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Ecology

Ecology

Ecology, or ecological science, is the scientific study of the distribution and abundance of living organisms and how these properties are affected by interactions between the organisms and their environment. The environment of an organism includes both the physical properties, which can be described as the sum of local abiotic factors like 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; the word is derived from the Greek oikos ("household") and logos ("study")–therefore, "ecology" means the "study of the household of nature".

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 said 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 Krebbs' (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, maintaining biodiversity and related ecological goals have provided a scientific basis for expressing the goals of environmentalism and have given scientific methodology, measure, and terminology to environmental issues. 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 behavioral 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

: Main article: Disciplines of ecology Ecology is a broad science which can be subdivided into major and minor sub-disciplines. The major sub-disciplines include (in a nested series from the smallest to the largest in scope):
- Physiological Ecology (or ecophysiology), which studies the influence of the biotic and abiotic environment on the physiology of the individual, and the adaptation of the individual to its environment;
- Behavioral ecology, which studies the ecological and evolutionary basis for animal behavior, and the roles of behavior in enabling animals to adapt to their ecological niches;
- Population ecology (or autecology), which deals with the dynamics of populations within species, and the interactions of these populations with environmental factors;
- Community ecology (or synecology) which studies the interactions between species within an ecological community;
- Ecosystem ecology, which studies the flows of energy and matter through ecosystems;
- Landscape ecology, which studies the interactions between discrete elements of a landscape;
- Global ecology, which looks at ecological questions at the global level, often asking macroecological questions. Ecology can also be sub-divided on the basis of target groups:
- Animal ecology, plant ecology, insect ecology; Ecology can also be sub-divided from the perspective of the studied biomes:
- Arctic ecology (or polar ecology), tropical ecology, desert ecology (temperate zone ecology could also exist as a distinct sub-field, but ecology as a whole has an overwhelmingly temperate bias, so the sub-field is redundant). Spanning all of the above is:
- Evolutionary ecology.

History of ecology

: Main article: History of ecology
Fundamental principles of ecology

Biosphere and biodiversity
Main articles: Biosphere, Biodiversity, Unified neutral theory of biodiversity 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. Multicellular organisms then appeared and colonized benthic zones. 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 dependant 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
: Main article: Ecosystem 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 (called the biocoenosis) and the medium that life exists in (the biotope). Within the ecosystem, species are connected and dependent upon one another in the food chain, 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, 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 watershed. The main questions when studying an ecosystem are:
- How could the colonization of a barren area be carried out?
- What are the ecosystem's dynamics and changes
- How does an ecosystem interact at local, regional and global scale
- Is the current state stable?
- What is the value of an ecosystem? How does the 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 (or terrestrial), such as forest ecosystems, meadow ecosystems (meadows, steppes, savannas), or agro-ecosystems (agricultural systems).
- As ecosystems of inland waters, such as lentic ecosystems (lakes, ponds) or lotic ecosystems (rivers)
- As oceanic ecosystems (seas, oceans). Another classification can be done by reference to its communities (for example a human ecosystem).
Dynamics and stability
: Main articles: biogeochemistry, Homeostasis, Population dynamics 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
: Main articles: Biome, ecozone 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 vast region, such 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 (as in Brazil) 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 -- plants which are capable of photosynthesis
- 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. Thus, from an energy point of view, it is more efficient for humans to be primary consumers (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 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 is what occurs when the environment of a species or a population evolves in a way unfavourable to that 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 because of the large amount of radiation generated by the meltdown.
See also

- ELDIS, a database on ecological aspects of economical development.
- Ecology movement
- List of ecologists
- List of ecology topics
- List of biology topics
- Important publications in ecology Category:Environmental science Category:Agronomy als:Ökologie ko:생태학 ms:Ekologi ja:生態学 simple:Ecology th:นิเวศวิทยา

Life
:For other uses, see Life and Living Life is a multi-faceted concept. Life may refer to the ongoing process of which living things are a part, the period between the conception (or a point at which the entity can be considered to be an individualized being) and death of an organism, the condition of an entity that has been born (or reached the point in its existence at which it can be established to be alive) and has yet to die, and that which makes a living thing alive.
Defining the concept of life
How can one tell when an entity is a lifeform? It would be relatively straightforward to offer a practical set of guidelines if one's only concern were life on Earth as we know it (see biosphere), but as soon as one considers questions about life's origins on Earth, or the possibility of extraterrestrial life, or the concept of artificial life, it becomes clear that the question is fundamentally difficult and comparable in many respects to the problem of defining intelligence. Also, loosely speaking, some theories are grounded in the basic assumption that "ideas have a life of their own".
A conventional definition
In biology, a lifeform has traditionally been considered to be a member of a population whose members can exhibit all the following phenomena at least once during their existence: #Growth, full development, maturity #Metabolism, consuming, transforming and storing energy/mass; growing by absorbing and reorganizing mass; excreting waste #Motion, either moving itself, or having internal motion #Reproduction, the ability to create entities that are similar to, yet separate from, itself or consisting solely of entities that exhibit the quality of reproduction. #Response to stimuli - the ability to measure properties of its surrounding environment, and act upon certain conditions. This property is also called homeostasis.
Exceptions to the conventional definition
These criteria are not without their uses, but their disparate nature makes them unsatisfactory from a number of perspectives; in fact, it is not difficult to find counterexamples and examples that require further elaboration. For example, according to the above definition, one could say:
- (most) mules and people who are infertile cannot reproduce and thus would not qualify as lifeforms. Also worker bees and other organisms living in colonies would not qualify; only the queen and the drones (or the whole colony) can be considered 'alive'.
- Fire and stars could be considered lifeforms.
- A virus does not grow and cannot reproduce outside of a host cell and thus would not qualify as a lifeform. Many individual organisms are incapable of reproduction and yet are still considered to be lifeforms; see mules and ants for examples. This is because the term "lifeform" applies on the level of entire species or of individual genes. (For example, see kin selection for information about one way by which non-reproducing individuals can still enhance the spread of their genes and the survival of their species.) It is important to keep in mind the difference between a "lifeform" and "a being that is alive." One example of sterility does not render the rest of the species a non-lifeform, any more than one dead animal renders the rest of the species dead. Note also that the two cases of fire and stars fitting the definition of life can be simply remedied by defining metabolism in a more biochemically exact way. Fundamentals of Biochemistry by Donald Voet and Judith Voet (ISBN 0471586501) defines metabolism as follows: "Metabolism is the overall process through which living systems acquire and utilize the free energy they need to carry out their various functions. They do so by coupling the exergonic reactions of nutrient oxidation to the endergonic processes required to maintain the living state, such as the performance of mechanical work, the active transport of molecules against concentration gradients, and the biosynthesis of complex molecules." This definition, in use by most biochemists, makes it clear that fire is not alive, because fire releases all the oxidative energy of its fuel as heat. (Note: Actually, the definition does not help much at all, for it is circular. What we are looking for, after all, is a definition of "living entity." We agreed that part of the definition is "capable of metabolism." We then tried to define "metabolism" in order to get clear on which entities are capable of it and which not. But the definition of "metabolism" just offered is in terms of living systems, and those are exactly what we are trying to define!) This could also be remedied by adding the requirement of locality, where there is an obvious structure that delineates the spatial extension of the living being, such as a cell membrane. A conceptual problem with saying that fire is life is that it collapses the distinction between "growth" and "reproduction." It is possible to think of a spreading flame as either growing or reproducing, but what would it mean to say that the same act is both growth and reproduction? Viruses reproduce, flames grow, some software programs mutate and evolve, future software programs will probably evince (even high-order) behavior, machines move, and some form of proto-life consisting of metabolizing cells without the ability to reproduce presumably existed. Still, some would not call these entities alive. Generally, all five characteristics are required for a population to be considered a lifeform.
Other definitions
Biologists who are content to focus on terrestrial organisms often note some additional signs of life, including these: # Living organisms contain molecular components such as: carbohydrates, lipids, nucleic acids, and proteins. # Living organisms require both energy and matter in order to continue living. # Living organisms are composed of at least one cell. # Living organisms maintain homeostasis for some period of time. # Species of living organisms will evolve. All life on Earth is based on the chemistry of carbon compounds. Some assert that this must be the case for all possible forms of life throughout the universe; others describe this position as 'carbon chauvinism'. The systemic definition is that living things are self-organizing and autopoietic (self-producing). These objects are not to be confused with dissipative structures (e.g. fire). Variations of this definition include:
- Francisco Varela and Humberto Maturana's definition of life (also widely used by Lynn Margulis) as an autopoietic (self-producing), water based, lipid-protein bound, carbon metabolic, nucleic acid replicated, protein readout system
- "a system of inferior negative feedbacks subordinated to a superior positive feedback" ([http://www.mol.uj.edu.pl/~benio/cyber_def_life.pdf J. theor Biol. 2001])
- Tom Kinch's definition of life as a highly organized auto-cannibalizing system naturally emerging from conditions common on planetary bodies, and consisting of a population of replicators capable of mutation, around each set of which a homeostatic metabolizing organism, which actively helps reproduce and/or protect the replicator(s), has evolved
- Stuart Kauffman's definition of life as an autonomous agent or a multi-agent system capable of reproducing itself or themselves, and of completing at least one thermodynamic work cycle
- Robert Pirsig's definition of life, found in his book Lila: An Inquiry into Morals, as that which maximizes its range of possible futures, in other words, that which makes decisions that result in the most future choices, or that which strives to keep its options open.
- A system converting entropy to negentropy, using flow of energy. Other definitions:
- That which seeks to continue its own existence (attributed to Clifford A. Schaffer).
- A self-replicating system that evolves through mutation.
Descent with modification: a "useful" characteristic
A useful characteristic upon which to base a definition of life is that of descent with modification: the ability of a life form to produce offspring that are like its parent or parents, but with the possibility of some variation due to chance. Descent with modification is sufficient by itself to allow evolution, assuming that the variations in the offspring allow for differential survival. The study of this form of heritability is called genetics. In all known life forms (assuming prions are not counted as such), the genetic material is primarily DNA or the related molecule, RNA. Another exception might be the software code of certain forms of viruses and programs created through genetic programming, but whether computer programs can be alive even by this definition is still a matter of some contention.
Origin of life
Main article: Origin of life There is no truly "standard" model of the origin of life, but most currently accepted scientific models build in one way or another on the following discoveries, which are listed roughly in order of postulated emergence: #Plausible pre-biotic conditions result in the creation of the basic small molecules of life. This was demonstrated in the Urey-Miller experiment. #Phospholipids spontaneously form lipid bilayers, the basic structure of a cell membrane. #Procedures for producing random RNA molecules can produce ribozymes, which are able to produce more of themselves under very specific conditions. There are many different hypotheses regarding the path that might have been taken from simple organic molecules to protocells and metabolism. Many models fall into the "genes-first" category or the "metabolism-first" category, but a recent trend is the emergence of hybrid models that do not fit into either of these categories.
The possibility of extraterrestrial life
Main articles: Extraterrestrial life, Astrobiology As of 2005, Earth is the only planet in the universe known by humans to support life. The question of whether life exists elsewhere in the universe remains open, but analyses such as the Drake equation have been used to estimate the probability of such life existing. There have been a number of claims of the discovery of life elsewhere in the universe, but none of these have yet survived scientific scrutiny. Today, the closest that scientists have come to finding extraterrestrial life is fossil evidence of possible bacterial life on Mars (via the ALH84001 meteorite). Searches for extraterrestrial life are currently focusing on planets and moons believed to possess liquid water, at present or in the past. Recent evidence from the NASA rovers Spirit and Opportunity supports the theory that Mars once had surface water. See Life on Mars for further discussion. Jupiter's moons are also considered good candidates for extraterrestrial life, especially Europa, which seems to possess oceans of liquid water. Other highly speculative and somewhat doubtful places for present or past life include the atmosphere of Venus, Titan cryovolcanoes, or even Enceladus.
See also

- Animal
- Artificial life
- Bacteria
- Biology
- Death
- Fungi
- Biological kingdom
- Biological life cycle
- Monera
- Odic force
- Origin of life (disambiguation)
- Plant
- Prehistoric life
- Protista
References

- Kauffman, Stuart. The Adjacent Possible: A Talk with Stuart Kauffman. Retrieved Nov. 30, 2003 from [http://www.edge.org/3rd_culture/kauffman03/kauffman_index.html]
External links

- [http://www.lifetheory.com Express your theory and meaning of life]
- [http://www.edge.org/3rd_culture/kauffman03/kauffman_index.html "The Adjacent Possible: A Talk with Stuart Kauffman"]
- [http://www.quotesandpoem.com/poems/SelectedPoetryTopic/Life Poems and Quotes about life and living]
- [http://www.angelfire.com/linux/vjtorley/ Animals and other living things: their interests, mental capacities and moral entitlements]
- [http://tolweb.org/tree?group=life Tree of Life Web Project - Life on Earth]
- [http://plato.stanford.edu/entries/life/ Stanford Encyclopedia of Philosophy entry]
- [http://web.archive.org/web/20041030074958/http://people.cornell.edu/pages/tg21/DHB.html The Deep Hot Biosphere Theory (Thomas Gold)] Category:Biology ja:生命 ko:생명 ms:Benda hidup simple:Life

Natural environment

The natural environment comprises all living and non-living things that occur naturally on Earth. In its purest sense, it is thus an environment that is not the result of human activity or intervention. The natural environment may be contrasted to "the built environment." For some, there is a difficulty with the term "natural environment" in that nearly all environments have been directly or indirectly influenced by humans at some point in time. In order to address this concern, some level of human influence is thus allowable without the status of any particular landscape ceasing to be "natural." The term's meaning, however, is usually dependent more on context than a set definition. Many natural environments are the product of the interaction between nature and humans. For this reason, the term ecosystem has been used to describe an environment that contains nature, and includes people. It follows then that environmental problems are human or social problems. Some also consider it dangerously misleading to regard "environment" as separate from "people." It is the common understanding of natural environment that underlies environmentalism—a broad political, social, and philosophical movement that advocates various actions and policies in the interest of protecting what nature remains in the natural environment, or restoring or expanding the role of nature in this environment. While wilderness is increasingly rare, wild nature (e.g., unmanaged forests, uncultivated grasslands, wildlife, wildflowers) can be found in many locations previously inhabited by humans. Goals commonly expressed by environmentalists include: reduction and clean up of man-made pollution, with future goals of zero pollution; reducing societal consumption of non-renewable fuels, development of alternative, green, low carbon or renewable energy sources; conservation and sustainable use of scarce resources such as water, land and air; protection of representative or unique or pristine ecosystems; preservation and expansion of threatened or endangered species or ecosystems from extinction; the establishment of nature and biosphere reserves under various types of protection, and, most generally, the protection of biodiversity and ecosystems upon which all human and other life on earth depends. More recently, there has been a strong concern about climatic changes caused by anthroprogenic releases of greenhouse gases, most notably carbon dioxide, and their interactions with human uses and the natural environment. Efforts here have focused on the mitigition of greenhouse gases that are causing climatic changes (i.e., through the Climate Change Convention and the Kyoto Protocol), and ondeveloping adaptative strategies to assist species, ecosystems, humans, nations and regions in adjusting to these climatic changes.

Climate

The climate (ancient Greek: κλίμα) is the weather averaged over a long period of time. The Intergovernmental Panel on Climate Change (IPCC) glossary definition is: : Climate in a narrow sense is usually defined as the “average weather”, or more rigorously, as the statistical description in terms of the mean and variability of relevant quantities over a period of time ranging from months to thousands or millions of years. The classical period is 30 years, as defined by the World Meteorological Organization (WMO). These quantities are most often surface variables such as temperature, precipitation, and wind. Climate in a wider sense is the state, including a statistical description, of the climate system.[http://www.grida.no/climate/ipcc_tar/wg1/518.htm]

Climate vs weather

In the most succinct words, weather is the combination of events in the atmosphere and climate is the overall accumulated weather in a certian location. The exact boundaries of what is climate and what is weather are not well defined and depend on the application. For example, in some senses an individual El Niño event could be considered climate; in others, as weather. When the original conception of climate as a long-term average came to be considered, perhaps towards the end of the 19th century, the idea of climate change was not current, and a 30 year average seemed reasonable (but see note 1). Given the current availability of long-term trends in the temperature record, it is harder to give a precise contradiction-free definition of climate: over a 30 year period, averages may shift; over a shorter period, the statistics are less stable.

Climate determinants

In a given geographical region, the climate generally does not vary over time on the scale of a human life span. However, over geological time, climate can vary considerably for a given place on the Earth. For example, Scandinavia has been through a number of ice ages over hundreds of thousands of years (the last one ending about 10,000 years ago). Paleoclimatology is the study of these past climates, their origin, and by extension, the origin of today's climate. Over historic time spans there are a number of static variables that determine climate including: altitude, proportion of land to water, and proximity to oceans and mountains. Other climate determinants are more dynamic: The Thermohaline circulation of the ocean distributes heat energy between the equatorial and polar regions; other ocean currents do the same between land and water on a more regional scale. Degree of vegetation coverage affects solar heat absorption, water retention, and rainfall on a regional level. Alterations in the quantity of atmospheric greenhouse gases determines the amount of solar energy retained by the planet, leading to global warming (or cooling). The variables which determine climate are numerous and the interactions complex but there is general agreement that the broad outlines are understood, at least in so far as the determinates of historical climate change are concerned.

Climate indices

Scientists use climate indices in their attempt to characterize and understand the various climate mechanisms that culminate in our daily weather. Much in the way the Dow Jones Industrial Average, which is based on the stock prices of 30 companies, is used to represent the fluctuations in the stock market as a whole, climate indices are used to represent the essential elements of climate. Climate indices are generally identified or devised with the twin objectives of simplicity and completeness, and each typically represents the status and timing of the climate factor they represent. By their very nature, indices are simple, and combine many details into an generalized, overall description of the atmosphere or ocean which can be used to characterize the factors which impact the global climate system. Because the climate indices are generally determined from measurements made in a localized area, they can have impacts in other areas around the globe, through processes sometimes called teleconnections. References:
- [http://www.arctic.noaa.gov/essay_bond.html Why and how do scientists study climate change in the Arctic? What are the Arctic climate indices?]
- [http://www.arctic.noaa.gov/climate.html Climate index and mode information]

Classifications

In the original sense, climate is a concept used to divide the world into regions sharing similar climatic parameters. Climate regions can be classified on the basis of temperature and precipitation alone. Examples of such climate schemes are the Köppen climate classification or the Thornthwaite climate classification schemes. For more details about specific climates, please see:
- Tropical climate
- Subtropical climate
- Arid climate
- Semiarid climate
- Mediterranean climate
- Temperate climate
- Oceanic climate
- Continental climate
- Alpine climate
- Subarctic climate
- Polar climate
- Climate of Antarctica To understand a climate of a specific place or area, please see the article on that place or area.

Historical climates

- Climate changes of 535-536
- Medieval climate optimum

National climates

- Climate of the Alps
- Climate of India
- Climate of the United Kingdom

External links

- [http://climateapps2.oucs.ox.ac.uk/cpdnboinc/ Climate Prediction Project]
- [http://www.worldclimate.com WorldClimate]
- [http://www.atmosphere.mpg.de/enid/1442 ESPERE Climate Encyclopaedia]
- [http://www.weatherbase.com Weatherbase]
- [http://www.climate-zone.com Global Climate Data]
- [http://www.limaperunet.com/climate/climateall.html The Climate of Peru]
- [http://www.arctic.noaa.gov/climate.html Climate index and mode information]
- [http://www.arctic.noaa.gov/essay_bond.html Why and how do scientists study climate change in the Arctic? What are the Arctic climate indices?]
- [http://www.arctic.noaa.gov/detect/ A near-realtime Arctic Change Indicator Website]
- [http://www.beringclimate.noaa.gov/ A current view of the Bering Sea Ecosystem and Climate]

Notes

# In "Climatology" by W G Kendrew (OUP; 3rd edition 1949; chapter 38; page 359) we find: "A well-known cycle is one with a mean period of about 35 years... which was worked out by Bruckner... the reality of this cycle seems to be well established, though it is of little use for actual forecasting; it is a basis of the choice of 35 years as the period estimated to give true mean values of climate elements." Category:Ecology ko:기후 ja:気候 simple:Climate

Habitat (ecology)

Habitat (from the Latin for "it inhabits") is the place where a particular species lives and grows. It is essentially the environment—at least the physical environment—that surrounds (influences and is utilized by) a species population. We use "species population" instead of "organism" here because, while it is possible to describe the habitat of a single black bear, we generally mean not any particular or individual bear, but the grouping of bears that comprise a breeding population and occupy a certain geographical area. Further, this habitat could be somewhat different from the habitat of another group or population of black bears living elsewhere. Thus, it is neither the species, nor the individual, for which the term habitat is typically used. A microhabitat is the immediate surroundings and other physical factors of an individual plant or animal within its habitat. However, the term "habitat" can be used more broadly in ecology. It was originally defined as the physical conditions that surround a species, or species population, or assemblage of species, or community (Clements and Shelford, 1939). Thus, it is not just a species population that has a habitat, but an assemblage of many species, living together in the same place that essentially share a habitat. Ecologists would regard the habitat shared by many species to be a biotope. Habitat destruction is a major factor in causing a species population to decrease, eventually leading to being endangered, or even extinct. A biome is the set of flora and fauna which live in a habitat and occupy a certain geography.

Reference

- Clements, Frederic E., and Victor E. Shelford. 1939. Bio-ecology. John Wiley & Sons, New York. 425 pp. Category:Ecology

Ernst Haeckel

Ernst Heinrich Philipp August Haeckel (February 16, 1834 — August 8, 1919), also written von Haeckel, was a German biologist and philosopher who popularized Charles Darwin's work in Germany. Haeckel was a physician, an accomplished artist and illustrator, and later a professor of comparative anatomy. He was one of the first to consider psychology as a branch of physiology. He also proposed many now ubiquitous terms including "phylum" and "ecology." His chief interests lay in evolution and life development processes in general, including development of nonrandom form, which culminated in the beautifully illustrated Kunstformen der Natur (Art forms of nature). Haeckel advanced the "recapitulation theory" which proposed a link between ontogeny (development of form) and phylogeny (evolutionary descent), summed up in the phrase "ontogeny recapitulates phylogeny". He supported the theory with embryo drawings that have been shown to be inaccurate and the theory has been largely discredited. Haeckel was also known for his "biogenic theory", in which he suggested that the development of races paralleled the development of individuals. He advocated the idea that "primitive" races were in their infancies and needed the "supervision" and "protection" of more "mature" societies. He extrapolated a new religion or philosophy called Monism from evolutionary science. In Monism, all economics, politics, and ethics are reduced to "applied biology." His writings and lectures on Monism provided scientific (or quasi-scientific) justifications for racism, nationalism and social darwinism. It has even been argued that monism thus became the de facto religion of Nazi Germany. Some scholars disagree, arguing that Nazi ideology was not comfortable with evolutionary theory, which argues for a common descent of all human races. Haeckel was a flamboyant figure whose popularity with the public was substantially greater than it was with his scientific peers. He sometimes took great (and non-scientific) leaps from available evidence. For example, at the time that Darwin first published On the Origin of Species by Means of Natural Selection, no remains of human ancestors had yet been found. Haeckel postulated that evidence of human evolution would be found in the Dutch East Indies (now Indonesia), and described these theoretical remains in great detail. He even named the as-of-yet unfound species, Pithecanthropus alalus, and charged his students to go find it. Remarkably, one of them did so — a young Dutchman named Eugene Dubois went to the East Indies and dug up the remains of Java Man, the first human ancestral remains ever found. (These remains originally carried Haeckel's Pithecanthropus label, though they were later reclassified as Homo erectus.) Although Haeckel's ideas are important to the history of evolutionary theory, and he was a competent invertebrate anatomist most famous for his work on radiolaria, most of the speculative concepts that he championed are now seen as incorrect. For example, Haeckel described and named hypothetical ancestral micro-organisms that have not been found as of date. His concept of recapitulation called "strong recapitulation" has been disputed. Haeckel did not support Darwin's "survival of the fittest", rather believing in a Lamarckian inheritance of acquired characteristics. Richard and Oskar Hertwig were Haeckel´s most important students. Mount Haeckel is a 4090 m (13,418') summit in the Eastern Sierra Nevada, overlooking the Evolution Basin, named in honor of Ernst Haeckel. So is the asteroid 12323 Häckel.

Sources

Richard Milner, "The Encyclopedia of Evolution: Humanity's Search for Its Origins", Henry Holt, 1993

External links

- [http://www.ucmp.berkeley.edu/history/haeckel.html Ernst Haeckel biography]
- [http://www.slate.com/id/2124625/ Ernst Haeckel – Evolution's controversial artist.] A slide-show essay about Ernst Haeckel.
- [http://caliban.mpiz-koeln.mpg.de/~stueber/haeckel/kunstformen/natur.html Kunstformen der natur, scanned] (from [http://www.biolib.de/] Stuebers Online Library)
- [http://draves.org/pix/kdn/ PNG alpha-transparencies of Haeckel's "Kustformen der natur"]

Books

- Art Forms from the Ocean: The Radiolarian Atlas of 1862, by Ernst Haeckel, Prestel Verlag, 2005 ISBN 3791333275
- Haeckel, Ernst Haeckel, Ernst Haeckel ja:エルンスト・ヘッケル

Biology

Biology is the study, or science, of life. It is concerned with the characteristics and behaviors of organisms, how species and individuals come into existence, and the interactions they have with each other and with the environment. Biology encompasses a broad spectrum of academic fields that are often viewed as independent disciplines. However, together they address the phenomenon of life over a wide range of scales. At the atomic and molecular scale, life is studied in the disciplines of molecular biology, biochemistry, and molecular genetics. At the level of the cell, it is studied in cell biology, and at multicellular scales, it is examined in physiology, anatomy, and histology. Developmental biology studies life at the level of an individual organism's development or ontogeny. Moving up the scale towards more than one organism, genetics considers how heredity works between parent and offspring. Ethology considers group behavior of more than one individual. Population genetics looks at the level of an entire population, and systematics considers the multi-species scale of lineages. Interdependent populations and their habitats are examined in ecology and evolutionary biology. A speculative new field is astrobiology (or xenobiology), which examines the possibility of life beyond the Earth.

Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle

Principles of biology

Unlike physics, biology does not usually describe systems in terms of objects which obey immutable physical laws described by mathematics. Nevertheless, the biological sciences are characterized and unified by several major underlying principles and concepts: universality, evolution, diversity, continuity, homeostasis, and interactions.

Universality: Biochemistry, cells, and the genetic code

mathematics]] Main articles: Life The most salient example of biological universality is that all living things share a common carbon-based biochemistry and in particular pass on their characteristics via genetic material, which is based on nucleic acids such as DNA and which uses a common genetic code with only minor variations. Another universal principle is that all organisms (that is, all forms of life on Earth except for viruses) are made of cells. Similarly, all organisms share common developmental processes. For example, in most metazoan organisms, the basic stages of early embryonic development share similar morphological characteristics and include similar genes.

Evolution: The central principle of biology

Main article: Evolution The central organizing concept in biology is that all life has a common origin and has changed and developed through the process of evolution (see Common descent). This has led to the striking similarity of units and processes discussed in the previous section. Charles Darwin established evolution as a viable theory by articulating its driving force, natural selection (Alfred Russell Wallace is recognized as the co-discoverer of this concept). Genetic drift was embraced as an additional mechanism of evolutionary development in the modern synthesis of the theory. The evolutionary history of a species— which describes the characteristics of the various species from which it descended— together with its genealogical relationship to every other species is called its phylogeny. Widely varied approaches to biology generate information about phylogeny. These include the comparisons of DNA sequences conducted within molecular biology or genomics, and comparisons of fossils or other records of ancient organisms in paleontology. Biologists organize and analyze evolutionary relationships through various methods, including phylogenetics, phenetics, and cladistics (The major events in the evolution of life, as biologists currently understand them, are summarized on this evolutionary timeline).

Diversity: The variety of living organisms

evolutionary timeline, based on rRNA gene data, showing the separation of the three domains bacteria, archaea, and eukaryotes as described initially by Carl Woese. Trees constructed with other genes are generally similar, although they may place some early-branching groups very differently, presumably owing to rapid rRNA evolution. The exact relationships of the three domains are still being debated.]] Despite its underlying unity, life exhibits an astonishingly wide diversity in morphology, behavior, and life histories. In order to grapple with this diversity, biologists attempt to classify all living things. Scientific classification seeks to reflect the evolutionary trees (phylogenetic trees) of the organism being classified. Classification is the province of the disciplines of systematics and taxonomy. Taxonomy places organisms in groups called taxa, while systematics seeks to define their relationships with each other. This clasification technique has evolved to reflect advances in cladistics and genetics, shifting the focus from physical similarities and shared characteristics to phylogenetics. Traditionally, living things have been divided into five kingdoms: :Monera -- Protista -- Fungi -- Plantae -- Animalia However, many scientists now consider this five-kingdom system to be outdated. Modern alternative classification systems generally begin with the three-domain system: :Archaea (originally Archaebacteria) -- Bacteria (originally Eubacteria) -- Eukaryota These domains reflect whether the cells have nuclei or not, as well as differences in the cell exteriors. There is also a series of intracellular parasites that are progressively "less alive" in terms of metabolic activity: :Viruses -- Viroids -- Prions

Continuity: The common descent of life

Main article: Common descent Up into the 19th century, it was commonly believed that life forms could appear spontaneously under certain conditions (see abiogenesis). This misconception was challenged by William Harvey's diction that "all life [is] from [an] egg" (from the Latin "Omne vivum ex ovo"), a foundational concept of modern biology. It simply means that there is an unbroken continuity of life from its initial origin to the present time. A group of organisms is said to share a common descent if they share a common ancestor. All organisms on the Earth have been and are descended from a common ancestor or an ancestral gene pool. This last universal common ancestor of all organisms is believed to have appeared about 3.5 billion years ago. Biologists generally regard the universality of the genetic code as definitive evidence in favor of the theory of universal common descent (UCD) for all bacteria, archaea, and eukaryotes (see: origin of life).

Homeostasis: Adapting to change

Main article: Homeostasis Homeostasis is the ability of an open system to regulate its internal environment to maintain a stable condition by means of multiple dynamic equilibrium adjustments controlled by interrelated regulation mechanisms. All living organisms, whether unicellular or multicellular, exhibit homeostasis. Homeostasis manifests itself at the cellular level through the maintenance of a stable internal acidity (pH); at the organismic level, warm-blooded animals maintain a constant internal body temperature; and at the level of the ecosystem, as when atmospheric carbon dioxide levels rise and plants are theoretically able to grow healthier and remove more of the gas from the atmosphere. Tissues and organs can also maintain homeostasis.

Interactions: Groups and environments

organ of the genus Amphiprion that dwell among the tentacles of tropical sea anemones. The territorial fish protects the anemone from anemone-eating fish, and in turn the stinging tentacles of the anemone protects the anemone fish from its predators]] Every living thing interacts with other organisms and its environment. One reason that biological systems can be difficult to study is that so many different interactions with other organisms and the environment are possible, even on the smallest of scales. A microscopic bacterium responding to a local sugar gradient is responding to its environment as much as a lion is responding to its environment when it searches for food in the African savannah. For any given species, behaviors can be co-operative, aggressive, parasitic or symbiotic. Matters become more complex when two or more different species interact in an ecosystem. Studies of this type are the province of ecology.

Scope of biology

Main article: List of biology disciplines Biology has become such a vast research enterprise that it is not generally regarded as a single discipline, but as a number of clustered sub-disciplines. This article considers four broad groupings. The first group consists of those disciplines that study the basic structures of living systems: cells, genes etc.; the second group considers the operation of these structures at the level of tissues, organs, and bodies; the third group considers organisms and their histories; the final constellation of disciplines focuses on their interactions. It is important to note, however, that these boundaries, groupings, and descriptions are a simplified characterization of biological research. In reality, the boundaries between disciplines are fluid, and most disciplines frequently borrow techniques from each other. For example, evolutionary biology leans heavily on techniques from molecular biology to determine DNA sequences, which assist in understanding the genetic variation of a population; and physiology borrows extensively from cell biology in describing the function of organ systems.

Structure of life

DNA sequences and structures]] Main articles: Molecular biology, Cell biology, Genetics, Developmental biology Molecular biology is the study of biology at a molecular level. This field overlaps with other areas of biology, particularly with genetics and biochemistry. Molecular biology chiefly concerns itself with understanding the interactions between the various systems of a cell, including the interrelationship of DNA, RNA, and protein synthesis and learning how these interactions are regulated. Cell biology studies the physiological properties of cells, as well as their behaviors, interactions, and environment. This is done both on a microscopic and molecular level. Cell biology researches both single-celled organisms like bacteria and specialized cells in multicellular organisms like humans. Understanding cell composition and how they function is fundamental to all of the biological sciences. Appreciating the similarities and differences between cell types is particularly important in the fields of cell and molecular biology. These fundamental similarities and differences provide a unifying theme, allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types. Genetics is the science of genes, heredity, and the variation of organisms. In modern research, genetics provides important tools in the investigation of the function of a particular gene, or the analysis of genetic interactions. Within organisms, genetic information generally is carried in chromosomes, where it is represented in the chemical structure of particular DNA molecules. Genes encode the information necessary for synthesizing proteins, which in turn play a large role in influencing (though, in many instances, not completely determining) the final phenotype of the organism. Developmental biology studies the process by which organisms grow and develop. Originating in embryology, modern developmental biology studies the genetic control of cell growth, differentiation, and "morphogenesis," which is the process that gives rise to tissues, organs, and anatomy. Model organisms for developmental biology include the round worm Caenorhabditis elegans, the fruit fly Drosophila melanogaster, the zebrafish Brachydanio rerio, the mouse Mus musculus, and the weed Arabidopsis thaliana.

Physiology of organisms

Main articles: Physiology, Anatomy Physiology studies the mechanical, physical, and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole. The theme of "structure to function" is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology, but the principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells. The field of animal physiology extends the tools and methods of human physiology to non-human species. Plant physiology also borrows techniques from both fields. Anatomy is an important branch of physiology and considers how organ systems in animals, such as the nervous, immune, endocrine, respiratory, and circulatory systems, function and interact. The study of these systems is shared with medically oriented disciplines such as neurology and immunology.

Diversity and evolution of organisms

immunology of a population of organisms is sometimes depicted as if travelling on a fitness landscape. The arrows indicate the preferred flow of a population on the landscape, and the points A, B, and C are local optima. The red ball indicates a population that moves from a very low fitness value to the top of a peak]] Main articles: Evolutionary biology, Botany, Zoology Evolutionary biology is concerned with the origin and descent of species, as well as their change over time, and includes scientists from many taxonomically-oriented disciplines. For example, it generally involves scientists who have special training in particular organisms such as mammalogy, ornithology, or herpetology, but use those organisms as systems to answer general questions about evolution. Evolutionary biology also makes use of paleontologists, who use the fossil record to answer questions about the mode and tempo of evolution, as well as theoreticians in areas such as population genetics and evolutionary theory. In the 1990s, developmental biology re-entered evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology. Related fields which are often considered part of evolutionary biology are phylogenetics, systematics, and taxonomy. The two major traditional taxonomically-oriented disciplines are botany and zoology. Botany is the scientific study of plants. Botany covers a wide range of scientific disciplines that study the growth, reproduction, metabolism, development, diseases, and evolution of plant life. Zoology involves the study of animals, including the study of their physiology within the fields of anatomy and embryology. The common genetic and developmental mechanisms of animals and plants is studied in molecular biology, molecular genetics, and developmental biology. The ecology of animals is covered under behavioral ecology and other fields.

Classification of life

The dominant classification system is called Linnaean taxonomy, which includes ranks and binomial nomenclature. How organisms are named is governed by international agreements such as the International Code of Botanical Nomenclature (ICBN), the International Code of Zoological Nomenclature (ICZN), and the International Code of Nomenclature of Bacteria (ICNB). A fourth Draft BioCode was published in 1997 in an attempt to standardize naming in these three areas, but it has yet to be formally adopted. The International Code of Virus Classification and Nomenclature (ICVCN) remains outside the BioCode.

Interactions of organisms

International Code of Virus Classification and Nomenclature]] Main articles: Ecology, Ethology, Behavior, Biogeography Ecology studies the distribution and abundance of living organisms, and the interactions between organisms and their environment. The environment of an organism includes both its habitat, which can be described as the sum of local abiotic factors such as climate and geology, as well as the other the organisms that share its habitat. Ecological systems are studied at several different levels, from individuals and populations to ecosystems and the biosphere. As can be surmised, ecology is a science that draws on several disciplines. Ethology studies animal behavior (particularly of social animals such as primates and canids), and is sometimes considered a branch of zoology. Ethologists have been particularly concerned with the evolution of behavior and the understanding of behavior in terms of the theory of natural selection. In one sense, the first modern ethologist was Charles Darwin, whose book The expression of the emotions in animals and men influenced many ethologists. Biogeography studies the spatial distribution of organisms on the Earth, focusing on topics like plate tectonics, climate change, dispersal and migration, and cladistics.

History of the word "biology"

Formed by combining the Greek βίος (bios), meaning 'life', and λόγος (logos), meaning 'study of', the word "biology" in its modern sense seems to have been introduced independently by Gottfried Reinhold Treviranus (Biologie oder Philosophie der lebenden Natur, 1802) and by Jean-Baptiste Lamarck (Hydrogéologie, 1802). The word itself is sometimes said to have been coined in 1800 by Karl Friedrich Burdach, but it appears in the title of Volume 3 of Michael Christoph Hanov's Philosophiae naturalis sive physicae dogmaticae: Geologia, biologia, phytologia generalis et dendrologia, published in 1766.

History

Main articles: History of biology, History of medicine, History of genetics Major discoveries in biology include:
- Cell theory
- Germ theory of disease
- Genetics
- Evolution
- DNA

External links

- [http://www.rom.on.ca/biodiversity/biocode/biocode1997.html BioCode]: A proposal for organism naming.
- [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=Books NCBI Open-Access Books]
- PhyloCode, [http://www.ohiou.edu/phylocode/index.html]
- [http://tolweb.org/tree/phylogeny.html The Tree of Life]: A multi-authored, distributed Internet project containing information about phylogeny and biodiversity.
- [http://www.bioone.org/perlserv/?request=index-html BioOne] Bioscience research journals.
- [http://www.bionews.in/biologynews.htm Biology News] Biology News, Articles and Research discoversies.

Organism

In biology and ecology, an organism (in Greek organon = instrument) is a complex adaptive system of organs that influence each other in such a way that they function as a more or less stable whole and have properties of life. The origin of life and the relationships between its major lineages are controversial. Two main grades may be distinguished, the prokaryotes and eukaryotes. The prokaryotes are generally considered to represent two separate domains, called the Bacteria and Archaea, which are not closer to one another than to the eukaryotes. The gap between prokaryotes and eukaryotes is widely considered a major missing link in evolutionary history. Two eukaryotic organelles, namely mitochondria and chloroplasts, are generally considered to be derived from endosymbiotic bacteria. The phrase complex organism describes any organism with more than one cell.

Organizational terminology

Biological Organization

Viruses

Viruses are not typically considered to be organisms because they are not capable of independent reproduction or metabolism. However, according to the United States Code, they are considered to be microorganisms in the sense of biological weaponry and malicious use. This controversy is problematic, though, since some parasites and endosymbionts are incapable of independent life either. Although viruses do have enzymes and molecules characteristic of living organisms, they are incapable of surviving outside a host cell and most of their metabolic processes require a host and its 'genetic machinery'. The origin of such parasites is uncertain, but it appears most likely that they are derived from their host.

Life span

One of the basic parameters of organism is its life span. Some animals live as short as one day, while some plants can live thousands of years. Aging is important when determining life span of most organisms, bacterium, a virus or even a prion.

External links

- [http://news.bbc.co.uk/1/hi/sci/tech/944790.stm BBCNews: 27 September, 2000, When slime is not so thick] Citat: "...It means that some of the lowliest creatures in the plant and animal kingdoms, such as slime and amoeba, may not be as primitive as once thought...."
- [http://www.spaceref.com/news/viewpr.html?pid=4742 SpaceRef.com, July 29, 1997: Scientists Discover Methane Ice Worms On Gulf Of Mexico Sea Floor]
- [http://www.science.psu.edu/iceworms/iceworms.html The Eberly College of Science: Methane Ice Worms discovered on Gulf of Mexico Sea Floor] download Publication quality photos
- [http://www.sb-roscoff.fr/Ecophy/PDF/00-Fisher-NatWis.pdf Artikel, 2000: Methane Ice Worms: Hesiocaeca methanicola. Colonizing Fossil Fuel Reserves]
- [http://www.spaceref.com/news/viewnews.html?id=339 SpaceRef.com, May 04, 2001: Redefining "Life as We Know it"] Hesiocaeca methanicola In 1997, Charles Fisher, professor of biology at Penn State, discovered this remarkable creature living on mounds of methane ice under half a mile of ocean on the floor of the Gulf of Mexico.
- [http://news.bbc.co.uk/1/hi/sci/tech/2585235.stm BBCNews, 18 December, 2002, 'Space bugs' grown in lab] Citat: "...Bacillus simplex and Staphylococcus pasteuri...Engyodontium album...The strains cultured by Dr Wainwright seemed to be resistant to the effects of UV - one quality required for survival in space...."
- [http://news.bbc.co.uk/1/hi/sci/tech/3003946.stm BBCNews, 19 June, 2003, Ancient organism challenges cell evolution] Citat: "..."It appears that this organelle has been conserved in evolution from prokaryotes to eukaryotes, since it is present in both,"..."
- [http://www.anselm.edu/homepage/jpitocch/genbios/bi04syllabsu03.html Interactive Syllabus for General Biology - BI 04, Saint Anselm College, Summer 2003]
- [http://www.personal.psu.edu/users/j/s/jsf165/Bio110.html Jacob Feldman: Stramenopila]
- [http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Root NCBI Taxonomy entry: root] (rich)
- [http://www.anselm.edu/homepage/jpitocch/genbios/surveybi04.html Saint Anselm College: Survey of representatives of the major Kingdoms] Citat: "...Number of kingdoms has not been resolved...Bacteria present a problem with their diversity...Protista present a problem with their diversity...",
- [http://www.species2000.org/ Species 2000 Indexing the world's known species]. Species 2000 has the objective of enumerating all known species of plants, animals, fungi and microbes on Earth as the baseline dataset for studies of global biodiversity. It will also provide a simple access point enabling users to link from here to other data systems for all groups of organisms, using direct species-links.
- [http://www.abc.net.au/science/news/enviro/EnviroRepublish_828525.htm The largest organism in the world may be a fungus carpeting nearly 10 square kilometers of an Oregon forest, and may be as old as 8500 years.]
- [http://tolweb.org/tree/phylogeny.html The Tree of Life]. zh-min-nan:Seng-bu̍t ko:생물 ja:生物 th:สิ่งมีชีวิต

Nucleic acid

A nucleic acid is a complex, high-molecular-weight biochemical macromolecule composed of nucleotide chains that convey genetic information. The most common nucleic acids are deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nucleic acids are found in all living cells and viruses. cells Nucleic acid, so called because of its prevalence in cellular nuclei, is the generic name of family of biopolymers. The monomers are called nucleotides, and each consists of three components: a nitrogenous heterocyclic base (either a purine or a pyrimidine), a pentose sugar, and a phosphate group. Differ

Ecology

Scope

Disciplines of ecology

History of ecology

Fundamental principles of ecology

Biosphere and biodiversity

The ecosystem concept

Dynamics and stability

Spatial relationships and subdivisions of land

Ecosystem productivity

Ecological crisis

See also

Life

Defining the concept of life

A conventional definition

Exceptions to the conventional definition

Other definitions

Descent with modification: a "useful" characteristic

Origin of life

The possibility of extraterrestrial life

See also

References

External links

Natural environment

See also

Climate

Climate vs weather

Climate determinants

Climate indices

Classifications

See also

Historical climates

National climates

External links

Notes

Habitat (ecology)

See also

Reference

Ernst Haeckel

Sources

External links

Books

Biology

Principles of biology

Universality: Biochemistry, cells, and the genetic code

Evolution: The central principle of biology

Diversity: The variety of living organisms

Continuity: The common descent of life

Homeostasis: Adapting to change

Interactions: Groups and environments

Scope of biology

Structure of life

Physiology of organisms

Diversity and evolution of organisms

Classification of life

Interactions of organisms

History of the word "biology"

History

Related topics

External links

Further reading

Organism

Organizational terminology

Viruses

Life span

See also

External links

Nucleic acid