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Ecology
*** Shopping-Tip: Ecology
{{dablink|For the journal see
Ecology (journal).}}
{{dablink|The word "ecology" is often used in common parlance as a synonym for the
natural environment or
environmentalism.}}
'''Ecology''', or '''ecological science''', is the scientific study of the distribution and abundance of
life 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 (ecology) habitat. The term ''oekologie'' was coined in
1866 by the German biologist
Ernst Haeckel; the word is derived from the
Greek language 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
cell (biology) 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
Interdisciplinary 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 (soil study) 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, ecological knowledge such as the quantification of
biodiversity and
population dynamics have provided a scientific basis for expressing the goals of
environmentalism and evaluating its goals and policies. Additionally, a
holism 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
drone (bee) 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:
Ecology (disciplines) Disciplines of ecology''
Ecology is a broad discipline comprised of many sub-disciplines. A common, broad classification, moving from lowest to highest complexity, where complexity is defined as the number of entities and processes in the system under study, is:
*
Physiological Ecology (or '''ecophysiology''') and
Behavioral ecology examine adaptations of the individual to its environment.
*
Population ecology (or '''autecology''') studies the dynamics of populations of a single species.
*
Community ecology (or '''synecology''') focuses on the interactions between species within an ecological community.
*
Ecosystem ecology studies the flows of energy and matter through the biotic and abiotic components of
ecosystems.
*
Landscape ecology examines processes and relationship across multiple ecosystems or very large geographic areas.
Ecology can also be sub-divided according to the species of interest into fields such as
animal ecology,
plant ecology,
insect ecology, and so on. Another frequent method of subdivision is by
biome studied, e.g.,
Arctic ecology (or
polar ecology),
tropical ecology,
desert ecology, etc. The primary technique used for investigation is often used to subdivide the discipline into groups such as
chemical ecology,
genetic ecology,
field ecology,
statistical ecology,
theoretical ecology, and so forth. Note that these different systems are unrelated and often applied at the same time; one could be a theoretical plant community ecologist, or a polar ecologist interested in animal genetics.
History of ecology
: ''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
earth's atmosphere atmosphere (or sphere of the air). The
biosphere (or sphere of life), sometimes described as "the fourth envelope", is all living matter on the planet or that portion of the planet occupied by life. It reaches well into the other three spheres, although there are no permanent inhabitants of the atmosphere. Relative to the volume of the Earth, the biosphere is only the very thin surface layer which extends from 11,000 meters below sea level to 15,000 meters above.
It is thought that life first developed in the hydrosphere, at shallow depths, in the
photic zone. (Although recently a competing theory has emerged, that life originated around
hydrothermal vents in the deeper ocean. See
Origin of life.) Multicellular organisms then appeared and colonized
benthos benthic zones.
Cyanobacteria Photosynthetic organisms gradually produced the chemically unstable oxygen-rich atmosphere that characterizes our planet. Terrestrial life developed later, after the
ozone layer protecting living beings from
Ultraviolet UV rays formed. Diversification of terrestrial species is thought to be increased by the continents
continental drift drifting apart, or alternately, colliding. Biodiversity is expressed at the ecological level (ecosystem), population level (intraspecific diversity), species level (specific diversity), and genetic level. Recently technology has allowed the discovery of the deep ocean vent communities. This remarkable ecological system is not dependent on sunlight but bacteria, utilising the chemistry of the hot volcanic vents, are at the base of its food chain.
The biosphere contains great quantities of elements such as
carbon,
nitrogen and
oxygen. Other elements, such as
phosphorus,
calcium, and
potassium, are also essential to
life, yet are present in smaller amounts. At the ecosystem and biosphere levels, there is a continual recycling of all these elements, which alternate between the mineral and organic states.
While there is a slight input of geothermal energy, the bulk of the functioning of the ecosystem is based on the input of
solar energy. Plants and photosynthetic microorganisms convert
light into chemical energy by the process of
photosynthesis, which creates
glucose (a simple sugar) and releases free
oxygen. Glucose thus becomes the secondary energy source which drives the ecosystem. Some of this glucose is used directly by other organisms for energy. Other sugar molecules can be converted to other molecules such as
amino acids. Plants use some of this sugar, concentrated in
nectar (plant) 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.
airstream 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, 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:
* Whether the colonization of a barren area could be carried out
* Investigation the ecosystem's dynamics and changes
* The methods of which an ecosystem interacts at local, regional and global scale
* Whether the current state is stable
* Investigating the value of an ecosystem and the ways and means that interaction of ecological systems provide benefit to humans, especially in the provision of healthy water?
Ecosystems are often classified by reference to the biotopes concerned. The following ecosystems may be defined:
* As
continental ecosystems, such as
forest ecosystems,
meadow ecosystems such as
steppes or
savannas), or
Agroecology agro-ecosystems
* As ecosystems of inland waters, such as
lentic ecosystems such as
lakes or
ponds; or
lotic ecosystems such as
rivers
* As
oceanic ecosystems.
Another classification can be done by reference to its communities, such as in the case of an
human ecosystem.
Dynamics and stability
: ''Main articles:''
biogeochemistry,
Homeostasis,
Population dynamics
'''Ecological factors''' which can affect dynamic change in a
population or
species in a given ecology or
natural environment environment are usually divided into two groups: abiotic and biotic.
'''Abiotic factors''' are geological, geographical,
ecohydrology 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
natural environment milieu
*
Earth's atmosphere 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 pH,
Salinity in Australia 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,
inbreeding 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'''—
biological interaction 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
predator 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
ecological succession succession of events, the
climax (biology) 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
geographical pole 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
photosynthesis 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'' --
bacterium 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 reactor 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
{{Book}}
*
ELDIS, a database on ecological aspects of economical development.
*
Ecology movement
*
Deep Ecology
*
List of ecologists
*
List of ecology topics
*
List of biology topics
*
List of publications in biology#Ecology Important publications in ecology
{{Biology-footer}}
{{Natural sciences-footer}}
Category:Ecology *
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'''
Ecology''' is the branch of science that studies the distribution and interactions between
organism living things and between living things and the physical
natural environment environment.
This
:Category category does not cover
:Category:Environmentalism environmentalism, or
:Category:Ethics ethics topics.
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