
   species in a given ecology or environment are usually divided into two
   groups: abiotic and biotic.

   Abiotic factors are geological, geographical, hydrological and
   climatological parameters. A biotope is an environmentally uniform
   region characterized by a particular set of abiotic ecological factors.
   Specific abiotic factors include:
     * Water, which is at the same time an essential element to life and a
       milieu
     * Air, which provides oxygen, nitrogen, and carbon dioxide to living
       species and allows the dissemination of pollen and spores
     * Soil, at the same time source of nutriment and physical support
          + Soil pH, salinity, nitrogen and phosphorus content, ability to
            retain water, and density are all influential
     * Temperature, which should not exceed certain extremes, even if
       tolerance to heat is significant for some species
     * Light, which provides energy to the ecosystem through
       photosynthesis
     * Natural disasters can also be considered abiotic

   Biocenose, or community, is a group of populations of plants, animals,
   micro-organisms. Each population is the result of procreations between
   individuals of same species and cohabitation in a given place and for a
   given time. When a population consists of an insufficient number of
   individuals, that population is threatened with extinction; the
   extinction of a species can approach when all biocenoses composed of
   individuals of the species are in decline. In small populations,
   consanguinity (inbreeding) can result in reduced genetic diversity that
   can further weaken the biocenose.

   Biotic ecological factors also influence biocenose viability; these
   factors are considered as either intraspecific and interspecific
   relations.

          Intraspecific relations are those which are established between
          individuals of the same species, forming a population. They are
          relations of co-operation or competition, with division of the
          territory, and sometimes organization in hierarchical societies.

          Interspecific relations— interactions between different
          species—are numerous, and usually described according to their
          beneficial, detrimental or neutral effect (for example,
          mutualism (relation ++) or competition (relation --). The most
          significant relation is the relation of predation (to eat or to
          be eaten), which leads to the essential concepts in ecology of
          food chains (for example, the grass is consumed by the
          herbivore, itself consumed by a carnivore, itself consumed by a
          carnivore of larger size). A high predator to prey ratio can
          have a negative influence on both the predator and prey
          biocenoses in that low availability of food and high death rate
          prior to sexual maturity can decrease (or prevent the increase
          of) populations of each, respectively. Selective hunting of
          species by humans which leads to population decline is one
          example of a high predator to prey ratio in action. Other
          interspecific relations include parasitism, infectious disease
          and competition for limiting resources, which can occur when two
          species share the same ecological niche.

   The existing interactions between the various living beings go along
   with a permanent mixing of mineral and organic substances, absorbed by
   organisms for their growth, their maintenance and their reproduction,
   to be finally rejected as waste. These permanent recyclings of the
   elements (in particular carbon, oxygen and nitrogen) as well as the
   water are called biogeochemical cycles. They guarantee a durable
   stability of the biosphere (at least when unchecked human influence and
   extreme weather or geological phenomena are left aside). This
   self-regulation, supported by negative feedback controls, ensures the
   perenniality of the ecosystems. It is shown by the very stable
   concentrations of most elements of each compartment. This is referred
   to as homeostasis. The ecosystem also tends to evolve to a state of
   ideal balance, reached after a succession of events, the climax (for
   example a pond can become a peat bog).

Spatial relationships and subdivisions of land

   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 biome.

   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.

   Biomes correspond rather well to subdivisions distributed along the
   latitudes, from the equator towards the poles, with differences based
   on to the physical environment (for example, oceans or mountain ranges)
   and to the climate. Their variation is generally related to the
   distribution of species according to their ability to tolerate
   temperature and/or dryness. For example, one may find photosynthetic
   algae only in the photic part of the ocean (where light penetrates),
   while conifers are mostly found in mountains.

   Though this is a simplification of more complicated scheme, latitude
   and altitude approximate a good representation of the distribution of
   biodiversity within the biosphere. Very generally, the richness of
   biodiversity (as well for animal than plant species) is decreasing most
   rapidly near the equator and less rapidly as one approaches the poles.

   The biosphere may also be divided into ecozone, which are very well
   defined today and primarily follow the continental borders. The
   ecozones are themselves divided into ecoregions, though there is not
   agreement on their limits.

Ecosystem productivity

   In an ecosystem, the connections between species are generally related
   to food and their role in the food chain. There are three categories of
   organisms:
     * Producers -- usually plants which are capable of photosynthesis but
       could be other organisms such as bacteria around ocean vents that
       are capable of chemosynthesis.
     * Consumers -- animals, which can be primary consumers (
       herbivorous), or secondary or tertiary consumers ( carnivorous).
     * Decomposers -- bacteria, mushrooms which degrade organic matter of
       all categories, and restore minerals to the environment.

   These relations form sequences, in which each individual consumes the
   preceding one and is consumed by the one following, in what are called
   food chains or food network. In a food network, there will be fewer
   organisms at each level as one follows the links of the network up the
   chain.

   These concepts lead to the idea of biomass (the total living matter in
   a given place), of primary productivity (the increase in the mass of
   plants during a given time) and of secondary productivity (the living
   matter produced by consumers and the decomposers in a given time).

   These two last ideas are key, since they make it possible to evaluate
   the load capacity -- the number of organisms which can be supported by
   a given ecosystem. In any food network, the energy contained in the
   level of the producers is not completely transferred to the consumers.
   And the higher one goes up the chain, the more energy and resources is
   lost and consumed. Thus, from an energy—and environmental—point of
   view, it is more efficient for humans to be primary consumers (to
   subsist from vegetables, grains, legumes, fruit, cotton, etc.) than as
   secondary consumers (from eating herbivores, omnivores, or their
   products, such as milk, chickens, cattle, sheep, etc.) and still more
   so than as a tertiary consumer (from consuming carnivores, omnivores,
   or their products, such as fur, pigs, snakes, alligators, etc.). An
   ecosystem(s) is unstable when the load capacity is overrun and is
   especially unstable when a population doesn't have an ecological niche
   and overconsumers.

   The productivity of ecosystems is sometimes estimated by comparing
   three types of land-based ecosystems and the total of aquatic
   ecosystems:
     * The forests (1/3 of the Earth's land area) contain dense biomasses
       and are very productive. The total production of the world's
       forests corresponds to half of the primary production.
     * Savannas, meadows, and marshes (1/3 of the Earth's land area)
       contain less dense biomasses, but are productive. These ecosystems
       represent the major part of what humans depend on for food.
     * Extreme ecosystems in the areas with more extreme climates --
       deserts and semi-deserts, tundra, alpine meadows, and steppes --
       (1/3 of the Earth's land area) have very sparse biomasses and low
       productivity
     * Finally, the marine and fresh water ecosystems (3/4 of Earth's
       surface) contain very sparse biomasses (apart from the coastal
       zones).

   Humanity's actions over the last few centuries have seriously reduced
   the amount of the Earth covered by forests ( deforestation), and have
   increased agro-ecosystems (agriculture). In recent decades, an increase
   in the areas occupied by extreme ecosystems has occurred (
   desertification).

Ecological crisis

   Generally, an ecological crisis occurs with the loss of adaptive
   capacity when the resilience of an environment or of a species or a
   population evolves in a way unfavourable to coping with perturbations
   that interfere with that ecosystem, landscape or species survival.

   It may be that the environment quality degrades compared to the species
   needs, after a change in an abiotic ecological factor (for example, an
   increase of temperature, less significant rainfalls).
   It may be that the environment becomes unfavourable for the survival of
   a species (or a population) due to an increased pressure of predation
   (for example overfishing).
   Lastly, it may be that the situation becomes unfavourable to the
   quality of life of the species (or the population) due to a rise in the
   number of individuals ( overpopulation).

   Ecological crises may be more or less brutal (occurring within a few
   months or taking as long as a few million years). They can also be of
   natural or anthropic origin. They may relate to one unique species or
   to many species (see the article on Extinction event).

   Lastly, an ecological crisis may be local (as an oil spill) or global
   (a rise in the sea level due to global warming).

   According to its degree of endemism, a local crisis will have more or
   less significant consequences, from the death of many individuals to
   the total extinction of a species. Whatever its origin, disappearance
   of one or several species often will involve a rupture in the food
   chain, further impacting the survival of other species.

   In the case of a global crisis, the consequences can be much more
   significant; some extinction events showed the disappearance of more
   than 90% of existing species at that time. However, it should be noted
   that the disappearance of certain species, such as the dinosaurs, by
   freeing an ecological niche, allowed the development and the
   diversification of the mammals. An ecological crisis thus paradoxically
   favored biodiversity.

   Sometimes, an ecological crisis can be a specific and reversible
   phenomenon at the ecosystem scale. But more generally, the crises
   impact will last. Indeed, it rather is a connected series of events,
   that occur till a final point. From this stage, no return to the
   previous stable state is possible, and a new stable state will be set
   up gradually (see homeorhesy).

   Lastly, if an ecological crisis can cause extinction, it can also more
   simply reduce the quality of life of the remaining individuals. Thus,
   even if the diversity of the human population is sometimes considered
   threatened (see in particular indigenous people), few people envision
   human disappearance at short span. However, epidemic diseases, famines,
   impact on health of reduction of air quality, food crises, reduction of
   living space, accumulation of toxic or non degradable wastes, threats
   on keystone species (great apes, panda, whales) are also factors
   influencing the well-being of people.

   During the past decades, this increasing responsibility of humanity in
   some ecological crises has been clearly observed. Due to the increases
   in technology and a rapidly increasing population, humans have more
   influence on their own environment than any other ecosystem engineer.

   Some usually quoted examples as ecological crises are:
     * Permian-Triassic extinction event 250 million of years ago
     * Cretaceous-Tertiary extinction event 65 million years ago
     * Global warming related to the Greenhouse effect. Warming could
       involve flooding of the Asian deltas (see also ecorefugees),
       multiplication of extreme weather phenomena and changes in the
       nature and quantity of the food resources (see Global warming and
       agriculture). See also international Kyoto Protocol.
     * Ozone layer hole issue
     * Deforestation and desertification, with disappearance of many
       species.
     * The nuclear meltdown at Chernobyl in 1986 caused the death of many
       people and animals from cancer, and caused mutations in a large
       number of animals and people. The area around the plant is now
       abandoned by humans because of the large amount of radiation
       generated by the meltdown. Twenty years after the accident, the
       animals have returned.

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