Ecology is the branch of science that studies the distributionand abundance of living organisms , their habitats , and the interactions between them and their environment — which includes both abiotic (non-living) elements like climate and geology , and biotic ones like other species. The term was coined in 1866 by the German biologist ErnstHaeckel from the Greek oikos meaning "household" andlogos meaning "science:" the "study of the household of nature."
Human ecology is a related but distinct academicdiscipline which studies humankind , the organized activity of this species, andits environment; it overlaps biological ecology, sociology , and otherdisciplines.
Outside scientific contexts, the word ecology is often used as synonym of "the environment ", i.e. the ensemble of all wild organisms that are livingmostly in their ages-old environment and manner, with little human interference; and especially of that part of it that is mostimportant to humans , for any reason — economical , medical , aesthetical , hedonistic , sentimental, etc.. This sense usuallyapplies when one says that something is good or bad for the "ecology", and in political ecology .
Others may use the word ecology to mean not a science, but a philosophical or even religious system, which implies a specificvision of the universe and specific values and moral imperatives — e.g. that the totality of life is a coherent system,possibly with a purpose; that the extinction of higher species is "bad"; that people should live in harmony with other livingbeings; and that nature should be protected from human interference. Ecology in this sense is also called environmentalism .
Ecology is usually considered a branch of biology , the general science thatstudies living beings . These can be studied at several levels, from proteins and nucleic acids (in biochemistry and molecular biology ), cells (in cellular biology ), organisms (in botanics , zoology , and other similar disciplines), and finally at thelevel of populations, communities, and ecosystems — which are the subjectsof ecology. Conversely, some people consider ecology to be the parent discipline and biology to be the sub-disciple, since ecology includes not only the interactions between organsisms, but also theirinteractions with their surroundings.
Because of its focus on the broadest level of life and on the interrelations between living beings and their environment , ecology draws heavily on other branches ofscience, such as geology and geography , meteorology , pedology , chemistry , and physics . For this reason, ecology is often said to be a holistic science.
Disciplines of ecology
Ecology is a broad science that encompasses many specialized branches, including
Ecology also plays important roles in many inter-disciplinary fields:
Finally, ecology has also inspired (and lent its name to) other non-biological disciplines such as
Fundamental principles of ecology
Biosphere and biodiversity
The Earth, from an ecological point of view, consists of several compartments, the hydrosphere (or sphere of water), the lithosphere (orsphere of soils and rocks) and the atmosphere (or sphere ofthe air). The biosphere , sometimes described as fourth envelope, is the part ofthe planet on which the life developed. It is a very thin surface layer, which goes down to 11000 meters of depth to rising up to15000 meters of altitude, although the majority of life live in the zone located between -100 meters and +100 meters.
Life first developed in the hydrosphere, at low depth, in the photic zone .Multicellular organisms then appeared and colonized benthic zones . Terrestrial lifedeveloped 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. Biosphere andbiodiversity are inseparable characteristics of the Earth. Biosphere is defined as being the sphere of life, whereas biodiversity is its diversity. The sphere is the container, whereas diversity isthe contents. This diversity is expressed at the same time at the ecological level (ecosystem), population level (intraspecificdiversity) and species level (specific diversity).
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 . At theecosystem and biosphere level, there is a permanent recycling of all these elements, which alternate between the mineral stateand the organic state.
While there is a slight input of geothermal energy, the bulk of the functioning of the ecosystem is primarily based on theinput of solar energy . Plants convert light into chemical energy by the process of photosynthesis , which creates glucose (a simple sugar) andreleases free oxygen . Glucose thus becomes the secondary energy source which drives theecosystem. Some of this glucose is used directly by other organisms for energy. Other sugar molecules can be converted to othermolecules such as amino acids . Plants use some of this sugar, concentrated in nectar to entice pollinators to aid them in reproduction. (Honeybees concentratethe sugar still further as honey, which can be said to be "stored summer sunshine").
Cellular respiration is the process by which organisms(like mammals ) breakdown the glucose back to its constituents, water and carbon dioxide , gaining back the storedenergy the sun originally gave to the plants. The proportion of photosynthetic activity of plants to the respiration of otherorganisms determines the specific composition of the Earth's atmosphere, particularly its oxygen level. Global air currents mix the atmosphere andmaintain nearly the same balance in areas of intense biological activity and areas of slight biological activity.
Water is also exchanged between the hydrosphere, the lithosphere, the atmosphere and the biosphere in regular cycles . The oceans are large tanks, which store water, ensure a thermal and climatic stability,as well as the transport of the chemical elements thanks to large oceanic currents .
For better understanding of how the biosphere works, and the dysfunctions related to human activity, American scientistscarried out, under greenhouses , a small-scale model of the biosphere, called Biosphere II .
The concept of an ecosystem
Main article: Ecosystem
The first principle of ecology is that each living organism has an ongoing and continual relationship with every other elementthat makes up its environment. An ecosystem can be defined as any situation wherethere is interaction between organisms and their environment.
The ecosystem is composed of two entities, the entirety of life (called the biocenose ) and the medium that life exists in (the biotope ). Withinthe ecosystem, species are connected and dependent upon one another in the foodchain , and exchange energy and matter between themselves and with their environment.
The concept of an ecosystem can apply to units of variable size, such as a pond , afield, or a piece of deadwood. A unit of smaller size is called a microecosystem . For example, anecosystem can be a stone and all the life under it. A mesoecosystem could be a forest , and a macroecosystem a whole ecoregion , with its watershed .
The main questions when studying an ecosystems are:
Ecosystems are often classified by reference to the biotopes concerned. The following ecosystems may be defined :
Another classification can be done by reference to its communities (for example a human ecosystem ).
Dynamics and stability
The biotope is a region environmentally uniform, characterized by a whole set of geological, geographical and climatologicalparameters, which are called abiotic ecological factors :
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 cohabiting in a given place and at a given time. When a population consists of an insufficient numberof individuals, the species is threatened with extinction, either by underpopulation, or by because of consanguinity . A population can be reduced for several reasons, for example, disappearance of its habitat(destruction of a forest) or by excessive predation (such as the hunting of a given species).
Biocenose is characterized by biotic ecological factors of two types: intraspecificand interspecific relations.
Intraspecificrelations are those which are established between individuals of the same species, forming a population. They are relationsof co-operation or competition , with division of the territory, and sometimes organization in hierarchical societies.
Interspecificrelations , i.e. those existing between different species, are numerous, and usually described according to their beneficial,detrimental or neutral effect (for example, symbiosis (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, itselfconsumed by a carnivore, itself consumed by a carnivore of larger size). Ecological niche is the area shared by two species when they live at the same place with the same type of diet .
The existing interactions between the various living beings go along with a permanent mixing of mineral and organicsubstances, 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 biogeochemicalcycles . They guarantee a durable stability of the biosphere (at least when human influence and extreme weather phenomena are left aside). This self-regulation, supported bynegative feedback controls, ensures the perenniality of the ecosystems. It is shownby 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 marinesystems 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 vast region, such as tundra or steppes . The biosphere comprises all of the Earth's biomes -- the entirety of places where life ispossible -- 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 physicalenvironment (for example, oceans or mountain ranges) and to the climate . Theirvariation 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 (aswell for animal than plant species) is decreasing most rapidly near the equator (asin Brazil ) and less rapidly as one approaches the poles .
The biosphere may also be divided into ecozone , which are very well defined todayand primarily follow the continental borders. The ecozones are themselves divided into ecoregions , though there is not agreement on their limits.
These relations form sequences, in which each individual consumes the preceding one and is consumed by the one following, inwhat are called food chains or food network . In a food network, therewill 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 givenplace), of primaryproductivity (the increase in the mass of plants during a given time) and of secondaryproductivity (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 oforganisms which can be supported by a given ecosystem. In any food network, the energy contained in the level of the producers isnot completely transferred to the consumers. Thus, from an energy point of view, it is more efficient for humans to be primaryconsumers (to get nourishment from grains and vegetables) than as secondary consumers (from herbivores such as beef and veal),and more still than as a tertiary consumer (from eating carnivores).
The productivity of ecosystems is sometimes estimated by comparing three types of land-based ecosystems and the total ofaquatic ecosystems:
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 ).
It may be that the environment quality degrades compared to the species needs, after a change of abiotic
(for example, an increase of temperature, lesssignificant rainfalls).
Ecological crises may be more or less brutal (occurring between a few months to a few million years). They can also be ofnatural or anthropic origin. They may relate to one unique species or on the contrary, to a high number of species (see thearticle on Extinction event ).
According to its degree of endemism, a local crisis will have more or less significant consequences, from the death of manyindividuals to the total extinction of a species. Whatever its origin, disappearance of one or several species often will involvea rupture in the food chain , further impacting the survival of otherspecies.
In the case of a global crisis, the consequences can be much more significant; some extinction events showed the disappearanceof more than 90% of existing species at that time. However, it should be noted that the disappearance of certain species, such asthe dinosaurs, by freeing an ecological niche, allowed the development and the diversification of the mammals. An ecologicalcrisis thus paradoxically favored biodiversity.
Sometimes, an ecological crisis can be a specific and reversible phenomenon at the ecosystem scale. But more generally, thecrises impact will last. Indeed, it rather is a connected series of events, that occur till a final point. From this stage, noreturn 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 remainingindividuals. Thus, even if the diversity of the human population is sometimes considered threatened (see in particular indigenous people ), few people envision human disappearance at shortspan. However, epidemicdiseases , famines , impact on health of reduction of air quality , food crises , reduction of living space,accumulation of toxic or non degradable wastes, threats on keystonespecies (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. Dueto the increases in technology and a rapidly increasing population, humans have more influence on their own environment than anyother ecosystem engineer .
Some usually quoted examples as ecological crises are
History of ecology
One of the first ecologists may have been Aristotle who had interest in many species of animals. He was followed by numerous naturalists such as Buffon and Carolus Linnaeus ,whose work is usually considered the origin of modern ecology.
The botanical geography and Alexander von Humboldt
Throughout the 18th and the beginning of the 19th century , the great maritime powers such as France and Germany, launched manyworld exploratory expeditions to develop maritime commerce with other countries, and to discover new natural resources, as well as to catalogthem. At the beginning of the 18th century , about twenty thousand plantspecies were known, versus forty thousand at the beginning of the 19thcentury , and almost 400,000 today.
These expeditions were joined by many scientists, including botanists , such as theGerman explorer Alexander von Humboldt . Humboldt isoften considered the true father of ecology. He was the first to take on the study of the relationship between organisms andtheir environment . He exposed the existing relationships between observedplant species and climate , and described vegetation zones using latitude and altitude , a discipline now knownas geobotany .
In 1804 , for example, he reported an impressive number of species, particularly plants,for which he sought to explain their geographic distribution with respect to geological data. One of Humboldt's famous works was "Idea for a Plant Geography" ( 1805 ).
Other important botanists include Aimé Bonpland and Eugenius Warming .
The notion of biocenose: Charles Darwin and Alfred Wallace
Towards 1850 there was a breakthrough in the field with the publishing of the work of Charles Darwin on The Origin of Species : Ecology passed from a repetitive, mechanical model to a biological, organic,and hence evolutionary model.
Alfred Russel Wallace , contemporary and competitor toDarwin, was first to propose a "geography" of animal species. Several authors recognized at the time that species were notindependent of each other, and grouped them into plant species, animal species, and later into communities of living beings or biocenose . This term was coined in 1877 by Karl Möbius .
The biosphere - Eduard Suess and Vladimir Vernadsky
By the 19th century , ecology blossomed due to new discoveries in chemistry by Lavoisier and de Saussure , notably the nitrogen cycle . After observing the fact that life developed only within strict limits of each compartmentthat makes up the atmosphere , hydrosphere , and lithosphere , the Austrian geologist Eduard Suess proposed the term biosphere in 1875 . Suess proposed the name biosphere for the conditionspromoting life, such as those found on Earth , which includes flora , fauna , minerals , matter cycles , et cetera.
In the 1920s Vladimir I. Vernadsky , a Russian geologist who had defected to France, detailed the idea of thebiosphere in his work "The biosphere" ( 1926 ), and described the fundamental principles ofthe biogeochemical cycles . He thus redefined the biosphereas the sum of all ecosystems .
First ecological damages were reported in the 18th century , as themultiplication of colonies caused deforestation . Since the 19th century , with the industrial revolution , more and more pressing concerns have grown about the impact of human activityon the environment . The term ecologist has been in use since the end of the 19thcentury .
The ecosystem: Arthur Tansley
Over the 19th century , botanical geography and zoogeography combined toform the basis of biogeography . This science, which deals with habitats ofspecies, seeks to explain the reasons for the presence of certain species in a given location.
It was in 1935 that ArthurTansley , the British ecologist , coined the term ecosystem , the interactive system established between the biocenose (the group of living creatures), and their biotope , theenvironment in which they live. Ecology thus became the science of ecosystems.
Human ecology began in the 1920s , through the study of changes in vegetation succession in the city of Chicago .It became a distinct field of study in the 1970s . This marked the first recognition thathumans, who had colonized all of the Earth's continents , were a major ecological factor . Humans greatly modify the environment through thedevelopment of the habitat (in particular urban planning ), by intensiveexploitation activities such as logging and fishing , and as side effects of agriculture , mining , and industry . Besides ecology andbiology, this discipline involved many other natural and social sciences, such as anthropology and ethnology , economics , demography , architecture and urban planning , medicine and psychology , and many more.The development of human ecology led to the increasing role of ecological science in the design and management of cities .
James Lovelock and the Gaia hypothesis
The Gaia theory , proposed by James Lovelock , in his work Gaia: A New Look at Life on Earth,advanced the view that the Earth should be regarded as a single living macro-organism. In particular, it argued that the ensembleof living organisms has jointly evolved an ability to control the global environment — by influencing major physicalparameters as the composition of the atmosphere, the evaporation rate, the chemistry of soils and oceans — so as tomaintain conditions favorable to life.
This vision was largely a sign of the times, in particular the growing perception after the Second World War that human activities such as nuclear energy , industrialization , pollution , and overexploitation of natural resources , fueled by exponential population growth , were threatening to create catastrophes on aplanetary scale. Thus Lovelock's Gaia hypothesis, while controversial among scientists, was embraced by many environmental movements as an inspiring view: theirEarth-mother, Gaia , was "becoming sick from humans and theiractivities".
Conservation and environmental movements
Indeed, since the 19th century, ecology has been obviously relevant to social and philosophical movements related to protection of the natural environment , such as conservationism and environmentalism . Today ecology is a major political topic , and a source of ideology for majorpolitical organizations such as the Green Party and Greenpeace .
Ecology and global policy
Ecology became a central part of the World's politics as early as 1971 , UNESCO launched a research program called Man and Biosphere , withthe objective of increasing knowledge about the mutual relationship between humans and nature. A few years later it defined theconcept of Biosphere Reserve .
In 1972 , the United Nations held the first international conference on the human environment in Stockholm ,prepared by René Dubos and otherexperts. This conference was the origin of the phrase "Think Globally, Act Locally". The next major events in ecology were thedevelopment of the concept of biosphere and the appearance of terms "biological diversity" -- or now more commonly biodiversity -- in the 1980s . These termswere developed during the Earth Summit in Rio de Janeiro in 1992 , where the concept of the biosphere wasrecognized by the major international organizations, and risks associated with reductions in biodiversity were publiclyacknowledged.
Then, in 1997 , the dangers the biosphere was facing were recognized from aninternational point of view at the conference leading to the KyotoProtocol . In particular, this conference highlighted the increasing dangers of the greenhouse effect -- related to the increasing concentration of greenhouse gases in the atmosphere, leading to global changes in climate . In Kyoto , most of the world's nationsrecognized the importance of looking at ecology from a global point of view, on a worldwide scale, and to take into account theimpact of humans on the Earth's environment.
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